New Insights into the Biodiversity of Benthic Hydroids (Cnidaria, Hydrozoa) from Seamounts in the Remote Macquarie Ridge, with the Description of Three New Species

© 2024 Academia Sinica, Taiwan Open Access New Insights into the Biodiversity of Benthic Hydroids (Cnidaria, Hydrozoa) from Seamounts in the Remote Macquarie Ridge, with the Description of Three New Species Álvaro Luis Peña Cantero* Instituto Cavanilles de Biodiversidad y Biología Evolutiva / Departamento de Zoología, Universidad de Valencia, Valencia, Spain, Apdo. Correos 22085, 46071 Valencia, Spain. *Correspondence: E-mail: [email protected] (Peña Cantero) Received 23 March 2023 / Accepted 14 March 2024 / Published 20 June 2024 Communicated by Benny K.K. Chan The Macquarie Ridge is a major seafloor feature in the Southern Hemisphere between New Zealand and the Antarctic continent, and its marine communities have been poorly explored. During the MacRidge 2 TAN0803 survey conducted on board the R/V Tangaroa, several seamounts of the Macquarie Ridge were sampled. Among the benthic samples obtained, a collection of hydroids was present. Eleven species were recorded, including Acryptolaria seamountensis sp. nov., Filellum liberum sp. nov. and Nemertesia macquariensis sp. nov. Anthoathecata is represented only by Eudendrium sp. The collection is essentially dominated by Leptothecata, with ten species, belonging to the families Campanulariidae, Lafoeidae, Phylactothecidae, Plumulariidae and Sertularellidae. Lafoeidae is by far the most diversified family, accounting for half of the leptothecate species. At the generic level, the collection is dominated by the deep-water genus Acryptolaria, with four species; all the remaining genera are represented by a single species. Seven species represent new records for the area and Calamphora quadrispinosa Watson, 2003 is recorded for the second time. Key words: Hydrozoans, New species, New records, Biodiversity, Sub-Antarctic BACKGROUND The Macquarie Ridge is a prominent elevation on the southern hemisphere seafloor between New Zealand and the Antarctic continent, extending from the Antarctic Balleny Islands region northwards through Macquarie Island towards New Zealand (Brodie and Dawson 1965). It is a rather continuous feature, forming an important boundary between the deep waters of the Pacific and Indian Oceans and also interrupting the flow of the Antarctic Circumpolar Current (ACC), the world′s largest current and the dominant feature of the Southern Ocean circulation. In 2008, the MacRidge 2 TAN0803 scientific survey was carried out to study the Macquarie Ridge and its adjacent sediment basins. One of the cruise objectives was to investigate the biodiversity and habitat of the seamounts associated with the ridge. These distinctly elevated features of the ridge have rarely been sampled and there is great interest in assessing their biodiversity (Samadi et al. 2007; Stocks and Hart 2007). As far as benthic hydroids are concerned, only one study has so far dealt with this zoological group from this large seafloor feature. Watson (2003) reported 27 species of hydrozoans, including six new to science, from a collection obtained during a survey of subAntarctic areas north, south, east and west of Macquarie Island (Fig. 1), between latitudes 53°0'S and 56°17'S and longitudes 158°30'E and 159°25'E. The aim of this study is to increase scientific Citation: Peña Cantero ÁL. 2024. New insights into the biodiversity of benthic hydroids (Cnidaria, Hydrozoa) from seamounts in the remote Macquarie Ridge, with the description of three new species. Zool Stud 63:17. doi:10.6620/ZS.2024.63-17. Zoological Studies 63:17 (2024) doi:10.6620/ZS.2024.63-17 1 © 2024 Academia Sinica, Taiwan knowledge of the biodiversity of benthic hydroids inhabiting the Macquarie Ridge through the study of the collection of benthic hydrozoans collected during the MacRidge 2 TAN0803 survey, hosted by the National Institute of Water and Atmospheric Research (NIWA). The results of this study are presented here. MATERIALS AND METHODS The material studied was collected during the New Zealand-Australia MacRidge 2 TAN0803 scientific survey conducted on board the R/V Tangaroa, from 26 March to 26 April 2008. Samples studied here were gathered using an epibenthic sledge in two seamounts of the Macquarie Ridge, north and south of Macquarie Island (Fig. 1), at depths between 119 and 750 m (Table 1). Hydrozoans were preserved in 70% ethanol. The materials studied here are deposited in the National Institute of Water and Atmospheric Research Invertebrate Collection at Wellington (NIWA), New Zealand. A reference publication, for both specialist and non-specialist readers, with valuable descriptions and figures of the characters used in the identification of hydrozoans, together with diagnoses and keys of the families and genera, is An introduction to Hydrozoa by Bouillon et al. (2006). I have included below a key for the identification of the species studied, and a figure illustrating the diversity of hydrothecal shapes and the main morphological characters used in their identification (Fig. 2). Fig. 1. Area of study and location of the sampling stations of the present study (see Table 1 for more details), represented with circles, and those surveyed by Watson (2003), indicated with triangles and white numbers. Table 1. Station data Station Date Latitude (S) Longitude (E) Depth (m) Locality 63 09/04/2008 52.48733–52.48383 160.415–160.40916 350–560 Seamount 6 65 09/04/2008 52.497–52.49916 160.48916–160.49183 119–125 Seamount 6 71 09/04/2008 52.34416–52.344 160.68133–160.68766 488–542 Seamount 6 98 16/04/2008 56.24633–56.2415 158.50566–158.515 676–750 Seamount 9 Hjort page 2 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Fig. 2. Types of hydrothecae found in the collection studied and their main morphological characters. Abbreviations: aad, adnate adcauline wall; ab, abcauline wall; ad, adcauline wall; aint, ahydrothecate intermediate internode; c, cusp; d, diaphragm; des, desmocytes; fad, free adcauline wall; ht, hydrotheca; int, internode; lnt, lateral nematotheca; mnt, medial infrahydrothecal nematotheca; n, node; nt, nematotheca; ped, pedicel; pr, perisarc ridge; r, rim; ren, renovation; stn, stolon. page 3 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan RESULTS TAXONOMY Key for the identification of the species found in the studied collection 1. Definite hydrothecae present (Leptothecata) (Fig. 2) ................. 2 - Definite hydrothecae absent (Anthoathecata) ..... Eudendrium sp. 2. Colony exclusively stolonal (Fig. 2A−B) .................................. 3 - Colony with erect stems ............................................................. 4 3. Without hydrothecal pedicel, rim of hydrothecal aperture even ... ............................................... Filellum liberum sp. nov. (Fig. 2A) - With hydrothecal pedicel, rim of hydrothecal aperture with 4 cusps ................................. Calamphora quadrispinosa (Fig. 2B) 4. Without nematothecae (Fig. 2A−E) ........................................... 5 - With nematothecae (Fig. 2F−G) ............................................... 10 5. Rim of hydrothecal aperture with cusps (Fig. 2C) ..................... 6 - Rim without cusps, tubiform hydrotheca (Fig. 2E) .................... 7 6. Rim with 4 cusps .................................. Sertularella sp. (Fig. 2C) - Rim with 12 weakly marked cusps, tulip-shaped hydrotheca ....... .............................................................. Tulpa tulipifera (Fig. 2D) 7. Hydrotheca relatively small, diameter at aperture less than 150 µm ....................................................................... Acryptolaria minuta - Diameter of hydrothecal aperture larger than 150 µm ............... 8 8. Hydrothecae in a marked zigzag pattern, horn-shaped ................. ............................................................................. Acryptolaria sp. - Hydrotheca arranged approximately in a straight line (Fig. 2E) ... ..................................................................................................... 9 9. Hydrothecae cylindrical at free part, diameter decreasing basally at basal third, diameter at aperture 330−340 µm, nematocysts 14–15 × 4.5–6 µm .................................. Acryptolaria operculata - Hydrotheca distinctly cylindrical, diameter constant, only slightly narrowing at basal end, diameter at aperture 160−210 µm, nematocysts 22−26 × 10.5−13 µm ................................................ .............................. Acryptolaria seamountensis sp. nov. (Fig. 2E) 10. Hydrotheca much reduced, saucer-shaped, arranged alternately along branch ..................................... Hydrodendron sp. (Fig. 2F) - Well-developed hydrothecae, unilaterally arranged on one side of branch ................... Nemertesia macquariensis sp. nov. (Fig. 2G) Family Eudendriidae L. Agassiz, 1862 Eudendrium sp. Material examined: Stn 98, numerous monosiphonic stems up to 70 mm high, with gonophores, in very poor condition, growing on the axis of a gorgonian (NIWA 114752). Description: Monosiphonic stems up to 70 mm high, scarcely branched (up to second-order branches present). Perisarc dark brown, fading to light brown distally, and smooth, except for a few rings at origin of stems, branches and pedicels. No polyps present, but remnants of a few mature female gonophores observed. Remarks: The material is unidentifiable, as it is in very poor condition, devoid of polyps and with only remnants of a few mature female gonophores. Regarding the cnidome, only a few empty capsules could be observed, some 9−10 × 3−3.5 µm and one 20 × 10 µm. Watson (2003) reported four species of Eudendrium Ehrenberg from the area, only two of which have monosiphonic stems, Eudendrium deforme Hartlaub, 1905, with stems up to 70 mm high, and Eudendrium macquariensis Watson, 2003, with stems up to 7 mm high. According to this, the present material would be closer to the former. Ecology and distribution: The material was collected from Seamount 9 Hjort, south of Macquarie Island, at a depth of 676−750 m. Family Lafoeidae Hincks, 1868 Acryptolaria minuta Watson, 2003 (Fig. 3A) Acryptolaria minuta Watson, 2003: 163−164, fig. 13A–C; Peña Cantero and Vervoort, 2010: 302–304, figs. 18, 30; Peña Cantero, 2020: 288, figs. 1D, 3E−F, 5G. Material examined: Stn 98, one stem fragment 9 mm long with several hydrothecae, without coppinia (NIWA 114754). Description: Stem fragment 9 mm long, with hydrothecae arranged alternately in two planes forming a very open angle. Hydrotheca markedly curved outwards, tubular, free part cylindrical, diameter barely dwindling basally at adnate part. Hydrotheca adnate to internode for about two-thirds of its length. Free adcauline wall strongly convex; adnate part much less so. Abcauline wall concave, but nearly straight at basal part. Hydrothecal aperture circular, directed outwards, often parallel to longitudinal axis of branch; rim even, with up to four renovations. Measurements (in µm): Hydrothecae: abcauline wall 680−700, free part of adcauline wall 230−350, adnate part of adcauline wall 550−570, adcauline wall 850−860, diameter at aperture 110−130, diameter at base 80. Cnidome (taken with × 40): putative macrobasic mastigophores, range 17.5–20 × 7.5. Remarks: The material consists of a single stem fragment, 9 mm long; however, the specimen corresponds well to recent descriptions of the species by Peña Cantero and Vervoort (2010) and Peña Cantero (2020). The species is well characterised by the shape and size of the hydrotheca and the size of the larger nematocysts (e.g., 17–19 × 7–8 µm in Peña Cantero and Vervoort 2010). Ecology and distribution: Acryptolaria minuta has been collected from depths of 300 (Peña Cantero and Vervoort 2010) to 1422 m (Watson 2003); present material from 676 to 750 m. This species has been previously recorded north page 4 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Fig. 3. Acryptolaria minuta Watson, 2003: A, hydrothecae. Acryptolaria operculata Stepanjants, 1979; B, distal part of hydrotheca. Acryptolaria seamountensis sp. nov.: C−F, hydrothecae and hydrothecal disposition; G, putative macrobasic mastigophore (arrow). Acryptolaria sp.: H, hydrothecae and hydrothecal disposition. Scale bars: A−F, H = 200 μm; G = 10 μm. page 5 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan of Macquarie Island (Watson 2003), from the Loyalty Islands and Norfolk Ridge areas (Peña Cantero and Vervoort 2010) and off Antipodes Island, southeast of New Zealand (Peña Cantero 2020). The material studied here was collected from Seamount 9 Hjort, south of Macquarie Island. Acryptolaria operculata Stepanjants, 1979 (Fig. 3B) Acryptolaria operculata – Peña Cantero et al., 2007: 258–261, figs. 12, 16D, 18D, 19E; Peña Cantero, 2020: 288−291, figs. 1E, 6B, 7E. Acryptolaria patagonica – Watson, 2003: 162−163, fig. 12A–C. Material examined: Stn 71, one stem fragment 11 mm long with several hydrothecae, without coppinia, in bad condition (NIWA 114754). Description: Stem fragment 11 mm long, with two short lateral branches. Hydrothecae arranged alternately in two planes forming an obtuse angle. Hydrotheca markedly curved outwards, fusiform, largest diameter at the middle; diameter barely decreasing toward aperture, more noticeably basally at adnate part. Hydrotheca adnate to internode for around half its length. Adcauline wall convex. Abcauline wall concave. Hydrothecal aperture circular, directed upand outwards; rim even, with a few short renovations. Measurements (in µm): Hydrothecae: abcauline wall 1400, free part of adcauline wall 900−950, adnate part of adcauline wall 700−1050, adcauline wall 1650−1970, diameter at aperture 330−340, diameter at base 180−190. Cnidome (taken with × 40): putative macrobasic mastigophores, 15 × 6. Remarks: Although scarce, the material examined undoubtedly corresponds to A. operculata (for recent descriptions, see Peña Cantero et al. 2007; Peña Cantero 2020). This species is well characterised by the shape and large size of the hydrotheca and the small size of the nematocysts (e.g., 14–15 × 4.5–5.5 µm in Peña Cantero 2020). In terms of hydrotheca size, the material studied here is closer to that of Peña Cantero (2020) from the Tasman Sea, with hydrothecae significantly smaller than his material from the southwest Atlantic. Ecology and distribution: The species has been collected at depths between 98 (El Beshbeeshy 2011) and 4740 m (Peña Cantero 2020); present material was gathered from depths of 488 to 542 m. Acryptolaria operculata is mainly distributed in sub-Antarctic waters, although it penetrates into Antarctic waters along part of the Scotia Arc (Peña Cantero 2020). It has been reported in sub-Antarctic waters of the southwest Atlantic: the Patagonian shelf (Stepanjants 1979; El Beshbeeshy 2011), the Burdwood Bank (Soto Àngel and Peña Cantero 2015), and the area between Staten Island (Tierra del Fuego), the Falkland Islands and South Georgia (Peña Cantero 2020). In the sub-Antarctic waters of the Pacific it has been documented in the Macquarie region (Watson 2003), New Zealand waters (Vervoort and Watson 2003) and the Tasman Sea (Peña Cantero 2020). It is also known from Antarctic waters of the Scotia Arc, from Shag Rocks to Discovery Bank (Soto Àngel and Peña Cantero 2015). Present material was collected from Seamount 6, north of Macquarie Island. Acryptolaria seamountensis sp. nov. (Figs. 3C−G, 4A, 5A−C) urn:lsid:zoobank.org:act:795B3DE1-6785-4708-8C7D3B72F08ACD79 Material examined: Stn 63, a complete stem 65 mm high, without coppinia (Holotype, NIWA 40133) and several stem fragments up to 50 mm long (Paratype, NIWA 126561). Etymology: The specific name seamountensis is formed with the Latin adjectival suffix –ensis to indicate that the species originates from a seamount on the Macquarie Ridge. Diagnosis: Stem polysiphonic, frequently branched. Branches practically straight. Hydrotheca cylindrical, smoothly curved outwards; adcauline wall convex, adnate over three-fourths of its length; abcauline wall concave towards the middle, practically straight at basal and distal thirds. Aperture directed outwards and upwards. Cnidome consisting of large macrobasic mastigophores and small microbasic mastigophores. Description: Stem up to 65 mm high. Branching frequent, at least of fifth order. In some parts of the colony, mainly distal, branches alternate every third hydrotheca (i.e., there are two hydrothecae between branches) and slightly disposed in two planes. Branching more irregular at basal parts (probably due to loss of branches). Branches practically straight. Hydrothecae alternate, in one or two planes forming a very obtuse angle. Hydrotheca cylindrical; diameter constant, slightly narrowing in basal part. Hydrotheca smoothly curved outwards; adcauline wall convex throughout, adnate to internode over three-fourths of its length (adnate/free ratio 2.6−3.6); abcauline wall concave towards the middle, practically straight at basal and distal thirds. Hydrothecal aperture circular, directed upwards and outwards. Rim even, often with a few short renovations. Measurements (in µm): Hydrothecae: abcauline wall 740−900, free part of adcauline wall 160−420, adnate part of adcauline wall 630−820, adcauline wall page 6 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan 900−1150, diameter at aperture 160−210, diameter at base 80−120. Cnidome: large putative macrobasic mastigophores, 23.8 ± 1.0 × 11.7 ± 0.7 (n = 12), range 22−26 × 10.5−13, small putative microbasic mastigophores 8 × 4. Remarks: The present material cannot be assigned to any of the known species of the genus and it is therefore considered a new species to science. Acryptolaria seamountensis sp. nov. is similar to Acryptolaria minima Totton, 1930 in the shape of the hydrotheca, almost completely cylindrical, with its diameter only slightly decreasing at the basal part, and with the aperture directed outwards and upwards. However, the hydrotheca is much smaller in A. minima, about half the size of the present species (e.g., abcauline length 392–480 µm or diameter at aperture 120−136 µm, in the holotype of A. minima, in Peña Cantero et al. 2007). On the contrary, nematocysts are slightly longer and thinner (25.8 ± 0.8 × 9.8 ± 0.4, 25−27 × 9−10). Furthermore, in A. minima the abcauline wall is slightly convex at the basal part, with a clear discontinuity with the previous internode (Fig. 6A−B in Vervoort and Watson 2003 and Fig. 16B in Peña Cantero et al. 2007), whereas in Acryptolaria seamountensis sp. nov. the abcauline wall is straight, and essentially a prolongation of the preceding internode. Finally, Totton’s species is characterized by having hydrothecae almost completely adnate to the branch (about four-fifths of their adcauline length are adnate to the internode), whereas in the present species a greater proportion of the adcauline wall is free. Vervoort and Watson (2003) assigned to A. minima material from Sta. BS 756 that differed from their remaining material, including type material, by “the slightly longer hydrothecae, the greater length being principally due to the longer free hydrothecal portion” (Vervoort and Watson 2003: 48). Their figures and measurements are in agreement with the present species. However, without information about the cnidome it is not possible to assign it to Acryptolaria seamountensis sp. nov. The present species is also morphologically close to Acryptolaria bathyalis Peña Cantero and Vervoort, 2010 in the general shape of the hydrotheca: cylindrical, with a constant diameter throughout, decreasing only at its base. However, the species are clearly distinguishable because in A. bathyalis, the hydrotheca is markedly curved outwards and, therefore, the hydrothecal aperture is roughly parallel to the long axis of the branch, whereas in Acryptolaria seamountensis sp. nov., the hydrotheca is less bent and, consequently, the aperture is clearly directed upwards. In addition, the hydrothecae in A. bathyalis are smaller (e.g., abcauline length 680−770 µm) and the nematocysts are shorter and thinner (21.6 ± 0.8 × 8.5 ± 0.4 µm) (Peña Cantero and Vervoort 2010). Finally, Acryptolaria seamountensis sp. nov. Fig. 4. Holotypes: A, Acryptolaria seamountensis sp. nov. (NIWA 40133); B, Nemertesia macquariensis sp. nov. (NIWA 40094). Scale bar = 10 mm. page 7 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan agrees with the holotype of Acryptolaria gracilis (Allman, 1888) in the size of hydrothecae and nematocysts (23.5−26 × 9 µm), although Peña Cantero et al. (2007) were able to take measurements of only two nematocysts from the holotype. However, the shape of the hydrotheca is clearly different due to the absence in the present species of the characteristic basal bottleneck described from the holotype of A. gracilis. According to Peña Cantero et al. (2007: 250) “Hydrotheca tubular, cylindrical at distal half, diameter approximately constant from hydrothecal aperture to the middle of hydrothecal length, then slightly decreasing up to become more or less constant, forming a kind of bottleneck at the most basal part.” Ecology and distribution: Acryptolaria seamountensis sp. nov. was collected from Seamount 6, north of Macquarie Island, at depths between 350 and 560 m. Acryptolaria sp. (Fig. 3H, 5D−E) Material examined: Stn 98, one stem 5 mm high with a few hydrothecae, without coppinia, on the axis of a dead gorgonian (NIWA 130063). Description: Monosiphonic, incipient stem, 5 mm high, with six hydrothecae in a marked zigzag, arranged alternately in two planes forming an obtuse angle. Hydrotheca tubular, free part almost cylindrical, its diameter only slightly narrowing from aperture to where adcauline wall becomes adnate; more pronounced afterwards. Hydrotheca gently curved outwards. Hydrotheca adnate to internode for more than half its length. Free adcauline wall straight or slightly convex; adnate part initially convex, becoming roughly straight basally, forming a sort of bottleneck. Abcauline wall concave by the middle, practically straight at basal and distal thirds. Hydrothecal aperture circular, directed upand outwards. Rim even, with up to four renovations. Measurements (in µm): Hydrothecae: abcauline wall 770−850, free part of adcauline wall 310−450, adnate part of adcauline wall 510−530, adcauline wall 840−930, diameter at aperture 160−200, diameter at base 60−70. Cnidome (taken with × 40): large putative macrobasic mastigophores, range 14−17.5 × 7.5. Remarks: The diameter of most hydrothecae gradually decreases in their adnate part until about the basal fourth, from where it remains approximately constant, forming a sort of basal bottleneck, much like that found in A. gracilis. The present material agrees with Acryptolaria corniformis Naumov and Stepanjants, 1962 in having internodes in zigzag, in the general shape of the hydrotheca and in the size of the nematocysts. However, it differs in the size of the hydrotheca, which is significantly smaller in the present material (e.g., abcauline length 1600−1900 µm and diameter at aperture 320−400 µm in the holotype of A. corniformis, in Peña Cantero et al. 2007), although this could be related to the fact that the material studied here consists of an incipient stem with only six hydrothecae. All previously described material of A. corniformis consists of four stem fragments up to 20 mm long, and therefore knowledge of this species is incomplete (Peña Cantero 2020). For example, in the material studied by Peña Cantero (2020), the smallest diameter at the hydrothecal aperture reached 270 µm, closer to that found in the present material. On the other hand, considerable variation in the size of the hydrotheca has been reported in some species of Acryptolaria, like Acryptolaria angulata (Bale, 1914) and Acryptolaria bulbosa (Stechow, 1932) (Peña Cantero and Vervoort 2010). However, it is important to highlight that the present material differs from the holotype of A. corniformis in other details. In the holotype, the branches are slightly zigzagged, whereas in the present specimen the zigzagging is more pronounced; the hydrotheca is smoothly curved outwards and the hydrothecal aperture is strongly directed upwards in A. corniformis, whereas in the present species the hydrotheca is more curved outwards and the aperture is less directed upwards. The scarcity of the available material and the differences indicated do not allow me to assign the present material with certainty to A. corniformis. The present material is also similar to Acryptolaria gemini Peña Cantero and Vervoort, 2010 in the size and general shape of the hydrotheca. They differ because in A. gemini the branches are approximately straight, the adcauline wall of the hydrotheca is free for more than half its length and there is a sharp reduction in the hydrothecal diameter at the point where the hydrotheca becomes adnate. The other species with a similar hydrothecal shape is Acryptolaria longitheca (Allman, 1877), but it has distinctly larger hydrothecae and nematocysts. Ecology and distribution: Acryptolaria sp. was collected from Seamount 9 Hjort, south of Macquarie Island, at depths between 676 and 750 m. Filellum liberum sp. nov. (Figs. 6−8) urn:lsid:zoobank.org:act:F34F6C2C-4C39-41AB-82D2AA22A527A87C Lafoea tenellula – Watson, 2003: 156−157, fig. 6A–C. Material examined: Stn 98, numerous hydrothecae and several coppiniae, growing on Eudendrium sp. page 8 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Fig. 5. Acryptolaria seamountensis sp. nov.: A−C, hydrothecae and hydrothecal disposition. Acryptolaria sp.: D−E, hydrothecal arrangement and shape of hydrothecae. Scale bar = 250 µm. page 9 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Fig. 9. Tulpa tulipifera (Allman, 1888): A, hydrotheca and pedicel; B, distal part of hydrotheca showing aperture; C, incomplete gonotheca. Calamphora quadrispinosa Watson, 2003: D, hydrotheca; E, distal part of hydrotheca showing aperture; F, gonotheca. Sertularella sp.: G, stem; H−I, stem fragments showing hydrothecae and origin of branch; J, fragment of stem showing longitudinal striation. Scale bars: A, G = 3 mm; B−F, H−I = 200 μm; J = 100 μm. page 16 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan diverticulum. As a result, I am retaining the species in Calamphora, pending molecular studies to establish its precise taxonomic position. Ecology and distribution: Calamphora quadrispinosa had been found at depths from 453 to 1422 m (Watson 2003); present material between 676 and 750 m. Gonothecae are known in January (Watson 2003) and April (present material). The species has been reported from north and south of Macquarie Island (Watson 2003); present material was collected from Seamount 9 Hjort, south of Macquarie Island. Sertularella sp. (Fig. 9G−J) Material examined: Stn 63, five stems up to 8 mm high, without gonothecae, growing on Nemertesia macquariensis sp. nov. (NIWA 144258). Description: Monosiphonic stems with up to six hydrothecae. Stems unbranched or with only one lateral branch with up to two hydrothecae. Stems divided into long internodes by slightly marked oblique nodes; stem internodes linear, branch internodes in zigzag. Perisarc of internodes finely longitudinally striate. Hydrothecae arranged alternately in one plane, flask-shaped, outwardly curved. Adcauline wall adnate to internode for about half its length; free part slightly convex, with two slightly marked undulations; adnate part straight or slightly convex. Abcauline wall straight, but outwardly curved in distal part. Rim of hydrothecal aperture with four equal cusps separated by shallow embayments. Measurements (in µm): Internodes: length 1240−1600, diameter at hydrothecal base 180–220. Hydrotheca: abcauline length 370−410, free adcauline length 250−270, adnate adcauline length 250−330, adcauline length 500−580, diameter at aperture 200−220, diameter at diaphragm 100−120, maximum diameter 250−270. Remarks: The present species differs from all the species of Sertularella Gray considered by Galea et al. (2017) in their revision of the genus from southern South American and sub-Antarctic waters. It belongs to the group of species with hydrothecae bent outwards, but it differs from all of them primarily by the size of the hydrotheca, which is smaller in the present material, but also by having long stem internodes arranged in a straight line. Some species in this group have polysiphonic stems and unique branching patterns. However, making direct comparisons could be misleading because the material studied here (monosiphonic stems, unbranched, or with only one lateral branch with up to two hydrothecae) may represent incipient, rather than well-developed stems. Further distinctions involve the precise shape of the hydrotheca, the adnate/free proportions of the adcauline hydrothecal wall, and the presence of internal hydrothecal cusps. Consequently, even when the material studied differs from those species in one or a combination of these characteristics, the scarcity of the available material and its infertile condition make it more reasonable not to assign a specific name to this material. Ecology and distribution: Sertularella sp. was collected from Seamount 6, north of Macquarie Island, at depths between 350 and 560 m. Family Phylactothecidae Stechow, 1921 Hydrodendron sp. (Fig. 10) Material examined: Stn 65, a few stem fragments up to 40 mm long, without gonothecae (NIWA 40219). Description: Stem and branches strongly polysiphonic, with anastomoses. Only a few short hydrocladia left, with only a few hydrothecae visible. Hydrothecae on a short, usually adnate hydrophore (some with a short free part). Hydrothecae completely free, low, with a ring of desmocytes between diaphragm and aperture; abcauline wall straight, adcauline wall slightly adcaudally directed. Hydrothecal aperture circular, strongly tilted abcaudally. Secondary hydrothecae usually present, on a short hydrophore, also with ring of desmocytes, aperture circular, rim slightly everted. No nematothecae left, but their positions clearly visible. One nematophore per internode, on opposite side of hydrotheca (some internodes seem to have another on hydrothecal side). With accessory hydrothecae arising from accompanying stolons, short and completely free, with diaphragm and desmocytes. Measurements (in µm): Internodes: length 480, diameter at distal node 310. Hydrophore: adnate part 230−260, free part 20−40. Hydrothecae: height 30−50, diameter at aperture 230−250, diameter at diaphragm 230−260. Accessory hydrothecae: height 40−50, diameter at aperture 220−230, diameter at diaphragm 210. Remarks: Although there are no nematothecae left, their positions are clearly visible, indicating that this material belongs to Hydrodendron Hincks. As mentioned above, there are short and completely free hydrothecae, provided with diaphragm and desmocytes, arising from accessory stolons, which are also present in Hydrodendron arboreum (Allman, 1888) (see Fig. 2A in Peña Cantero and García Carrascosa 1995). It is not possible to assign the present material to page 17 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan any species of the genus. It could belong to either H. arboreum or Hydrodendron tottoni Rees and Vervoort, 1987, but the difference between these two species is not clearly established. According to Vervoort and Watson (2003), H. tottoni is characterised by the slanting hydrothecal rim, although the degree of tilt varies within and between colonies. They kept it separate from H. arboreum, suggesting that in Allman’s species the hydrophore appears to be considerably elongated, with the hydrothecal diaphragm a considerable distance above the node. Vervoort and Watson (2003) also noted that in H. tottoni the hydrothecal rim is not perfectly flat, but is laterally curved downward to varying degrees, and that desmocytes were not observed. In the present material, the hydrotheca is clearly tilted abcaudally and the hydrophore does not project the hydrotheca beyond the distal node, bringing it closer to H. tottoni. However, the hydrotheca is approximately straight and desmocytes are present, which would place it closer to H. arboreum. Apparently, H. arboreum and H. tottoni also differ in the size of the nematotheca, as it is larger in the former. Unfortunately, this character cannot be considered here, as nematothecae are missing in the present material. The species described by Watson (2003) as Halecium sp. may actually be a species of Hydrodendron and be conspecific with the present material. In my opinion, it is plausible that the “gonothecae” she describes are actually nematothecae. They are “on proximal part of internode opposite a hydrophore” (Watson 2003: 167), a typical position of nematothecae in Hydrodendron species (e.g., H. arboreum). Watson herself described the “gonothecae” as “minute to small, base subspherical, perisarc very thin” and “arising without pedicel” (Watson 2003: 167). These features are consistent with what could be the description of a nematotheca of Hydrodendron. Furthermore, the width of the “gonothecae” reported by Watson, around 120 µm, is similar to that of nematothecae in Hydrodendron species; for instance, Peña Cantero Fig. 10. Hydrodendron sp.: A, internode with hydrotheca; B, detail of primary and secondary hydrothecae; C, internode showing hydrothecae and position of missing nematothecae (arrows); D, accessory hydrotheca. Scale bars: A = 200 μm; B−D = 100 μm. page 18 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan and García Carrascosa (1995) reported nematothecae 60−110 µm high and 50−80 µm in diameter at aperture in H. arboreum. Watson’s material also appears to have hydrothecae originating from accessory tubes; according to her description, “hydrocladium issuing from inside a hydrotheca on peripheral tube of stem or polysiphonic tube of branch” (Watson 2003: 167). Watson’s material is similar to the present species in having hydrophores with a short free part, but differs in that they are longer and have a larger free part (304−416 µm and 56−100 µm adnate and free part, respectively) and in that the hydrotheca, opposite or just above the node, slightly widens to a weakly everted rim. In addition, Watson’s material was collected at depths between 818 and 1158 m, significantly deeper than the present material (see below). Ecology and distribution: Hydrodendron sp. was collected from Seamount 6, north off Macquarie Island, at depths between 119 and 125 m. Family Plumulariidae McCrady, 1859 Nemertesia macquariensis sp. nov. (Figs. 4B, 11−12) urn:lsid:zoobank.org:act:45EE4511-7F5E-47E1-9865CDAAD4D4055B Material examined: Stn 63, one stem 120 mm high, without gonothecae (Holotype, NIWA 40094) and four stems up to 170 mm high, without gonothecae (Paratype, NIWA 144254); Stn 71, two stems, 180 and 130 mm high, without gonothecae (NIWA 40351). Etymology: The specific name macquariensis is formed with the Latin adjectival suffix –ensis to indicate that the species originates from the Macquarie Ridge. Diagnosis: Stems polysiphonic, planar, frequently branched. Hydrocladia on cauline apophyses arranged in decussate pairs, not at right angles, resulting in four longitudinal rows; apophyses with one mamelon (two also observed), two axial nematothecae and another pair more above mamelon. Hydrocladia divided into alternating hydrothecate and ahydrothecate internodes, starting with a hydrothecate internode. Ahydrothecate internode with a basal nematotheca. Hydrothecate internode with one hydrotheca in the middle and three nematothecae: two flanking hydrothecal aperture, and one mesial infrahydrothecal nematotheca not reaching hydrothecal base. Internode with strongly developed perisarc ridges. Hydrotheca low, about as high as wide; abcauline wall straight, directed outwards. Hydrothecal aperture circular, slightly tilted adcaudally; rim even. Nematothecae with scooped rim. Paired nematothecae of hydrothecate internodes similar to infrahydrothecal ones. Description: Stems strongly polysiphonic, branched, up to 180 mm high and 5 mm in diameter at base. Hydrorhiza disc-shaped or rhizoidal. Stems deprived of branches for a large basal part. Branching in one plane, rather irregular, alternate in some places, sub-opposite in others; branches up to sixth order, arising from accessory tubes. Hydrocladia originating from cauline apophyses arranged in decussate pairs in X (i.e., not at right angles), giving rise to four longitudinal rows. Branches divided into internodes by straight transverse nodes, with variable number of hydrocladia per internode. Hydrocladia with up to fourteen hydrothecae. Cauline apophyses with one mamelon (two also observed), two axial nematothecae and another pair more above mamelon. Hydrocladia divided into internodes by oblique nodes, alternately hydrothecate and ahydrothecate, starting with a hydrothecate internode. Ahydrothecate internode with a basal nematotheca resting on upper side of basal swelling of internode. Hydrothecate internode with one hydrotheca resting approximately in the middle of internode and three nematothecae: two lateral, flanking hydrothecal aperture, and one mesial infrahydrothecal resting on basal swelling of internode and not reaching hydrothecal base. Internode with strongly developed perisarc ridges: one before mesial nematotheca, one in the middle between mesial nematotheca and hydrotheca, one at base of hydrotheca, one just above hydrothecal aperture and a fifth before distal node (a sixth ridge present in some internodes just above mesial nematotheca). Ahydrothecate internodes typically with two perisarc ridges, one basal and one distal. Hydrotheca low, about as high as wide. Abcauline wall straight, directed outwards. Hydrothecal aperture circular, slightly tilted adcaudally; rim even. Nematothecae bithalamic; distal chamber with scooped rim. Paired nematothecae of hydrothecate internodes similar to infrahydrothecal nematothecae. Measurements (in µm): Cauline apophyses: length 300–350. Hydrothecate hydrocladial internodes: length 330−350, diameter at hydrothecal base 75–105. Ahydrothecate hydrocladial internodes: length 180−200. Hydrotheca: abcauline length 60–90, adcauline length 50–65, diameter at aperture (frontal view) 70–90. Lateral nematotheca: height 80−85, diameter at aperture 50−60, diameter at diaphragm 30, height of distal chamber 20. Mesial nematotheca: height 70, diameter at aperture 45−50, diameter at diaphragm 30, height of distal chamber 20−25. Remarks: The colonies are strongly polysiphonic, except for the most distal, lowest-order branches. The internodes of stems and branches are very variable in length (some have only one pair of hydrocladia, but others up to five pairs), probably page 19 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Fig. 11. Nemertesia macquariensis sp. nov.: A, stem fragment showing hydrocladial arrangement; B, stem fragment with cauline apophysis showing mamelon (arrow) and one axillary nematotheca; C, detail of cauline apophysis showing mamelon (arrow); D−G, hydrocladial internodes showing hydrothecae and nematothecae; H, detail of hydrotheca and nematotheca with scooped rim (arrow). Scale bars: A = 200 μm; B, D−G = 100 μm; C, H = 50 μm. page 20 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Fig. 12. Nemertesia macquariensis sp. nov. A−B, cauline apophyses showing mamelon and nematothecae (A with two mamelons); C−D, fragments of hydrocladia showing division into hydrothecate and ahydrothecate internodes, hydrothecae and nematothecae. Scale bars: A−B, D = 250 μm; C = 500 μm. page 21 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan because they are just the result of growth interruptions, as is also indicated by the decrease in diameter (e.g., from 200−210 µm at the first internode to 170−180 µm at distal one). As mentioned above, hydrocladia originate from cauline apophyses arranged in decussate pairs which are not at right angles. Lower-order branches typically originate in the narrower sides of the X and, as a result, it is possible to observe a bilateral symmetry in the colonies, with the hydrocladia and branches confined to the laterals, and the anterior and posterior parts devoid of them, giving rise to the final planar structure of the colony. As previously stated, branching is in one plane, but is quite irregular. In some parts of the colony it appears to be alternate, with branches widely separated, but in other parts the branches are close together and then appear to form sub-opposite pairs, yet in other parts the alternate order is reversed. Branches, or lower-order stems, arise from accessory stolons and start with an apophysis, which may be followed by an intermediate athecate internode, and a first internode with hydrocladia at different levels and positions. The following internode already has apophyses with more or less the typical arrangement. In the general colony shape, Nemertesia macquariensis sp. nov. is allied to Nemertesia pinnatifida Vervoort and Watson, 2003, which has a fanshaped colony with all branches and the main stem in one plane. They also share the heteromerous division of the hydrocladia, starting with a hydrothecate internode. However, they differ in several aspects. In N. pinnatifida the secondary or lower-order branches are quite short (10−20 mm long) and pinnately arranged in close opposite or sub-opposite pairs, whereas in the present species branches are longer (30 mm long) and, as mentioned above, branching is quite irregular. In N. pinnatifida, the number of longitudinal rows of apophyses is quite irregular, whereas in Nemertesia macquariensis sp. nov. the apophyses are arranged in decussate pairs in X and, consequently, the number of longitudinal rows is always four. The number of associated nematothecae on the cauline apophyses is higher in N. pinnatifida (5 to 6). According to Vervoort and Watson (2003: 284), “1 or a pair may occur in the axil, 1 halfway mamelon, 1 or a pair above mamelon, and 1 on slight elevation almost at end of apophysis”. In Nemertesia macquariensis sp. nov. there are four nematothecae, one pair at the axil and another pair above the mamelon. The nematothecae in N. pinnatifida are significantly longer (height 67−100 µm) than in the present species, whereas the hydrothecae are smaller (abcauline length 34−45 µm, in Vervoort and Watson 2003). As a result, the nematothecae are very long compared to the hydrothecae in N. pinnatifida. In addition, the hydrotheca is located in the middle of the internode in the present species, whereas it is clearly below the middle in N. pinnatifida. The species also differ in the development and number of the perisarc ridges of the hydrothecate internodes. In N. pinnatifida, there are incomplete septa at both ends of the internode, just above the insertion of the median inferior nematotheca and at the base of the hydrotheca. In Nemertesia macquariensis sp. nov., the perisarc ridges are more developed and more numerous. Nemertesia macquariensis sp. nov. shares with Nemertesia cymodocea (Busk, 1851), the polysiphonic, branched stems, and the structure of the hydrocladial apophyses. They differ because in N. cymodocea the cauline apophyses are usually arranged in decussate verticils of three or four apophyses, although decussate pairs are also found in younger parts of the colony (Ramil and Vervoort 2006); in Nemertesia macquariensis sp. nov., however, there are only decussate pairs arranged in X. They also share the heteromerous division of the hydrocladia into internodes with alternating hydrothecate and ahydrothecate internodes. However, they differ because in N. cymodocea the first hydrocladial internode is ahydrothecate, whereas in the present species it is hydrothecate. The colony structure is also completely different, with the stem provided with long branches arising just above the base and the branches rebranching basally into long upwardly directed shoots in N. cymodocea (Vervoort and Watson 2003). Finally, there are biogeographical reasons, as N. cymodocea seems to be restricted to temperate waters. Nemertesia macquariensis sp. nov. shares with Nemertesia ciliata Bale, 1914, the presence of branched and polysiphonic stems and the heteromerous division of the hydrocladia into internodes. However, in Bale’s species the hydrocladia start with an ahydrothecate internode. They also differ because in N. ciliata the cauline apophyses are typically arranged in verticils of three or four, although decussate or even alternate pairs are also present in younger parts (Ramil and Vervoort 2006). Finally, the hydrotheca is well below the middle of the internode. The geographically closer records of N. ciliata are from Tasmania, New Zealand and waters around South Africa. Ecology and distribution: Nemertesia macquariensis sp. nov. was collected from Seamount 6, north of Macquarie Island, at depths between 350 and 560 m. page 22 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan DISCUSSION The only previous study dealing with benthic hydroids from the Macquarie Ridge is by Watson (2003). She studied a collection gathered north, south, east and west of Macquarie Island (Fig. 1), between latitudes 53°0'S and 56°17'S and longitudes 158°30'E and 159°25'E, at depths ranging from 364 to 1422 m. In the present study, the collection was obtained between 52.34−52.49'S and 160.40−160.68'E, south of Macquarie Island, and at 56.24'S and 158.50−158.51'E, north of the island, at depths between 119 and 750 m. Watson (2003) reported 27 species, six of which are new to science. In the present studied collection, I found 11 species, three of them new to science. Since the material assigned by Watson to L. tenellula is considered to be conspecific with Filellum liberum sp. nov., and the material assigned to T. diverticulata is considered to correspond to T. tulipifera, the number of known species in the region is increased to 32. The occurrence of hydroids in this study was very low. With the exception of Nemertesia macquariensis sp. nov., which was found at two stations, all species were found at only one station. The station with the highest species diversity was Stn 98 with six species, followed by Stn 63 with three, Stn 71 with two and Stn 65 with only one species. It is worth mentioning that the last, the station with the lowest biodiversity, is the shallowest (119−125 m), while Stn 98, the station with the highest species diversity and the only station north of Macquarie Island, is the deepest (676−750 m). In Watson’s (2003) study, the station with the highest number of species (14) was also north of Macquarie Island and at a similar depth (500–600 m). As shown above, Anthoathecata has a very low representation in the collection studied, with only one species present (Eudendrium sp.), representing 9.1% of the total. Leptothecata is clearly the dominant group and accounts for the remaining species diversity. In Watson’s (2003) study, Leptothecata was also dominant, but she found a greater presence of Anthoathecata (four species of Eudendrium and one species of Hydractinia Van Beneden), representing 18.5% of the total. As seen above, Lafoeidae is by far the most diverse family in the collection studied, accounting for half of the leptothecate species. In Watson’s (2003) study, Lafoeidae was also the dominant family, with seven species (31.8% of Leptothecata). Acryptolaria, a genus of deep-water species, is clearly the dominant genus in the present study with four species. Watson (2003) also reported a relatively high number of species in this genus (three), but Halecium Oken was the dominant genus in her study with five species. The Macquarie Ridge benthic hydroid fauna has a great originality in its species composition. Four of the six new species described by Watson (2003) are known only from this area. With the three new species described here, there are now seven species endemic to this important seafloor feature of the sub-Antarctic region. CONCLUSIONS The results of this study have provided new information for a better understanding of the diversity of benthic hydroids inhabiting the under-explored Macquarie Ridge. Despite the small size of the collection studied, the known species diversity of the area significantly increased, with six new records, including three species new to science, showing that the area is still very poorly known. The relatively high number of endemism also indicates the great originality of its hydrozoan fauna. Further studies are needed to better assess its benthic hydrozoan diversity and to establish its position within the framework of Southern Hemisphere marine biogeography and its role as a potential bridge between the Southern Ocean and subAntarctic New Zealand. Acknowledgments: This work and the three new species names were registered with ZooBank under urn:lsid:zoobank.org:pub:B2E8ECDB-E6EA-441698A6-884F31C8C657. I would like to thank the NIWA Invertebrate Collection, Sadie Mills, Di Tracey and Diana Macpherson (NIWA) for providing access to samples and associated sample data. I would also like to acknowledge the research programme that funded the collection studied. The material was collected during the interdisciplinary New Zealand-Australia “MacRidge 2” research voyage (TAN0803), the biological component of which was part of NIWA’s research project “Seamounts: their importance to fisheries and marine ecosystems” funded by the New Zealand Foundation for Research, Science and Technology, and CSIRO’s Division of Marine and Atmospheric Research project “Biodiversity Voyages of Discovery” funded by the CSIRO Wealth from Oceans Flagship. Finally, I am grateful to two anonymous referees for their comments and corrections that contributed to improving the manuscript. Authors’ contributions: The author carried out all aspects of the present study. Competing interests: The author declares that he has no conflict of interests. page 23 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Availability of data and materials: All the material studied, including type material, is deposited in the National Institute of Water and Atmospheric Research Invertebrate Collection at Wellington (NIWA), New Zealand. Consent for publication: Not applicable. Ethics approval consent to participate: Not applicable. REFERENCES Agassiz L. 1862. Contributions to the natural history of the United States of America. Vol. IV. Little, Brown and Company, Boston, USA. doi:10.5962/bhl.title.12644. Allman GJ. 1877. Report on the Hydroida collected during the exploration of the Gulf Stream by L.F. de Pourtalès, assistant United States Coast Survey. Mem Mus Comp Zoölogy Harv Coll 5:1–66, pls. 1–34. doi:10.5962/bhl.title.10420. Allman G. 1888. Report on the Hydroida dredged by H.M.S. Challenger during the years 1873–76. Part II. The Tubularinae, Corymorphinae, Campanularinae, Sertularinae and Thalamophora. Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873–76. Zoology (part 70): i-lxix, 1-90, pl. 1-39. Bale WM. 1914. Report on the Hydroida collected in the Great Australian Bight and other localities. Part 2. Fish Zool (Biol) Res Fishing Exper F.I.S. Endeavour, 1909–1914, 2(4):164–188, pls. 35–38. Brodie JW, Dawson EW. 1965. Morphology of North Macquarie Ridge. Nature 207:844–845. doi:10.1038/207844b0. Bouillon J, Gravili C, Pagès F, Gili JM, Boero F. 2006. An introduction to Hydrozoa. Mém Mus Natl Hist Nat 194:1–591. Busk G. 1851. A list of sertularian zoophytes and Polyzoa from Port Natal, Algoa Bay, and Table Bay, in South Africa; with remarks on their geographical distribution, and observations on the genera Plumularia and Catenicella. Rep Br Ass Advmt Sci 20(2):118–120. Calder DR. 1991. Shallow-water hydroids of Bermuda. The Thecatae, exclusive of Plumularioidea. Life Sci Contrib R Ont Mus 154:1– 140. Calder DR. 2013. Some shallow-water hydroids (Cnidaria: Hydrozoa) from the central east coast of Florida, USA. Zootaxa 3648(1):1– 72. doi:10.11646/zootaxa.3648.1.1. Cunha AF, Collins AG, Marques AC. 2017. Phylogenetic relationships of Proboscoida Broch, 1910 (Cnidaria, Hydrozoa): Are traditional morphological diagnostic characters relevant for the delimitation of lineages at the species, genus, and family levels? Mol Phylogenet Evol 106:118–135. doi:10.1016/ j.ympev.2016.09.012. El Beshbeeshy M. 2011. Thekate Hydroiden von Patagonischen Schelf (Cnidaria, Hydrozoa, Thecata). Edited by G. Jarms. Verh Naturwiss Ver Hamburg 46:19–233. Fleming J. 1820. Observations on the natural history of Sertularia gelatinosa of Pallas. Edinburgh Philos J 2:82–89. Galea HR, Schories D, Häussermann H, Försterra G. 2017. Taxonomic revision of the genus Sertularella (Cnidaria: Hydrozoa) from southern South America and the subantarctic, with the descriptions of five new species. Rev Suisse Zool 124:255–321. doi:10.5281/zenodo.893519. Hartlaub C. 1904. Hydroiden. Résult voyage S.Y. Belgica 1897–1899 (Zool)7:1–19, pls. 1–4. Hartlaub C. 1905. Die Hydroiden der magalhaensischen Region und chilenischen Küste. Zool Jahrb (Suppl) Zool 6:497–714. Hincks T. 1868. A history of the British hydroid zoophytes. John Van Voorst, London, UK. doi:10.5962/bhl.title.99946. Hirohito, Emperor of Japan. 1995. The hydroids of Sagami Bay. II, Thecata. Publications of the Biological Laboratory, Imperial Household, Tokyo, Japan. Johnston G. 1836. A catalogue of the zoophytes of Berwickshire. Hist Berwicksh Nat Club 1:107–108. Maronna MM, Miranda TP, Peña Cantero AL, Barbeitos MS, Marques AC. 2016. Towards a phylogenetic classification of Leptothecata (Cnidaria, Hydrozoa). Sci Rep 6:18075. doi:10.1038/srep18075. Marques AC, Peña Cantero AL, Miranda TP, Migotto A. 2011. Revision of the genus Filellum Hincks, 1868 (Lafoeidae, Leptothecata, Hydrozoa). Zootaxa 3129:1–28. doi:10.11646/ zootaxa.3129.1.1. McCrady J. 1859. Gymnopthalmata of Charleston Harbor. Elliot Soc N H Charleston Pr 1:103–221. Millard NAH. 1975. Monograph on the Hydroida of southern Africa. Ann S Afr Mus 68:1–513. Naumov DV, Stepanjants SD. 1962. Hydroida (Thecaphora) collected by the Soviet Antarctic Expedition on the M/V Ob in antarctic and subantarctic waters. In: Biol res Soviet Antarct Exped, 1955–1958, 1. Issled Fauny Morei 1(9):68–106. Oliveira OMP, Miranda TP, Araujo EM, Ayón P, Cedeño-Posso C et al. 2016. Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters. Zootaxa 4194(1):1–256. doi:10.11646/zootaxa.4194.1.1. Peña Cantero AL. 2010. Benthic hydroids (Cnidaria: Hydrozoa) from Peter I Island (Southern Ocean, Antarctica). Polar Biol 33:761– 773. doi:10.1007/s00300-009-0754-7. Peña Cantero AL. 2020. Species of Acryptolaria Norman, 1875 (Cnidaria: Hydrozoa) collected by US Antarctic and subAntarctic expeditions. Zootaxa 4767(2):277–294. doi:10.11646/ zootaxa.4767.2.4. Peña Cantero AL, García Carrascosa AM. 1995. Hidrozoos bentónicos de la campaña Antártida 8611. Publ Espec Inst Esp Oceanogr 19:1–148. Peña Cantero AL, Horton T. 2017. Benthic hydroids (Cnidaria, Hydrozoa) from bathyal and abyssal depths of the Northeast Atlantic held in the modern Discovery Collections. Zootaxa 4347(1):1–30. doi:10.11646/zootaxa.4347.1.1. Peña Cantero AL, Vervoort W. 2010. Species of Acryptolaria Norman, 1875 (Cnidaria, Hydrozoa, Lafoeidae) collected in the Western Pacific by various French expeditions, with the description of nineteen new species. Zoosystema 32(2):267–332. doi:10.5252/ z2010n2a5. Peña Cantero AL, Marques A, Migotto A. 2007. Revision of the genus Acryptolaria Norman, 1875 (Cnidaria, Hydrozoa, Lafoeidae). J Nat Hist 41(5–8):229–291. doi:10.1080/00222930701228132. Peña Cantero AL, Svoboda A, Vervoort W. 2004. Antarctic hydroids (Cnidaria: Hydrozoa) of the families Campanulinidae, Lafoeidae and Campanulariidae from recent Antarctic expeditions with R.V. Polarstern, with the description of a new species. J Nat Hist 38:2269–2303. doi:10.1080/00222930310001647361. Ramil F, Vervoort W. 2006. Nemertesia tropica spec. nov. from Indonesian waters near Bali. Description of the new species and a review of the genus Nemertesia Lamouroux, 1812 (Leptothecata, Hydrozoa, Cnidaria). Zool Med Leiden 80–1(9):113–158. Rees WJ, Vervoort W. 1987. Hydroids from the John Murray Expedition to the Indian Ocean, with revisory notes on Hydrodendron, Abietinella, Cryptolaria and Zygophylax (Cnidaria: Hydrozoa). Zool Verh 237:1–209. page 24 of 25Zoological Studies 63:17 (2024) © 2024 Academia Sinica, Taiwan Samadi S, Schlacher T, Richer de Forges B. 2007. Seamount benthos. In: Pitcher TJ, Morato T, Hart PJB, Clark MR, Haggen N, Santos RS (eds) Seamounts: Ecology, Fisheries and Conservation. Blackwell Publishing, Oxford, UK. doi:10.1002/9780470691953. ch7. Schuchert P. 2001. Hydroids of Greenland and Iceland (Cnidaria, Hydrozoa). Meddel Grønland, Bioscience 53:1–184. doi:10.7146/mogbiosci.v53.142616. Soto Àngel JJ, Peña Cantero AL. 2015. On the benthic hydroids from the Scotia Arc (Southern Ocean): new insights into their biodiversity, ecology and biogeography. Polar Biol 38:983–1007. doi:10.1007/s00300-015-1660-9. Soto Àngel JJ, Peña Cantero AL. 2019. Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica). Zootaxa 4570(1):1–78. doi:10.11646/zootaxa.4570.1.1. Stechow E. 1921. Neue Genera und Species von Hydrozoen und anderen Evertebraten. Arch Naturgesch A87:248–265 Stechow E. 1932. Neue Hydroiden aus dem Mittelmeer und dem Pazifischen Ozean, nebst Bemerkungen über einige wenig bekannte Formen. Zool Anz 100(3–4):81–92. Stepanjants SD. 1979. Hydroids of the Antarctic and Subantarctic waters. Biol res Soviet Antarct Exped 6. Issled Fauny Morei 20:1–200. (in Russian) Stocks KI, Hart PJB. 2007. Biogeography and biodiversity of seamounts. In: Pitcher TJ, Morato T, Hart PJB, Clark MR, Haggen N, Santos RS (eds) Seamounts: Ecology, Fisheries and Conservation. Blackwell Publishing, Oxford, UK. doi:10.1002/9780470691953.ch13. Totton AK. 1930. Coelenterata. Part V. Hydroida. Nat Hist Rep Br Antarct Terra Nova Exped, 1910, Zoology 5(5):131–252, pls. 1–3. Vervoort W, Watson J. 2003. The marine fauna of New Zealand: Leptothecata (Cnidaria: Hydrozoa) (Thecate Hydroids). NIWA Biodivers Mem 119:1–538. Watson JE. 2003. Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island. Mem Mus Vic 60:151–180. doi.org/10.24199/ j.mmv.2003.60.18. page 25 of 25Zoological Studies 63:17 (2024)