Species account
Oceaniidae Eschscholtz, 1829
Turritopsis sp.
(Fig. 2)
Material examined. TAN 1802/186, a few stems up to 5 mm high, on a bryozoan.
Description. Hydrorhiza stolonal, creeping on bryozoan, giving rise to unbranched, erect stems up to 5 mm high, each with a single distal polyp. Stem covered with firm double-layered perisarc (Fig. 2a); outer layer not reaching pedicel end (Fig. 2b). Hydranth 350–400 µm high, 200 µm in maximum diameter, with about 12 filiform tentacles at different levels (Fig. 2c-e).
Cnidome (Fig. 2f-h) consisting of microbasic euryteles (8.6±0.4 x 5.0±0.2 µm, range 8-9 x 4.5-5 µm) and desmonemes (5.5 x 3.5 µm).
Remarks. The material is infertile, and only a few poorly preserved polyps are present, preventing a complete characterization and identification of the species.
The only material from Antarctic waters so far assigned to the genus Turritopsis is that described by Peña Cantero et al. (2013), which is also based on infertile material. The material studied here differs by having unbranched stems, but this could be related to the smaller size of the stems (up to 5 mm high here and up to 15 mm in the material studied by Peña Cantero et al. 2013). These authors indicated that Stepanjants’ (1979) material of Corydendrium could actually belong to Turritopsis.
Ecology and distribution. The material studied by Peña Cantero et al. (2013) was collected at a depth of 20 m from Tethys Bay, in the Ross Sea. Present material comes from much deeper waters (652–654 m).
Family Lafoeidae Hincks, 1868
Acryptolaria frigida Peña Cantero, 2014
(Fig. 3a)
Material examined. TAN1802/186, three stems 150, 150 and 130 mm high, one of them with coppinia, basibiont of Lafoea dumosa.
Description. Polysiphonic stem up to 150 mm high. Branching alternate, almost in one plane, usually every third hydrotheca; branches up to third order observed. Hydrothecae alternately arranged approximately in one plane.
Hydrotheca markedly curved abcaudally (Fig. 3a), tubular, cylindrical at free part, smoothly tapering basally at adnate portion. Hydrotheca adnate to internode for about two- thirds of its length. Adcauline wall strongly convex. Abcauline wall concave, especially at distal half. Hydrothecal aperture circular, directed outwards. Rim even, sometimes with a few short renovations.
Coppinia without defensive tubes; gonothecae distally broken.
Measurements (in µm). Hydrothecae: abcauline wall 1450–1650, free part of adcauline wall 380–810, adnate part of adcauline wall 1200–1350, adcauline wall 1730–2010, diameter at aperture 280. Cnidome: larger microbasic mastigophores 20.0±0.6 x 6.8±0.4 (n=10), range 19.0–20.5 x 6.5–7.5 µm.
Remarks. The material studied perfectly matches previous descriptions of the species in both the shape and size of the hydrotheca and the cnidome.
Ecology and distribution. Acryptolaria frigida is known from depths between 85 (Peña Cantero 2010) and 728 m (Peña Cantero 2014); present material at a depth of 652−654 m. Coppiniae in March.
Circum-Antarctic distribution (Peña Cantero 2014). It has been reported from the Weddell Sea (Peña Cantero et al. 2004; Soto Àngel and Peña Cantero 2019; Peña Cantero 2020), off Peter I Island (Peña Cantero 2010) and from the Bellingshausen Sea (Peña Cantero 2012), in West Antarctica, and off Queen Mary Coast (Peña Cantero 2014), in East Antarctica. Present material represents the first record for this sector of the Antarctic region.
Filellum liberum Peña Cantero, 2024
(Fig. 3b-d)
Material examined. TRIP2993/20, several hydrothecae, on axis of dead gorgonian, with coppinia.
Description. Stolonal colony consisting of stolons creeping on a gorgonian axis, giving rise to erect, tubiform, completely free hydrothecae (Fig. 3b-c) of highly variable shape and size (up to 770 µm high). Hydrothecal diameter clearly increasing distally from origin; hydrothecal aperture circular (120–150 µm in diameter), rim even, slightly flared, frequently with several renovations of variable length (Fig. 3b-c).
Coppinia consisting of tightly packed gonothecae surrounded by a fence of protective tubes arching over them, creating a protective brooding chamber. Defensive tubes unforked, distally open, and basally partially coalescent. Gonothecae flask-shaped, with a circular aperture on a short distal neck, distally flared (Fig. 3d).
Remarks. The present material perfectly agrees with the orginal description of both the hydrothecae and the coppinia. The species is characterised by having completely free hydrothecae.
Ecology and distribution. Filellum liberum seems to be a deep-water species. It was known from depths between 505 and 1064 m (Waston 2003 as Lafoea tenellula Allman, 1877, see Peña Cantero 2024); present material collected at depths between 1541 and 1770 m, distinctly increasing its lower bathymetric limit. Coppiniae are known in January (Watson 2003), April (Peña Cantero 2024) and December (present study).
Filellum liberum is known only from waters around Macquarie Island (Peña Cantero 2024) and the Long Ridge area (present study).
Lafoea dumosa (Fleming, 1820)
(Fig. 3e)
Material examined. TAN1802/186, a few stems up to 15 mm high, on A. frigida.
Description. Monosiphonic stems up to 12 mm high, unbranched, with up to 15 hydrothecae alternately arranged in two planes, forming an acute angle. Two polysiphonic stems also present, 16 and 10 mm high, with five and two primary branches, respectively. Branches originating from accessory tubes. Hydrothecae straight (Fig. 3e), mostly cylindrical, tapering at their basal third into a twisted pedicel. Hydrothecal aperture circular; rim even.
Measurements (in µm). Hydrotheca: height from ring of desmocytes 550–630, pedicel 200–250, diameter at aperture 160–200. Total length (hydrotheca plus pedicel): 750–880. Cnidome: isorhizas 20.4±0.8 x 10.6±0.7 (n=5), range 19.0–21.0 x 10.0–11.5.
Ecology and distribution. In Antarctic waters, Lafoea dumosa is known from depths between 12 (Stepanjants 1979) and 1157 m (Peña Cantero 2014); present material at a depth of 652–654 m.
Cosmopolitan distribution (Stepanjants 1979). In the region, reported from the Ross Sea (Totton 1930; Peña Cantero 2017, 2023) and the Balleny Islands (Peña Cantero 2021).
Lafoea sp.
(Fig. 3f-g)
Material examined. TRIP2993/20, several stems up to 13 mm high, on axis of a dead gorgonian and Halecium divergens sp. nov.
Description. Stems up to 13 mm high, either monosiphonic or polysiphonic. Branching present only on polysiphonic stems; branches originating from accessory tubes. Hydrothecae alternately arranged in two planes, forming an acute angle. Hydrothecae typically curved abcaudally (Fig. 3f), relatively long and thin, cylindrical for most of their length, tapering only at their basal fourth into a twisted pedicel. Hydrothecal aperture circular; rim even, usually with numerous renovations (up to ten observed).
Measurements (in µm). Hydrotheca: height 450–500, diameter at aperture 80–120. Total length (hydrotheca plus pedicel): 600. Cnidome: microbasic mastigophores 6–6.5 x 2.5–3.
Remarks. There are also stolonal hydrothecae, on both Halecium divergens sp. nov. and the gorgonian axis.
The present material is clearly different from L. dumosa, both in the shape and size of the hydrotheca (e.g. 160–200 µm in diameter at the aperture in the material of L. dumosa studied here), as well as in the cnidome. After several attempts to study the cnidome of this species, I have been unable to find the large isorhizas characterising L. dumosa (Schuchert 2001). Only small microbasic mastigophores were found (Fig. 3g). Although I could not observe them discharged, I did find a broken nematocyst exposing a short, isometric shaft (Fig. 3g). The scarcity of the available material and the absence of coppinia prevent me from fully characterising this species.
Ecology and distribution. Lafoea sp. was collected at depths between 1541 and 1770 m, epibiotic on the axis of a gorgonian and on H. divergens sp. nov.
Family Campanulariidae Johnston, 1836
Tulpa diverticulata Totton, 1930
(Fig. 3h)
Material examined. TAN 1802/186, several stems up to 60 mm, on axis of dead gorgonian, basibiont of Symplectoscyphusnesioticus.
Description. Stems up to 60 mm high, monosiphonic, with alternate hydrothecae in an almost unilateral arrangement. Hydrothecae on pedicels of variable length, frequently with regenerations. Hydrotheca tubular (Fig. 3h), with diameter increasing from diaphragm to basal third, then slightly decreasing to distal third, and finally widening again to aperture. Rim of hydrothecal aperture even, but everted and sinuous. Hydrothecal wall with more or less marked facets, fading basally. A few short renovations of hydrothecal rim might be present. Hydrotheca with distal diverticulae (Fig. 3h).
Measurements (in µm). Stolon: diameter 380. Pedicel: length 1800–4000. Hydrotheca: height 2900–3400, diameter at aperture 1000–1300.
Remarks. There are a few records of the species, but most of them are dubious because the peculiar diverticulae characterising this species (Totton 1930) were neither described nor depicted; only Ralph (1957) noted their presence in her material.
Ecology and distribution. Tulpa diverticulata is known for sure from a depth of 456 m (Totton 1930); present material collected at a depth of 652−654 m.
The species is certainly present in New Zealand waters (Totton 1930; Ralph 1957).
Symplectoscyphidae Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016
Symplectoscyphus frondosus Peña Cantero, 2010
(Fig. 4a)
Material examined. TRIP 2996/1, one stem 100 mm high, broken into three main fragments, on coral.
Description. Stem erect, 100 mm high, rigid, markedly tortuous, strongly polysiphonic (diameter at basal part 3 mm). Branches more or less perpendicular to long axis of stem, strongly polysiphonic over great extent, tightly packed, and approximately of similar development, giving stem a bottlebrush appearance. Primary branches spirally arranged, completing a turn every five branches.
Branches and stems divided into short internodes by alternating oblique nodes, each internode with one hydrotheca. Hydrothecae alternately arranged in approximately one plane, densely packed, with distal part of each hydrotheca clearly overlapping basal part of following one (Fig. 4a). Hydrotheca slightly curved abcaudally. Adcauline wall adnate to internode for about half its length; free part of adcauline wall slightly convex or straight. Abcauline wall slightly convex basally and slightly concave distally. Rim of hydrothecal aperture with three cusps separated by deep embayments. Hydrothecal diameter distinctly decreasing towards aperture.
Measurements (in µm). Hydrotheca: abcauline wall 360–400, free part of adcauline wall 210–260, adnate part of adcauline wall 210–270, adcauline wall 420–500, diameter at aperture 110–130, maximum diameter 150, diameter at base 110.
Ecology and distribution. Shelf and slope species, known from depths between 321 and 2283 m (Peña Cantero 2019); present material collected at a depth of 1637 m.
Previously considered endemic to the eastern Ross Sea (Peña Cantero 2017, 2019), the present material, outside the typical area, represents its northernmost recorded occurence.
Symplectoscyphus nesioticus Blanco, 1977
(Fig. 4b)
Material examined. TAN 1802/186, a few stems up to 10 mm high, on T. diverticulata and axis of a dead gorgonian.
Description. Monosiphonic, unbranched stems up to 10 mm high and nine hydrothecae. Stem internodes in marked zigzag, each with a distal hydrotheca.
Hydrotheca tubular, free for most of its adcauline wall (Fig. 4b); free part of adcauline wall slightly convex. Hydrotheca usually with distinct inflexion point where adcauline wall becomes free. Abcauline wall slightly concave. Hydrothecal aperture with three sharp cusps separated by deep embayments. Hydrothecal diameter usually increasing distally.
Measurements (in µm). Hydrotheca: abcauline wall 370–430, free part of adcauline wall 230–400, adnate part of adcauline wall 80–100, adcauline wall 310, diameter at aperture 180–200.
Ecology and distribution. Shelf species (Peña Cantero 2017), collected at depths from 56 (Peña Cantero 2006) to 701 m (Peña Cantero 2014); present material found at a depth of 652–654 m.
Circum-Antarctic distribution (Peña Cantero 2014). In the region, known from the Ross Sea (Peña Cantero 2017) and from a seamount of the nearby Scott Island (Peña Cantero 2019).
Haleciidae Hincks, 1868
Halecium divergens sp. nov.
(Figs 5–6)
Material examined. TRIP 2993/20, several stems up to 10 mm high, with gonothecae, on axis of dead gorgonian (Holotype, NIWA 131355).
Description.Monosiphonic stems, up to 10 mm high, arising from stolons creeping on axis of dead gorgonian. Stems resting on stolonal apophyses (Fig. 5a–b), sometimes followed by an athecate internode (Fig. 5b). First hydrothecate internode either ‘typical’ (Fig. 5b) with distal hydrotheca and apophysis supporting successive internode, or without apophysis and first regular internode originating within distal hydrotheca (Figs 5a, 6b). Successive typical internodes in marked zigzag (Fig. 6a) (angle about 70°) and resting on strong apophysis originating from below hydrotheca (Fig. 5a–b). New branches originating from hydrophores of lower-order hydrothecae. Distance between hydrotheca and apophyses small (Fig. 6b-d), resulting in a free and very short hydrophore. Internodes usually very long, with a basal swelling.
Hydrothecae alternately arranged in one plane (Fig. 6a), placed at end of a short, free hydrophore (Figs 5a–c, 6b–c); ratio between adcauline length of hydrophore and diameter at diaphragm 0.2–0.5. Without pseudodiaphragm, but sometimes with thin perisarc projection on adcauline side of hydrophore (Fig. 5b). Hydrothecae usually at level of basal node of following internode (Figs 5a–b, 6b–d), relatively high, strongly widening distally (Figs 5a–c, 6b–d), with everted rim (Fig. 6d) and ring of desmocytes above diaphragm. Up to third-order hydrothecae observed on long and smooth hydrophores.
Gonothecae extremely flat and concave (spoon-shaped), with distal aperture, resting on a short pedicel originating directly from stolon (Fig. 6e). Putative male gonotheca roughly rounded (Figs 5e, 6g). Putative female gonotheca larger (Figs 5d, 6e), with distinctly longer pedicel, two basal lobes, and aperture forming a sort of embayment (Figs 5d, 6f).
Measurements (in µm).Stolonal apophyses: length 100-150 (350), width 110–140. Internodes: length 1400–1800 (up to hydrothecal diaphragm), wide 120–150. Hydrothecae: height 60–90, diameter at aperture 210–270, diameter at diaphragm 150–170. Adcauline length of hydrophore: 30–50. Lower-order hydrophore: length up to 950. Female gonothecae: height 1450, width 1100, aperture 200. Male gonotheca: height 1000, width 870, aperture 190. Cnidome: microbasic euryteles 10–11 x 4.5–5.5 and microbasic mastigophores 7.5 x 2.
Remarks.The extreme flatness of the gonothecae is likely due to the fact that they have already shed their contents. On one occasion, a gonotheca was found originating from below the hydrotheca of the first stem internode; the rest of the many gonothecae present in the studied material arise directly from the stolons.
As mentioned earlier, there are two types of stems based on the structure of the first internode. Some stems begin with a regular internode that includes a distal hydrotheca and an apophysis below it supporting the following internode (Fig. 5b). In contrast, other stems start with an internode that has a distal hydrotheca but lacks an apophysis. In this case, the next internode originates from the hydrophore of a lower-order hydrotheca, typically a secondary hydrotheca (Fig. 5a), although it may also originate from an even lower-order hydrotheca.
The species has free hydrophores, a feature shared with a group of other Antarctic species of Halecium (H. antarcticum Vanhöffen, 1910, H. banzare Watson, 2008, H. exaggeratum Peña Cantero, Boero and Piraino, 2013, H. frigidum Peña Cantero, 2010, H. interpolatum Ritchie, 1907, H. pallens Jäderholm, 1904 and H. pseudodelicatulum Peña Cantero, 2014). However, it differs from all these species because the hydrophore is distinctly much shorter. The closest species in this feature is H. interpolatum, although that length is still significantly longer in Ritchie’s species; the ratio between the adcauline length of the hydrophore and the diameter at the diaphragm is around 0.8–0.9 in H. interporlatum, but only 0.2–0.5 in the present species.
By the size and general shape of the hydrotheca it is also closest to H. interpolatum. However, they differ in colony and internode structure. In Ritchie’s species, the stems, basally polysiphonic and slightly geniculate, give rise to paired branches originating from the hydrophore of a primary hydrotheca. Halecium interpolatum is also distinctive in the shape of the internodes, which have a long and straight basal part followed by one or two annulations. Neither of those features are found in the present species. Finally, while the gonothecae develop from within the hydrotheca in H. interpolatum, in the present species, as mentioned earlier, they arise from the stolons.
Ecology and distribution. Halecium divergens sp. nov. was collected at depths between 1541 and 1770 m, on the axis of a dead gorgonian. Gonothecae in December.
Etymology. The specific name divergens makes reference to the marked different directions taken by the successive internodes. From New Latin divergens.
Halecium jaederholmi Vervoort, 1972
(Fig. 7)
Material examined. TRIP 2993/11, a few stems up to 60 mm high, with one female gonotheca, on axis of a dead gorgonian.
Description. Stems up to 60 mm high, honey-coloured, polysiphonic and branched. Branching irregular, sometimes branches almost unilateral and nearly perpendicular to plane of hydrothecae. Branches resting on large apophysis originating from hydrophore of a hydrotheca, usually on one lateral, although closer to abcauline side. Typically, one ahydrothecate internode after apophysis (Fig. 7a), sometimes more (Fig. 7b). Occasionally, branches originating from inside a hydrotheca.
Stem and branches divided into internodes by slightly oblique alternating nodes; one hydrotheca per internode. Hydrothecae arranged alternately in two planes, forming an angle of about 70°. Primary hydrothecae resting on sessile hydrophores (Fig. 7a–c). Adcauline hydrothecal wall much more developed than abcauline one and completely adnate to internode (Fig. 7a, c–d), frequently extending to distal node (Fig. 7d). Hydrothecal aperture slightly directed downwards (Fig. 7b). One secondary hydrotheca sometimes present, not resting on a hydrophore and, therefore, practically within primary hydrotheca. Secondary hydrotheca approximately equally developed all around.
Female gonotheca kidney-shaped (Fig. 7e), with two hydrothecae at the concave side.
Measurements (in m). Internode: length 750–1000, wide 150–180. Hydrothecae: height 30–40, diameter at aperture 180–190, diameter at diaphragm 160–180. Hydrophore: adcauline length 120–150. Gonotheca: height 1500, maximum diameter 600. Cnidome: microbasic euryteles 11.0±0.7 x 5.1±0.2 (n= 10), range 10–12 x 5.0–5.5, microbasic mastigophore 7.5 x 3.
Remarks. There is usually an ahydrothecate internode after the apophyses supporting the branches, although there may be even more (up to eight have been observed). However, this seems to be related to fractures. In fact, ahydrothecate internodes may also be found along the branches, clearly indicating that they formed following a fracture.
Ecology and distribution.Shelf and slope species, collected at depths from 24 (Vervoort 1972) to 950 m (Peña Cantero 2019); present material found at a depth of 1533 m, extending significantly its lower bathymetric limit.Gonotheca in December.
Pan-Antarctic distribution (Peña Cantero 2014). In the region, reported from the Ross Sea (Peña Cantero 2017) and from seamounts of the nearby Scott Island (Peña Cantero 2019).
Family Sertularellidae Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016
Sertularella pseudovervoorti Peña Cantero, 2019
(Fig. 4c–f)
Material examined. TRIP 2993/20, a few stems up to 10 mm high, on axis of a dead gorgonian.
Description. Monosiphonic stems up to 10 mm high and five hydrothecae, unbranched or scarcely branched (up to second-order branches present). Branches originating below a hydrotheca (Fig. 4c–e). Stem divided into relatively long and thin internodes by slightly marked, alternating, oblique nodes. Internodes arranged in a marked zigzag pattern. First stem internode much longer.
Hydrotheca cylindrical, practically straight, free for most of its adcauline length (Fig. 4c–f). Maximum diameter distinctly above adnate part; diameter slightly decreasing distally and more markedly basally. Abcauline wall either approximately straight or slightly convex basally and concave distally. Free part of adcauline wall slightly convex, with three or four slight undulations; adnate part practically straight. With distinct inflexion point between free and adnate parts of adcauline wall. Rim of hydrothecal aperture with four small, equally developed cusps, separated by shallow embayments.
Measurements (in μm): Internodes: length 1220–4400 (first internode 2600–4400), diameter at hydrothecal base 170–200. Hydrothecae: length of abcauline wall 500–550, free part of adcauline wall 320–450, adnate part of adcauline wall 150–250, adcauline wall 550–640, diameter at aperture 190–250, maximum diameter 230–290.
Remarks. The stems are either unbranched or scarcely branched. Only four stems are branched, usually having one or two primary branches; only one stem has a second-order branch. This particular stem, approximately 8 mm high, has a primary branch originating below its fourth hydrotheca. This primary branch, in turn, gives rise to an incipient secondary branch at its third hydrotheca, which has not yet formed a hydrotheca.
The position of the primary branch is variable; it has been observed at the first, second, fourth, or fifth hydrotheca in different stems.
The main axis of the stems has up to five hydrothecae, although some of the branched stems have up to eight hydrothecae in total.
The first internode is distinctly longer than the remaining stem internodes, their length decreasing distally; for instance, in one stem, the length of the first four internodes was 4400, 2100, 1420 and 1220 µm, respectively.
The colony structure and the shape of the hydrotheca in the studied material perfectly agree with the type material of S. pseudovervoorti, although the hydrothecae are distinctly smaller. However, this difference could be attributed to intraspecific variation. It is important to note that knowledge of this species is based on very limited material. Sertularella pseudovervoorti was previously known only from the original description, which was based on a few stems up to 15 mm high. Consequently, I am considering the present material as belonging to S. pseudovervoorti, which, in addition, was discovered in the nearby Scott Island area.
Ecology and distribution. Sertularella pseudovervoorti was previously known from depths between 1520 and 1560 m (Peña Cantero 2019); present material collected between 1541 and 1770 m, slightly increasing its lower bathymetric limit. It has been found growing on the axis of dead gorgonians (Peña Cantero 2019; present material).
This represents the second record of the species. It was previously known only from a seamount off Scott Island (Peña Cantero 2019).
Phylactothecidae Stechow, 1921
Hydrodendron arboreum (Allman, 1888)
(Fig. 4g–h)
Material examined. TAN 1802/186, three stems up to 50 mm, on axis of gorgonian.
Description. Stems polysiphonic, up to 50 mm high, branched. Branching in one plane, in subopposite pairs. Only primary branches present, monosiphonic. Stem and branches divided into relatively long internodes bearing one hydrotheca each.
Hydrothecae alternately arranged in one plane. Hydrotheca on a short hydrophore provided with a distinct free part (Fig. 4g). Hydrothecae completely free (Fig. 4g), low, with a ring of desmocytes between diaphragm and aperture; abcauline and adcauline wall straight, the former slightly abcaudally directed. Hydrothecal diameter barely increasing distally. Hydrothecal aperture circular, markedly tilted abcaudally; rim even. Lower-order hydrothecae (up to fourth-order observed) usually present (Fig. 4g), on short hydrophores, with a ring of desmocytes, and a circular aperture (rim slightly everted); hydrothecal diameter distinctly increasing distally. Typically, one nematophore per internode, on opposite side of hydrotheca, but an extra nematophore also common on abcauline side of primary hydrophore (Fig. 4g). Nematophores provided with small cone-shaped nematotheca with desmocytes (Fig. 4h).
Measurements (in m). Internode: length 840–1500, diameter at distal node 180–210. Hydrothecae: height 20–30, diameter at aperture 210–240, diameter at diaphragm 200–230. Hydrophore: adnate part 230–240, free part 20–70. Nematotheca: height 60–80, diameter at aperture 75–80.
Remarks. All the stems are polysiphonic, although they are provided with a significant monosiphonic distal part. The stems are also branched, except for the smallest. The branches are typically monosiphonic, although one branch has a small basal portion with incipient polysiphony.
Branching appears to occur in subopposite pairs, which is evident in the most developed stem. This stem has six primary branches arranged in three subopposite pairs.
Ecology and distribution. Eurybathic species found at depths from 18 (Hickson and Gravely 1907) to 1370 m (Peña Cantero and Ramil 2006); present material collected at a depth of 652−654 m.
Pan-Antarctic distribution (Peña Cantero and Ramil 2006). In the region, frequently reported from the Ross Sea (cf. Peña Cantero 2017) and once from the Balleny Islands (Peña Cantero 2009).