Didemnum spumante, Kott, 2010

Kott, Patricia, 2010, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 2), Journal of Natural History 38 (26), pp. 2455-2526 : 2500-2506

Didemnum spumante sp. nov.

( figures 9A , 20D )

Distribution. Type locality: Western Australia (Green Head, near Leeman, in crevice, high tide, coll. M. and D. Griffiths, 4 July 1989, holotype WAM 195.90; paratype WAM 194.90).

Description. Colonies are thin white sheets, opaque with crowded spicules and some sandy debris incorporated in the basal test. The small, crowded spicules are interrupted around the branchial apertures by circles of minute spherical vesicles. Similar vesicles are present throughout the test giving it a foamy consistency. Spicules are crowded in the linings of the branchial apertures. The spicules are small, to 0.03 mm diameter, with 9–11 blunt conical to rounded rays in optical transverse section. The spicule rays are relatively short and are made up of not very tightly compacted parallel crystals, and some are bipartite with a short conical tip in the centre of a cylindrical basal portion. The common cloacal cavity is shallow and thoracic.

Zooids are very small, but contracted, with a short retractor muscle from the posterior end of the thorax. Seven coils of the vas deferens surround the undivided testis. Small larvae have the tail wound three-quarters of the way around the 0.36 mm-long trunk containing four club-shaped ectodermal ampullae each side of the three antero-median adhesive organs.

Remarks. Although there are no particularly distinctive characters in either colony or zooids of this hard, encrusting species, its spicules provide a compelling difference from other species. They are a similar form to the spicules of D. elongatum Sluiter, 1909 and D. vahatuio Monniot and Monniot, 1987 (which, however, has spicules with more rays), both species having some stellate spicules with terminal cones on cylindrical bases. Nevertheless, both these species have larger spicules than the very small ones of the present species.

Didemnum tabulatum Sluiter, 1909

( figure 20E )

Didemnum tabulatum Sluiter, 1909: 49 ; Kott, 2001: 241.

Distribution. Previously reported (see Kott, 2001): Western Australia (W of Port Hedland), Indonesia. New record: Western Australia (Dongara WAM 143.93).

The newly recorded colony is from 219 m.

Description. The colony is sheet-like, about 1.0 mm thick, growing over a sponge. Occasional common cloacal apertures have about seven pointed spiculefilled lobes around the rim that project into the opening. These are the continuations of the radial ribs that surround the aperture in the roof of the common cloacal cavity. Spicules are crowded throughout the colony. Zooids are evenly spaced, the thoraces crossing the common cloacal cavity each with a ventral strip of spicule-filled test. Abdomina are embedded in the basal test. Spicules are to 0.07 mm diameter, stellate, with up to 20 or more conical or fusiform pointed rays. Also there are occasional spicules with flat-tipped or truncated rays, some almost globular. Zooids have short cylindrical branchial siphons, sessile atrial openings, six stigmata in the first two rows and five and four, respectively, in the last two rows. Those in the last two rows are circular perforations. Gonads were not detected.

Remarks. The stellate, many-rayed spicules of this seldom-reported species are distinctive. Although similar to those of D. multispirale Kott, 2001 , they have longer and more needle-like rays, and most resemble the spicules of the dubius group in the genus Leptoclinides . Although globular spicules and flat-tipped rays have not previously been reported for this species, they probably have been overlooked, all other characters reported being the same as in the newly recorded colony.

Didemnum ternerratum Kott, 2001

( figures 10 , 20F )

Didemnum ternerratum Kott, 2001: 241 and synonymy.

Distribution. Previously recorded (see Kott, 2001): South Australia (Great Australian Bight, Wright I., Ward I.), Victoria (Western Port). New record: South Australia (Kangaroo I., SAM E2920).

Description. Dome-shaped, brownish colonies have terminal common cloacal apertures on elevations about 5 mm diameter. The surface is quilted, with depressions over the primary common cloacal canals. Dark brown zooids are along each side of the primary common cloacal canals. Small stellate to globular spicules (to 0.046 mm diameter) are crowded in the surface and basal layers of test, but are patchy elsewhere. The spicules have 15–17 rays in optical transverse section. The small zooids have a forked atrial lip on the anterior rim of the wide, sessile atrial opening, a small pointed but strong retractor muscle, eight coils of the vas deferens and a large brown egg.

Remarks. This well-defined species is known only from the south-eastern corner of the continent.

Didemnum vahatuio Monniot and Monniot, 1987

( figure 20G )

Didemnum vahatuio Monniot and Monniot, 1987: 43 ; Kott, 2001: 246 and synonymy.

Distribution. Previously recorded (see Kott, 2001): Queensland (Swain Reefs), New Caledonia, French Polynesia. New record: Western Australia (Jurien Bay, WAM 204.93).

The new record is the first of this species in the Indian Ocean.

Description. The new record is of scraps of white, brittle, encrusting sheet. Branchial apertures are stellate, surrounded but not outlined by crowded stellate spicules. The spicules are large (to 0.08 mm diameter) with 9–11 well-spaced conical rays in optical transverse section. They are crowded throughout and the smooth upper surface of the colony is raspy with them. The surface test is thin. Each thorax crosses the common cloacal cavity with an independent ventral strip of test. Abdomina are embedded in the basal test, which is half of the whole thickness of the colony.

Remarks. Kott (2001) reported 13–15 spicule rays in optical transverse section. However, revision of the material on which this count was made has shown this to be incorrect, there being 9–11 rays as in the present material.

Trididemnum paracyclops Kott, 1980

Trididemnum paracyclops Kott, 1980: 12 ; 2001: 276 and synonymy.

Distribution. Previously recorded (see Kott, 2001): Queensland (Capricorn Group, Lizard I.), Palau Is, New Caledonia, Guam, Philippines, Fiji, French Polynesia. New record: Western Australia (Shoalwater Bay-Cockburn Sound, WAM Z10921 ).

The record is the most southerly record for this species and the first for the Indian Ocean.

Description. The specimen appears to have been dried out at some stage. It has been identified by the presence of a posterior abdominal common cloacal cavity and by its spicules. The spicules are globular, burr-shaped and stellate, to 0.08 mm diameter and have 13–15 short, blunt rays in optical transverse section.

Remarks. In describing the spicules of the present species, Kott (2001: figure 174A) appears to have overlooked their similarity to those of T. cyclops Michaelsen 1921 , which, although smaller, have the same globular, burr-like and stellate shapes, and some stellate spicules with rays of various lengths.

Trididemnum pigmentatum Kott, 2001

Trididemnum pigmentatum Kott, 2001: 278 and synonymy.

Distribution. Previously recorded (see Kott, 2001): Western Australia (Montebello Is, Kimberley), Queensland (Hervey Bay, Capricorn, Sarina, Lizard I.), Indonesia, Fiji. New records: Northern Territory (Angler Reef, QM G308619; Mandorah Jetty, QM G308635).

Description. Colonies are thin, flexible, grey sheets, black in life with a smooth surface. Minute black pigment cells are in the aspiculate superficial layer of test. Beneath this there are moderately crowded spicules in the upper (zooid) layer of the test, but there are no spicules in the lower (posterior abdominal) layer of the colony where some faecal pellets and embryos are embedded. Internally the test is yellowish. The large (to 0.1 mm diameter) stellate spicules have 13–15 long, crowded pointed conical rays in optical transverse section. Sometimes there are lobes and ridges projecting from the surface of the colony.

The zooids are covered in black squamous epithelium which obscures their structure. A long retractor muscle projects from the top of the oesophageal neck. Each of the branchial lobes has a black pigment spot in the tip. There is a posteriorly directed atrial siphon. The pyloric end of the gut loop is bent ventrally at right angles to the longitudinal axis of the zooid.

Remarks. Although the species resembles other Trididemnum spp. in some respects, the large spicules with many pointed rays help to distinguish it. Faecal pellets are embedded in the basal layer of the colony but they do not form a distinct layer as they do in T. savignii . The layer of black squamous epithelium around the zooids has been reported previously for this species, although the black pigment in the superficial layer of test has not.

Trididemnum pseudodiplosoma (Kott, 1962)

Didemnum pseudodiplosoma Kott, 1962: 321 .

Trididemnum pseudodiplosoma: Kott, 2001: 279 .

Trididemnum inermum Monniot and Monniot, 2001: 263 .

Distribution. Previously recorded (see Kott, 2001; Monniot and Monniot, 2001): South Australia (Gulf St Vincent), Coral Sea. New records: South Australia (Reevesby I., SAM E2912), Northern Territory (South Shell I., QM G308633, G308650; Angler Reef, QM G308649).

Description. The colonies from the Northern Territory are soft with outgrowths from the surface forming spongy, complex three-dimensional masses. There is a gradation in the amount of pigment in the three newly recorded colonies, those from South Shell Is sometimes having minute, oval black pigment cells massed together to form irregular black streaks in the surface while the colony from Angler Reef has a smooth black surface. Internally all three specimens are translucent and whitish in preservative. There are no spicules. Common cloacal cavities are oesophageal and posterior abdominal. Also, the overgrowths from the surface of the colony enclose secondary external spaces inside the colony. The test is very soft. The colonies from South Australia are small aspiculate plates, to 1.0 cm diameter with a few, stray, burr-like to stellate, spicules to 0.04 mm diameter and juvenile zooids lacking gonads.

Zooids have an extensive prestigmatal unperforated area in the pharynx, three rows of stigmata with 12 in the anterior row, a posteriorly directed atrial siphon, a delicate retractor muscle projecting from the posterior end of the thorax, an oesophageal sphincter muscle consisting of a few delicate fibres about halfway down the oesophageal neck, and branchial and atrial sphincters. Zooids do not have an endostylar pigment cap. Branchial tentacles are conspicuously long. Gonads were detected in one of the specimens (QM G308633) in which eight coils of the vas deferens surround the undivided spherical testis. Characteristic larvae (see Kott, 2001) are present in the colony from Angler Reef. Both specimens were collected in September.

Remarks. The species lacks the black squamous epithelium and endostylar pigment cap of T. discrepans and has fewer stigmata. Trididemnum pseudodiplosoma (Kott, 1962) has a distinctive larva with many blastozooids, and the larvae in the newly recorded colony (QM G308649) are identical to those in previously recorded material (see Kott, 2001). Colonies and zooids of the type material of T. inermum are identical with those of the present species.

Trididemnum savignii (Herdman, 1886)

Didemnum savignii Herdman, 1886: 261 .

Trididemnum savignii: Kott, 2001: 281 ; 2002c: 39.

Distribution. Previously recorded (see Kott, 2001, 2002c): Western Australia

(Nares Rock), Queensland (Heron I., Lizard I.), Northern Territory (Darwin), Indonesia;?Florida, Bermuda, West Indies. New records: Northern Territory (Plater Rock, QM G308618; Weed Reef II, QM G308626).

Description. Colonies are gelatinous but firm with terminal common cloacal apertures on surface elevations. A conspicuous superficial bladder cell layer overlies a layer of spicules at thorax level but spicules are sparse in the remainder of the test. The common cloacal cavity is posterior abdominal and the basal layer of test beneath it varies in thickness, sometimes being twice the thickness of the zooid layer. A thick layer of faecal pellets is in the base of the colony. Spicules are large, to 0.11 mm diameter, with 11–13 pointed conical rays in optical transverse section. Zooids are relatively small, the atrial aperture on a posteriorly directed siphon, the tapering retractor muscle projecting from the posterior end of the thorax, about 12 stigmata per row and eight coils of the vas deferens around the undivided testis. There is no black squamous epithelium on the zooid.

Remarks. Trididemnum pigmentatum has spicules like those of the present species, with similar strong conical pointed rays. However, in the present species the spicules have a more restricted distribution, the rays are not so crowded and they are less numerous, the superficial bladder cell layer is more conspicuous and there is a distinct layer of faecal pellets in the base of the colony. Although the zooids of this species have previously been reported to have black squamous epithelium, it was not found in the newly reported specimens; nor were there irregularly shaped black pigment cells in the superficial bladder cell layer.

Trididemnum sibogae (Hartmeyer, 1910)

Didemnum sibogae Hartmeyer, 1910: 1489 nom. nov. for Didemnum ramosum Sluiter, 1909: 63 .

Trididemnum sibogae: Kott, 2001: 281 and synonymy; 2002c: 39; 2004.

Distribution. Previously recorded (see Kott, 2001, 2002c, 2004): Western Australia (Cape Jaubert), South Australia (Cape Jaffa, Port Turton, Kingston, Flinders and Kangaroo I.), Victoria (Western Port); Tasmania (Swan I., southern Tasmania), New South Wales (Port Hacking, Sydney Harbour, Arrawarra), Queensland (Fraser I., Bargara, Cairns, Princess Charlotte Bay), Northern Territory (Darwin, Gulf of Carpentaria), New Caledonia, Indonesia, India. New record: Northern Territory (Angler Reef, QM G308605).

Description. The newly recorded colony is grey in life, but becomes greenish yellow in preservative. It consists of hard, thin, paper-like lamellae forming a spherical three-dimensional reticulum of coalescing branches. The upper surface of each branch is rounded and even, forming the smooth outer surface of the sphere. Branchial siphons protrude through a thin superficial layer of bladder cells that overlies the crowded spicules in the relatively thin zooid layer of test that surrounds the central common cloacal cavity. Thin spicule-filled supporting rods of test connect the zooid layer of test with a thin layer that lines the internal cavity, i.e. across the posterior abdominal cavity. The central cavity has openings into the posterior abdominal cavity and connects with the thoracic cavities around the zooids. These hard supporting rods of test often project out from the surface in pointed papillae—always crowded with spicules. Spicules are large (to 0.09 mm diameter), stellate, with 11–13 long, narrow, pointed rays in optical transverse section.

Zooids have an endostylar pigment cap, about 12 stigmata per row, and eight coils of the vas deferens around the undivided testis.

Remarks. The colony superficially resembles Didemnum spongioides Sluiter, 1909 , which also has a complex three-dimensional colony and pointed spiculefilled papillae on the surface. The zooids are characteristic of the genus Trididemnum and, with the spicules, conform with previously reported colonies of the present species.

Figures

FIG. 9. Didemnum spumante (WAM 194.90). (A) Thorax; (B) larva. Scale bars: 0.1 mm.

FIG. 20. (A) Didemnum poecilomorpha (WAM 142.93); (B) Didemnum scopi (WAM 203.93); (C) Didemnum sordidum (WAM 189.93); (D) Didemnum spumante (WAM 194.90); (E) Didemnum tabulatum (WAM 143.93); (F) Didemnum ternerratum (SAM E2920); (G) Didemnum vahatuio (WAM 204.93); (H) Lissoclinum coactum (WAM 1136.89).

FIG. 10. Didemnum ternerratum (SAM E2920). (A) Colony surface; (B) thorax; (C) abdomen. Scale bars: 1.0 cm (A); 0.1 mm (B, C).