Lissoclinum coactum Kott, 2004b

Kott, Patricia, 2005, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (Part 3), Journal of Natural History 39 (26), pp. 2409-2479 : 2463-2464

Lissoclinum coactum Kott, 2004b

( Figures 13A–C , 17G )

Lissoclinum coactum Kott 2004b, p 2506 .

Distribution

Previously recorded (see Kott 2004b): Western Australia (Hopetoun, southern coast). New record: Western Australia (off Mason Bay , 38 ° 57940S, 120 ° 289100E, WAM 120.90 ). The newly recorded specimen is from almost the same location as has previously been recorded for this species .

Description

The newly recorded colony is large, hard and sheet-like, with the surface marked off into ridges and prominences, and with common cloacal apertures on the high parts of these prominences. Sometimes branchial apertures can be seen to be in double series each side of surface depressions over the circular common cloacal canals that surround zooid-free areas. The thick spicule-filled surface test is interrupted abruptly by the delicate, spicule-free test around the conspicuous stellate branchial apertures, outlined in spicules, which are depressed into the hard, smooth colony surface. A black dot, where the dark zooid is visible, is in the centre of each branchial aperture. Common cloacal apertures also have black margins where the spicules are absent from the test. The zooids often have their ventral surface supported by the stands of test surrounded by the common cloacal canals, but other zooids cross the common cloacal canal in their own sheath of test. These stands and sheaths of test are always crowded with spicules and are stiff and hard. Common cloacal canals are deep and often the whole zooid or group of zooids is surrounded by the cavity and is connected to the basal test by a stiff, narrow ligament. Spicules are to 0.04 mm diameter, with up to 13 rays in optical transverse section. The majority of the spicules are burr-like to globular with thick flat-tipped rod-like rays, but occasional spicules have long club-shaped rays. Other spicule rays appear to have subdivided, possibly an artefact resulting from their collection and preservation.

Zooids have a large sessile atrial aperture exposing most of the branchial sac directly to the common cloacal cavity. Two male follicles and a straight vas deferens are in the usual position. Large larvae are present in the zooid-free stands of test, just beneath the surface, presumably about to be released. The larvae have six ampullae along each side of the three antero-ventral adhesive organs.

Remarks

The newly recorded specimen does not have the same soft consistency that Kott (2004b) reported for the type material. Also, possibly as a result of a breakdown in the spicules, there is a greater range in the number of spicule rays than Kott (2004b) recorded for the type material. However, the depressed branchial apertures (albeit they occur in other species of this genus) together with the thick spicule rays, almost globular spicules and the occasional spicules with long, club-shaped rays distinguish this species from other Lissoclinum spp. So far it has been recorded only from a restricted part of the southern Australian coast.

Figures

Figure 13. (A–C) Lissoclinum coactum (WAM 120.90): (A) colony surface; (B) zooid; (C) larva. (D, E) Clitella nutricula (SAM E 3275): (D) thorax; (E) abdomen. Scale bars: 1.0 mm (A); 0.1 mm (B–E).

Figure 17. Scanning electron micrographs of the calcareous spicules of: (A) Trididemnum dispersum (WAM 1044.89); (B) Trididemnum nobile (SAM E3262); (C) Trididemnum pigmentatum (QM G308714); (D) Lissoclinum agriculum sp. nov. (WAM 179.93, syntypes); (E) Lissoclinum bistratum (WAM 1018.89); (F) Lissoclinum clavatum sp. nov. (SAM E3260, holotype); (G) Lissoclinum coactum (WAM 120.90); (H) Lissoclinum diversum (WAM 153.86).