Trididemnum amiculum Kott, 2001

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 : 2453-2454

Trididemnum amiculum Kott, 2001

( Figures 10A–C , 16G , 21A )

Trididemnum amiculum Kott 2001, p 256 ; 2004a, p 760.

Distribution

Previously recorded (see Kott 2001, 2004a): Tasmania (Devonport); New South Wales (Cronulla, Coogee). New record: Tasmania (Port Davey, SAM E3263).

Description

The newly recorded colony is similar to previously reported specimens (see Kott 2001, Figure 21a , 2004a), being a large, vertical mass with a sessile, terminal common cloacal aperture with a spicule-free rim around the opening. Robust rounded vertical ridges and some projecting branches from the upper part of the colony that fuse with it near the base form prop-like buttresses supporting the vertical colony. A large common cloacal cavity beneath the terminal aperture connects with other cavities that extend down the length of the vertical ridges. The outer zooid-bearing layer of test is connected to a branching central test core by ligaments that cross the cloacal cavities. Spicules are present throughout the test, but are especially crowded in the branching central test core which forms an internal skeletal support for the colony. Spicules are to 0.108 mm diameter and have 9–11 relatively long pointed rays in optical transverse section.

Zooids are small, with black squamous epithelium. The branchial siphon is short and the atrial siphon is posteriorly orientated and trumpet-shaped. A small retractor muscle is at the posterior end of the thorax. A previously recorded specimen (AM Z1681) has been reexamined and, as in the newly recorded specimen, seven coils of the vas deferens were detected, rather than the five coils Kott (2001) erroneously reported.

Remarks

The massive vertical colonies of this species appear to be characteristic. At this stage, smaller colonies have not been assigned to the species and may look quite different. Although the large stellate spicules are not unusual in the species of this genus forming complex three-dimensional colonies, the relatively few vas deferens coils is unusual, T. nobile Kott, 2001 having 10 coils, and T. pigmentatum Kott, 2001 , T. sibogae ( Hartmeyer, 1910) and T. pseudodiplosoma ( Kott, 1962) having eight. Trididemnum lapidosum Kott, 2001 from north-western Australia also has seven coils like the present species. However, although T. lapidosum forms a three-dimensional colony, its colony lobes are flat, its branchial siphon is short and its spicules are to 0.16 mm diameter.

The spicule distribution in the present species appears to be variable. Both the newly recorded colony and the one from Coogee reported on by Kott (2004a) have spicules throughout but they are especially crowded in the central test mass. However, Kott (2001) reported a spicule-free central test mass and spicules in layers at the surface and lining the common cloacal canals.

Figures

Figure 10. Trididemnum amiculum (SAM E3263). (A) Colony; (B) thorax; (C) abdomen. Scale bars: 1.0 cm (A); 0.1 mm (B, C).

Figure 16. Scanning electron micrographs of the calcareous spicules of: (A) Didemnum incanum (SAM E3238); (B) Didemnum leopardus sp. nov. (QM G308719, holotype); (C) Didemnum moseleyi (WAM 175.93); (D) Didemnum plebeium sp. nov. (WAM 155.93, syntypes); (E) Didemnum stragulum (WAM 162.93); (F) Didemnum ternerratum (SAM E3240); (G) Trididemnum amiculum (SAM E3263); (H) Trididemnum areolatum (QM G308746).

Figure 21. In situ images of: (A) Trididemnum amiculum (SAM E3263); (B) Trididemnum nobile (SAM E3262); (C) Trididemnum pigmentatum (QM G308714); (D) Trididemnum savignii (QM G308721); (E) Lissoclinum calycis (QM G308749); (F) Lissoclinum clavatum (SAM E3260, holotype); (G) Lissoclinum concavum (SAM E3242); (H) Lissoclinum levitum (SAM E3254).