Didemnum fragum 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 : 2441-2443

Didemnum fragum Kott, 2001

( Figures 7A–C , 15H , 20A )

Didemnum fragum Kott 2001, p 179 and synonymy.

Distribution

Previously recorded (see Kott 2001): South Australia (Eyre Peninsula, West I., Souttar Pt, Nuyts Archipelago, Gulf St Vincent); Victoria (Bass Strait, Western Port, Port Phillip Bay ) ;

Tasmania (E coast); New South Wales (Coffs Harbour, Manning Bight, off Cape Three Points). New record: Tasmania ( Port Davey , SAM E3239 E3266 ) .

Description

One newly recorded colony (SAM E3239) is sessile and divided into two lobes with a smooth and even surface. The other is a solid stalked lobe, the test of the stalk harder than that of the head and its surface is transversely wrinkled with a particularly crowded layer of spicules in the surface, which is raspy. Spicules are tightly packed in the surface of the colony but are less crowded internally where the test is softer, gelatinous and translucent. Spicules are stellate, up to 0.09 mm diameter, but they have a large size range. They have 9–13 short, robust conical rays in optical transverse section. The spicule rays are not especially crowded at the base. Common cloacal cavities are relatively shallow thoracic or oesophageal spaces but they become more extensive toward the top of the heads and extend into some posterior abdominal cavities near the base of the heads. Some spherical masses of minute dark brown globular bodies are in the test amongst and behind the zooids. Orange pigment cells are scattered in the test and in the body wall of the zooids. An in situ photograph of the newly recorded stalked specimen (SAM E3266) is of a conspicuous, bright red and white mottled lobe with two large distended terminal common cloacal apertures.

In the preserved specimen, branchial apertures are seen as small whitish points on the surface rather than stellate openings, but that could be the result of contraction. The small zooids have a relatively long branchial siphon, sessile, transverse atrial openings, a short retractor muscle from halfway down the oesophageal neck and the gut forming a double loop. Large yellow eggs are present and the vas deferens coils 11 times around the testis.

Remarks

The species is characterized by the robust, lobed colonies, and the large spicules with numerous short conical rays crowded in the surface of the colony lobes. The species is known only from temperate waters.

Figures

Figure 7. Didemnum fragum (SAM E3266). (A) Colony; (B) thorax; (C) abdomen. Scale bars: 1.0 cm (A); 0.1 mm (B, C).

Figure 15. Scanning electron micrographs of the calcareous spicules of: (A) Polysyncraton millepore (WAM 122.93); (B) Polysyncraton orbiculum (WAM 128.90); (C) Polysyncraton papyrus (SAM E3253); (D) Didemnum astrum (WAM 601.89); (E) Didemnum cilicium sp. nov. (SAM E3251, holotype); (F) Didemnum corium sp. nov. (SAM E3249, holotype); (G) Didemnum cygnuus (QM G308716); (H) Didemnum fragum (SAM E3266).

Figure 20. In situ images of: (A) Didemnum fragum (SAM E3266); (B) Didemnum fuscum (QM G308730); (C) Didemnum incanum (SAM E3252); (D) Didemnum jucundum (SAM E3236); (E) Didemnum leopardus (QM G308719, holotype); (F) Didemnum microthoracicum (SAM E3256); (G) Didemnum moseleyi (QM G308713); (H) Didemnum pellucidum (SAM E3271).