Ascidia scaevola ( Sluiter, 1904 )

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234 : 210-211

Ascidia scaevola ( Sluiter, 1904)

( Figure 10G )

Styelopsis scaevola Sluiter 1904, p 89 .

Ascidia scaevola: Kott 1985, p 53 and synonymy.

Distribution

Previously recorded (see Kott 1985): South Australia (Great Australian Bight, St Vincent Gulf); Victoria (Lakes Entrance, Sale, Port Phillip Bay ); Queensland (Moreton Bay, Gladstone, Bowen Townsville, Nymph I.); Indonesia. New records: South Australia (Edithburgh, 3–4 m, SAM E2871 ); Tasmanian Canyons (40.79269 ° S, 144.21916 ° E, 94 m) .

Description

The specimens are up to 14 cm long. As usual, they are dorso-ventrally flattened with the body wall closely adherent to the stiff, brittle, thin, sandy test. The sessile branchial and atrial openings, respectively, are at the base of the incurrent and excurrent pseudosiphons, which rise vertically from the upper surface. In the largest specimen the outer half of each tube is bent in the same direction. Internally the thin body wall, branchial wall, short transverse muscle bands, large branchial fold and flat, double gut loop are as previously described ( Kott 1985).

Remarks

The collector has noted that the Edithburgh specimens are buried in sand, only the pseudosiphons projecting above the sea floor. The pseudosiphons of the present species are distinctive, as are the short muscle bands. But in some respects the species resembles Phallusia polytrema ( Herdman, 1906) and Microgastra granosa (see below) and they all appear to occupy sea-floor habitats where they are buried in sand. They all have thin, brittle sand-filled test, a thin body wall adhering closely to the test and delicate branchial sacs. However, in the former species, the descending limb of the gut loop accumulates sand and the gut forms a simple J-shaped loop; while in the latter species (which has a dorsal branchial fold like A. scaevola ), the small gut loop is evaginated from the body wall and the distinctive gonads and neural organs with their associated part of the body wall, are embedded in the test.

Figures

Figure 10. In situ images of: (A) Synoicum sacculum (SAM E2864); (B) Synoicum sacculum (SAM E3288); (C) Synoicum sphinctorum (SAM E3283); (D) Aplidium abditum (SAM E3268); (E) Aplidium brevilarvacium (SAM E3284); (F) Aplidium clivosum (SAM E3390); (G) Ascidia scaevola (SAM E2871); (H) Botryllus stewartensis (SAM E3289).