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: 210-212

publication ID

http://doi.org/ 10.1080/00222930600621601

persistent identifier

http://treatment.plazi.org/id/011D87C1-FFD9-CD6E-1FBF-FC9BE631FD44

treatment provided by

Felipe

scientific name

Ascidia scaevola ( Sluiter, 1904 )
status

 

Ascidia scaevola ( Sluiter, 1904)  

( Figure 10G View Figure 10 )

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 View Materials ); Tasmanian Canyons (40.79269 ° S, 144.21916 ° E, 94 m) GoogleMaps   .

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.

Ascidia thompsoni Kott, 1952  

( Figure 7E View Figure 7 )

Ascidia thompsoni Kott 1952, p 312   ; 1985, p 56 and synonymy.

Ascidia challengeri: Kott 1985, p 32   .

Distribution

Previously recorded (see Kott 1985): Tasmania (Great Taylor Bay, Port Davey ); South Australia ( St Vincent Gulf ). New records: Tasmania ( Port Davey , SAM E2889 View Materials ); Tasmanian Canyons ( Pieman Canyon , 472.8 m, QM G308827)   .

Description

The newly recorded individuals are 10 and 15 cm long, respectively, narrow anteriorly and increasing to about 4 cm wide posteriorly. The surface is even but rough and the test is firm, even and translucent. The body is laterally flattened. The terminal branchial aperture has about eight lobes and the margin is fringed (although this is obscured in this specimen). The sessile atrial aperture is two-thirds of the body length along the dorsal surface. About 100 long, curved branchial tentacles are crowded around the base of the branchial siphon. The dorsal ganglion can be seen about halfway between the dorsal tubercle (behind the tentacular ring) and the atrial siphon. The slit on the dorsal tubercle is basically U-shaped with the opening directed anteriorly. The horns are turned in or out and sometimes it is interrupted or slightly convoluted and sometimes the dorsal tubercle slit is pulled out into sharp angles (see QM G9325 from St Vincent Gulf and the newly recorded specimen QM G308827). A meshwork of muscles is on the right side of the body. The branchial sac has about six stigmata per mesh. The inside curve of the tight secondary gut loop is swollen with mud. The long stomach with its fine longitudinal fold occupies at least half of the outer (ascending) limb of the primary loop, and is overlaid by this mud-filled portion of the gut. The distal part of the rectum is bent back postero-dorsally to terminate at the base of the short atrial siphon. Shallow lobes are on the anal border. Gonads are usually in the primary loop of the gut, although they appear to be senescent in the large specimen from Pieman Canyon. Small intermediate branchial papillae are only at the junctions of parastigmatal with internal longitudinal vessels.

Remarks

The species is distinguished from Ascidia sydneyensis   (which has a mud-filled gut and translucent test) by its numerous branchial tentacles, body musculature, the position of the dorsal ganglion and the relatively simple U-shaped slit on the dorsal tubercle, and the postero-dorsal bend of the distal part of the rectum. With the exception of its musculature, these characters distinguish the species from A. saccula   n. sp. and the Antarctic A. challengeri Herdman, 1882   (which both have translucent tests and mud-filled gut).

SAM

South African Museum

QM

Queensland Museum

Kingdom

Animalia

Phylum

Chordata

Class

Ascidiacea

Order

Phlebobranchia

Family

Ascidiidae

Genus

Ascidia

Loc

Ascidia scaevola ( Sluiter, 1904 )

Kott, Patricia 2006
2006
Loc

Ascidia scaevola: Kott 1985 , p 53

Kott P 1985: 53
1985
Loc

Ascidia challengeri: Kott 1985 , p 32

Kott P 1985: 32
1985
Loc

Ascidia thompsoni

Kott P 1952: 312
1952
Loc

Styelopsis scaevola

Sluiter CP 1904: 89
1904