Atriolum tubiporum Kott, 2001

Kott, Patricia, 2008, Ascidiacea (Tunicata) from deep waters of the continental shelf of Western Australia, Journal of Natural History 42 (15 - 16), pp. 1103-1217 : 1166-1167

Atriolum tubiporum Kott, 2001

( Figures 12A ; 16A ) Atriolum tubiporum Kott 2001, p. 29 and synonymy.

Distribution

Previously recorded (see Kott 2001): Western Australia (Dongara, Green Pools, Albany). New records: Western Australia CSIRO SS10/05 (Albany, Stn 26, 212 m, 23.11.05, QM G328440; Bald I., Stn 35, 157 m, 24.11.05, QM G328004; Bald I., Stn 39, 99 m, 24.11.05, QM G328102; Albany, Stn 47, 179 m, 25.11.05, QM G328139).

The newly recorded material represents many hundreds of specimens. The species appear to have a range limited to the southern half of the Western Australian coast.

Description

Colonies are single or branched lobes, each lobe with a large terminal common cloacal aperture on a short cylindrical protrusion from the surface. Colonies are firm and tough with a relatively restricted central cavity. They have a smooth even surface and are a pinkish-cream colour in preservative. Stellate branchial apertures are evenly spaced over the surface, each with six, spicule-filled lobes. Stellate spicules are evenly distributed in a layer at the surface and they line the common cloacal cavity but are sparse elsewhere. They are up to 0.06 mm diameter and have 11–13 relatively short, evenly spaced, conical rays in optical transverse section.

Zooids are robust, with the long atrial siphon stretched between the zooid at the surface and the central common cloacal cavity. A circular lateral organ is on each side of the thorax, level with the fourth row of stigmata. The gut forms a voluminous double loop, divided into oesophagus, spherical stomach, conspicuous duodenum, a small almost spherical posterior stomach opening into a wide proximal part of the rectum. The latter is separated from the distal section of the rectum by a narrow midintestinal connecting tube. The stomach and the posterior part of the rectum are yellow in preservative. Gonads consisting of six coils of the vas deferens around an undivided testis were detected for the first time in the newly recorded material from Albany (QM G328440).

Remarks

Atriolum irregulare Kott, 2007 has fewer regular colonies without the cylindrical lobes and the large terminal common cloacal apertures of the present species and its spicules are fewer but larger (to 0.1 mm diameter) and with shorter rays than the present species. Atriolum robustum Kott, 1983 also has similar but more irregular colonies with smaller common cloacal apertures and although its spicules are a similar size (to 0.06 mm diameter) they have more (up to 18) short conical rays in optical transverse section.

Figures

Figure 12. Atriolum tubiporum (QM G328004): A, colony. Leptoclinides fungiformis: B1,2 (QM G328106, QM G328105), colonies; C (QM G328105), zooid; D (QM G328105); larva Leptoclinides multilobatus (QM G328128): E, abdomen showing gut loop and gonads. Scales: A, 1.0 cm; B, 2.0 cm; C, 0.1 mm; D, E, 0.2 mm.

Figure 16. Scanning electron micrographs of didemnid spicules: A, Atriolum tubiporum, QM G328004; B, Leptoclinides durus, QM G328158; C, Leptoclinides fungiformis, QM G328444; D, Leptoclinides vesica, QM G328458; E, F, Polysyncraton calculum, QM G328140; G, Polysyncraton dealbatum, QM G328119; H, Polysyncraton fistulum, QM G328446.