Atriolum irregulare, Kott, 2007

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1165-1167

Atriolum irregulare sp. nov.

( Figures 1A , 6A )

Distribution

Type locality: Tasmanian Canyons (King I. Canyon, 236.6 m, holotype QM G323245 ) .

Description

The newly recorded specimen is a small (about 1.5 cm maximum dimension), firm, lumpy portion of a larger colony. It grows around a cylindrical (possible weed) stalk, which forms an axis through the centre of the colony. A large horizontal cloacal cavity is beneath the surface zooid-bearing layer. Cloacal apertures were not detected and may not be present in this mutilated portion of a colony. The spicules are crowded in the surface layer of test, which is raspy to the touch. They are less crowded internally. Spicules are stellate, to 0.10 mm diameter, with 11–15 moderately long, pointed, crowded rays in optical transverse section. The zooids are characteristic of this genus, with a long tubular atrial siphon projecting back to open directly into the common cloacal cavity. The branchial siphon is about half the length of the atrial siphon. Four rows of about 8–10 (per side) long rectangular stigmata are in the branchial sac. The gut loop is relatively simple, short, and vertical. Five coils of the vas deferens surround the large undivided testis. A retractor muscle was not detected. Larvae are present in the inner layer of test, behind the zooids. They are large, the trunk to 0.84 mm long, and the tail winds two-thirds of the way around it. Three lateral ampullae are along each side of the three anteromedian adhesive organs. Median ampullae are not present. The larval oozooid is well developed, occupying the posterior part of the trunk. It has well-developed branchial and atrial siphons, a vertical gut loop, and four rows of stigmata in the larval pharynx. Larvae are well developed, and a brood pouch attached to the top of the thoracic neck was not detected.

Remarks

The present species has pointed conical spicule rays about 0.1 mm diameter that resemble the spicules of Atriolum buccinum , a species also recorded from Western Australia. However, the latter species has only 9–11 rays in optical transverse section while the present species has 11–15. Atriolum robustum and A. lilium both have shorter spicule rays than the present new species and the former species is also distinguished by its small spicules (to 0.04 mm diameter). Spicules of the present species (from the southeastern part of the continental shelf in waters over 200 m) resemble those of A. tubiporum Kott, 2001 (from waters to 130 m off the southwestern corner of the continent) but they are larger with longer and more numerous rays and the colonies are not the conspicuously cylindrical lobes of the Western Australian A. tubiporum .

The present species has the large undivided testis, coiled vas deferens, long cylindrical atrial siphon, and large larvae that are characteristic of the genus Atriolum (see Kott 2001).

Figures

Figure 1. (A) Atriolum irregulare (QM G323245 holotype): larva. (B, C) Leptoclinides fluxus (QM G308817 holotype): (B) colony surface; (C) zooid. (D–F) Polysyncraton gratum (QM G308891): (D) thorax; (E) abdomen; (F) larva. (G) Polysyncraton reticulum (QM G323330): larva. Scale bars: 0.1 mm (A, C–G); 1 mm (B).

Figure 6. Scanning electron micrographs. (A) Atriolum irregulare (QM G323245); (B) Leptoclinides albamaculatus (QM G308876); (C) Leptoclinides dubius (QM G308892); (D) Leptoclinides durus (QM G308894); (E) Leptoclinides fluxus (QM G308817); (F) Leptoclinides placidus (QM G308766); (G) Polysyncraton cuculliferum (QM G3088458); (H) Polysyncraton gratum (QM G308891).