Euclavella claviformis ( Herdman, 1899 )

Kott, Patricia, 2007, Taxonomic affinities of three stalked colonial species of the Ascidiacea (Tunicata) from the central coast of New South Wales and indications of a trans-Tasman connection, Journal of Natural History 41 (9 - 12), pp. 633-645 : 635-636

Euclavella claviformis ( Herdman, 1899)

Figures 1A, B ; 3A

Colella claviformis Herdman 1899, p. 67 . (syntypes: AM U151, U241, G12248) Euclavella claviformis: Kott 1990, p. 79 and synonymy.

Distribution

Previously recorded (see Kott 1990). New South Wales (Ballina, Jervis Bay, Port Hacking, Port Jackson, Port Stephens); New Zealand (Bay of Islands, North Island).

New record. New South Wales ( Port Stephens , QM G308883 ). Known from 15 to 20 m.

Description

Both newly recorded colonies have a short thick stalk, about 1 cm in diameter. The outside of the stalk has an opaque, yellowish wrinkled cuticle, but internally the test is soft, gelatinous and translucent. The spherical head of one colony is 3 cm in diameter and the other has a conical head about 3 cm long. Zooids are relatively large and open all around the transparent, globular or conical head. In the newly recorded specimens zooids are contracted and the two anterior siphons with their apertures constricted into transverse openings are conspicuous and turned slightly away from one another. The top of the thorax (around the apertures) is flattened or slightly concave. About 10 fine longitudinal muscles are on each side of the thorax and extend down onto the abdomen and the posterior abdominal stolons, which are long and crowded extending parallel to one another down the length of the stalk. The branchial sac has eight long rows of about 30–40 long narrow stigmata in each half row although stigmata are shorter in the posterior rows. The interstigmatal bars are flattened into wide membranes. The gut loop is narrow, vertical and relatively short, being only about twice the length of the thorax and the anus opens about halfway up the branchial sac. Gonads were not detected in these specimens although previously they have been observed in the gut loop. A developmental sequence of up to eight embryos to tailed larvae is in the distal part of the oviduct. In contracted zooids this part of the oviduct, with the embryos it contains, forms a horizontal loop crossing the dorsal line from the left to the right and projects out like a collar around the top of the oesophageal neck. The most advanced larvae are released into the right peribranchial cavity. The larvae are spherical with four rows of small stigmata and an ocellus and otolith. Three triradially arranged deeply invaginated tubular adhesive organs are at the anterior end of the larval trunk.

Remarks

Kott (1990) erroneously reported the lack an otolith in larvae of this species. On reexamination of the specimens she described from Port Stephens and Port Jackson (New South Wales) and the Bay of Islands ( New Zealand) a small spherical otolith can be seen, partly obscured by the ocellus. The short larval tail that Kott (1990, Fig, 27d) observed in a mature larva possibly is in the process of being withdrawn into the trunk. A short larval tail is not a characteristic of the Australian populations which usually have a long tail wound almost the whole way around the trunk as in New Zealand specimens. Differences in the specimens of this species from each side of the Tasman Sea have not been detected.

Figures

Figure 1. Euclavella claviformis (QM G308883): (A) colony; (B) developmental sequence of embryos in the distal part of the oviduct forming a collar around the top of the oesophageal neck. Hypsistozoa distomoides (QM G308880): (C) colony; (D) zooid; (E) zooid (with denticles on the atrial lip); (F) larva (left side with ectotrophic membranes pulled away from the trunk); (G) larva (with ectotrophic membranes intact); (H) larva (right side with ectotrophic membranes pulled away from the trunk). Scale bars: A, B, 10 mm; C–G, 0.2 mm.

Figure 3. In situ colour images: (A) Euclavella claviformis; (B) Hypsistozoa distomoides colony lying flat on the sea floor at low slack tide; (C) Sigillina cyanea from high-energy location, showing tip of colony worn by abrasion on sea floor sediments. The possibly commensal nudibranch Nembrotha sp. is associated with the colony.