Pseudodiazona claviformis ( Kott, 1963 )

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234 : 178-179

Pseudodiazona claviformis ( Kott, 1963)

( Figure 8A )

Protopolyclinum claviforme Kott 1963, p 72 .

Pseudodiazona claviformis: Kott 1990a, p 31 and synonymy.

Distribution

Previously recorded (see Kott 1990a): South Australia (Great Australian Bight, Gulf St Vincent ); Victoria ( Port Phillip Bay , off Cape Howe , Eden ); New South Wales ( Jervis Bay ). New records: Tasmania ( Bathurst Channel , Port Davey , 6–8 m, SAM E3280 ; Five Mile Bluff) .

The newly recorded location is the most southerly known for this species, which is known only from the southeastern corner of the Australian continent.

Description

The newly recorded colonies consist of thick, sandy vertical stalks arising from a common basal mat, the top half of each stalk expanding slightly into a naked, transparent and glassy head. Vertical, parallel thread-like zooids can be seen opening around the top of the head by separate branchial and atrial apertures that project slightly from the surface. The apertures are each on short siphons of variable length, the length varying with the contraction of the thorax. The thorax is relatively large with numerous long rows of stigmata and internal longitudinal vessels extending the length of the branchial sac. The gut loop is short, the stomach smooth, and the rectum extends along the side of the pharynx, opening near the base of the atrial siphon. Gonads are in a posterior abdomen as previously reported for this species.

Remarks

Taxa with separately opening atrial and branchial siphons, the anal opening near the top of the relatively large thorax and gonads in a posterior abdomen are discussed in Kott (1990a, 1992a). The type species of Homoeodistoma , H. michaelseni Redikorzev, 1927 from the Sea of Okhotsk, was found to be a synonym of Placentela crystallina Redikorzev, 1913 (see Kott 1992a; Sanamyan 1993) which lacks internal longitudinal branchial vessels and has the heart in the abdomen. Although Millar (1963) first proposed the Japanese Homoeodistoma longigona Tokioka, 1959 as a member of the family Diazonidae , a hypothesis supported by Kott (1990a), its relationship to either Placentela or to Pseudodiazona Millar, 1963 (with internal longitudinal vessels and the heart at the end of the posterior abdomen) is not resolved (see Kott 1992a). Kott (1990a) has drawn attention to its similarity to the present species (a relationship so far unresolved).

Figures

Figure 8. In situ images of: (A) Pseudodiazona claviformis (SAM E3280); (B) Pycnoclavella tabella (SAM E3290); (C) Stomozoa australiensis (SAM E3285); (D) Sigillina exigua (SAM E3300, syntype); (E) Distaplia australiensis (SAM E3294); (F) Distaplia australiensis (SAM E3295); (G) Distaplia florida (SAM E3293); (H) Distaplia pallida (SAM E3273).