Pseudodiazona longigona ( Tokioka, 1959 )

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 : 1121-1122

Pseudodiazona longigona ( Tokioka, 1959)

( Figures 2C–E )

Homoeodistoma longigona Tokioka 1959, p. 224 .

Pseudodiazona claviformis: Kott 1990a, p. 31 and synonymy, 2005b, p. 29; 2006, p. 178.

Distribution

Previously recorded (see Kott 2005b): South Australia (Great Australian Bight, Gulf St Vincent); Victoria (Port Phillip Bay, Eden, Cape Howe); Tasmania (Port Davey, Five Mile Bluff); New South Wales (Jervis Bay, Botany Bay); Japan (Sirahama). New record: Western Australia CSIRO SS10/05 (Albany, Stn 22, 100 m, 22.11.05, QM G328066).

Apart from the type specimen from Sirahama ( Japan) previous reports of this species are only from the south-eastern quarter of the Australian continent in shallow waters (to 10 m), generally in embayments. The new record from deeper waters in the south-west considerably extends its range. The Japanese type specimen is from a similar depth (120 m) .

Description

The newly recorded specimen is conical, to 14 cm high and about 12 cm diameter at the base. It is fixed to the substrate by a small area in the centre of the basal surface. An accessory lateral lobe of the colony arises from the base of the cone. The test is soft, gelatinous and translucent. Unfortunately the zooids in this specimen are contracted and their structure is obscured. Zooid openings are evenly spaced over the surface. Separate branchial and atrial apertures, both six-lobed, are evenly spaced over the outer surface. Strong longitudinal muscles extend along the whole length of the zooids, and a strong band is along each side of the abdomen and the posterior abdomen. About 30 rows of crowded stigmata can be detected in the branchial sac. Triangular dorsal languets are on transverse vessels where they cross the mid-dorsal line. Papillae supporting crowded internal longitudinal vessels are on the transverse branchial vessels. The oesophagus is relatively short and the smoothwalled stomach in the middle of the descending limb of the gut loop is separated from an oval posterior stomach by a short section of mid-intestine. The rectum occupies the whole extent of the distal (ascending) limb of the gut loop and extends up to the anterior third of the long branchial sac, opening near the base of the atrial siphon. Numerous testis follicles are strung out along the length of the posterior abdomen, although they are usually bunched either at the posterior end or along its whole length, presumably as a result of contraction.

Remarks

Pseudodiazona claviformis ( Kott, 1963) and its synonyms (see Kott 2005b) formerly known from the south-eastern quarter of Australia were, on the basis of their entire internal longitudinal branchial vessels, thought to be species of the Diazonidae . However, in Pseudodiazona the heart is at the end of a long posterior abdomen, which contains the gonads, while in Diazonidae there is no posterior abdomen, the heart is at the end of the abdomen and the gonads are also in the abdomen (in the gut loop). Pseudodiazona appears to belong to the Protopolyclinidae , differing from the monotypic genus Protopolyclinum only in having entire internal longitudinal branchial vessels rather than relicts of them as branchial papillae. Indeed, Kott (1963) may have been correct in originally assigning the present species to the genus Protopolyclinum , rather than the genus Pseudodiazona Millar, 1963 which was erected later the same year in the family Diazonidae . Homoeodistoma longigona Tokioka, 1959 from Sirahama (120 m) also has a long posterior abdomen with a long series of male testis follicles and ova lined up in the oviduct extending from the posterior abdomen into the thorax. Other aspects of the zooids, including their apertures, musculature, gut, gonads and the anal opening are similar to Pseudodiazona claviformis ( Kott, 1963) and although the internal longitudinal branchial vessels have not been reported for the Japanese specimens they are most likely to be present (see Millar 1963; Kott 1990a). At this stage Kott’s (1990a, p. 33) view that the Japanese species is distinguished by its more robust colony does not appear to be a valid reason for separating these species. Accordingly, Pseudodiazona longigona ( Tokioka, 1959) appears to be the senior synonym of Pseudodiazona claviformis Kott, 1963 and its synonyms (see Kott 1990a).

The newly recorded colony is different from those previously reported with a sandy base and rounded to flat-topped heads on cylindrical stalks (see Kott 1990a). The upright conical shape of the newly recorded specimen has not previously been reported for this species. The long posterior abdomina and crowded internal longitudinal branchial vessels appear to be the same as those previously reported. The soft test is reminiscent of a number of species of Pseudodistoma (e.g. P. gracilum Kott, 1992a ), however Pseudodistoma has only three rows of stigmata and other distinctive characteristics, such as a brood pouch with no more than three developing embryos (see Kott 2007).

It should be noted that Homoeodistoma longigona Tokioka, 1959 was erroneously assigned to Homoeodistoma Redikorzev, 1927 . It is not related to Homoeodistoma michaelseni Redikorzev, 1927 (, Placentela crystallina Redikorzev, 1913 from the Sea of Ohotsk). Placentela Redikorzev, 1913 is the type genus of the monotypic family Placentelidae , which has gonads in a posterior abdomen, although the heart is in the abdomen rather than at the posterior end of the posterior abdomen (see Kott 1992a). Placentela areolata Kott, 1963 , from Mackay (Queensland), has gonads in a posterior abdomen, separately opening apertures and lacks branchial papillae. However, unlike the genus Placentela , its heart is at the end of the posterior abdomen. Kott (1992a) designated it the type species of a new genus, Condominium , in the family Protopolyclinidae , distinguished from other genera in the family by its lack of either branchial papillae or internal longitudinal vessels.

Ritterella rete Monniot C. and F., 1991, taken from 200–300 m off New Caledonia is completely encrusted with sand, as is Condominium floreum sp. nov., although its zooids are reported to be completely embedded rather than projecting from the common test at their anterior ends (as in the latter species). The New Caledonian species resembles Ritterella spp. and Condominium spp. in the longitudinal and transverse muscles on the thorax and the longitudinal muscles extending along the abdomen and the posterior abdomen. The species is distinguished by the apparent absence of stigmata in the mature zooids despite the small round perforations with parastigmatic vessels reported in the less mature zooids. Monniot C. and F. (1991, Figure 6F ) reported branchial perforations in R. rete to be stigmata that have lost their ciliated epithelium. However, from their description and accompanying figure, the branchial wall appears to be delineated by a framework of transverse and longitudinal vessels homologous with the vessels in the reduced branchial sacs of many abyssal species. Nevertheless, whatever the actual homology of the branchial sac of this New Caledonian species, it is readily distinguished from Ritterella in the absence of stomach folds. It may be more accurately assigned to Pseudodiazona .

Figures

Figure 2. Eudistoma convocatum sp. nov. (QM G328114): A, colony; B, zooid. Pseudodiazona longigona:(QM G328066) C, colony, with two small accessory lobes and sandfilled pharynges evident in some parts of the surface; D, thorax and abdomen; E, posterior abdomen with gonads. Scales: A, 5 cm; B, D, E, 1.0 mm; C, 5 cm.

Figure 6. Synoicum pseudogrisiatum sp. nov. (QM G328118): A, colony; B, thorax and abdomen; C, posterior abdomen; D, anterior part of pharynx showing neural complex. Synoicum rapum sp. nov. (QM G328012): E, colony; F, thorax; G, part of branchial sac showing branchial papillae on transverse vessels. Scales: A, E, 2.0 cm; B–D, F, 1.0 mm.