Eucoelium coronaria ( Monniot, 1988 )

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 : 1119-1121

Eucoelium coronaria ( Monniot, 1988)

Polycitorella coronaria Monniot, 1988, p. 228 ; Kott 1990a, p. 184 and synonymy.

Distribution

Previously recorded (see Kott 1990a): Western Australia (from North-West Cape to Cockburn Sound ); South Australia ( Great Australian Bight , Pearson and Ward Islands ); Victoria ( Port Phillip Bay ). New record: Western Australia CSIRO SS10 / 05 (Kalbarri, Stn 102, 96– 98 m, 05.12.05, QM G328017 ) .

The new record is within the range formerly recorded for the species.

Remarks

Eucoelium coronaria ( Monniot, 1988) displays a range of colony shapes, from sessile cushions or sessile to stalked cones like the present ones. The present preserved colonies lack the black pigment often found in the test of the upper surface of the previously recorded preserved specimens. The posterior end of the gut loop in these newly recorded contracted zooids is drawn up into a wide loop in the same way as previously reported for this species (see Kott 1990a, Figure 68g).

Family PROTOPOLYCLINIDAE Kott, 1992

The type genus Protopolyclinum Millar, 1960 from the North Island, New Zealand, is monotypic. Its type species, P. pedunculatum , has colonies consisting of small, oval heads each on a long, narrow stalk. The zooids have vestiges of internal longitudinal vessels in the form of biramous branchial papillae on the transverse vessels.

The family Protopolyclinidae as originally defined contains genera with separately opening six-lobed apertures, large pharynges with numerous long rectangular stigmata, and gonads in a posterior abdomen with testis follicles sometimes bunched behind the ovary. A large and smooth stomach is about halfway down a relatively short abdomen, the rectum extending nearly to the base of the atrial siphon. The large stomachs of all Protopolyclinidae are smooth externally but usually have irregular creases in the internal epithelium that presumably are artefacts of their collapse. Occasionally these creases have been erroneously interpreted as folds.

Kott (1992a) included in the family the genera Protopolyclinum Millar, 1960 , Monniotus Millar, 1988 and Condominium Kott, 1992a . In the present work Pseudodiazona Millar, 1963 , with entire longitudinal branchial vessels (formerly considered a genus of the Diazonidae ) has been included in the Protopolyclindae, having, like most other genera in the family, its gonads in a posterior abdomen rather than enclosed in the gut loop (as in Diazonidae ). Genera in this family appear to represent successive stages in the evolution of aplousobranch ascidians which, with increasingly prolific replication, have progressively smaller zooids with a smaller and more simplified branchial sac. Most closely related to an aplousobranch ancestor with a large branchial sac, possibly like Ciona , is Pseudodiazona , with numerous rows of stigmata and entire internal longitudinal vessels. Protopolyclinum Millar, 1960 and Monniotus Millar, 1988 lack entire internal longitudinal branchial vessels but retain one or more branchial papillae (presumed to be the relicts of internal longitudinal vessels) on the transverse vessels. They have progressively fewer rows of fewer stigmata. In Condominium Kott, 1992a branchial papillae have not been detected.

With the exception of Pseudodiazona , genera of the Protopolyclinidae have zooids arranged in systems (albeit not cloacal systems) that separate the excurrent water driven out of the forward projecting atrial apertures from that drawn into the posteriorly directed branchial apertures. In Condominium areolatum ( Kott, 1992a) , completely embedded zooids have branchial and atrial apertures along opposite sides of the margin of the colony. Where zooids are only partially embedded or separate from one another, as in C. floreum sp. nov. (below) and Monniotus spp. , branchial apertures are directed down from the sometimes flat antero-ventral surface of the zooid, while the atrial apertures are directed up from the opposite side of the terminal anterior end of each zooid.

Ritterellidae Kott, 1992a , a related family with separately opening zooids, a short abdomen and a posterior abdomen, is separated from the present family by its distinct parallel external folds in the stomach wall. Colonies of Ritterellidae have numerous zooids forming systems similar to those of Condominium and there has been some confusion in generic assignations. Ritterella multistigmata Kott, 1992a appears to be a synonym of Monniotus australis ( Kott, 1957) , having similar zooids and colonies, including its meshwork of thoracic muscles. Its stomach folds are internal, and are artefacts. It should also be noted that, although Kott (1992a) recorded two species of Monniotus from Australia, their ranges overlap and their differences may be associated with age and/or contraction. Ritterella rete Monniot F. and C., 1991, an irregular colony covered in sand, has a regular mesh of longitudinal and transverse vessels on the thorax and longitudinal muscles on the remainder of the zooid. It lacks stigmata, as do so many abyssal species. However, the pharyngeal wall does have the frame of the internal longitudinal branchial vessels like those in Pseudodiazona and this, with the lack of external stomach folds and the long posterior abdomen, suggests that the species should be assigned to Pseudodiazona (see below) rather than to the Ritterellidae . Another deep water species, Ritterella folium Monniot C. and F., 1991, with true stomach folds and a short posterior abdomen, appears to be correctly assigned.

Pseudodistomidae and Euherdmaniidae also have separately opening zooids and a posterior abdomen but are distinguished from the Protopolyclinidae and Ritterellidae by many characters. Pseudodistomidae have a smooth-walled, fourchambered stomach more or less halfway down a moderately long abdominal gut loop, a brood pouch at the posterior end of the thorax, and only three rows of stigmata. Euherdmaniidae is clearly distinguished by its long oesophagus and stomach at the end of the long abdomen (as in the genera Eudistoma and Polycitor of the Polycitoridae ). The long abdomen and eversible tubular adhesive organs are both characters it shares with Pycnoclavellidae and, despite the lack of a posterior abdomen in the latter family, this may indicate a relationship between Pycnoclavellidae and Euherdmaniidae .

Larvae are known for only few of the species in these related families. Larvae of the general polyclinid type, with ectodermal ampullae and vesicles, are known for Monniotus australis , and for Ritterella pedunculata and Dumus areniferus (Ritterellidae) . These larvae are clearly different from those of Euherdmaniidae with their inverted tubular adhesive organs.