POLYCITORIDAE Michaelsen, 1904

Kott, Patricia, 2009, Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia, Journal of Natural History 43 (31 - 32), pp. 1947-1986 : 1958

Family POLYCITORIDAE Michaelsen, 1904

Type genus: Polycitor Renier, 1804 .

Species in this family can be distinguished by their long abdominal region (many times the length of the thorax) and by the position of the stomach (near the posterior end of the abdomen in the pole of the gut loop). Even when the length of the abdomen is reduced by contraction, the convolutions of the rectum and oesophagus crowded in it give an indication of its length in the relaxed zooid. Other unique features of the Polycitoridae include the conspicuously muscular zooids with an almost continuous internal coat of circular muscles on the thorax and separate longitudinal bands that continue along the whole length of the zooid. In the Diazonidae and Clavelinidae , families with zooids and colonies that superficially are similar to those of the Polycitoridae , the muscles referred to as “transverse” actually are branches or curved terminal ends of the longitudinal bands. Zooids in the Polycitoridae usually are embedded in relatively tough test, often with sand and other inclusions. Often (but not always) the zooids, while maintaining their separate independent openings to the exterior, are arranged in circles (their excurrent openings in the centre of the circle) forming rudimentary common cloacal systems ( Kott 1990). Like Diazonidae , the separate branchial and atrial apertures of Polycitoridae have six-lobed openings (different from the smooth-rimmed apertures of clavelinids). Also, like the Diazonidae , replication in the Polycitoridae is by strobilation of the abdomen, while in Clavelinidae vegetative buds form in the ectodermal terminal ampullae of test vessels.

Gonads are in the pole of the gut loop (as they are in all aplousobranch taxa that lack a posterior abdomen). Unique to the Polycitoridae (but not reported for all known species), is the fertilization of eggs in the base of the abdomen and their incubation as they move up the oviduct into the atrial cavity. Also, with some exceptions (as in Policitor circes in which they are triradially arranged) the adhesive organs in the larvae of the Polycitoridae are usually in an antero-median row distinguishing them from the Diazonidae and Clavelinidae , which have triradially arranged adhesive organs.

The lack of a posterior abdomen and the presence of the gonads in the posterior end of the long gut loop distinguish the Polycitoridae from the Polyclinidae and related families which often have bulky colonies and sand embedded in the test.

The most speciose genus in the family is Eudistoma , which has relatively uniform zooids, but is distinguished from the less diverse but often reported genus Polycitor by having only three rows of stigmata, more sand and other inclusions in the common test and usually smaller zooids and larvae. Other genera, Polycitorella and Cystodytes , both very contractile, distinguished by their calcareous spicules that resemble those of the Didemnidae , are not represented in this collection.