Pycnoclavella Garstang, 1891 (Pycnoclavellidae)

KOTT, PATRICIA, 2003, New syntheses and new species in the Australian Ascidiacea, Journal of Natural History 37 (13), pp. 1611-1653 : 1616-1617

Genus Pycnoclavella Garstang, 1891 (Pycnoclavellidae)

Monniot and Monniot (1996) and Monniot (1997a) reject the validity of Pycnoclavella , and the family Pycnoclavellidae on the grounds that differences in budding and larvae of Pycnoclavella and Clavelina , as demonstrated by Trason (1963), are insignificant and that other differences set out by Kott (1990a) are also invalid. Monniot and Monniot (1996: 204) invoke the fact that Garstang (1895) did not mention Pycnoclavella ‘in his work describing budding in Tunicata’ in support of their view that the budding process is not different in Clavelina and Pycnoclavella . Further, they believe that, as Cloney (1977, 1978, 1990) has demonstrated nine different kinds of adhesive organs in 28 species (‘one per thousand of the described ascidian species’—Monniot and Monniot, 1996: 204), it is inappropriate to regard a ‘single kind of papilla’ as a character justifying the genus and family. Neither argument is relevant to the assessment of phylogenetic relationships of these two genera. Larvae from many more than 28 species of the Ascidiacea are well documented and are well known to exhibit significant phylogenetic characters; and there is a significant difference between a cone of adhesive cells and an eversible tube with adhesive cells in its base that can hardly be dismissed as insignificant.

Pycnoclavella and the Pycnoclavellidae have a number of compelling differences from Clavelina and the Clavelinidae . In addition to differences identified by Trason (1963) in the larvae and budding process, in Pycnoclavellidae the abdomen is relatively long; gonads relatively small (the testis often being one or two follicles, or forming a compact mass in the posterior end of the gut loop at the side of a saclike ovary); fertilization is at the base of the oviduct, embryos being brooded as they pass up the oviduct in a developmental sequence; and the larvae lack a frontal plate (which, in Clavelina , carries the adhesive organs). These characteristics are discussed in full in Kott (1990a), where other aspects raised by the Monniots (1996) are also addressed. Further, the genus Archidistoma (type species Archidistoma aggregatum Garstang, 1891 ) to which the Monniots (1996) and Monniot (1997a) have assigned their specimens of Pycnoclavella spp. , is a genus of the Polycitoridae . It has, as do all Polycitoridae , a short vascular process, six-lobed branchial and atrial apertures, larval epidermal ampullae, antero-median stalked adhesive organs with an adhesive cone in an epidermal cup, usually embryos developing in the atrial cavity and replication by abdominal strobilation—none of which occur in Pycnoclavella . In a few species of Polycitoridae ( Polycitor annulus , P. calamus and P. circes ), eggs are known to be fertilized at the base of the oviduct and embryos start development in the abdomen (see Kott, 1990a), although others with equally long abdomina are fertilized in the thorax. Nevertheless, all polycitorids are readily distinguished from species of Pycnoclavellidae by their lobed apertures and the larval adhesive organs and ampullae.

The specimens of Pycnoclavella erroneously assigned to Archidistoma are A. diminuta: Monniot and Monniot, 1996 and Monniot, 1997a, and A. dubium: Monniot, 1997a from Mozambique. The latter species differs from P. diminuta (Kott, 1957a) only in being twice the size and having twice the number of stigmata per row.