Ceratopera axi ( Riedl, 1954 ) Den Hartog, 1964

Willems, W., Artois, T., Vermin, W., Backeljau, T. & Schockaert, E., 2005, ‘‘ Typhloplanoida’ ’ (Platyhelminthes: Rhabdocoela) from the Indian Ocean, with the description of six new taxa, Journal of Natural History 39 (19), pp. 1561-1582 : 1565-1566

Ceratopera axi ( Riedl, 1954) Den Hartog, 1964

ceratopera-axi ( Riedl, 1954) Den Hartog, 1964

Proxenetes axi Riedl, 1954 . Ceratopera bifida Ehlers and Ax, 1974 .

Localities

New locality. Port Couvreux (Kerguelen): between filiform green algae, mid-eulittoral, 0.4 m deep at high tide (25 November 1992) .

Other locality in the Indian Ocean. La Réunion ( Artois et al. 2000).

Known distribution. Gulf of Naples and Sicily ( Riedl 1954); Galapagos ( Ehlers and Ax 1974); Falkland Islands and California ( Karling 1986); Weddell Sea ( Artois et al. 2000); Eastern Australia ( Willems et al. 2004b).

Material

Observations on live specimens and one whole mount. Whole mounts from Falklands and California (collections of SMNH) and Australia (collections of LUC).

Remarks The stylet of the specimen from Kerguelen measures 121 Mm (88 Mm if measured as in Ehlers and Ax 1974). The bursal appendage (or mouthpiece) is 117 Mm long. These measurements correspond with those on the specimen from the Weddell Sea ( Artois et al. 2000), they are slightly larger than those of the specimen from La Réunion ( Artois et al. 2000) and much larger than those of the Australian ( Willems et al. 2004b) and the Galapagos specimens ( Ehlers and Ax 1974). The last-mentioned population was formerly described as a different species, C. bifida Ehlers and Ax, 1974 . According to Karling (1986), Artois et al. (2000) and Willems et al. (2004b), C. bifida Ehlers and Ax, 1974 is considered a junior synonym of C. axi ( Riedl, 1954) Den Hartog, 1964 .

As the variation in stylet size within C. axi is rather large, it would not be surprising that this ‘‘morphological plasticity’’ in fact hides a complex of cryptic species, as is the case for Gyratrix hermaphroditus Ehrenberg, 1831 (see Curini-Galletti and Puccinelli 1989, 1990, 1994, 1998; Artois et al. 2000; Artois and Schockaert 2001) or the ‘‘ setigerum species complex’’ within the taxon Trigonostomum (see Willems et al. 2004a). However, since the only known difference between the different populations of C. axi is this size variation of the stylet, it is at the moment highly arbitrary to split this complex into different formal species. Such an action should be backed up by a much more thorough morphological (and molecular) study of the species, which is clearly not within the scope of this study.