Chaetopleura debruini ( Strack, 1996 )

Schwabe, Enrico, 2006, Taxonomic notes on chitons. On some species of Chaetopleura from South Africa (Mollusca: Polyplacophora: Ischnochitonidae), African Invertebrates 47, pp. 23-30 : 28-29

Chaetopleura debruini ( Strack, 1996)

Fig. 5

The species Strack (1996) originally placed in the genus Lepidozona Pilsbry, 1892 has reticulate tegmentum sculpture, consisting of longitudinally arranged ribs on the central and antemucronal areas and radially arranged ribs on the head valve and on the postmucronal and lateral areas, each connected by minute bridges. Strack’s original placement is understandable, and was caused by the general appearance strongly resembling Lepidozona ( Fig. 5 ). In particular, the scale-like spicules of the perinotum reinforce this impression. Most recently, Kaas et al. 2006 placed the species in the genus Chaetopleura , although the argumentation was weak. The authors pointed out that the ventral perinotum scales are ‘...not featureless elongate rectangular elements like in Lepidozona (and several other genera), but the outer ends are differently sculptured’. However, their suggestion is supported by own examinations.

Several points justify transferring this species to Chaetopleura :

the dorsal perinotum shows minute tufts of hyaline hairs among the scale-like spicules

(ZSM Mol 20041059);

the central radular tooth is rectangular and stocky ( Strack 1996), a character that is

more common in members of the genus Chaetopleura , whereas species of

Lepidozona have a more elongate-rectangular central tooth that is usually tapered

centrally ( Kaas & Van Belle 1987); the nephridiopore is situated between the third and fourth ctenidia from the posterior in

wet-preserved specimens in a sample from Algoa Bay (ZSM Mol 20041059).

This corresponds well with the study of Sirenko (1993), who pointed out that in

members of the genus Chaetopleura the nephridiopore is situated between ctenidia

3 and 4 (from the posterior), while species of Lepidozona have their nephridiopore

behind ctenidium 5 from the posterior (he gave a range of between ctenidia 5/6 to

8/9).

DISCUSSION

With five species, the genus Chaetopleura is represented in South African waters by about 19% of the described species in the world (Kaas & Van Belle 1998). The genus was extensively revised by Kaas and Van Belle (1987, 1990) with full species descriptions, bibliographies and distribution data. Unfortunately, minor corrections are necessary to clarify the taxonomic position of some of the species. Chaetopleura pertusa (Reeve, 1847) was mentioned as having the holotype in the BMNH. The status of the available type remains unclear, and to enable further work on this topic, photographs of the relevant valves for determination are presented here for the first time. Examination of the species also has shown that two other taxa, Chiton pustulatus and Chaetopleura destituta , have to be removed from the synonymy of this species. A syntype of the first species was available for study, allowing differentiation from the probable holotype of Chiton pertusus , mainly on the basis of coarser valve sculpture. Chaetopleura destituta has a rather smooth valve with the exception of faint longitudinal jugal and antemucronal striation.The general appearance of this species strongly resembles that of Chaetopleura papilio , of which a good illustration of the type is available in Kaas and Knudsen (1992), and thus C. destituta is here synonymised with C. papilio .

Chaetopleura natalensis Kaas & Van Belle, 1990 is here regarded as a junior synonym of Chiton pustulatus Krauss, 1848 on the basis of a direct comparison of the primary types of both species. The South African Lepidozona debruini Strack, 1996 , although having a Lepidozona -like tegmentum, has a scale-like perinotum coverage interrupted by hyaline hairs, a broad rectangular central radula tooth ( Strack 1996), which may interpreted as Chaetopleura -like, and its nephridiopore position corresponds well with the condition described by Sirenko (1993) for other members of the genus Chaetopleura . Therefore, the transfer of Lepidozona debruini to Chaetopleura is here confirmed.

Thus, the five Chaetopleura species occuring in South Africa are:

Chaetopleura debruini ( Strack, 1996) , C. papilio (Spengler, 1797) , C. pertusa (Reeve, 1847) , C. pomarium Barnard, 1963 and C. pustulata ( Krauss, 1848) .

Figures

Fig. 5. Chaetopleura debruini (Strack, 1996), dorsal view of two specimens from Algoa Bay (ZSM Mol 20041059), anterior at top. Scale bar = 5 mm.