Pseudomonocelis pardii Schockaert and Martens, 1987

Curini-Galletti, Marco & Casu, Marco, 2005, Contribution to the knowledge of the genus Pseudomonocelis Meixner, 1943 (Rhabditophora: Proseriata), Journal of Natural History 39 (24), pp. 2187-2201 : 2192-2193

Pseudomonocelis pardii Schockaert and Martens, 1987

( Figure 2L )

Material examined

Tanzania: Dongwe, east coast of Zanzibar island, upper intertidal in mixed sediment: silty medium-fine sand with shell fragments (January 1999). Two specimens sagittally sectioned; three specimens studied karyologically .

Description

Sectioned specimens closely correspond to the original diagnosis, based on specimens from the Somali coast (Djezira). The main differences are:

1. Cilia in P. pardii are described as ‘‘extremely densely packed and short (2–3 M m)’’ and ‘‘difficult to discern, even at high power magnification’’ ( Schockaert and Martens 1987, p 104). They are longer (about 4 M m), with a ‘‘normal’’ density, in Tanzanian specimens.

2. P. pardii has been originally described as provided with a highly muscular, wholly unciliated horizontal canal connecting the vertical vaginal duct to a large bursa resorbiens ( Schockaert and Martens 1987, p 110; Figure 2 ). In Tanzanian specimens, the ‘‘horizontal canal’’ is subdivided into two distinct, enlarged regions: an outer, ciliated portion, connected to the vaginal duct, and an inner, unciliated portion, connected to a comparatively smaller bursa resorbiens ( Figure 2L ). Both regions of the canal are provided with a coating of circular musculature.

Karyology

With three isobrachial chromosomes in its haploid set, with the third pair markedly smaller (nearly three-fifths) than the first. Karyotype formula: 13.3¡0.3 M m; NF56; chromosome 1: 39.24¡1.27; 44.97¡0.77 (m); chromosome 2: 37.32¡0.84; 37.12¡0.95 (sm); chromosome 3: 23.44¡0.73; 41.69¡0.90 (m).

Remarks

Pseudomonocelis pardii is a large, stocky species, characterized by pigmentation and by the shape of the copulatory organ and of the complex vagina–bursa system ( Schockaert and Martens 1987). A very similar species ( P. schockaerti, Curini-Galletti and Cannon 1995 ) inhabits the ‘‘overlap zone’’ (southern Queensland–northern New South Wales) of eastern Australia, and a sister species relationship has been proposed for them ( Curini-Galletti and Cannon 1995). The shape of the ‘‘horizontal canal’’ of the female system, as described for Tanzanian specimens referred here to P. pardii , recalls that of P. schockaerti (in which the canal is however a veritable bursa), consisting of an outer, ciliated region, and of an unciliated inner region with thick vacuolar walls ( Curini-Galletti and Cannon 1995). Available data do not allow us to infer whether morphological differences between Somali and Tanzanian specimens are artefacts due to differential quality of histological mounts, allowing for more detailed observations, or reflect actual differences among populations to be inferred. Karyotype is at present only known for Tanzanian specimens: it is very similar to that of P. schockaerti , the main difference among sets being the centromeric index of chromosome 3, metacentric in Tanzanian specimens and acrocentric in P. schockaerti ( Curini-Galletti and Cannon 1995) . In particular, in no other Pseudomonocelis species is chromosome 3 so markedly smaller than the other two pairs. This feature may thus constitute a further synapomorphy for the two species.

Figures

Figure 2. (A–C) Pseudomonocelis caribbea sp. n.: (A) copulatory organ; (B) female genital organs; (C) spermatogonial mitosis. (D–G) P. ophiocephala, spermatogonial mitoses from different populations: (D) CAL; (E) HAI; (F) MLK; (G) OCC. (H, I) P. cf. caυernicola: live animals showing cephalic pigmentation. (L) P. pardii: section of the female genital region at the ‘‘horizontal canal’’ level. See text for abbreviations. Scale bar: 5 Mm (C–G); 10 Mm (A, B, H, L); 100 Mm (I).