Pseudomonocelis, Meixner, 1943

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 : 2193-2194

Pseudomonocelis cf. caIJernicola Schockaert and Martens, 1987

( Figure 2H, I )

Material examined

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

Description

The original description of P. caυernicola, based on specimens from the Somali coast (Hawadli, N of Mogadisciu), is particularly detailed. Only major differences from Schockaert and Martens (1987) are dealt with here:

• Somali specimens were unpigmented. Tanzanian specimens had an overall yellowish pigmentation, with a distinct, ovoid patch of dark brown pigment in front of the statocyst ( Figure 2H, I ).

• In Somali specimens, ventral ciliation begins just cranial of the accessory organ, with cilia 4–5 M m long, over all of the body. In Tanzanian specimens, ciliation begins anterior of the male pore, and ventral cilia, in the posterior region of the body, are particularly short (about 1–1.5 M m long) and sparse. Cilia progressively increase in density and length anteriorly, reaching 2.5–3 M m about midbody.

• In Somali specimens, vagina opens to the outside about midway between male pore and mouth. In Tanzanian specimens, distance between mouth and vagina is about one-third longer than distance between vagina and male pore.

• Somali specimens had a nearly spherical copulatory bulb, about 90 M m wide and 90 M m high, lined with a muscular sheath about 9 M m in diameter. Tanzanian specimens had a similarly shaped but smaller copulatory bulb, ranging from 40 to 60 M m in diameter and from 44 to 65 M m in height in the four specimens sectioned. Thickness of the muscular coating ranged from 5 to 13 M m.

Karyology

With three isobrachial chromosomes in its haploid set. Karyotype formula: 10.1¡0.5 M m; NF56; chromosome 1: 37.01¡0.38; 47.54¡0.41 (m); chromosome 2: 34.83¡0.52; 41.87¡1.11 (m); chromosome 3: 28.16¡0.37; 45.89¡0.97 (m).

Remarks

Somali and Tanzanian specimens present obvious similarities, especially in the presence of an unarmed accessory organ, located halfway between male and female pores, which closely agrees in morphological details and size in the two populations. There is also a general correspondence in the morphology of the reproductive organs, although the copulatory bulb appears consistently larger in Somali specimens. With respect to congenerics, both populations show a reduction of the ventral ciliation, particularly evident in Tanzanian specimens, where the area around the male pore is unciliated, and cilia are much sparser and shorter on both ventral and dorsal sides. The most obvious difference between the two populations lies in the pigmentation of Tanzanian specimens. Presence of a reddish brown pigment girdle in the cephalic area is a widespread feature in the genus Pseudomonocelis , probably arisen independently in different biogeographical areas ( P. cetinae Meixner, 1943 and P. agilis (Schultze, 1851) in the Atlanto-Mediterranean region; P. pardii , P. schockaerti and two undescribed species (cf. Curini-Galletti and Cannon 1995) in the Indo-Pacific region). In none of the species above, however, has an intra- or inter-populational variability in the expression of the pigmentation ever been documented. Interestingly, the unpigmented Somali specimens were collected in a coastal cave, where reduction of light may have inhibited the expression of pigmentation. It is, however, worth noting that the population collected at Dongwe ( Tanzania) has been cultured in our laboratory ever since, far from any direct sunlight, and depigmented specimens have never been observed in cultures. Lack of knowledge on the intraspecific variability of P. caυernicola, both within the type locality and in neighbouring, extra-cave habitats, prevents any further inference on the taxonomic attribution of Tanzanian specimens.

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).