Pseudomonocelis caribbea, Curini-Galletti & Casu, 2005

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 : 2189-2192

Genus Pseudomonocelis Meixner, 1943 Pseudomonocelis caribbea sp. n.

( Figures 1 , 2 A–C)

Material examined

Holotype: Belize: San Pedro (Ambergris Cay) (17 ° 579N, 87 ° 559W), beach at the northern end of the town, about 30 cm deep in well-sorted medium sand (August 1992); sagittally sectioned ( SMNH type-5969) . Other material: three specimens (same data as holotype) studied alive and processed for karyology.

Etymology

The specific epithet is coined after the geographical location of the type locality.

Description

The sectioned specimen is about 0.8 mm in length. Anterior end rounded, provided with numerous oily droplets and with two pigmented eyespots lateral to the statocyst. Posterior end rounded, with numerous adhesive papillae. The epidermis, with depressed nuclei, is ciliated except at the caudal tip. Cilia are 3–4 M m long, slightly longer dorsally than ventrally. With numerous, elongate and comparatively large rhabdoid glands (12–15 M m long in sections), particularly evident in the caudal area. Large numbers of ovoid glands, whose necks pierce the epithelium, are present all over the body: they are particularly numerous dorsally at the caudal tip. These glands are about 11 M m long, with flat nucleated lining and very fine, granular eosinophilous content. The high number of these glands, as well as of rhabdoids, gives the animal’s body a distinctive ‘‘opaque’’ appearance. Body musculature appears weakly developed, with one layer of external circular muscles, and very few layers (one to three) of inner longitudinal fibres.

The tubular pharynx is nearly in the middle of the body. It is almost twice as long as broad. Its epithelia are ciliated (external cilia about 1.5 M m long; luminal cilia about 2.5 M m long) apart from its most distal tip, where pharyngeal glands discharge. The luminal epithelium is also unciliated in a narrow proximal area, adjacent to the very short oesophagous (about one-eighth of the pharynx length). Musculature of the pharynx consists of weak outer longitudinal muscle layers and strong inner circular layers on both the external and luminal sides.

Male genital organs. Numerous testes (30–40) occur medially in front of the pharynx. The copulatory bulb, of the simplex type, is ovoid, 55 M m long and 28 M m wide in sections. It consists of a seminal vesicle and a narrowly pointed penis papilla, about 10 M m long. The seminal vesicle is lined by a very thin nucleated epithelium, which becomes glandular (‘‘prostatoid’’) distally, with nuclei located outside the bulb. The muscular coating of the bulb is formed by inner circular and outer longitudinal muscles. It is very thin proximally (about 1 M m); distally, it thickens to about 3 M m. The male antrum is narrow and unciliated proximally; it opens to the exterior through a male pore located nearly halfway between vagina and female pore.

Female genital organs. Vitellaria extend from about the level of the first testes to in front of the copulatory bulb. Two ovaries lie ventro-laterally behind the pharynx. A small (about 25 M m wide in sections) vacuolar bursa, mostly of the resorbiens type, lies between the ovaries. From the bursa, a ventrally and posteriorly orientated, ciliated vaginal duct originates, surrounded by a coating of circular muscle fibres, particularly thick distally. The vagina opens to the outside nearly halfway between the mouth and the male pore. The common female duct is unciliated and runs from the postero-ventral part of the bursa to the female pore, which is surrounded by numerous female glands.

Karyology

With three isobrachial chromosomes, nearly even in length, in its haploid set. Karyotype formula: 15.5¡0.4 M m; NF56; chromosome 1: 34.74¡1.44; 36.11¡0.89 (sm); chromosome 2: 34.12¡0.58; 43.12¡0.73 (m); chromosome 3: 31.14¡0.44; 36.09¡0.98 (sm).

Remarks

This is a minute, unpigmented Pseudomonocelis species without accessory organ, characterized by a markedly ovoid copulatory bulb, with a very weak muscular coating and a pointed penis papilla, unlike any known so far in the genus (cf. Schockaert and Martens 1987; Curini-Galletti and Cannon 1995; Curini-Galletti 1997). Furthermore, it is the only species in the genus where ventral pores (i.e. mouth, vagina, male and female pore) appear nearly regularly spaced. Albeit eosinophilous glands, as those described above for the new species, are of common occurrence in the genus Pseudomonocelis (cf. Schockaert and Martens 1987), in none of the species studied by the authors are they so densely packed, especially dorsally and caudally, that the observation of anatomical details in semisquashed specimens is somewhat obscured.

The female genital system of the new species appears similar to that of P. caυernicola Schockaert and Martens, 1987. The two species are, however, immediately recognizable as P. caυernicola, among other differences, has a unique accessory organ located between male and female pores, and a rounded copulatory bulb provided with an evenly thick muscular coating.

Pseudomonocelis caribbea n. sp. is the only species of the genus known so far from the entire American continent.

Figures

Figure 1. Pseudomonocelis caribbea sp. n. (A) General organization of a live animal; (B) reconstruction of the genital organs from sagittal sections.

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).