Material and methods
Specimens were collected in sandy habitats by scooping up the superficial layer of sediment. Extraction of the animals from the sediment was done with MgCl2 decantation (Martens, 1984). Each species was first studied alive by slight squeezing under the cover-slip. Preservation techniques routinely adopted for Proseriata were used (see Martens et al., 1989b); whole mounts were made with lactophenol. For microscopical analysis material was fixed in Bouin’s fluid, embedded in 60ºC Paraplast and serial sagittal sections were cut at 4 µm, stained with Hansen’s haematoxylin and eosin-orange and mounted in Eukitt.
The karyotype was determined from acetic orcein stained spermatogonial mitoses, as described by Curini-Galletti et al. (1989). Relative lengths (r. l. = length of chromosome × 100/total length of haploid genome) and centrometric indices (c. i. = length of short arm × 100/length of entire chromosome) were obtained from measurements of camera lucida drawings of metaphase plates. The fundamental number (FN) (i.e. the number of chromosome arms in the karyotype) is derived according to Matthey (1949) and the chromosome nomenclature employed is that of Levan et al. (1964): m = metacentric; sm = submetacentric; st = subtelocentric; t: acrocentric.
Type material is deposited in the collections of the Swedish Museum of Natural History (Stockholm, Sweden) (SMNH). Additional material, when present, is deposited in the collection of the Zoological Museum of the University of Sassari (Italy) (CZM).
Abbreviations used in figures are: a: atrium; b: bursa; bc: bursal canal; bn: bursal nozzles; br: brain; cm: circular musculature; cp: common genital pore; cs: copulatory spine; fd: female duct; fg: female glands; g: gut; gl: gut lumen; lm: longitudinal musculature; ov: ovary; ph: pharynx; pv: prostatic vesicle; r: rhabdoid gland; sf: sensory furrow; st: statocyst; sv: seminal vesicle; t: testis; tr: “transverse ridge”; vi: vitellaria.