Olisthanella truncula ( Schmidt, 1858 ) Voigt, 1892

Steenkiste, Niels Van, Tessens, Bart, Krznaric, Kathleen & Artois, Tom, 2011, Dalytyphloplanida (Platyhelminthes: Rhabdocoela) from Andalusia, Spain, with the description of four new species, Zootaxa 2791, pp. 1-29 : 17-18

Olisthanella truncula ( Schmidt, 1858) Voigt, 1892

( Figs. 7 A–7C)

syn. Mesostomum trunculum Schmidt, 1858 syn. Turbella truncula Diesing, 1862

syn. Mesostomum banaticum Graff, 1875 syn. Mesostoma nassonoffii Graff, 1882 syn. Mesostoma splendidum Graff, 1882 syn. Mesostoma truncatum Graff, 1882

syn. Olisthanella nassonoffii Graff, 1882 syn. Olisthanella splendida Graff, 1882 syn. Mesostomum truncatum Voigt, 1892 syn. Mesostomum trunculum Voigt, 1892

New localities in Spain. Doñana National Park, Provincia de Huelva, Spain (36°58’48.80”N, 6°28’55.60”W). Laguna de Santa Olalla: submersed parts of sedges along the western shore of the lake (19/03/2008).

Doñana National Park, Provincia de Huelva, Spain (36°58’50”N, 6°29’11”W). Laguna Dulce: floating algae and submersed vegetation on the border of the marsh and open water and swamp vegetation on the northern edge of the lake (06/04/2008; 19/03/2008).

Other localities in Spain. Central areas (Sierra de Guadarrama and river Tajo basin, see Gamo & Noreña- Janssen 1998); Beleña (Provincia de Guadalajara, Castilla-La Mancha) ( Gamo 1987a; Gamo & Schwank 1987); Alburquerque (Provincia de Badajoz, Extremadura) ( Noreña et al. 1999).

New locality outside Spain. Nearctic: Cootes Paradise, Hamilton, Ontario, Canada (43°16’03”N, 79°55’13”W). Submersed aquatic vegetation in southern inlet of the impoundment (17/05/2009).

Known distribution. Widespread throughout the Palearctic: many localities in Europe, Western Russia, Siberia and Japan (see Luther 1963 for localities and references), Western Europe ( the Netherlands: Friesland) ( Young 1972a), Central Europe ( Germany: Thuringia, Lake Constance, Franconia, Oberhessen, South Lower Saxony, Elbe estuary; Austria: Burgenland) ( Kraus 1965; Pörner 1966; Kaiser 1967; Rixen 1968; Bauchhenss 1971; Schwank 1981; Heitkamp 1981, 1982; Müller & Faubel 1993), Western Russia (Urals, upper Volga River) ( Rogozin 1996; Korgina 2002) and Siberia ( Rogozin 1996); Nearctic: Canada (Ontario) ( Gregory et al. 2000); Afrotropic: East Africa ( Kenya: Rift Valley Province) ( Young 1976; Young & Young 1976); Neotropic: eastern Amazon floodplain ( Peru) ( Noreña et al. 2006).

Material. Observations on several live animals from Spain and Canada. Eight serially-sectioned specimens and eight whole mounts from the new localities in Spain.

Description and remarks. Habitus and internal organization indicate these specimens belong to Olisthanella truncula ( Schmidt, 1858) Voigt, 1892 , a widespread and relatively common freshwater species of Olisthanellinae Luther, 1904 , a monogeneric taxon of Typhloplanidae characterized by separate nephridiopores and testes dorsal to the vitellaria (for a recent discussion on this taxon see Van Steenkiste et al. 2010).

Although this species has been described and discussed by numerous authors (e.g. Schmidt 1858; Graff 1882, 1913; Dorner 1902; Sekera 1912; Nasonov 1917; Findenegg 1930; Luther 1963), an overall reconstruction of the genital system is lacking. Therefore, we give a reconstruction of the genital system as observed in the specimens from Andalusia (see Fig. 7 C).

The animals are between 1.1–1.5 mm and have vivid red-pigmented areas dispersed throughout the body, accentuating the internal organs. Two dark red eyes are present at about 5%. Although the conspicuous marbled red colouration, typical for the specimens from Spain, is not always mentioned in other accounts of this species (e.g. Schmidt 1858; Findenegg 1930; Luther 1963), it seems to be described in most accounts as a yellow to reddish brown perivisceral “Flüssigkeit” (e.g. Graff 1882, 1913). Specimens of Olisthanella truncula have been described as many different species (see list of synonyms), which were later lumped together into one species.

The two testes lie dorsally to the vitellaria and fill a large part of the body in front of the pharynx. Vasa deferentia leave from each testis, merging when entering the copulatory bulb. The latter is filled with prostate secretion from extracapsular prostate glands, and contains a large intracapsular seminal vesicle in its proximal part. In its distal part the simple, sclerotized ejaculatory duct is present. This ejaculatory duct is relatively long, surrounded by a plasmatic tissue and evacuates the prostate secretion (see Luther 1904 and Sekera 1912 for a detailed description of the ejaculatory duct). The exact position where the seminal vesicle merges with the ejaculatory duct could not be observed in the serial sections. The copulatory organ enters the common genital atrium through a sphincter. The common genital atrium is lined with a high cellular epithelium and surrounded by circular muscles. A protrusion of the common genital atrium ventrally from the copulatory organ is often denoted as an uterus (see e.g. Luther 1963) although its function is not fully clear.

The female duct enters the common genital atrium through a well-developed sphincter and is lined with a ciliated epithelium and provided with circular muscles. Proximally it receives the eosinophilic female glands, the ovovitelloduct and the enormous female bursa. The ovary stretches rostrally on the left hand side of the body. The oviduct is broad and receives the vitelloducts to form an ovovitelloduct. The vitellaria stretch dorsolaterally at both sides, and are situated ventrally from the testes. A sphincter separates the female bursa from the female duct. The female bursa is large and consists of several large vacuoles filled with sperm. These vacuoles are interconnected (seemingly tube-like in some live animals). Although this organ has a glandular wall and probably has some kind of a resorbing function, most authors describe it as a seminal receptacle ( Luther 1963) or a bursa seminalis ( Graff 1882). We prefer to describe it as a female bursa by reason of its glandular appearance and position in the female genital system. A similar construction of the female bursa is also mentioned by several authors (e.g. Nasonov 1917) and is, combined with the other diagnostic characters of Olisthanella , a relatively easy feature to recognize this species. A copulatory bursa, described in most accounts of this species, was not observed in the specimens from Spain.

Figures

FIGURE 7. Olisthanella truncula (Schmidt, 1858) Voigt, 1892 (A) Live animal. (B) Atrial organs. (C) Reconstruction of the atrial organs from the right hand side.