Protoplanella simplex Reisinger, 1924

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 : 6-7

Protoplanella simplex Reisinger, 1924

( Fig. 3 )

New locality. La Puebla del Rio, Provincia de Sevilla, Spain (37°13’39”N, 6°10’52”W). Area recreativa Pozo de los Conejos along road A3114 from La Puebla del Rio to Aznalcazar: mosses on bank of dried up temporal brook in open coniferous forest (21/03/2008).

Other localities in Spain. Central areas (Sierra de Guadarrama and river Tajo basin; see Gamo & Noreña- Janssen 1998).

Known distribution. Palearctic: Northern Europe ( Finland) ( Luther 1963) and Central Europe ( Austria: Eastern Alps) ( Reisinger 1924, 1954; An der Lan & Franz 1954; An der Lan 1963).

Material. One drawing of a live animal and two serially-sectioned specimens.

Remarks. As is also the case for other representatives of Protoplanellinae Reisinger, 1924 , Protoplanella simplex Reisinger, 1924 is difficult to identify (for a recent discussion on Protoplanellinae , see Van Steenkiste et al. 2010). Not many accounts of this species are known from the literature ( Reisinger 1924, 1954; An der Lan & Franz 1954; Luther 1963; Gamo & Noreña-Janssen 1998). Therefore a more detailed description and discussion is provided here.

At 0.4 mm long (measured on the serial sections), the animals from Andalusia are relatively small when compared to other populations (0.8–0.9 mm for Central and Northern European populations; see Reisinger 1924 and Luther 1963). The ciliated epidermis is cellular and its apical end is darkly stained.

The first third of the body is filled with two bundles of massive rhabdite glands, almost entirely encompassing the brain. The rhabdites are oblong, but seem to be variable in shape. The proximal parts of the gland cells are clearly visible as basophilic cells containing packages of rhabdites. Only adenal rhabdites are present.

The mouth is situated at about 50–55%. The pharynx rosulatus is typical of Typhloplanidae and has a central position. Two separate nephridiopores open on the ventral body surface slightly caudally to the mouth. The gonopore lies at 70%.

The paired, globular testes lie laterally behind the pharynx, ventrally to the vitellaria. Between the testes, an oviform copulatory organ provided with circular muscles is present. Proximally it contains a great amount of sperm, while distally the faint contours of a muscular ejaculatory duct were visible. The copulatory organ enters the common genital atrium dorsally. Rostral to the copulatory organ, the common genital atrium enlarges significantly. This sack-like protrusion (bs in Fig. 3 ) is provided with well-developed, circular muscles, as is the common genital atrium.

The female system is relatively simple. Paired vitellaria stretch dorsolaterally at both sides up to the frontal part of the pharynx. At the caudal end of the left vitellarium is an ovary, which is partly embedded in this vitellarium, thus forming an ovovitellarium. The oviduct merges with a spherical female bursa with a relatively thick epithelium. The female bursa contains remnants of (disintegrated) sperm. Both the epithelium of the oviduct and the proximal part of the female bursa contain a large number of cell nuclei. The female duct (ductus communis in Reisinger 1924) is surrounded by circular muscles and enters the common genital atrium caudally. Eosinophilic glands surround the oviduct, but their exact entry position could not be determined. An uterus is absent.

Discussion. The specimens from Spain can be placed in the taxon Protoplanella Reisinger, 1924 , because they have all diagnostic features of this taxon: adenal rhabdites in the rod tracks, a typical pharynx rosulatus, a muscular ejaculatory duct and the presence of an ovovitellarium. At present Protoplanella contains two species: P. s i m p l e x and P. macrorhabdiphora An der Lan, 1955. However, as stated by An der Lan (1955), the position of P. m a c - rorhabdiphora is highly questionable since the construction of the genital system was not clear. Therefore P. s i m - plex remains the only certain representative of Protoplanella .

Protoplanella strongly resembles another monotypic taxon within the Protoplanellinae , i.e. Olisthanellinella Reisinger, 1924 ( O. rotundula Reisinger, 1924 ), but the latter taxon has a separate ovary and vitellaria. Luther (1963) also refers to the position of the testes as being a valuable field character in discerning Protoplanella from Olisthanellinella , although this is not mentioned by Reisinger (1924). In the taxon Protoplanella the testes are situated behind the pharynx, while the testes of O. rotundula lie next to or in front of the pharynx.

Despite their small size, the Spanish specimens can be placed within Protoplanella simplex because they share all diagnostic characters. In addition, Reisinger (1924) describes the female bursa as a seminal receptacle. We prefer to describe it as a female bursa because it is relatively thick-walled and contains disintegrated sperm. Many older authors denote the female duct in Typhloplanidae as a ductus communis (e.g. Graff 1882; Sekera 1912; Dorner 1902; Findenegg 1930; Luther 1963). In more recent taxonomic accounts on Typhloplanidae , the terms ductus communis (e.g. Gamo & Schwank 1987; Müller & Faubel 1993; Noreña et al. 1999), female common duct (e.g. Kolasa & Schwartz 1988), female duct (e.g. Artois et al. 2004; Willems et al. 2005) and female canal (e.g. Noreña-Janssen 1995) are used to describe the distal part of the female genital system, while Noreña and Faubel (1992) consider the female duct as the collective name for the germarium (ovary), oviduct, seminal receptacle and distal ductus communis in their review on the Mesostominae . We prefer to use the term female duct to avoid confusion with other ducts in the genital system and to stress its presence in the female system.

Finally we would like to remark that the specimens were sampled in spring when the area regularly receives rainfall. During summer (June to September), this area is prone to long periods of drought, suggesting this species might be anhydrobiotic (see Van Steenkiste et al. 2010).

Figures

FIGURE 3. Protoplanella simplex Reisinger, 1924. Habitus based on observations on live animals and serial sections.