Planaria torva (Müller, 1773) Müller, 1776

Diez, Yander L. & Schmidt-Rhaesa, Andreas, 2024, Little neighbours in Hamburg: free-living aquatic flatworms (Platyhelminthes), Evolutionary Systematics 8 (2), pp. 279-310 : 279-310

Planaria torva (Müller, 1773) Müller, 1776

Fig. 13

Known distribution.

Species broadly distributed in West Europe ( United Kingdom, Ireland, Belgium, Finland, Sweden, Denmark, Germany, Greece, France, and Italy) ( Arndt 1926; Luther 1961; Ronneberger 1975; Ball and Reynoldson 1981; Müller and Faubel 1993; Martin and Brunke 2012), East Europe ( Estonia, Latvia, Littauen, Ukraine, Poland, and Czech Republic) ( Luther 1961; Pinchuk 1979), and Russia ( Grimm 1877; Luther 1961).

Material.

Six specimens studied alive and preserved in absolute ethanol for future molecular analyses; one collected in Wandse river, submerged vegetation with organic matter, 0.1 m deep; one in Planten un Blomen park, submerged litter, 0.3 m deep; and four in Kirchwerder-Fünfhausen, submerged vegetation and litter in an irrigation channel, 0.1–0.2 m deep.

Remarks.

Live adult specimens measuring 0.5–1.5 cm, dark pigmented, with a pair of anterior eyes (Fig. 13 A – C : e). Squeezed specimens show the pharynx and atrial organs. The pharynx (Fig. 13 C, D : ph) is located in the second body half and the mouth opens anterior to the male copulatory organ (Fig. 13 A, C, D : mco). The seminal ducts form false seminal vesicles (Fig. 13 A, C, D : fsv) beside the anterior part of the pharynx. The male copulatory organ receives medially, independently, both seminal ducts, which evacuate the sperm in a single proximal seminal vesicle. Distally, the bulb forms a muscular penial papilla. One adenodactyl (Fig. 13 C, D : ad) opens into the common atrium, at the right side of the male bulb; it is oriented backwards. The adenodactyl is distally bent and the central lumen makes it look hollow. The single observed structure of the female system was the bursa (Fig. 13 D : b), located to the right side of the male organ.

Planaria torva is a species widely distributed throughout West Europe, and it is frequently mentioned in taxonomic literature on triclads in the region. However, accurate identification of this species can be challenging without a detailed examination of internal morphology. The taxonomic history of P. torva has been contentious, with several studies mistakenly associating it with species of Dugesia ( Ball et al. 1969) . In light of these issues, we based the identification of our specimens on descriptions provided by Luther (1961) and Ball et al. (1969). The presence of an adenodactyl serves as a key distinguishing feature between our studied specimens of P. torva and species of Dugesia ( Luther 1961) . Furthermore, the overall structure of the atrial organs in our specimens, particularly the male bulb and the adenodactyl, unequivocally supports their classification within P. torva . For a more comprehensive comparison of this species with related congeners, refer to Ball et al. (1969).

Figures

Figure 13. Planaria torva. A. Habitus of swimming specimen; B – D. Squeezed specimen.