Macrostomum rostratum Papi, 1951

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

Macrostomum rostratum Papi, 1951

Fig. 3

Known distribution.

Species with a broad known distribution including Europe ( United Kingdom, The Netherlands, Germany, Finland, Spain, and Italy) ( Papi 1951; Luther 1960; Rixen 1961; Young 1970, 1973; Tulp 1974; Farias et al. 1996; Noreña et al. 2007), Russia ( Luther 1960), and Kenya ( Young 1976).

Material.

Two specimens studied alive, one preserved in ethanol for future molecular analyses, the second cut in two pieces, the posterior part containing the stylet for whole mounting and the anterior part preserved for molecular analyses. Collected in Wandse river, submerged vegetation with organic matter, 0.1 m deep.

Description. Animals 0.8–0.9 mm long (n = 2), unpigmented and with a pair of eyes (Fig. 3 A, B : e). General morphology corresponds to that in previously described specimens (see Papi 1951). Epidermis fully ciliated, with some larger cilia distributed though the body. False seminal vesicle absent and true seminal vesicle (Fig. 3 C – E : sv) opening into the prostate vesicle (vesicula granulorum). The prostate vesicle (Fig. 3 C – F : pv) opens proximally into the stylet (Fig. 1 A, C – F : st). One specimen had a fully developed stylet, measuring 60 µm in length; it is hook shaped and with the distal part twisted; aperture subdistal and dorsal. Well-developed eggs observed (Fig. 3 A, C : eg).

According to the drawings of Papi (1951: figs 32–33) the stylet of this species measures 42–65 µm, which is in the range of our collected specimen. In other populations recorded from Germany, the stylet is 65–77 µm long ( Rixen 1961). The most characteristic traits for this species are the distal turn and the dorsal aperture of the stylet; therefore, we identify our specimen as M. rostratum .

Figures

Figure 1. Stenostomum gotlandense. A. Habitus of a swimming specimen; B. Anterior part of the body; C. Anterior part of the body showing the brain; D. Posterior part of the body. Abbreviations: ab anterior brain; br brain; cp ciliated pits; ep excretophore; i intestine; m mouth; pb posterior brain; ph pharynx; pn protonephridia. Scale bars: 50 μm (A, C); 100 μm (B, D).

Figure 3. Macrostomum rostratum. A. Habitus of a swimming specimen; B. Anterior part of the body; C – F. Posterior part of the body. Abbreviations: e eye; eg egg; ph pharynx; pv prostate vesicle; st stylet; sv seminal vesicle. Scale bars: 200 μm (A); 50 μm (B – F).