Byrsophlebs caligulachaena (Ehlers & Ehlers, 1981) Karling 1985

Byrsophlebs caligulachaena (Ehlers & Ehlers, 1981) Karling, 1985

(Fig. 11 C)

syn. Maehrenthalia caligulachaena Ehlers & Ehlers, 1981

New locality. Playa Grande, Parque Nacional de Santa Teresa, Departamento de Rocha, Uruguay (34°1’55.17”S, 53°32’14.52”W). On algae (Corallimorpha sp.) in intertidal pools (18/07/2004).

Known distribution. Egedesminde, Greenland (Levinsen 1879); White Sea, Solovki Islands, Russia (Sabussow 1900); Plymouth Sound, United Kingdom (Gamble 1893); Port Erin, Man Island (Jameson 1896); Jekaterinhafen and Bergen, Norway (Graff 1905; Luther 1936); Tomales Bay, California, USA (Karling 1985).

Material. Observations on a live animal. One whole mount.

Discussion. The examined animal is very small and measures only 0.3 mm in the whole mount. The parenchym has a vivid red colour. Although the form of the stylet is not completely clear in the whole mount, it seems to be a funnel-shaped, oblong tube with a length of ± 25–30 μm and a distally-bent apex. The vasa deferentia are very broad near the pharynx and narrow caudally from the pharynx to strongly widen again as seminal vesicles laterally from the copulatory apparatus. These broad seminal vesicles fuse before penetrating the copulatory apparatus as one single broad seminal vesicle. In the live animal, two larger organs were observed caudally from the copulatory bulb. These are possibly a bursa and seminal receptacle.

Karling (1985) reviewed the taxonomy and systematics of the Byrsophlebidae, in which he recognized four genera. These four genera are separated based on clear characters, but in practice sections are often needed to asses these characters. All species of Maehrenthalia Graff, 1905 and Byrsophlebs Jensen, 1878 have a female bursa, a structure that can normally be seen in the live animal. Such a bursa is lacking in species of Maehrenthaliella Karling, 1985 and Parabyrsophlebs Karling, 1985. Byrsophlebs differs from Maehrenthalia by the following features: a globular-oviform copulatory bulb with two layers of strong spiral muscle fibres, a female duct with a seminal receptacle and bursa without terminal resorptive vesicle. Maehrenthalia, on the contrary, has a cylindrical copulatory bulb with a single layer of strong spiral muscle fibres, a female duct without a seminal receptacle and a bipartite bursa consisting of a uterus and terminal resorptive vesicle (Karling 1985).

The stylet observed in the live specimen from Uruguay mostly resembles that of Byrsophlebs caligulachaena. Although the red colour is only found in Maehrenthalia agilis (Levinsen, 1879) Graff, 1905, the tip of the stylet of M. agilis is more pointed and curved, than that of B. caligulachaena, which is shoeshaped as in the Uruguayan specimen (see Ehlers & Ehlers 1981; Karling 1985). Therefore the Uruguayan specimens are provisionally considered as Byrsophlebs caligulachaena. Also the possible presence of a seminal receptacle (see above) suggests that the species found belongs to the taxon Byrsophlebs rather than Maehrenthalia.