Pulchritia dorsicornuta Van Oye 1926

Female (Figs 1, 2a–b; male unknown): Body: Head largely retracted in trunk lorica, with two lateral stiffened elements protruding from the head aperture. A pigmented spot (eye?) present. Trunk loricate, elliptic in outline, longer than wide, dorso-ventrally compressed. Ventral and dorsal plates fused laterally and caudally, leaving a broad head aperture and a smaller foot aperture. Dorsal plate medially with two semi-longitudinal ridges forming a Y-shaped double dorsal keel, fused to a single dorsal keel terminally. Posterior of dorsal lorica with a weakly protruding rounded margin bearing two pairs of short ridges over the foot aperture. Openings of the lateral antennae in posterior third of body, about halfway between dorsal keel and lateral margin of lorica. Dorsal head aperture margin concave. Ventral plate flat, with two protruding, weakly S-shaped and diverging spines antero-laterally, these separated by a shallow U-shaped sinus. Posterior of ventral plate with a well-defined foot aperture, with rounded anterior and diverging lateral margins. Anal segment indistinct, poorly developed (also in poorly contracted specimens). Foot subterminally, consisting of a short, bilaterally constricted first and an elongate, parallel-sided second foot pseudosegment. Two long, equal toes, these mostly parallel-sided, terminating in a sharp tip. Trophi (Figs 2c–e) malleate, almost symmetrical. Fulcrum short, with a small basal plate; rami relatively flat, triangular, with rounded postero-lateral corners and short, curved alulae, inner margins with asymmetrical, protruding teeth-shaped structures. Left uncus with two large frontal and three minor dorsal webbed teeth, right with a single large frontal and four minor teeth, all minor teeth gradually reduced in size from frontal to dorsal. Manubria symmetrical, with elongate and weakly procurved shaft. Head broad, with clear ventral, median and dorsal chambers, anterior chamber with an additional rounded triangular apophysis, dorsal chamber with a recurved hook.

Pulchritia dorsicornuta comb. n. is only known from the two localities cited above, and from Ruki River near Eala (Van Oye 1926), near Mbandaka, Equator province, DR Congo. Its close relative Pulchritia kostei com b. n. is known only from a coastal lagoon, State of Rio de Janeiro, Brazil. We hypothesize that the two represent a vicariant species pair. This is remarkable as there are few examples of such vicariant sister-taxa, possibly originating from allopatric speciation, in rotifers, and patters are blurred by their purportedly superb dispersal potential (Segers 2008, Segers and De Smet 2008). Some have been identified before in the genus Lecane (see Segers 1996), but the most notorious example of such a vicariant species-pair is Kellicottia longispina (Kellicott) and Kellicottia bostoniensis (Rousselet), in which the former is hypothesized to be of Palaearctic, the latter of Nearctic origin (Pejler 1977).