Pulchritia dorsicornuta (Van Oye, 1926) Van Oye, 1926

Luo, Yongting & Segers, Hendrik, 2013, On Pulchritia new genus, with a reappraisal of the genera of Trichotriidae (Rotifera, Monogononta), ZooKeys 342, pp. 1-12 : 5-7

Redescription of Pulchritia dorsicornuta (Van Oye, 1926) comb. n.

Material examined.

Type material: Neotype (labelled: " Pulchritia dorsicornuta (Van Oye, 1926) Neotype. Lohulu River near Bomane, DR Congo, 24 May 2010 (KM-048)") in Royal Belgian Institute of Natural Sciences, Brussels Belgium (IG32450, RIR 212).

Other material: Abundant specimens of the species were found in two localities: Lulu River near Basoko (sample KM-028: 1.2958°N, 23.6497°E (DD, GPS waypoint Mac 079), altitude. ca. 350 m asl., water temp. 25.8° C, conductivity 16.5 µS /cm), and Lohulu River near Bomane (samples KM-048, KM-049: 1.2486°N, 23.7280°E (DD, GPS waypoint Mac 089), altitude. ca. 410 m asl., water temp. 24.3° C, conductivity 30.4 µS /cm, oxygen 0.45 mg/l), both in Orientale province, DR Congo. All samples are from running water. One permanent trophi preparation, and nine permanent slides containing one, three slides containing two, and three slides containing three specimens. Deposited in RBINS and in the CSB-UK.

Diagnosis.

Pulchritia dorsicornuta comb. n. is unmistakable by the large, S-shaped antero-lateral projections of its ventral lorica. These are completely absent in its closest relative Pulchritia kostei comb. n.

Description.

Female (Figs 1, 2 a–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 2 c–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.

Measurements

(in µm. N=12; range, mean).Total length (incl. foot): 180-205, 192; lorica width 92-122, 106; antero-lateral spine length 20-32, 27; head aperture width 37-58, 47; foot aperture width 29-40, 33; length 23-34, 28; first foot pseudosegment length 9-14, 11; second foot pseudosegment length 46-54, 48; toe length 26-32, 29.

Distribution.

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).

Comments.

The main feature distinguishing Pulchritia dorsicornuta comb. n. and Pulchritia kostei comb. n. is the presence of well-developed antero-lateral spines in the former. As we observed only negligible variability of the antero-lateral spines of Pulchritia dorsicornuta comb. n., and as there are no indications at all of such spines in Pulchritia kostei comb. n., we can neither exclude nor confirm the possibility that this feature results from phenotypic plasticity and as such would not be taxonomically relevant. Examples of such environmentally induced spine development are common in rotifers, including Trichotriidae ( Gilbert 2011a, 2011b, Koste 1978, Luo et al. 2012, Wallace et al. 2006). We prefer to remain cautious and treat the two as separate taxa, pending proof to the contrary.