Aspelta secreta (Donner, 1951) n. comb. (Figs 5; 6)

Dicranophorus secretus Donner, 1951: 636, fig.24a-e; 1964: 283, fig. 19a-d. — Koste 1976: 205, pl. 9, fig. 2a, b.

NEOTYPE. — A female in a permanent glycerine glass slide preparation deposited in MNHN (AM 880). Additional type material: four stubs with one trophi preparation each for SEM in UA.

MATERIAL EXAMINED. — France. Rhône-Alpes, Ardèche, vegetation in a spring near river Louyre, 22.IV.2008, 5 ♀♀.

DESCRIPTION OF TROPHI (FIG. 6)

Trophi forcipate, weakly asymmetrical.Rami outline pear-shaped; median rami opening small, slit-shaped proximally and rounded distally, transition from slit to rounded part more or less angular; outer margin of rami weakly concave; right ramus of stouter build, terminating in blunt incurved tip, with small crest at base of tip; incurved tip of left ramus with 3 or 4 small teeth; the sub-basal chambers are flattened laterally, forming lamellar rounded alulae displaying a rounded opening; basal chambers with rounded opening proximally. Fulcrum rod-shaped in dorsal/ventral view, in lateral view elongate-triangular, slightly less ramus length. Unci more or less symmetrical, each composed of long ventral tooth resting on the ventral side of the ramus, and a shorter median tooth with dorsal prominence resting latero-ventrally on the ramus; subuncus (Fig. 6D: su) an U-shaped platelet. Manubria incus length, straight or very weakly undulate, incurved distally, head weakly expanded with inwardly directed projection and small opening.

Measurements of trophi: see Table 1.

REMARKS

Koste (1976) stressed the great similarity of the trophi of Dicranophorus secretus with these of the genus Aspelta, and points out (Koste 1978) its resemblance with A. circinator (Gosse, 1886). Awaiting for further study, De Smet (1997) left the species, with several others, in the genus Dicranophorus although regarded their position therein as by no means certain. The examination of the trophi of specimens fully agreeing with the species described by Donner (1951) under Dicranophorus secretus (Fig. 5), and characterized by a head with broad rostrum bearing typical lateral angular prominences, shows that their morphology is identical to that of genus Aspelta. Besides this similarity of the trophi, there is also an obvious similarity in the external and internal organization of the body. Given this overall similarity and seeing that trophi morphology is the most important character in the establishment of genera in Dicranophoridae (see e.g., De Smet 1997), the species should be reallocated to the genus Aspelta.

Comparison of the trophi of the different Aspelta species shows that A. secreta n. comb. is most closely related to A. circinator (Fig. 7) and A. curvidactyla Bērziņš, 1949 (see SEM of trophi pl. 15 in De Smet [1997]). The trophi structure of these species as revealed by SEM is basically identical, apart from minor differences in dimensions (Table 1): trophi elements appear somewhat longer in A. secreta n. comb. and the smallest in A. curvidactyla, with intermediate values for A. circinator. However, measurements are based on a small number of specimens and insignificant statistically. The prominence at the inner margin of the right ramus near the base of the anterior part of the median rami opening, considered specific for A. curvidactyla, is merely a quantitative character, as SEM reveals that it is present in the other two species as well. Such a prominence, likewise present on the left ramus, proves to be the distal part of the sub-basal rami chambers that slightly projects in the median rami opening. The three species cannot be discriminated unequivocally on basis of their general external and internal morphology of the body and shape of the toes; length of body and toes are similar as well. Only two external diagnostic features allow for some differentiation: the rostrum is small and rounded in A. circinator and A. curvidactyla, and broad with lateral triangular lamellae in A. secreta n. comb.; two tentacles laterally from the rostrum are apparently present in A. curvidactyla only. Aspelta circinator has two minute colourless eyespots at the base of its rostrum, whereas eyespots are absent, although they may have been overlooked, in the other two species. Considering these minor differences in morphology of the body and trophi between A. circinator, A. curvidactyla and A. secreta n. comb., the question arises whether we are dealing with valid morphospecies or mere morphological variability of a single species. Since the application of molecular techniques, there is increasing evidence of the commonness of cryptic species complexes (e.g., Gómez et al. 2002; Gilbert & Walsh 2005; Schröder & Walsh 2007), showing that rotifer diversity is largely underestimated. Morphological differences between cryptic species, if any, are minute or taxonomically unreliable because of large overlap (e.g., Campillo et al. 2005; Fontaneto et al. 2007), or restricted to the surface structure of the diapausing eggs (e.g., Schröder & Walsh 2007). Molecular investigations are needed to confirm the reliability of the delineations of A. circinator, A. curvidactyla and A. secreta n. comb. on the basis of morphology. This also holds for two other Aspelta species, A. psitta Harring et Myers, 1928 and A. bidentata Wulfert, 1961, apparently differing only in the shape of the rostrum.

Aspelta circinator, A. curvidactyla and A. secreta n. comb. key out sub A. curvidactyla in the key by De Smet (1997).

Aspelta secreta n. comb. is a widespread species known from Europe, the Eastern Mediterranean and Madagascar (De Ridder & Segers 1997; Segers 2007), inhabiting leaf litter, limnopsammon, aerophytic mosses and mosses of stagnant and running waters. There is a single record from France by Pourriot (1965), who found the species in a sphagnum bog at Grandvaux, near Brinon-sur-Sauldre, Cher. It is a voracious species preying on other rotifers. The gut content of the animals studied contained Cephalodella sp., Colurella uncinata (Müller, 1773), Lecane sp. and Lepadella spp.