Testudinella elliptica (Ehrenberg, 1834)

De, Willem H., 2009, A review of the marine and brackish-water species of Testudinella (Rotifera: Monogononta, Testudinellidae), with the description of two new species, Zootaxa 2092, pp. 1-20 : 13-14

Testudinella elliptica (Ehrenberg, 1834)

( Figs 11 & 12 )

Synonym: T. pseudoclypeata Bērziņš, 1943 , T. clypeata f. pseudoclypeata after Koste (1978)

non T. elliptica after Bartoš (1951, Figs 7 , 8 ) and Jersabek et al. (2003, ANSP Catalog Number 1828) Testudinella elliptica has often been confounded with T. clypeata , due to the rather similar lorica outline and shape. The antero-dorsal margin is convex, the antero-ventral one shows a broad V-shaped sinus; the two antero-ventral lobes are finely granulated. Ratio lorica length/lorica width 1.40–1.65 (average 1.53). The most characteristic features distinguishing T. elliptica from T. clypeata are its large, more or less semi-lunar ventral foot opening situated close to the posterior edge ( Fig. 11 A–C), the massive distal ( Fig. 11 E) and short penultimate foot pseudosegment, and the more anteriorly placed dorsal and lateral antennae, with the ratio lorica length/position of antenna(e) relative to dorsal anterior margin varying between 3.00–3.40 (average 3.16) and 3.30–3.60 (average 3.43) respectively. The lorica is usually also slightly, more or less abruptly narrowing anteriorly at the height of the lateral antennae. In cross-sectional view ( Fig. 11 D) the dorsal margin appears convex, the lateral edges are broadly rounded continuing more or less strongly flattened ventrally, and becoming separated from a more or less convex median part by shallow sulci. Two red eyespots.

The trophi ( Fig. 12 , and De Smet (2005)) have 16–17/16–17 (left/right) uncinal teeth, with very slender and only weakly offset heads, bearing two small lateral knobs at their base. The manubria consist of three large superimposed chambers and a strongly reduced sub-ventral chamber. The number of arched rami scleropili is ~50/46–66 (left/right). The fulcrum lacks a proximal opening frontally.

Measurements. Lorica length 170–250 µm, lorica width 105–205 µm, distal foot pseudosegment 36–40 µm.

Testudinella elliptica is a widespread species reported from the Palaearctic, Nearctic, Oriental and Neotropical regions ( De Ridder & Segers 1997). It is primarily an inhabitant of fresh waters, living among submerged vegetation and in benthos, or as epibiont on Asellus aquaticus (Linnaeus, 1758) (Crustacea, Isopoda ). The reports from marine and brackish habitats (see also Fontaneto et al. (2006)) have to be interpreted with caution and may concern occasional introductions or confusions with T. clypeata . In this respect it is interesting to mention that in culture experiments with T. elliptica , de Beauchamp (1928) observed that specimens died at a 0.2 % salt concentration, and he wonders claiming that ‘the species is euryhaline and living also in brackish waters’.

Bērziņš (1943) described T. pseudoclypeata from a freshwater pond in Lettland, and considered the species closely related to T. clypeata . According to Segers (2007) T. pseudoclypeata is a synonym of T. clypeata , occasionally considered an infrasubspecific variant of the latter. Bērziņš (1943) considered the transverse-oval foot opening and flattened shape of the ventro-lateral and medio-ventral margins as characters distinguishing it from T. clypeata . However, a large transversal foot opening, flattened ventro-lateral margins, as well as the ratio lorica length/position lateral antennae = 3.6 (which can be derived from Bērziņš’ Fig. 25) are typical for T. elliptica . The degree of flattening of the median ventral part largely depends on the state of development of the vitellarium. Consequently there are no characters differentiating between T. pseudoelliptica and T. elliptica , and it is concluded that the two names are synonyms.

Figures

FIGURE 7. Testudinella obscura, scanning electron microscope photographs of trophi. A. Complete set, frontal view. B. Detail left manubrium. C. Complete set, caudal view. D. Complete set, lateral view. Scale bars: 10 µm. a: alula, dc: dorsal chamber, fo: fulcrum opening, mc: median chamber, sc: sub-ventral chamber, vc: ventral chamber.

FIGURE 8. Testudinella clypeata. A – C. Loricae, ventral view. D – F. Loricae, cross-sectional view. G. Foot pseudosegments. Scale bars: A – F: 50 µm, G: 25 µm.

FIGURE 11. Testudinella elliptica. A – C. Loricae, ventral view. D. Lorica, cross-sectional view. E. Foot

FIGURE 12. Testudinella elliptica, scanning electron microscope photographs of complete set of trophi. A. Frontal view. B. Caudal view. Scale