Encentrum aluligerum, De Smet, Willem H., 2015

De Smet, Willem H., 2015, Rotifera from the Mediterranean Sea, with description of ten new species, Zootaxa 4028 (2), pp. 151-196 : 158-161

Encentrum aluligerum sp. nov.

( Figs 4 , 5 )

Diagnosis. Medium-sized (120–140 µm) Encentrum with oblique-frontal corona; rostrum broad, anteriorly almost straight; tail broad, rounded; trophi of subgenus Isoencentrum- type; rami outline more or less hexagonal; median rami opening pyriform; intramallei short; rami with single apical tooth; preuncinal teeth single, stout, set at right angle to trophi axis; outer margin of basal rami chambers with proximal, short ventral alula; inner margin of subbasal rami chambers with distal tooth.

Type locality. Cap Bénat, Baie du Lavandou, Côte d’Azur, France. In psammon collected on 0 3.06.2010, 50 m from shoreline, and depth of 20 m; water temperature 17 °C.

Holotype. A female in a permanent, glycerine glass slide mount deposited in the Royal Belgian Institute of Natural Sciences ( RBINS), Brussels, Belgium, No. IG 33082, RIR 217.

Paratypes. One female from type locality in RBINS, No. IG 33082, RIR 247; 5 mounted paratypes and 6 SEM trophi preparations in Department of Biology, University of Antwerp.

Additional material. Several specimens from sublittoral of the Costa Blanca and Costa Brava, Balearic Sea, the Côte d’Azur, and Elba Island, Tyrrhenian Sea (see Tab. 2 species list).

Etymology. The name of the species is composed of the Latin alula, a diminutive of ala meaning small wing, and the Latin gerere, to bear, and refers to the ventral alulae on the basal rami chambers.

Description of female. Body short fusiform ( Figs 4 A, B). Head c. 1/4 total length, offset by neckfold, narrower than trunk, slightly decurved ventrally. Corona oblique-frontal. Rostrum large, broad, anterior margin weakly rounded to almost straight. Dorsal antenna in posterior half of head. Trunk weakly arched dorsally, flattened ventrally, in dorsal view with constriction before tail. Tail broad, rounded. Lateral antennae near posterior margin of trunk. Foot short, broad, 3 pseudosegments. Toes short ( Figs 4 C, D), c. 1/6 total length; in dorsal view almost straight, tapering, more or less strongly indented before mid-length, with reservoir at indentation, tips acute; toes in lateral view weakly decurved ventrally. Shallow caudal antenna between bases of toes. Two colourless rostral eyespots? Brain saccate; small retrocerebral sac. Proventriculus offset from stomach; stomach and intestine weakly offset. Gastric glands spherical, with fairly long stalks. Pedal glands club-shaped. Vitellarium with 8 nuclei.

Trophi ( Figs 4 E, 5) of subgenus Isoencentrum- type ( De Smet 1997). Rami outline rounded-hexagonal; median rami opening pyriform. Rami each with stout, slightly offset and incurved apical tooth set at oblique angle to trophi axis; cardal apophysis of apical teeth well developed; inner margin of subbasal rami chambers with short triangular tooth distally; basal chambers ventrally with short, caudally pointing alula ( Figs 5 B −D: a). Prior to each apical ramus tooth a stout preuncinal tooth ventrally, set at right angle to trophi axis, composed of short shaft and head forming right angle; cardal apophysis reduced. Fulcum ramus length; narrow and parallel-sided in dorsal/ventral view; in lateral view weakly curved ventrally, with broad base tapering to obtuse distal end. Unci single-toothed, with offset head; head shaft length, expanded in plane of rami; dorsal apophysis well developed, ventral one reduced. Intramallei fairly short, thin, more or less rectangular. Supramanubria fairly short, elongate-trapezoidal. Manubria longer than incus, rod-shaped, straight, incurving and slightly tapering to crutched cauda; head with short, rounded dorsal expansion and acute ventral one.

Measurements. Body (N=5): total length 120‒140 µm, toe 20‒23 µm; trophi (N=5): length 19‒22 µm, ramus 6.1‒7.3 µm, fulcrum 7.3‒8.4 µm, uncus 5.2‒5.9 µm, intramalleus 1.2‒1.9 µm, manubrium 14.8‒16.1 µm.

Comments. Encentrum aluligerum sp. nov. is easily distinguished from its congeners by the specific shape of the trophi. The only other marine Encentrum of the subgenus Isoencentrum bearing alulae known to date is E. frenoti De Smet, 2002 , described from subantarctic Îles Kerguelen. Alulae of the latter are minute and dorsolateral, and both the other trophi features as well as the species’ external and internal morphology allow for an unequivocal distinction with the new species.

Distribution and ecology. The species was found in low numbers in sublittoral psammon samples from the Costa Blanca, Costa Brava, Côte d’Azur, and Tyrrhenian Sea, at distances of 50 m to 3.5 km from the shoreline, and depths between 15 and 50 m. It was present in samples of June, July, August, September, and October, at water temperatures of 15−23 °C.

Figures

FIGURE 4. Encentrum aluligerum sp. nov. A. Female, lateral view; B. female, dorsal; C. toe, dorsal; D. toe, lateral; E. trophi, dorsal. Scale bars: A, B: 50 µm; C − E: 10 µm.

FIGURE 5. Encentrum aluligerum sp. nov., SEM photographs of trophi. A. Complete set, dorsal; B. detail, dorsal; C. complete set, dorso-lateral: D. detail, ventral; E. detail, dorso-frontal. a: alula. Scale bars: 10 µm.