Encentrum (Tricellatum) uncinatoides, 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 : 168-170

Encentrum (Tricellatum) uncinatoides sp. nov. et subgen. nov.

( Figs 12 , 13 )

Diagnosis. Medium-sized species, 135-155 µm long. Toes long, c. 1/3 total length, with large claw; corona ventral; rostrum large, triangular, pointed; rami composed of subbasal, basal and apical chamber; rami outline oblong-oval; median rami opening narrow, wedge-shaped; apical rami teeth absent, instead short straight rami tips revolved around their axis; intramallei large, elongate trapezoid; supramanubria hook-shaped, broad basally.

Type locality. Cap Bénat, Baie du Lavandou, Côte d’Azur, France. In psammon collected on 0 1.06.2010, 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 221.

Paratypes. One female from type locality in RBINS, No. IG 33082, RIR 251; 5 mounted paratypes and 4 SEM trophi preparations in Department of Biology, University of Antwerp.

Additional material. In total 15 specimens from sublittoral of Côte d’Azur and Elba Island, Tyrrhenian Sea (see Tab. 2 species list).

Etymology. The specific name uncinatoides refers to the great external morphological resemblance of the new species with Encentrum uncinatum (Milne, 1886) , a wide-spread benthic-periphytic freshwater species.

Description of female. Body fusiform ( Figs 12 A, B). Head weakly offset by shallow neckfold, c. 1/3 total length, with faint dorso-lateral transversal fold anteriorly. Rostrum fairly large, triangular, pointed, offset from head by distinct transversal fold, at its base two tufts of long cilia. Corona ventral. Dorsal antenna in posterior third of head. Trunk slightly arched dorsally, almost flat ventrally. Tail extending over most of foot. Foot, short, conical, two indistinct pseudosegments. Toes ( Figs 12 C, D) long, c. 1/3 total length, slender, more or less straight in dorsal view, very weakly S-shaped in lateral view, tapering to fairly long offset lanceolate spur. Brain large, saccate; retrocerebral sac present. Two colourless frontal eyes. Gastric glands spherical, short-stalked. Pedal glands spherical. Vitellarium with 8 nuclei.

Trophi ( Figs 12 E, 13) with oblong-oval rami outline, widest in distal half; median rami opening very narrow, wedge-shaped. Rami straight, widening distally and narrowing again towards short blunt, more or less guttershaped tips revolving around their axis ( Figs 12 F, 13D), apical teeth absent. Each ramus composed of three chambers with opening: the subbasal chamber with large, rounded-triangular caudal subbasifenestra ( Fig. 13 C: s), the basal chamber with large, elongate dorsal basifenestra ( Fig. 13 C: b), and the apical chamber with large oval antero-lateral fenestra ( Fig. 13 C: a). Preuncinal teeth with very short shaft and lanceolate head; shaft with short dorsal proximal ridge resting on revolved ramus tip; preuncinal teeth firmly connected with unci, and weakly to rami by tiny ligament. Fulcrum less ramus length, narrow in dorsal view, proximal 1/3 triangular, distal 2/3 narrow, parallel-sided. Unci fairly slender, head 1/3 total length, head and shaft making obtuse angle; ventral apophysis of shaft absent, dorsal one resting on rami tip; head expanded in plane of rami. Intramallei long, elongate trapezoid, base with weak lateral projections; inner side with triangular basal opening. Supramanubria hook-shaped with broad triangular base. Manubria long, c. twice ramus length, rod-shaped, weakly curved; head fairly large, Vshaped, ventral branch of head parallel-sided, rounded distally with opening at inner side, dorsal branch tapering to more or less offset acute tip, with caudal opening; cauda weakly crutched.

Measurements. Body (N=5): total length 135‒155 µm, toe 37‒47 µm, spur 9‒12 µm; trophi (N=4): length 22‒24 µm, ramus 7.4‒8.3 µm, fulcrum 5.7‒6.0 µm, uncus 4.6‒5.9 µm, preuncinal tooth 2.6 µm, intramalleus 4.0‒4.3×2.6‒2.9 µm, supramanubrium 3.1‒4.3×2.7 µm, manubrium 15.4‒16.1 µm.

Comments. The shape of the rami, composed of three well developed chambers, is unique in Encentrum species and all other Dicranophoridae of which trophi have been thoroughly studied by SEM. Hitherto, apical chambers were considered to be strongly reduced and lacking a distinct opening in dicranophorids, and it was supposed that they became isolated from the rami or participated in the formation of the apical regions of the rami ( Markevich 1989). Another outstanding character of E. uncinatoides sp. nov. are the revolved gutter-shaped rami tips. Some revolving of the rami tips is only found in the dicranophorid Albertia vermiculus Dujardin, 1838 , which shows compact drawn out rami tips attached distally near the dorsal uncinal apophysis ( De Smet 1997).

Distribution and ecology. The species was found on four occasions at very low numbers in psammon from the sublittoral of the Côte d’Azur and Tyrrhenian Sea. Distance from the shore 50 m to 3.5 km, depth 17 to 40 m, June and September, water temperature 17−22 °C.

Figures

FIGURE 12. Encentrum (Tricellatum) uncinatoides sp. nov. A. Female, dorsal; B. female, lateral; C, D. toes, lateral; E. trophi, ventral; F. rami tips, dorsal. Scale bars: A, B: 50 µm, C − E: 10 µm; F: 1 µm.

FIGURE 13. Encentrum (Tricellatum) uncinatoides sp. nov., SEM photographs of trophi. A. Complete set, ventral; B. detail, ventral; C. detail, dorsal; D. detail rami tips, dorsal; E. detail, oblique ventro-lateral; F. detail, oblique ventro-frontal; G. detail, oblique dorso-frontal. a: apical ramus chamber, b: basal ramus chamber, s: subbasal ramus chamber. Scale bars: A − C, E − G: 10 µm; D: 1 µm.