Encentrum valkanovi Althaus, 1957

De Smet, Willem H., 2015, Rotifera from the Mediterranean Sea, with description of ten new species, Zootaxa 4028 (2), pp. 151-196 : 188-189

Encentrum valkanovi Althaus, 1957

This typical species ( Fig. 30 ) is characterized by its dorso-ventrally flattened body with large and broad anterior pseudosegment showing longitudinal folds, the wide apart-set toes, and the 2 close-set light-refracting globules displaced to the right at the posterior of the brain. The specimens seen fit the original description, except for some details: the toes are more drawn-out and more or less distinctly offset near mid-length; the ‘ovate structure’ in the toes consists of a light-refracting spherical reservoir and part of its supply canal; the 4 dorsal longitudinal folds on the anterior trunk segment are 2 double-folds; the ‘spine’ between the toes is a rounded caudal papilla with projecting cilia.

Encentrum valkanovi was not uncommon in the sublittoral of all areas studied, from 50 m up to 8 km off shore, and depths of 15‒40 m, June, July, August, September, water temperature 17−25 °C. To date the species was only known from sublittoral psammon of the Black Sea, Varna, Bulgaria ( Althaus 1957).

Redescription of trophi by SEM. Trophi ( Figs 30 D, 31) of subgenus Encentrum type. Trophi large, elongate, fairly slender. Rami outline longer than wide, ratio length:width of closed rami 1.8−1.9; dorsal outer margin of rami weakly concave laterally, angular posteriorly; ventral outer margins with shallow carina rami ( Figs 31 C, E: cr) near 3/7 from apical ramus tip; median rami opening elongate drop-shaped; subbasal chambers dorsally with small depression medio-caudally from basifenestrae; basifenestrae dorsal, small, ellipsoid; subbasifenestrae caudal, small, rounded. Each ramus with single, slightly offset apical tooth set at right angle to trophi axis; cardal apophyses very small. Prior to apical teeth a preuncinal tooth set at a right angle to trophi axis; preuncinal teeth with elongate triangular head and short shaft forming obtuse angle; head with small cardal apophysis. Fulcrum longer than ramus, in dorsal/ventral view distal end slightly widening; distal widening indented dorsally, with median prominence ventrally; in lateral view with broad base, quickly tapering, continuing parallel-sided. Unci medium long, slightly curved, head shorter than shaft, with dorsal and ventral apophyses; dorsal and ventral ribs fairly broad. Intramallei long, sock-shaped, with relatively long, rounded medio-lateral basal expansion bearing opening medio-caudally; inner side expanded, fitting lateral concavity of rami. Supramanubria absent. Manubria slightly less incus length, stout, rod-shaped, proximal half straight, distal half incurved with crutched cauda, head short, triangular.

Measurements. Body (N=5): total length 180‒210 µm, toe 28‒35 µm; trophi (N=5): length 24‒26 µm, ramus 8.5‒9.8 µm, fulcrum 11.6‒11.7 µm, uncus 5.6 µm, preuncinal tooth 2.4 µm, intramalleus 4.8×3.7 µm, manubrium 18.2‒18.7 µm.

Figures

FIGURE 30. Encentrum valkanovi Althaus. A. Female, dorsal; B. toe and caudal antenna, dorsal; C. toe, lateral. Scale bars: A: 50 µm; B − D: 10 µm.

FIGURE 31. Encentrum valkanovi Althaus, SEM photographs of trophi. A. Complete set, dorsal; B. detail, dorsal; C. detail, ventral; D. complete set, dorso-lateral; E. detail, ventro-lateral. cr: crina rami. Scale bars: 10 µm.