Notholca bythonoma, 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 : 156-158

Notholca bythonoma sp. nov.

( Figs 2 , 3 )

Diagnosis. Lorica 115−150 µm long, widest at anterior margin, dorsal plate tapering to rounded end with acute or cut-off caudal extension; antero-dorsal margin with six short spines; dorsal plate with longitudinal striation; two weak lateral folds running from base of caudal extension towards anterior; ventral plate protruding.

Type locality. Scoglio della Nave Enfola, Elba Island, Tyrrhenian Sea, Italy. In sublittoral psammon collected on 25.09.2006, 50 m seaward from shoreline and 40 m deep; water temperature 21°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 216.

Paratypes. One female from type locality in RBINS, No. IG 33082, RIR 246; 7 mounted paratypes and 6 SEM trophi preparations in Department of Biology, University of Antwerp.

Additional material. 18 specimens collected at the Côte d’Azur, and Elba Island, Tyrrhenian Sea (see Tab. 2 species list).

Etymology. The specific name bythonoma (Greek buthos, meaning depth, nomos, meaning dwelling-place, home) is an adjective referring to the environment the species was found.

Description of female. Lorica ( Fig. 2 ) longer than wide, ratio length:width c. 2, widest at anterior margin, gradually tapering towards rounded posterior end; dorsal plate prolonged into short to fairly long, acutely tapering or rectangular-truncate extension. Posterior extension not set off from trunk, occasionally marked off by basal swelling; laterally from base of caudal extension two folds run parallel over a short distance, and afterwards diverge, continuing laterally to anterior somewhat less 1/3 lorica length. Antero-dorsal margin with six short, fairly broad spines, median and lateral spines almost equally long, intermediate spines somewhat smaller; lateral spines with two reinforced ridges; antero-ventral margin with broad median notch, and arched or weakly undulate lateral edges. Dorsal plate with longitudinal striation. In lateral view fairly thick with protruding ventral plate. Ratio lorica length:position of lateral antennae to antero-dorsal margin 2.15−2.30.

Trophi of typical Notholca - type ( Fig. 3 ). Rami triangular, almost symmetrical in outline; right rostellum ( Fig. 3 F: r) slightly more robust than left one; alulae well developed, symmetrical, rounded; subbasifenestrae large, almost symmetrical; basifenestrae minute, rounded; medial surface of rostellum with opening, the fenestrula ( Fig.3 F: f); apophyses and teeth on inner margin of rami strongly asymmetrical, left stronger than right; sclerite elements composing apophyses and teeth stout, strongly fused, hardly recognizable individually; both ramus apophyses tricuspidate; rami teeth composed of two groups of four basally fused tooth-shaped projections, fitting into the spaces between the two major uncinal teeth; inner margin of rami anterior to right rostellum with two separate small blunt prominences, and a comb of about 8 small blunt appressed sclerite bodies ( Figs 3 B, F: cs), anterior to left rostellum a similar configuration of elements but comb-forming sclerite bodies less distinct. Fulcrum short, lamelliform, distal margin only weakly expanded, almost parallel-sided in lateral view with distal end strongly oblique. Unci almost symmetrical and equally developed; ventral margin with fairly pronounced outward bend proximally; two major teeth, the first and third the most robust, and two distinct minor teeth; left dorsal uncinal margin with three additional strongly reduced teeth, right dorsal margin with 1−2 additional reduced teeth; first tooth of major teeth slightly smaller than other major one (third teeth). Subunci a bundle of elongatefusiform scleropili. Manubria as usual for the genus, composed of large elongate dorsal chamber with large elongate opening, a long medial chamber with minute opening, and smaller ventral chamber with small, elongatetriangular opening. A strong ligament connects the lateral margin of the basal apophyses with the ventral margin of the head of the manubria, and a weaker one with the ventral margin of the unci.

Measurements. Lorica (N=10): length 115‒150 µm, width 50‒68 µm, median antero-dorsal spine 10‒13 µm, lateral antero-dorsal spine 10‒12 µm, intermediate antero-dorsal spine 6‒8 µm, caudal extension 8‒30 µm; trophi (N=5): length ~18 µm, ramus 13.1−14.2 µm, fulcrum 3.7−4.8 µm, uncus 12.2−13.9 µm, manubrium 18.0−19.8 µm.

Comments. Notholca bythonoma sp. nov. shows a superficial resemblance with N. intermedia Voronkov, 1917 , a freshwater species described from Lake Baikal. The latter species is larger, 200−220 µm (data from Kutikova 1970) vs. 115−150 µm in N. bythonoma , with the lorica broadest near its posterior half vs. lorica widest at anterior margin; its antero-lateral and antero-median spines are longer vs. spines short and only slightly different in length in the new species; the two weak lateral folds running from the base of the caudal extension towards anterior in N. bythonoma sp. nov. are lacking in N. intermedia . Varga (1939: p. 335, Fig. 9 ) pictured a Notholca sub N. heptodon Perty from freshwater Lake Balaton, Hungary, with the lorica widest at the anterior margin and narrowing caudally. He claims the species identical with the N. heptodon (Perty, 1850) as pictured in Brauer (1912), and actually considered an invalid junior subjective synonym of Notholca foliacea (Ehrenberg, 1838) , although his specimens apparently lacked the characteristic anteriorly pitted collar and dorsal pattern of striae of the latter. Varga’s animal differs from N. bythonoma sp. nov. by its undulate lateral lorica margins and the absence of the two caudo-lateral folds.

Distribution and ecology. The species was found in low numbers in sublittoral psammon samples from the Côte d’Azur and Tyrrhenian Sea, at distances of 50 m to 1 km from the shoreline, and depths between 20 and 40 m. It was present in samples of June, September, and October, at water temperatures of 17−23 °C.

Figures

FIGURE 2. Notholca bythonoma sp. nov. A, B. Loricae, dorsal view; C. Lorica, lateral view; D. Lorica, anterior margins, ventral view; E. Lorica, caudal extension. Scale bar: 50 µm.

FIGURE 3. Notholca bythonoma sp. nov., SEM photographs of trophi. A. Complete set, ventral; B. Complete set, dorsal; C. complete set, ventro-frontal; D. complete set, dorso-frontal; E. fulcrum, lateral; F. left ramus, oblique dorsal (uncus at the back); G. right manubrium, outer view; H. left manubrium, inner view. cs: comb of sclerite bodies; f: fenestrula; r: rostellum. Scale bars: 10 µm.

FIGURE 9. Encentrum loefgreni sp. nov., SEM photographs of trophi. A. Complete set, ventral; B. detail, dorsal; C. detail, ventral; D. complete set, ventro-lateral; E. detail, ventro-frontal. Scale bars: 10 µm.