Encentrum foroiuliense, 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 : 161-162

Encentrum foroiuliense sp. nov.

( Figs 6 , 7 )

Diagnosis. A fairly large Encentrum about 175 µm long (slightly contracted). Corona oblique; rostrum shallow, almost straight; large more or less rectangular tail; toes narrow basally, expanding for about 1/3 their length and tapering afterwards to ventrally curving tubular tip; large spherical proventriculus; trophi subgenus Encentrum - type; rami outline longer than wide, ratio length:width of closed rami 2.2−2.3; median rami opening elongate dropshaped; carina rami present; fulcrum ramus length; preuncinal teeth in line with apical rami teeth; intramallei long, with broad, rounded medio-lateral basal expansion.

Type locality. Baie de St. Raphaël, Golfe de Fréjus, ‘Le Jardin’, Côte d’Azur, France. In psammon collected on 23.10. 2008, 400 m from shoreline and depth of 66 m; water temperature 20 °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 218.

Paratypes. One female from type locality in RBINS, No. IG 33082, RIR 248; 3 mounted paratypes and 4 SEM trophi preparations in Department of Biology, University of Antwerp.

Additional material. Several specimens from sublittoral of Îlot de la Fourmigue and Cap Bénat, Baie du Lavandou, Côte d’Azur.

Etymology. The name foroiuliense is a Latin adjective of Forum Iulii, name given to the city of Fréjus by the Romans, and refers to the area of the type locality.

Description of female. Body more or less cylindrical ( Fig. 6 A). Head offset by distinct transversal fold. Rostrum broad, shallow, almost straight. Corona oblique. Dorsal antenna in posterior third of head. Trunk elliptical. Tail prominent ( Fig. 6 B), more or less rectangular, somewhat narrower proximally, slightly expanding distally and rounding off to straight or weakly indented distal margin. Foot cylindrical, two broad pseudosegments. Toes c. 1/6 total length, divergent, narrow at base, expanding for about 1/3 their length and tapering afterwards to tubular tip, in dorsal view more or less straight, in lateral view ( Fig. 6 C) with curved dorsal margin and more or less straight ventral margin, tubular tips decurved ventrally; a small rounded reservoir near midlength. Brain saccate; retrocerebral sac broad. Two colourless eyespots? Proventriculus large, spherical. Gastric glands rounded-ovate, stalks short. Pedal glands clubbed, relatively small. Vitellarium with 8 nuclei.

Trophi ( Figs 6 E, F, 7) subgenus Encentrum - type ( De Smet 1997). Trophi large, elongate, slender. Rami outline longer than wide, ratio length:width of closed rami 2.2−2.3; outer margin of rami weakly concave dorso-laterally, rounded-angular posteriorly; median rami opening elongate drop-shaped; latero-ventral margin of each ramus with shallow, rounded crest, the carina rami ( Fig. 7 E: cr), at 2/3 from ramus attachment to fulcrum; basifenestrae and subbasifenestrae small, elliptical to rounded. Each ramus with single, slightly offset incurved apical tooth set at obtuse angle to trophi axis; distinct cardal apophysis absent. Each ramus ventrally with single preuncinal tooth set at obtuse angle to trophi axis, in line with apical teeth; preuncinal teeth with short triangular head and short shaft forming obtuse angle; head without distinct cardal apophysis. Fulcrum ramus length, in dorsal/ventral view distal end slightly widening and indented; in lateral view with broad base, quickly tapering, continuing parallel-sided. Unci medium long, slightly curved; head less shaft length, with small dorsal apophysis, ventral apophysis vestigial; head expanded in plane of rami. Intramallei long, with broad, rounded, relatively short medio-lateral basal expansion ventrally, bearing small proximal opening; latero-ventral part expanded, fitting lateral concavity of rami. Supramanubria absent. Manubria slightly less incus length, stout, rod-shaped, more or less straight, distally incurved with crutched cauda, head short, triangular, with dorsal and ventral opening distally.

Description of male. Male ( Fig. 6 D) similar in habitus to female, but smaller and more slender; head distinctly offset; trunk elliptical; foot with broad penultimate pseudosegment and narrower distal one; toes similar to female ones, but with less pronounced tubular part; saccate brain and retrocerebral sac large; eyespot(s) and lateral antennae not observed. Trophi absent.

Measurements. Female, body (N=5): length (slightly contracted) up to 175 µm, toe 30‒31 µm; trophi (N=4): length 26 µm, ramus 12.2‒13.5 µm, fulcrum 12.2‒13.1 µm, uncus 5.8‒6.8 µm, preuncinal tooth 2.5 µm, intramalleus 7.0‒7.4 µm, manubrium 21.4‒23.7 µm. Male (N=3): length 120 µm (slightly contracted), toe 24−26 µm.

Comments. Encentrum foroiuliense sp. nov. can not be confused with any other member of the subgenus Encentrum by its characteristic shape of the toes and tail. The shallow crest at the ventro-lateral margins of the rami, the carina rami, has to date also been observed in E. psammophilum and E. valkanovi ( Figs 31 C, E: cr). The position of these crests near the junction uncus-intramalleus suggests a role in the functioning of malleus and incus by, e.g., helping to keep the intramalleus-uncus in position, or as attachment of mastax muscles interconnecting the distal end of the intramallei and/or proximal part of the unci with the antero-lateral part of the rami. The intramallei of the Encentrum- type are usually well developed and long (‘sock-shaped’), and closely connected to the rami, in contrast to the small intramallei in the trophi of the Isoencentrum - type, which appear not connected directly to the rami (see Fig. 5 ). The intimate connection of the intramallei with the rami in the Encentrum - type comes about by their swollen latero-ventral part fitting into a long lateral cavity of the rami (e.g. Fig. 7 D), and their wing-shaped medio-lateral basal part grasping ventrally the base of the rami (e.g. Fig. 7 E), both moreover closely interconnected by strong ligaments ( Figs 7 E, 9C, 31C). These different trophi configurations suggest a different way of operating. In the Encentrum- type intramallei-unci and rami will act together to seize the prey (see Fig. 31 A), and its engulfing will be achieved by withdrawal of the whole trophi set, whereas in the Isoencentrum- type, grasping of the prey will be primarily by the protruding unci, followed by pulling the prey back through an inward movement of these unci by pivoting on the rami tips, and added by the movement of the co-operating flexibly jointed manubria.

Distribution and ecology. The species was found at low numbers in the sublittoral psammon samples from the Côte d’Azur and Tyrrhenian Sea, at distances of 50 m to 3.5 km from the shoreline and depths between 15 and 66 m. It was present in samples of June, September, and October, at water temperatures of 20−21 °C. Males were present in June.

Figures

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.

FIGURE 6. Encentrum foroiuliense sp. nov. A. Female, ventral: B. tail; C. toe, lateral; D. male, dorsal; E. trophi, dorsal; F. intramalleus. Scale bars: A, B, D: 50 µm; C, E, F: 10 µm.

FIGURE 7. Encentrum foroiuliense sp. nov., SEM photographs of trophi. A. Complete set, dorsal; B. complete set, ventral; C. detail, oblique dorso-frontal; D. detail, dorsal; E. detail, ventral. cr: carina rami. Scale bars: 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.