Hemicytherura trindadensis, Luz & Coimbra, 2022

Luz, Nathália Carvalho Da & Coimbra, João Carlos, 2022, Ostracods (Crustacea: Ostracoda) of the Vitoria-Trindade Chain, Southwestern Atlantic, Zootaxa 5188 (4), pp. 301-329 : 306-307

Hemicytherura trindadensis sp. nov.

Fig. 3 : 3–9

Type series. Holotype: MPO-2822, open carapace, RV length: 0.317 mm, RV height: 0.179 mm, LV length: 0.321 mm, height: 0.177 mm . Paratypes: MP-O-2823, open carapace, RV length: 0.299 mm, RV height: 0.177 mm, LV length: 0.304 mm, LV height: 0.169 mm; MP-O-2824, C, length: 0.323 mm, width: 0.183 mm .

Type locality. Trindade Island , site Cabritos Beach, Sample M18017 N.

Etymology. Regarding the type locality, Trindade Island.

Material. Dead assemblage: 12 RV, 2 LV, 6 C, and 3 juveniles . Living assemblage: 42 adults and 1 juvenile.

Diagnosis. A small subrectangular to subtriangular species of Hemicytherura with the greatest height in the middle. Caudal process well-developed, more acute, and adorned in RV. Surface ornamented mainly by six large fossae, each one with secondary reticulation and riblets. The subquadrate dorsal median the largest, containing a prominent curved central riblet from which appear smaller delicate riblets. Below the horizontal median ridge, two irregularly delimited fossae, the upper smaller and rounder, the lower larger and elongate.

Description. Carapace small and thick-shelled, subrectangular to subtriangular in lateral view. Valves unequal, RV higher and overlapping LV dorsally, LV overhangs RV in the caudal process and ventrally. Greatest height in the middle. Dorsal margin more evenly convex in RV. Ventral margin with conspicuous oral indentation, obscured by the ornamentation. Anterior margin obliquely rounded, slightly convex anterodorsally in RV, anteroventrally more protruded and ornamented by five small fossae. Posterior margin with an almost median caudal process, more acute and ornate in RV. Sagittate in dorsal view, widest medianly. Surface ornamented by fossae delimited by thick ridges; each fossa with delicate but conspicuous secondary reticulation and riblets. Six large fossae adorn the lateral surface, subquadrate dorsal median one the largest, containing a prominent curved central riblet from which appear smaller delicate riblets. Below the horizontal median ridge, two irregularly delimited fossae, the upper smaller and rounder, the lower larger and elongate.A vertical fossae ornaments the posterior region. Anteriorly, the median ridge separates two broad, elongate fossae; in some specimens, the lower one meets the elongate ventromedian fossae by a small interruption in the murus. Four more discrete fossae are visible laterally, two smaller, posteroventrally, two larger and elongate, anteroventrally. Between the dorsal ridge and the corresponding margin, arise five or six more elongate fossae. Inner lamella well-developed, much wider anteriorly. Line of concrescence separated from the inner margin anteriorly and posteroventrally; posterior vestibule smaller. Hinge merodont, RV with smooth elongate terminal teeth and a median smooth groove with thickened and crenulate ends. Sexual dimorphism not observed.

Remarks. Hemicytherura trindadensis sp. nov. is a small cytherurid so far restricted to Trindade Island, occurring mainly associated with algae, both live and dead specimens. This species resembles Hemicytherura bradyi ( Puri, 1960) but can be distinguished chiefly by the dorsal outline, which is more arched in H. trindadensis sp. nov., and the number and shape of the larger fossae.

Stratigraphic range. Holocene.

Occurrence and distribution. Trindade Island in the following localities: Cabritos Beach and Lixo Bay ( Tab. 3 ).

Figures

FIGURE 3. 1–2: Hemicytherura bradyi. 1) MP-O-2820, RV; 2) MP-O-2821, LV. 3–9: Hemicytherura trindadensis sp. nov. 3) MP-O-2822, RV, holotype; 4) MP-O-2822, LV, paratype; 5) MP-O-2823, RV, paratype; 6) MP-O-2823, LV, paratype; 7) MP- O-2823, RV, paratype, internal view; 8) MP-O-2823, LV, paratype, internal view; 9) MP-O-2824, paratype, dorsal view. 10–16: Semicytherura parva sp. nov. 10) MP-O-2825, female, RV, holotype.; 11) MP-O-2826, female, LV, paratype; 12) MP-O-2827, male, RV, paratype; 13) MP-O-2828, male, LV, paratype; 14) MP-O-2827, male, RV, paratype, internal view; 15) MP-O-2828, male, LV, paratype, internal view; 16) MP-O-2825, female, RV, paratype, hinge. 17–18: Semicytherura sp. 17) MP-O-2830, RV; 18) MP-O-2830, LV. 19–20: Callistocythere cranekeyensis. 19) MP-O-2818, carapace, RV; 20) MP-O-2819, carapace, LV. 21–22: Loxoconcha forda. 21) MP-O-2831, RV; 22) MP-O-2832, LV. 23–24: Loxoconcha foveata. 23) MP-O-2833, female, RV; 24) MP-O-2834, female, LV. Scale bar: 100 µm.