Bathyarca arcadia, Simone, 2024

Genus Bathyarca Kobelt, 1891 View in CoL Bathyarca arcadia new species

( Figs. 45 View Figure 45 , 46 View Figure 46 A-E) https://zoobank.org/ 6C0FC89C-AAE7-49CD-AB2D-E0622D676960

Types: Holotype MZSP 166512 View Materials , shell . Paratypes: MZSP 166514 View Materials , 20 View Materials shells, MNHN-IM-2000-39812, 3 shells from type locality. BRAZIL. Espírito Santo ; off ItaÚnas, 19°41′S 37°48′W, 790-940 m, MZSP 166516 View Materials , 40 View Materials shells, MNHN-IM-2000-39813, 20 shells ( R. V. Marión-Dufresne col., MD55 sta. CB77 , 27.v.1987) GoogleMaps .

Type locality: BRAZIL. Espírito Santo ; off ConceiÇão da Barra , 18°59′S 37°50′W, 637 m [ R. V. Marión-Dufresne col., MD55 sta. CB76 , 27.v.1987] GoogleMaps .

Diagnosis: SE Brazilian species with oblique outline, delicate outer sculpture. Hinge with very oblique teeth in both ends, middle teeth minute, narrow, deformed.

Description: Shell of ~ 7 mm, rather oblique; length similar to height; maximum inflation ~80% of length ( Fig. 45C, M View Figure 45 ). Color white ( Fig. 46 View Figure 46 A-F) to pale beige ( Fig. 45 View Figure 45 A-F),with hairy beige periostracum close to edges ( Figs. 45A, B, K View Figure 45 , 58E View Figure 58 ). Right valve slightly smaller than left valve, exceeding in ventral edge ( Fig. 45A, F, K View Figure 45 ). Prodissoconch elliptic, smooth, simple, of almost 1 mm ( Fig. 45J View Figure 45 : arrow). Umbones prominent, blunt, elevating ~6% shell height beyond hinge; separated from each other, locat- ed in anterior end of mid third of hinge. Lunule narrow, concave, ~10% of shell width, slightly broader anterior to umbones ( Fig. 45C, M View Figure 45 ). Dorsal edge straight; anteri- or edge rounded, slightly smaller than posterior edge; ventral edge bluntly angular in its division with posteri- or edge. Sculpture delicate reticulated; radial cords predominating in right valve ( Figs. 45A, K View Figure 45 , 46E View Figure 46 ), ~45 radial cords from anterior to posterior hinge edges; commarginal cords predominating in left valve ( Figs. 45B, L View Figure 45 , 46D View Figure 46 ). Hinge with 3-4 middle teeth very minute, narrow, rather deformed, located lightly posterior to umbo; anterior to them from 5 ( Fig. 46C View Figure 46 ) up to 8 ( Fig. 45 View Figure 45 G-I) very oblique teeth, prosogire, average angulation ~45° in relation to antero-posterior shell axis, second and third teeth as largest ones; posterior to narrow teeth 6 ( Fig. 46C View Figure 46 ) up to 8-9 ( Figs. 46 View Figure 46 G-H, 59B) very oblique teeth, opisthogire, average angulation ~45° in relation to antero-posterior shell axis, penultimate tooth as largest. Inner surface white, opaque; muscle scars of difficult delimitation; scars of anterior and posterior adductor muscles round- ed, located below both hinge ends.

Etymology: The specific epithet is in apposition and a make-up word, although has a meaning in Latin of adventuresome, an allusion to difficulty in finding this isolated population.

Distribution: Rio Grande do Norte ( Francisco, 2015) to Rio de Janeiro coasts.