Laubiericoncha myriamae, Cosel & Olu, 2008

Cosel, Rudo Von & Olu, Karine, 2008, A new genus and new species of Vesicomyidae (Mollusca, Bivalvia) from cold seeps on the Barbados accretionary prism, with comments on other species, Zoosystema 30 (4), pp. 929-944 : 933-936

publication ID	https://doi.org/ 10.5281/zenodo.4525869
persistent identifier	https://treatment.plazi.org/id/038C5736-FF9F-FF8D-17A1-BAB0FC10966C
treatment provided by	Felipe
scientific name	Laubiericoncha myriamae
status	sp. nov.

Treatment

Laubiericoncha myriamae n. sp.

( Figs 1 View FIG ; 2 View FIG ; 5C, D View FIG ; 7A View FIG )

“ Vesicomyidae sp.” – Faugères et al. 1987: 117. Vesicomya aff. chuni – Jollivet et al. 1990: 31; fig. 7b.

Vesicomya sp. – Olu et al. 1996: 371.

TYPE MATERIAL. — Holotype: Barbados accretionary prism, site Orénoque B (Dome 13), DIAPISUB, stn PL DS 10 /15, 10°19.97’N, 58°37.30’W, 1949 m, 2.I.1993, 1 spm. ( MNHN 20550 View Materials ). GoogleMaps

Paratype: same locality, site Orénoque A, 10°20.27’N, 58°53.73’W, 1730 m, DIAPISUB, stn PL DS 03/1, 1 spm. (MNHN 20551).

TYPE LOCALITY. — Southern part of Barbados accretionary prism, ESE of Trinidad.

ETYMOLOGY. — Dedicated to our colleague Myriam Sibuet, cruise leader of ZAIANGO BIOL 2, BIOZAIRE and BIOZAIRE 2.

OTHER MATERIAL EXAMINED. — Barbados accretionary prism (no precision), DIAPICAR cruise, 1 lv., 1 juv. rv., both older and discoloured brown (see Jollivet et al. 1990: fig. 7b). — Barbados accretionary prism, site Orénoque A, 10°19.72’N, 58°53.21’W, 1689 m, DIAPISUB, stn PL DS 04/2, 1 juv. spm. (all MNHN).

DISTRIBUTION. — Southern Caribbean, ESE ofTrinidad, only known from the type locality.

DESCRIPTION

Shell to 96 mm long (see Table 2), oblong-oval, rather thick and moderately tumid.Anterior margin

broadly rounded. Ventral margin convex, in the middle part straight. Posterior margin rounded, somewhat more narrowly rounded close to the horizontal midline. Umbones very shallow; beaks prosogyrous, well in front of the vertical midline, in fully grown specimens just before the end of the anterior third of the valve.

Surface with fine, dense, irregular commarginal ridges and some coarser irregular growth waves and stages, stronger and more pronounced towards the ventral part and close to the ventral margin. There are also some fine, irregular and more or less oblique wrinkles on the anterior and postero-dorsal part of the valves, partly becoming slightly laminar. Lunule and escutcheon absent. In place of the escutcheon and parallel to the postero-dorsal margin a sulcus with a rounded delimitation which can be characterized as a second posterior angle. Posterior angle closely below this ridge rounded but well marked and ending at the posterior extremity. Between the two “angles” a shallow radial depression, in which the wrinkly sculpture is more pronounced than on the rest of the shell. Periostracum yellowish, glossy on the earlier part of the shell, becoming more dull ventrally and posteriorly.

Hinge line short and rather narrow but strong. Right valve with a lower anterior, strong and laminar cardinal (1) starting almost parallel to the anterodorsal margin, then curving upwards and ending directly under the beaks, and a longer and stronger posterior cardinal, assumed to be fused 3a and 3b. It starts above the lower part of the anterior tooth (1) parallel to it, ascends towards the umbo and then descends backwards to beneath the anterior part of the ligament, with anterior limit almost vertical. Left valve anteriorly with a long, strong and somewhat irregular tooth 2a ascending towards the dorsal margin and situated under the umbo and in front of it. Cardinal 2b fused with cardinal 2a under the umbo, descending to the ventral margin of the hinge plate and inclined anteriorly. Posteriorly to the teeth 2a and 2b the shorter and laminar posterior cardinal (4b), inclined towards posteriorly. Ligament external, opisthodetic, rather short, on a narrow but strong nymphal plate. Subumbonal pit very small, shallow to indistinct. Pallial sinus short but well developed, nearly triangular, acute and pointing to about the middle of the anterior adductor scar; no prolongation of the pallial line on the anterior side of the sinus extremity. Anterior pedal retractor scar deep, separate from the anterior adductor scar. Posterior pedal retractor scar united with the posterior adductor scar. Inside of the valves with very faint, irregularly sized and spaced vermiculations or waves, more pronounced in the posterior part, and a very weak rib running from the umbonal cavity to the lower tip of the anterior adductor scar.

Valves entirely white.

Ctenidia large and fleshy, inner demibranch with about half the shell length (53 mm in the holotype), outer demibranch shorter, 45 mm in the holotype (see Fig. 5C View FIG ). Food groove very narrow and visible in both demibranchs. Exhalant and inhalant siphonal tubes small but rather long, fused over their whole length, with numerous very short tentacles around the common opening ( Fig. 5D View FIG ). Siphonal

tentacles with a small thickening at their ends. Inner mantle fold in its posterior part with very small, blunt tentacles for a length of about 3 mm (holotype) on both sides from the mantle fusion under the inhalant siphonal tube towards anterior. Foot muscular, laterally somewhat flattened.

BIOTOPE

Laubiericoncha myriamae n. sp. has been sampled on two cold seep sites on the southern part of the Barbados accretionary prism. The first site is located at the top of a diapiric ridge of the Orénoque A sector described by Faugères et al. (1987) and Jollivet et al. (1990) (DIAPICAR cruise) and by Olu et al. (1996) (DIAPISUB cruise with submersible). The species was living there together with two Bathymodiolus species, B. boomerang Cosel & Olu, 1998 and Bathymodiolus sp. aff. B. childressi Gustafson,Turner, Lutz & Vrijenhoek, 1998 (see also Olu-Le Roy et al. 2007b) and with several species of “vestimentiferan” worms ( Siboglinidae View in CoL , Polychaeta View in CoL ). Aggregates of a few tens of L. myriamae n. sp. were observed in the sedimentary areas and a few individuals were observed around the Bathymodiolus spp. aggregates, associated with carbonate concretions. Numerous shells were also observed; some of them were taken and dated, their age was between 10 000 and 20 000 years. Temperature gradient measurements in the sediment indicated active fluid venting at this site. The second site is located at the top of a mud dome of the Orénoque B sector ( Olu et al. 1996). Laubiericoncha myriamae n. sp. was living there in small aggregations in association with Bathymodiolus boomerang and Siboglinidae View in CoL .Temperature measurement indicated no active venting at this time.

REMARKS

Laubiericoncha myriamae n. sp. is close to L. chuni n. comb. (see below) but is slightly shorter and is distinguished by the more regular elongate-oval outline with more rounded and less tapering posterior margin, subparallel dorsal and ventral margins, the broader hinge plate, the less pronounced to obsolete commarginal wrinkles giving the surface a smooth appearance, and the periostracum which on the whole valve is glossy and not leafy as in L. chuni n. comb. The valves of L. myriamae n. sp. are somewhat thicker and heavier.The subumbonal pit is very small and almost indistinct, whereas in L. chuni it is small but deep and well distinguished. The umbones of L. chuni n. comb. are slightly more prominent and placed more forward than in L. myriamae n. sp. The tube uniting the fused siphons is slightly smaller and more delicate than in L. chuni n. comb.