Arcoscalpellum concavitectum, Carriol, René-Pierre, 2013

Carriol, René-Pierre, 2013, Two new species of scalpelliform barnacles (Cirripedia: Thoracica) from the Plio-Pleistocene of Cotentin, northwest France, Zootaxa 3641 (1), pp. 21-30 : 26-27

Arcoscalpellum concavitectum sp. nov.

Fig. 2A–J

Diagnosis. Carina with concave tectum, bordered on each side by rounded rib without longitudinal ridges, intraparietes wide; tergum with apico-basal line formed by convergence of growth zones; upper lateral with basiscutal angle more widely truncated than basi-tergal angle.

Etymology. Alluding to the concave tectum of the carina.

Occurrence. Piacenzian to Gelasian from ‘Champeaux’ (co-ordinates: x = 335.84; y = 1172.9) in the Marchésieux district of the Département de la Manche.

Material examined. Inventory, and designation of the type material, see Appendix 3

MEASUREMENTS.

Description. Tergum subrhomboidal, flat, thin; umbo apical. Carinal margin straight, upper part with barely visible prominence marking limit of upward extension of carina. Occludent margin convex. Scutal margin sinuous. Apico-basal ridge absent, line formed by convergence of growth zones extending down from apex to basal angle, near and parallel to carinal margin. Inner surface with occludent and upper carinal margins narrowly thickened, marked with growth lines meeting in rounded angle below apex.

Scutum trapezoidal, convex transversely, apical part bowed towards tergum; umbo apical. Occludent margin convex, folded abruptly inwards. Tergal margin concave. Lateral margin straight. Tergo-lateral angle produced, rounded. Basi-lateral angle rounded. Basal margin straight. Apico-basal ridge absent, line formed by convergence of growth zones extending down from umbo to lateral-basal angle. Inner surface with adductor muscle pit wide, deep or shallow. Deep pouch for complemental males on occludent side between adductor muscle pit and apex ( Fig. 2B ).

Carina moderately bowed inwards; umbo apical. Basal margin convex. Tectum concave, bordered on each side by rounded rib. Parietes somewhat concave. Intraparietes wide, inclined outwards.

Upper lateral pentagonal, height exceeding width, slightly thickened; umbo apical. Scutal margin concave, smaller than convex tergal margin. Basal margin convex, unequally truncated at sides, that on scutal side longer than on tergal side. Two lines extending from umbo, one to each of inner angles on truncated basal margin. Between scutal margin and former line, as between tergal margin and latter line, growth lines abruptly upturned.

Rostral lateral with rounded ridge extending down from umbo to lower part of rounded infra-median lateral end. Upper margin concave to straight; lower margin strongly concave on rostral half, convex on infra-median lateral half. Inner surface concave with rostral end rising upwards.

Affinities. Withers (1953) recorded only a single species of Arcoscalpellum from Pliocene strata, that is A. michelottianum (Seguenza, 1876) from the Piacenzian of Sicily and Calabria, Italy. Since 1953, no other species of Arcoscalpellum has been recorded from these strata.

Arcoscalpellum concavitectum sp. nov. differs from A. michelottianum in that the latter has a carina with a flat tectum bordered by ribs and longitudinal ridges on the parietes; the tergum has a ridge extending from the apex to the scutal margin, placed almost halfway from the basal angle; the upper lateral has the basal-scutal angle narrowly truncated.

Figures

FIGURE 2. A – J, Arcoscalpellum concavitectum sp. nov. A: paratype MNHN. F. A 45795, external side of right scutum; B: paratype MNHN. F. A 45796, internal side of left scutum; C: paratype MNHN. F. A 45794, internal side of left tergum; D: paratype MNHN. F. A 45793, external side of right tergum; E: paratype MNHN. F. A 45797, external side of right upper lateral; F: paratype MNHN. F. A 45798, internal side of left upper lateral; G 1 – 2: holotype MNHN. F. A 45791, external side of carina; H: paratype MNHN. F. A 45792, transverse section of carina; I: paratype MNHN. F. A 46422, external side of carina; J 1 – 2: paratype MNHN. F. A 46425, external and internal sides of left rostral lateral. K, Scalpellum sp. A, MNHN. F. A 46423, external side of right? upper lateral. L, Scalpellum sp. B, MNHN. F. A 46424, external side of left? upper lateral. Scale bars represent 1 mm.