Arcoscalpellum michelottianum

Arcoscalpellum michelottianum (Seguenza, 1876)

(Fig. 18)

Scalpellum michelottianum Seguenza, 1876: 381, pl. 6, figs 15-25, pl. 10, fig. 26.

Scalpellum velutinum Hoek, 1883: 96, pl. 4, figs 10- 11, pl. 9, figs 7-9.

Arcoscalpellum michelottianum – Newman & Ross 1971: 71, fig. 34, pl. 9b (with synonymy). — Young 1998a: 19, figs 13-14 (with synonymy).

MATERIALEXAMINED. — PROSPEC, stn CPH 10, 55°18.69’N, 10°14.83’W, 1589 m to 55°18.11’N, 10°15.38’W, 1578 m, 3 specimens, tl (cl) 29.5 (19.7) to 49.0 (33.4) mm (MNHN Ci 2869, MNRJ 13912). SAINT PAUL, stn SP 09-13, 01°00.73’N, 29°21.61’W, 3114 m, 1 specimen, tl (cl) 15.5 (12.2) mm (MNHN Ci 2870).

REMARKS

Arcoscalpellum michelottianum is probably a complex of several distinct species (Ross in litt. 1999). He noted conspicuous differences between specimens of Hoek’s types series of Scalpellum velutinum Hoek, 1883, photographed by Young (1998a: fig. 13a-d). The specimens differ in the relative development of the upper-latus, the position of the apex of the carina relative to the apex of the scutum and in the number and size of the plates on the peduncle. The specimens herein studied comprises the “ Arcoscalpellum velutinum ” type of Hoek, shown in Young (1998a: fig. 13c-d). A question about the peduncular pattern is if there are any changes in this pattern during the development? The three specimens record- ed have distinct sizes (tl of 29.5, 37.5 and 49.0 mm). If all the scales of the specimens are figured some differences can be observed. In the smaller stage the peduncular plate pattern is the basic eight-plate pattern with one row of rl-cl and another of sr-l-sc (Fig. 18A). The large specimen has a six-plated pattern lacking the cl plates (Fig. 18C). In the intermediate size individual, there is a change in the pattern from eight-plates to large plates in a six-plate pattern also with the exclusion of the cls (Fig. 18B). During ontogeny, the narrow basal part of the peduncle has irregularly spaced plates, which obscures the original pattern.

On the other hand, this observation reaffirms the supposition of an eight-plate pattern as a simplesiomorphic character in scalpellids (Newman & Ross 1998).