Arcoscalpellum Hoek, 1907

Young, Paulo S., 2002, Revision of the Scalpellidae (Crustacea, Cirripedia) in the collection of the Muséum national d’Histoire naturelle, France, studied by Abel Gruvel, Zoosystema 24 (2), pp. 309-345 : 321-325

Genus Arcoscalpellum Hoek, 1907

Arcoscalpellum atlanticum (Gruvel, 1900) ( Figs 10-12 )

Scalpellum atlanticum Gruvel, 1900a: 190 ; 1902a: 74, pl. 2, figs 3F, 17, 18; 1902c: 246; 1902d: 523; 1905: 68, fig. 76; 1920: 26, pl. 7, fig. 5. — Hoek 1914: 4. — Belloc 1959: 3.

Teloscalpellum atlanticum – Zevina 1978b: 1350; 1981a: 377, fig. 294.

Arcoscalpellum crenulatum Foster & Buckeridge, 1995: 170 , fig. 5a-f.

Arcoscalpellum tritonis non Arcoscalpellum tritonis ( Hoek, 1883) – Young 1998a: 19, figs 15, 16; 1998b: 36, fig. 1 (non Arcoscalpellum tritonis [ Hoek, 1883]). Arcoscalpellum atlanticum – Young 2001: 739, figs 23, 24.

TYPE MATERIAL. — Azores Region, Talisman, 1883 , drag. 128, 38°7’N, 29°32’W, 960-998 m, lectotype by present designation, only the capitulum, cl 11.4 mm ( MNHN Ci 398).

DIAGNOSIS. — Capitulum oval, flattened with smooth plates. Carina with tectum flat, bordered by lateral ridges. Carino-latus almost twice higher than wide, with umbo at carinal base, slightly projecting backward. Inframedian-latus triangular, slightly higher than wide. Rostro-latus slightly wider than high. Cirrus I with anterior ramus three quarters the length of posterior ramus. Caudal appendage slightly longer than protopodite of cirrus VI.

DESCRIPTION

Capitulum ( Fig. 10A ) oval, flattened, length almost twice the width, carinal margin more curved than occludent margin. Plates smooth, with thin growth lines, presenting alternate a hyaline white bands and other darker. Cuticle thin.

Tergum ( Fig. 10A ) with its surface area greater than scutum; inconspicuous apicobasal ridge. Basal margin convex. Carinal margin slightly convex at lower portion and concave near apex. Occludent margin convex. Apex curved toward carina.

Scutum ( Fig. 10A ) convex, with inconspicuous apicobasal ridge; height more than twice the greatest width. Basal margin straight. Tergal margin slightly concave, presenting a lid. Occludent margin nearly straight at mid-basal part and distally convex. Lateral margin convex except for upper concavity to accept apex of upper-latus. Apex curved, superimposed on tergum.

Carina ( Fig. 10A, C ) arching continuously, slightly wider at upper portion, with umbo apical. Tectum flat with undulated growth lines, bordered by lateral ridges; basal margin slightly concave.

Upper-latus ( Fig. 10A ) pentagonal with apex curved toward scutum, umbo sub-apical, projecting. Scutal margin largest, followed in size by tergal and carino-lateral margins with same length, carinal margin and the smallest rostro-lateral margin. Scutal margin concave; other margins straight.

Carino-latus ( Fig. 10A, C ) nearly pentagonal, almost twice higher than wide, with umbo at carinal base, slightly projecting backward; with a ridge from umbo to basal angle. Carino-latera with ridges posteriorly, but not interdigitating with one another below carina.

Inframedian-latus ( Fig. 10A ) triangular, slightly higher than wide, shorter than rostro-latus, with umbo straight.

Rostro-latus ( Fig. 10A, B ) triangular, slightly wider than high, with an inconspicuous apicobasal ridge.

Rostrum ( Fig. 10B ) small, reduced to small triangular point between rostro-latera.

Peduncle ( Fig. 10A ) not anymore available in the lectotype. There are only one sc, one rl and one l scales. In the figures of Gruvel (1920: pl. 2, figs 17, 18) the peduncle is one third the capitulum length and is covered by large scales; the rl-cl and l-sc scales can be observed ( Fig. 10A ). Therefore, I suppose this species has an eightplate whorl pattern: rl-cl; sr-l-sc.

Labrum ( Fig. 11A ) bullate, with one series of about 50 denticles. Palp ( Fig. 11A ) short, acuminate with few simple setae. Mandible ( Fig. 11B ) with three acute teeth, distance between first and second tooth more than twice distance between second and third; lower angle denticulate. Maxilla I ( Fig. 11C ) with anterior border having an inconspicuous, shallow, medial notch, and two large and 10 median unpaired spines. Maxilla II ( Fig. 11D ) nearly triangular, covered with numerous large and simple setae except for median region on anterior margin; papilla of maxillary gland strongly pronounced.

Cirrus I ( Fig. 12A ) with unequal rami, anterior ramus the three quarters length of posterior ramus; former with protuberant articles. Cirrus II with equal rami but shorter than posterior cirri. Cirri III to VI with equal, long rami. Median article of cirrus VI ( Fig. 12B ) less than twice longer than wide, five pairs of simple long setae and few fine setulae between larger pairs on anterior margin; three or four setulae on lateral surface; two setae on posterior angle. Setal-article ratio about 3.5:1. Caudal appendage ( Fig. 12C ) with six articles, slightly longer than protopodite of cirrus VI; articles with few, small setae on distal margins, and cluster of simple setae on apex. Penis absent. Number of articles of cirri I-VI and caudal appendage is presented in Table 4.

REMARKS

Gruvel (1900a) described Arcoscalpellum atlanticum based on two specimens collected from the Talisman Expedition , drag. 128, but only one specimen was found.

Arcoscalpellum atlanticum is difficult to diagnose and can be confused with A. tritonis ( Hoek, 1883) and also with small specimens of species of Meroscalpellinae , which still present capitulum with unreduced plates (e.g., the small forms of Neoscalpellum debile [Aurivillius, 1898] and Litoscalpellum meteoria Young, 1998 ). First, I thought A. atlanticum and A. tritonis were synonymous, but the shape of the carina, rostro-latus and inframedian-latus separate these species: A. tritonis has the carina with a simple, flat roof; the rostro-latus wider than high, with a conspicuous apico-basal ridge; the inframedian-latus thin with concave lateral margins, with the lateral margins concave and as high as the rostro-latus. Furthermore, there is a geographic separation between both species: A. tritonis has a more northern distribution in the North Atlantic, occurring from Faroe Channel and near Iceland ( Hoek 1883; Zevina 1981a), and A. atlanticum was recorded in more southern areas in the North Atlantic, between Azores and off Portugal coast south to Meteor seamounts and off Morocco coast (31 to 47°N and 7 to 29°W); A. tritonis was recorded from depths between 913-940 m and A. atlanticum from 950-1250 m to 3360-3600 m. The specimens examined by Young (1998a) (identified as A. tritonis ) differ from the type specimens in that the carina has a flat surface, with the basal margin rounded; the labrum lacks teeth, and the caudal appendages are biarticulate, with less than one half the length of coxopodite. The specimens were of smaller size, between 4 and 12 mm of capitular length, which can justify these differences.

Foster & Buckeridge (1995) described Arcoscalpellum crenulatum from Gibraltar region. Examining the type series I could observe that this species is A. atlanticum . All the capitular and appendages characters correspond to those of A. atlanticum , except to the “crenulate upper margin of rostro-latus”. But the crenulation in the specimens is very delicate, and probably related to erosion of the plates, not justifying the recognition of these specimens as a new species.

Figures

FIG. 10. — Arcoscalpellum atlanticum (Gruvel, 1900), lectotype (MNHN Ci 398); A, right lateral view; B, rostral view; C, carinal view. Scale bars: A, 3 mm; B, C, 1 mm.

FIG. 11. — Arcoscalpellum atlanticum (Gruvel, 1900), lectotype (MNHN Ci 398); A, labrum and palp; B, mandible; C, maxilla I; D, maxilla II. Scale bars: A, B, D, 0.5 mm; C, 0.2 mm.

FIG. 12. — Arcoscalpellum atlanticum (Gruvel, 1900), lectotype (MNHN Ci 398); A, cirrus I; B, median article of cirrus VI; C, protopodite of cirrus VI and caudal appendage. Scale bars: 0.5 mm.