Poecilasma crassa
Creators: name: Young, Paulo S.
Publisher: name: Zenodo
Year: 2001
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Maxillopoda
Pedunculata
Poecilasmatidae
Poecilasma
Poecilasma crassa

description: Poecilasma crassa (Gray, 1848)
(Figs 6-9) Anatifa crassa Gray, 1848: 44, pl. 3, figs 5, 6. Poecilasma crassa – Darwin 1852: 107, pl. 2, fig. 3. — Barnard 1924: 52. — Zevina 1982: 96, fig. 85; 1983: 1635; 1990: 184. — Southward 1998: 18.
Poecilasma crassum – Hoek 1883: 28; 1907a: 4. — Weltner 1897: 243; 1922: 78, pl. 4, fig. 17. — Gruvel 1902b: 525; 1905: 116, fig. 132; 1920: 38.
Poecilasma inaequilaterale breve Pilsbry, 1907a: 87, pl. 6, figs 9-10. — Nilsson-Cantell 1921: 254 (in part). — Barnard 1924: 53. — Henry 1954: 444. — Zullo 1968: 211. — Weisbord 1979: 42, pl. 4, figs 4-5. — Zevina 1982: 96.
Poecilasma (Poecilasma) crassa – Stubbings 1936: 6.
Trilasmis (Poecilasma) crassa – Hiro 1937: 409.
Trilasmis crassa – Nilsson-Cantell 1938: 9.
Trilasmis (Poecilasma) crassum – Stubbings 1967: 241. Trilasmis kaempferi inaequilaterale – Spivey 1981: 170. Non Poecilasma crassa – Visscher 1928: 199. — Hutchins 1952: 194.
MATERIALEXAMINED. — Mid-Atlantic Ridge, hydrothermal vents sites, DIVA II, stn PL 12, 37°50.54’N, 31°31.30’W, Menez Gwen, 866 m, 16 specimens on Chaceon affinis, tl (cl) 7.1 (5.0) to 22.0 (12.5) mm (MNHN Ci 2828, MNRJ 13888).
MARVEL, stn PL 1201, 37°50.54’N, 31°31.22’W, Menez Gwen, 850 m, 2 specimens, tl (cl) 6.7 (4.5) to 7.1 (4.4) mm (MNHN Ci 2829).
DESCRIPTION
Capitulum (Fig. 6A, B) strongly globose, asymmetric, with white plates; occludent margin slightly convex, nearly straight at upper portion; carinal margin convex. Peduncle (Fig. 6A, B) short, usually about half the capitular length.
Scutum (Fig. 6A, B) very convex with fine growth lines sparsely marked and thin longitudinal striae; apico-basal ridge prominent, usually with groove running along carinal side. Tergal portion with nearly straight area between apicobasal ridge and line between umbo and carinal apex, another strongly curved portion between carina and peduncle. Carinal margin convex, tergal straight, occludent margin straight at upper portion, slightly convex below. Internally with thick rim basally curving toward occludent margin, without umbonal teeth. Scuta of different sizes and curvatures, less convex with umbonal portion overlying more convex one.
Tergum (Fig. 6A) small, positioned between apico-basal ridge of scutum and carina apex; usually very eroded.
Carina (Fig. 6A, C, D) strongly curved at basal half, keeled basally, nearly flat apically; apex not inserting between terga; lower end with tooth projecting inward.
Labrum bullate (Fig. 7A) with one row of nearly 80 acute teeth. Palp (Fig. 7A, B) acuminate, short, covered by long finely pinnate setae on inner margin and setulae on outer margin. Mandible (Fig. 7C) with four equal teeth, denticulate on lower margin, lower angle produced with small tooth; large number of simple fine setae on lateral, lower and dorsoproximal margins. Maxilla I (Fig. 7D) with notch and lower portion produced; upper angle with one large and strong spine and five to seven medium-sized spines, below notch almost 20-22 small spines; large number of simple fine setae on lateral and lower margins. Maxilla II (Fig. 7E) quadrangular, with few simple setae, more densely present on upper portion.
Cirri of acanthopod type; articles with few finely and relatively small pinnate setae on anterodistal angle and several stout spines on postero-distal angle, which may be distributed in transverse row near distal margin; spaces between spines usually with multifid scales (Fig. 8B, C). Cirri I (Fig. 8A) and II (Fig. 8D) with proportionally short rami and large protopodites; rami unequal 3/2 and 4/3, respectively. Cirri III to VI (Fig. 8E) with subequal rami, length of medial articles equal to its width. Caudal appendage (Fig. 8E) smaller than coxopodite, uniarticulate, with tuft of long setae distally. Filamentary appendage large, wide, projecting anteriorly from base of cirrus I. Number of articles of cirri I-VI and caudal appendage is presented in Table 3. Penis annulated, covered with fine setae.
REMARKS
Poecilasma crassa was first described from Madeira on “Gorgonia” (Gray 1848: 44). All subsequent records are for individuals found on the carapace and appendages of crabs. There are no records of anything that look like Poecilasma on Madeira gorgonians. Probably the citation by Gray of a gorgonian as a substrate is a mistake. Poecilasma crassa was found on several samples of crab Chaceon affinis (A. Milne Edwards & Bouvier, 1894) observed from Madeira Island where and it was attached to the anterior region, usually on the maxillipeds of the crabs. The same crabs hosted Poecilasma aurantia Darwin, 1852 on the dorsum of the carapace. On the other hand, Southward (1998) observed P. crassa occurring more abundantly on the telson than on the limbs.
Nilsson-Cantell (1921: 254) considered Poecilasma inaequilaterale breve Pilsbry, 1907 to be synonymous with P.kaempferi Darwin, 1852 and Barnard (1924: 53) and Zevina (1982: 96) considered it synonymous with P. crassa. I have to agree with these last two authors in their synonymy. Pilsbry (1907a) described Poecilasma inaequilaterale breve and commented that it was distinguished from P. crassa only by “the straight occludent border of the scutum”. The figure 3 in Darwin (1852) indeed has a more convex occludent margin than found in P. inaequilaterale breve. The specimens examined vary greatly in size and show the variation in the curvature of the occludent margin of the scutum discussed by Darwin (1852: 107). The apico-basal ridge of the scutum sometimes has a conspicuous parallel groove and other times it is absent. The presence of an apico-basal ridge and groove on the scutum do not appear to be related to the size of the specimens. Therefore, both species should be considered synonymous. On the other hand, several characters in the shape of the plates of P. kaempferi separates it from P. crassa (Gray, 1848).
Darwin (1852) described briefly the cirri of P. crassa, but Pilsbry (1907a) did not describe them for P. inaequilaterale breve. The cirri of P. crassa are typically acanthopod, very different from the ctenopod type of P. kaempferi and P. inaequilaterale. Other characteristics of P. crassa which should be considered are the relative length of cirri I and II. Both rami have very short rami and long and very large protopodites.
Visscher (1928: 199) recorded P. crassa as a species fouling ships, which was cited in the list of fouling barnacles by Hutchins (1952: 194). P. crassa is a deep-sea species and does not occur in shallow waters. Essentially all records are between 217 and 1386 m, although Weltner (1922: 78) recorded it at shallower depths (25 m). Therefore, it is improbable this species can be found on ships.
P. crassa is commonly recorded in the Atlantic, especially in the northeastern part, where there have been a large number of dredgings. It is found on deep-sea crabs, especially on Chaceon affinis. This species occurs in the active vent field, very near mytilid mussels beds (Biscoito & Saldanha 2000, as Poecillasma [sic] cf. kaempferi [Darwin]).
In the Pacific, Hoek (1907a: 12) described P. obliqua from the Moluccas area, a species related to P. crassa, especially in the external characters of the plates. Both species have asymmetrical convex valves, with the scutum having a longitudinal groove, keeled carina and reduced terga. The appendages are also very similar: mandible with four equal teeth, with a denticulate lower margin, lower angle produced, with several setae; maxilla I with the upper angle with strong spines followed by a notch and the lower portion produced and covered by several setae; maxilla II quadrangular, with few setae. But, in P. obliqua Hoek, 1907 the scutum has an internal triangular tooth on the basal part of the occludent margin; the carina is internally convex, with a little fork basally and the cirri of both sides are unequal, the right side smaller. These characters justify the maintenance of P. obliqua as a valid species. P. obliqua was recorded from the Malayan Archipelago and Japan between 204-304 m on Macrocheira kaempferi (De Haan) as noted by Zevina (1982: 96).
description: Published as part of Young, Paulo S., 2001, Deep-sea Cirripedia Thoracica (Crustacea) from the northeastern Atlantic collected by French expeditions, pp. 705-756 in Zoosystema 23 (4) on pages 715-719, DOI: 10.5281/zenodo.4689055