Scleropactes zeteki, VAN NAME, 1926

Schmidt, Christian, 2007, Revision of the Neotropical Scleropactidae (Crustacea: Oniscidea), Zoological Journal of the Linnean Society 151, pp. 1-339 : 49-50

SCLEROPACTES ZETEKI VAN NAME, 1926

Scleropactes zeteki Van Name, 1926 – Van Name (1936); Arcangeli (1930); Leistikow & Wägele (1999 *); Leistikow (1999*); Schmalfuss (2003 *).

Material examined

Type specimens: Two ♂, two ♀ m, two ♀ without marsupium, two immature ♂, one immature ♀ (Paratypes, Panama, Canal Zone, Gatun Lake , Barro Colorado Island, leg. Van Name, April 1924, AMNH 5347 ) .

Other samples: Six ♂, two ♀ m, three immature ( Panama, Canal Zone , Barro Colorado Island, leg. J. Zetek, September–December 1941, AMNH 9635 ) ; eight ♂ and one posterior half, two ♀ m, eight ♀ and six immatures ( Panama, Canal Zone , Barro Colorado Island, leg. J. Zetek, January–February 1943, USNM 87610 ) ; five adult ♂, 49 immature ♂ attributable to three distinct stages, seven ♀ m, 11 adult ♀ without marsupium, 87 juveniles and immature &female’, four mancas and fragments of 40 further specimens ( Panama, Canal Zone , Barro Colorado Island, leg. J. Zetek, January–June 1944, USNM 87595 ) .

Description ( Fig. 134 )

Female 14.9 × 6.7 mm, immature males in three distinct stages: c. 4 × 2 mm, c. 6.5 × 3.5 mm, 10 × 5 mm. Adult male maximum 15.5 × 7.2 mm [illustrations are in Schmidt (2003)].

Tergites distinctly tuberculate, each tubercle bearing a tricorn-like seta; in contrast to Scleropactes pilosus , the surface is not pilose, but looks somewhat rough. Tergites medially light brown with pale muscle insertion spots; coxal plates and epimera mottled in some specimens and pale in others. The pigment seems to be more strongly developed at the posterior margins of the coxal plates. Second antennae with weak pigment on the basal two articles and the distal two flagellar articles; stronger pigment on peduncular articles 3 and 4 and the proximal half of article 5; distal half of peduncular article 5 and proximal flagellar article white. Lateral lobes of cephalothorax distinct in dorsal view, but not in frontal view. Along posterior margin of transverse furrow a row of pectinate scales. Eyes composed of 24–27 ommatidia in adult specimens; the number of ommatidia depends on body size: small specimens about 2 mm wide have only nine or ten ommatidia.

First antenna third article with two long apical aesthetascs and a group of subapical aesthetascs. Second antenna with three-jointed flagellum bearing a slen- der apical cone that is slightly longer than the third article and has a pair of short lateral setae. Mandibles with a large grinding surface formed by the pars incisiva in the right mandible and by the enormously enlarged lacinia mobilis in the left mandible. Left mandible with hairy lobe bearing two penicils and one single penicil between lacinia mobilis and the original pars molaris, right mandible with only a few very small hairs between the lacinia mobilis and the original pars molaris, which is represented by a tuft of hairy setae. First maxilla mesal endite with two very stout penicils and the laterodistal corner rounded and provided with a fringe of hairs. Lateral endite on distal margin with lateral group of four simple, stout teeth and a small triangular lobe and a short, slender seta, and mesal group of six more slender teeth with simple tips and a pair of very small subapical setae. The six mesal teeth are much smaller than the lateralmost three tooth setae. Second maxillae apically bilobate, both lobes equal in size and hairy; mesal lobe with a rounded corner bearing a field of sensilla. Maxilliped endite rectangular, hairy, with a small seta on the caudal face and a stout penicil on the frontal face near apical margin. Maxilliped palp three-jointed; basal article with two large setae, second article on inner margin with proximal group of two or three small setae, and a distal tuft of setae on a socket, beside which there are two small setae. Lateral margin of the second article with two or three slender setae and one broad seta. Distal article with apical tuft of setae and a single seta on the lateral margin. Delimitation between second and third article distinct only in caudal view; the frontal face bears some pectinate scales.

Pereiopod 1 with antennal brush composed of scales on carpus and propodus. Male pereiopod 2 carpus with a small, distal field of scales and pereiopod 3 carpus with only a small group of scales in the same position. Male pereiopod 7 ischium with very shallow depression along the distal margin, on the frontal face. Base of pereiopod 7 with water-conducting scale-row along a furrow. (The scale-row was quite indistinct at 100× magnification, and could easily be overlooked, but at 400× magnification it was clearly visible.) Dactyli with dactylar seta slightly projecting beyond the outer claw, apically with two fringes of setules. No inner claw present, but at its place there are three setae, two of which are supposed to be the ungual seta and its accessory seta. Uropods with gland pores on their lateral face (these were not seen, but their existence could be concluded from the presence of secretion at this place).

Pleopod 1 and 2 exopodites strongly and coarsely wrinkled, giving rise to some short and wide air tubules. Lateral margins of these respiratory fields irregularly folded. Exopodites 3–5 without trace of such fields. Male pleopod 1 endopodite approximately straight, with row of minute setae along the dorsal spermatic furrow. Male endopodite 2 at least as long as exopodite, which is extended into a long apical lobe (the tip of the endopodite is broken off, so the exact length could not be determined). All exopodites with marginal row of one to several setae, which are irregular in size and position.

Thanks to the abundant material, the (postmarsupial) development of the male pleopod 1 can be described. The exopodite has well-developed respiratory areas already present in small specimens (5.3 × 2.6 mm), and the mesal lobe increases slightly in length and bears one apical seta at all stages. The endopodite of the small male is approximately straight, except for the tip, and bears a small number of spine-shaped setae in a row along the spermatic furrow. In medium-sized immature males (8.0 × 3.6 mm and 10.9 × 4.8 mm), the shape remains similar and the row along the spermatic furrow consists of 34 setae. In contrast, adult males have a row of approximately 50 spine-like setae along the spermatic furrow, and the distal third of the portion projecting beyond the genital papilla is distinctly narrower and stick-shaped.

Geographical distribution

Up to now, Scleropactes zeteki has been recorded only from Barro Colorado Island, where it seems to be abundant.

Remarks

Owing to the presence of numerous specimens of varying size, it was possible to examine growth stages of the male pleopod 1. If the adult male is looked at, a distinctly constricted distal portion is seen, as in Globopactes . If only an immature male is examined, the shape appears more simple and, in a phylogenetic analyis, would be coded differently. Therefore, it is necessary to compare the same stages in an analysis.

Scleropactes zeteki is most similar to Scleropactes pilosus , with regard to the general shape and the surface structure. It is easily distinguished from all other species of Scleropactes by the much more differentiated respiratory fields. A remarkable feature is seen in the mandibles, with their enlarged grinding surface, which is not formed by the original pars molaris but by the pars incisiva and lacinia mobilis. An odd similarity to this is found in Scleropactes cotopaxii , Scleropactes ecuadoriensis and also in Spherarmadillo nebulosus (see below). However, the pars molaris is simple in Spherarmadillo nebulosus but composite in Scleropactes zeteki , and the conformation of right lacinia and hairy lobe is different. Together with the other differences, this favours the assumption of convergency rather than synapomorphy of Scleropactes zeteki and Spherarmadillo nebulosus . In contrast, the similar structure of the mandibles of the three species of Scleropactes may be inherited from a common ancestor; they do not group together in the present analysis, but the characters that in the cladogram contradict the homology assumption for the grinding surface in Scleropactes zeteki , S. cotopaxii and S. ecaudoriensis have a low complexity. Research concerning the function of these mandibles and of the food of both species would be of great interest.

In some other, probably related, species of Scleropactes , the mandibles could not be examined due to lack of material.

Figures

Figure 134. Scleropactes zeteki Van Name, 1926: pleopod 1 of males of different size: immature 5.3 × 2.6 mm, immature 8.0 × 3.6 mm, 15.5 × 7.2 mm [compare also with immature male of 10.9 × 4.3 mm in Schmidt (2003)]; whole pleopods drawn at the same scale, enlarged endopodites not at same scale (Panama, Canal Zone, Barro Colorado island, leg. J. Zetek, January–June 1944; USNM 87595).