Colomboniscus tristani, (ARCANGELI, 1930), 2007

Schmidt, Christian, 2007, Revision of the Neotropical Scleropactidae (Crustacea: Oniscidea), Zoological Journal of the Linnean Society 151, pp. 1-339 : 23-24

COLOMBONISCUS TRISTANI ( ARCANGELI, 1930)

COMB. NOV.

Scleropactes tristani Arcangeli, 1930 – Arcangeli (1931b); Van Name (1936 *); Schmalfuss (1980 *); Leistikow (1997 *); Leistikow & Wägele (1999 *); Schmalfuss (2003 *).

Material examined

Four ♂, three ♀ m, one ♀, one juvenile ( Venezuela, Caripe , 10°10′31″ N, 63°30′12″ W, 7 April 1998, cCS 229a) , one ♂, one ♀ m, one ♀ (same data, UCV) ; one ♂, seven ♀ ( Costa Rica, San José, leg.?, November 1911, MZUF 3958 ) ; four ♂, five ♀ ( Costa Rica, Originaco , leg.?, MZUF 3957 ) ; two ♀ m [ Costa Rica, ‘ Fed. Hort. Board. ’, Amaryllis bulbs, leg. C. A. Davis (without date), USNM 60596 ] (Map Fig. 36 ) .

Description ( Figs 38–44 )

Male 2.9 × 1.0 mm, cephalothorax 0.68 mm wide. Females with marsupium: cephalothorax width 0.74– 0.78 mm.

Very small, with endoantennal conglobation ability. Eyes and pigment entirely absent. Frontal shield in frontal and dorsal views with an obtuse angle on its upper margin. Coxal plate 1 with a weak furrow parallel to its margin. All coxal plates simple. Pleotelson short, slightly rounded. Noduli laterales very small, located on the hind margins of the tergites/coxal plates. Scale setae distinct, giving the animal a hirsute appearance.

First antenna three-jointed, apical article as long as basal two articles together, three subapical and two apical aesthetascs. Second antennae stout, the fivesegmented peduncle, especially its fifth article, strongly inflated. Flagellum of normal shape, three articles, and an apical cone equal in length to all three flagellar articles together. Apical cone with one small lateral sensillum.

Mandibles with pars incisiva of four cusps (or five cusps?) and lacinia mobilis of two cusps; left lacinia larger than right lacinia. Lobe basal to the lacinia mobilis with one penicil on the right mandible and two penicils on the left mandible. Both mandibles with one penicil between lobe and pars molaris, the latter consisting of a tuft of hairy setae. First maxilla mesal endite with two penicils, and distolateral corner rounded. Lateral endite with lateral group of four stouter and mesal group of six more slender teeth. At the base of the lateral group, there is a small, acute lobe and a short, slender tooth. Four teeth of the mesal group have their tip cleft. Second maxilla indistinctly bilobate, with some sensory spines on the mesal lobe. Maxilliped endite with three setae or lobes on the apical margin, and one extremely small spine or seta on the laterodistal corner. Maxilliped palp three-jointed. Basal article with two large setae, second article on the mesal margin with basal ‘tuft’ of only one seta, and distal tuft consisting of one very large and some smaller and more slenderer setae on a common socket. Distal article with one tuft of setae, among them one larger, similar to the large seta of the second article.

Pereiopod 1 carpus and propodus with brush of scales for cleaning the second antennae. Male pereiopods 1–4 on ventral face of merus and carpus with weakly developed brushes of scales. Pereiopod 7 on frontal face of basis and ischium with vestigial waterconducting scale-rows that seem to be non-functional. Ventral margin of male ischium 7 concave, with a submarginal fringe of scales. These are smaller in subadult males (cCS 229a). Dactyli with slightly curved ungual seta and dactylar seta apically hirsute. Inner claw at most half as long as outer claw. Uropods similar in shape to those of Scleropactes and Neosanfilippia .

Male pleopod 1 endopodite with row of setae that are large in comparison with those of Neosanfilippia . Apex simply rounded, with some hairs. Endopodite 2 exceeds the exopodite by about half its length. Pleopod 1 exopodite roughly triangular, and apically rounded, without marginal seta. Exopodites 2–5 with one marginal seta each. Pleopod 5 on the caudal (dorsal) face with a multiple row of pectinate scales.

Diagnosis

This species is easily distinguished from other small, unpigmented Scleropactidae by its three-jointed flagellum and the inflated appearance of the fifth peduncular article of the second antenna, in combination with the frontal shield, which is slightly recurved on the vertex. In frontal and dorsal view, the upper margin of the frontal shield is curved, not straight.

Habitat

Without doubt, this minute, unpigmented and eyeless species is adapted to an endogeic life. Two of the four samples were collected in gardens, one under flower pots, and the other in (?) Amaryllis bulbs; for the other two samples, no habitat information is known. Until this species is found in a natural habitat, its geographical origin will remain dubious.

Biology

The samples mentioned in Arcangeli (1930) contained 40 males and 149 females, which is a male/female ratio of 0.268 ( Arcangeli, 1931b). In the marsupium, he always counted four eggs or embryos.

Remarks

The type specimens are most probably lost (Ferrara & Taiti, pers. comm.), but fortunately specimens from one of the places mentioned in the original description (San José) were available for study. Schmalfuss (1980) noted that this species does not belong in the genus Scleropactes , as currently defined.

Figures

Figure 36. Geographical distribution of Colomboniscus: 1, C. regressus; 2, C. tristani.

Figure 38. Colomboniscus tristani (Arcangeli, 1930): ♀m, 1.05 mm wide, habitus and pleon; ♂, 0.75 mm, cephalothorax (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).

Figure 39. Colomboniscus tristani (Arcangeli, 1930): ♂, 0.75 mm wide, coxal plates, sternite 7 (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).

Figure 40. Colomboniscus tristani (Arcangeli, 1930): ♂, 0.75 mm wide, mouthparts (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).

Figure 41. Colomboniscus tristani (Arcangeli, 1930): ♂, 0.75 mm wide, pereiopods 1–3 frontal, second antenna (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).

Figure 42. Colomboniscus tristani (Arcangeli, 1930): ♂, 0.75 mm wide, pereiopods 4–6 and pereiopod 2 dactylus, frontal (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).

Figure 43. Colomboniscus tristani (Arcangeli, 1930): ♂, 0.75 mm wide, pereiopod 7, uropods (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).

Figure 44. Colomboniscus tristani (Arcangeli, 1930): ♂, 0.75 mm wide, pleopods 1–3 frontal, pleopods 4 and 5 caudal (Venezuela, Caripe, leg. C. Schmidt, 7 April 1998, cCS 229a).