Oniscodesmidae, De Saussure, 1860

The Oniscodesmidae View in CoL

as currently defined (Hoffman 1980 1982 b; Simonsen 1990) contains eight or nine nominal genera, all in South and/or Central America. Most genera are monobasic, only the southernmost Crypturodesmus Silvestri, 1897 ( Brazil and Argentina) is relatively species-rich. The conglobation pattern is similar to the previous case, but it varies even between genera.The spatulate, rounded, strongly enlarged lateral pieces of paraterga 2, sometimes ( Detodesmus Cook, 1896 ) have a distinctly elevated anterior margin and a narrowed and flattened dorsum (the latter often angular at the bases of paraterga, Figs 26, 27 View Figs 22–27 ), and they always possess a narrow hyposchism behind a lobuliform schism. This is small in Amphitomeus Verhoeff, 1942 ( Figs 24, 25 View Figs 22–27 ), with a typical overlap of the subsequent paraterga. During complete volvation the lateral ends of several paraterga subsequent to the second, rest over a narrow rim of the latter (cf. Golovatch et al. 2002). In Crypturodesmus ( Fig. 17 View Figs 12–21 ), the caudolateral margin of paratergum 3 is very strongly emarginate or sinuate for the accommodation of the anterolateral portion of paratergum 4, but posterior to this the overlap is typical, with the lateral ends of several paraterga subsequent to the fourth likewise resting over a narrow rim of paratergum 2.

The telson tends to become reduced. In Amphitomeus ( Figs 28–30 View Figs 28–31 ), the only 19-segmented oniscodesmid genus, the telson is still evidently exposed in dorsal view ( Figs 29, 31 View Figs 28–31 ), although the epiproct is short and strongly flattened ( Fig. 30 View Figs 28–31 ) (cf. Golovatch et al. 2002). In Crypturodesmus , the telson in dorsal aspect is completely hidden under the medially fused paraterga of the penultimate body segment ( Fig. 18 View Figs 12–21 ). In both cases, in a completely enrolled animal, a pygidium-like caudal body end rests tightly oppressed to the region of segments 2–5.

The family is characterised by small to medium-sized species (3–22 mm long). The tergal surface is usually polished, but sometimes finely microgranular or scaly ( Amphitomeus , Fig. 25 View Figs 22–27 ); the metaterga are often ( Fig. 17 View Figs 12–21 ) but not always tuberculate, or infrequently areate along the rear tergal margin behind a transverse sulcus or depression ( Oniscodesmus , Detodesmus and some others), and only rarely almost smooth ( Amphitomeus ). The paraterga are sometimes lobulate or crenulate at the lateral edge ( Crypturodesmus , Figs 18, 19 View Figs 12–21 ), and they are rarely incised at the base both anteriorly and, especially deeply, posteriorly ( Amphitomeus , Figs 24, 25 View Figs 22–27 ). The tergal limbus is (nearly) missing; antennomere 5 is longer and larger than antennomere 6; the pore formula is usually complete and normal, but the ozopores are small, and open flush on the surface near the base of the respective paraterga and more rarely the ozopores are absent altogether ( Crypturodesmus ); the legs are relatively slender; the gonopod aperture is transversely oval to subcordate ( Fig. 19 View Figs 12–21 ) and relatively large; the gonopod coxae are relatively small, subglobose, fused medially, largely sunken inside the aperture, and with normal cannulae; the telopodite is suberect, and the setose prefemoral part is always substantial ( Figs 19 View Figs 12–21 , 32 View Figs 32–36 ).

This family is deemed to be particularly closely related to the Dorsoporidae (Hoffman 1980 1982 b), while Simonsen (1990) has even merged both into a single family Oniscodesmidae . For practical reasons, however, Dorsoporus Loomis, 1958 does deserve a separate treatment.