Cyrtodesmidae, Cook, 1896

The Cyrtodesmidae View in CoL

is yet another small family containing only three accepted genera, two of which are oligotypic ( Oncodesmella Kraus, 1960 , 2 species, and Agnurodesmus Silvestri, 1910 , 4 species), and one which is rather more prolific ( Cyrtodesmus Cook, 1896 , about 25 species) ( Golovatch 2001). The family occurs on the island of Tobago, Central America from Costa Rica southwards, and northern South America southwards to Amazonia.

Volvation is either imperfect ( Agnurodesmus ), this being testified by the relatively short paraterga being only slightly deflexed ventrad below the level of sterna, or complete ( Cyrtodesmus , probably also Oncodesmella ). In the former case, the pattern is much like in Campodesmidae , with a strongly enlarged paratergum 2 which is emarginate caudolaterally for the accommodation of the anterolateral protuberance of paratergum 3. The latter is also strongly emarginate caudolaterally.There is neither a schism nor a hyposchism on paratergum 2, but starting from paratergum 3 the overlap is typical. The only peculiarity is that the broadened, dentate or crenulate paraterga show a lunular flange anteriorly and a caudal protuberance caudolaterally, with the latter fitting in the former of the next paratergum during volvation ( Fig. 37 View Figs 37–44 ). In contrast, conglobation in Cyrtodesmus involves the development of a lobuliform schism and a narrow hyposchism in a typically roundly spatuliform paratergum 2, and of a subacuminate, not broadened, end of each subsequent paratergum ( Fig. 20 View Figs 12–21 ). The overlap is retained in the typical form. This condition strongly resembles that of Amphitomeus among Oniscodesmidae .

Also as in Oniscodesmidae , the telson in cyrtodesmids tends to be reduced, being fully concealed under the paraterga of the penultimate body segment in Agnurodesmus ( Fig. 39 View Figs 37–44 ). In a completely enrolled Cyrtodesmus species, the small, somewhat pygidiumlike telson is fully exposed in dorsal view, the tip of the epiproct is nearly fully hidden underneath, and the entire caudal body end ( Fig. 21 View Figs 12–21 ) appears to rest on top of body segment 4. In Agnurodesmus siolii Golovatch, 2001 , it is placed on top of metatergum 5 or 6.

The above progression is more or less paralleled by a trend towards the complication of gonopod structure, from the relatively small gonocoxae and strongly exposed telopodites in Oncodesmella , to the strongly enlarged coxae and shield-like structures protecting the remaining parts inside the gonocoel in Agnurodesmus . Based on structural details, the genus Agnurodesmus can soundly be considered as especially disjunct. This opinion agrees with biogeographical evidence as well ( Golovatch 2001). Even though volvation in this genus appears incomplete, its pattern is unique among all ‘oniscoid’ Polydesmida .

Even amongst Cyrtodesmus species there is one, C. bicolor Loomis, 1964 , from Panama, in which, due to the much smaller paratergal lobes of the second segment, only incomplete volvation can be suggested (Loomis 1964), i.e. a kind of ‘plesiomorphic’ status like that of Proeilodesmus as opposed to Sphaeriodesmus in Sphaeriodesmidae . Hoffman (1999) lists C. bicolor among Cyrtodesmidae of uncertain generic position.

Among the other traits characteristic of Cyrtodesmidae , the usually blackish to piceous teguments with contrastingly pinkish antennae deserve mention. The body is relatively small (5–20 mm long), the teguments are rough ( Figs 20, 21 View Figs 12–21 , 37–40 View Figs 37–44 ), the metaterga are always tuberculate and often setose; the epicranial region is granulorugose ( Fig. 41 View Figs 37–44 ), the limbus is crenulate/dentate; antennomere 5 is usually but not always longer and larger than antennomere 6 ( Fig. 41 View Figs 37–44 ); the pore formula is usually but not always normal; the legs are relatively short and stout ( Fig. 42 View Figs 37–44 ); and the solenomere is always branched ( Figs 43, 44 View Figs 37–44 ). Further characteristics can be found in Golovatch (2001). Many of the traits in Cyrtodesmidae , however, appear to be shared with the definitely closely related but very large and diverse family Pyrgodesmidae .