Eutrichodesmus basalis Golovatch, Geoffroy, Mauriès & VandenSpiegel, 2009

Golovatch, Sergei, Geoffroy, Jean-Jacques, Mauriès, Jean-Paul & VandenSpiegel, Didier, 2009, Review of the millipede family Haplodesmidae Cook, 1895, with descriptions of some new or poorly-known species (Diplopoda, Polydesmida), ZooKeys 7 (7), pp. 1-53 : 8-13

Eutrichodesmus basalis Golovatch, Geoffroy, Mauriès & VandenSpiegel , sp. n.

urn:lsid:zoobank.org:act:49B81FBA-709E-40C4-BA47-0E36E1E39664

Figs 1-4 .

Type material. Vietnam, Vinh Ha Long Prov. (SW), Dao Bo Hon, Hang Bo Nau Cave , 12.VI.2003, leg. P. Trontelj & B. Sket, holotype ♂ ( MNHN JC 309 ) , paratypes: 1 ♂ ( MNHN JC 309 ), 1 ♀ ( SEM) .

Name. To emphasize the obvious basal position amongst the volvatory “doratodesmids”.

Diagnosis. Differs from congeners by the apparently imperfect volvation, due to particularly short paraterga, coupled with an especially simple gonopod structure.

Description: Length of adults of both sexes ca 4.8-5.0 mm, width 0.6-0.65 mm, body broadest at segment 3 or 4; ♂♂ a little smaller than ♀♀. Holotype ca 4.8 mm long and 0.6 mm wide. Coloration uniformly pallid or light yellowish.

Adults with 20 segments, body subcylindrical ( Fig. 1A ), pattern of conglobation typical of “ Doratodesmidae ” as described by Golovatch (2003), but volvation itself obviously somewhat imperfect in barely concealing all (especially hind) legs ( Figs 1A, C, D ). Head ( Fig. 2B ) slightly transverse, rather densely pilose, microgranular amd microvillose just below antennae and on vertex, with a pair of paramedian,

almost contiguous knobs; isthmus between antennal sockets very narrow. Antennae ( Fig. 2C ) very short and stout; antennomere 6 longer than 5, dorso-apically with an evident pit containing a tight group of minute bacilliform sensilla; antennomere 8 with the usual four sensory cones apically. Collum rather large, regularly convex, not covering the head from above, entire surface microvillose, with four transverse rows of round tubercles with a pit on top (apparently representing the former place of insertion of bisegmented, tactile setae, which are mostly lost) ( Fig. 2A ). Prozona very finely alveolate, collum and metaterga covered with a cerotegumental crust held by abundant microvilli; stricture between pro- and metazona broad and shallow, more finely alveolate-microgranular than prozona; limbus microcrenulate, nearly fully hidden by nearby abundant microvilli ( Figs 3C, D ). Metaterga behind collum with three transverse rows of tubercles ( Figs 1 A-F), some of which still retain long, bisegmented setae ( Fig. 3B ). Paraterga subvertical, very narrow, downwards barely reaching level of venter, clearly trisinuate caudolaterally at base due to two lobulations ( Figs 1C, D ; 2D; 3A); paraterga 2 strongly enlarged, with a series of lobulations anterolaterally, both schism and hyposchism very small; paraterga 3 and 4 slightly shorter than others ( Fig. 1B ), overlap of following paraterga typical, latter broadly rounded and evidently trilobate. Pore formula normal, ozopores located on top of a small porostele-like tubercle on ventrocaudal lobulation ( Fig. 3A ). Pleurotergal ridges very small, alveolate-microgranular like entire ventral surface. Epiproct short, also with tubercles, directed ventrocaudad, with the usual four cones (= spinneret setae) just below tip; para- and hypoprocts as in Figs 1F ; 2E.

Sterna usually with a deep, narrow, longitudinal depression between coxae ( Fig. 2F ), but sterna between coxae 6, 7 and 9 much wider ( Fig. 4A ). Gonopod aperture transverse-oval, relatively small, far from reaching lateral sides of segment 7. Legs very short; tarsal segment longest; claw usual, simple, very slightly curved ventrad; some setae sparsely microdenticulate ( Figs 2F ; 3E ).

Gonopods ( Figs 4B, C ) very simple. Coxae subquadrate, large, microtuberculate and abundantly setose ventrolaterally, with a conspicuous triangular lobe frontolaterally. Telopodite much longer than coxite, slender throughout, setose in its basal half, with a conspicuous, only apically denticulate, lateral, distofemoral process (dp) at about midway, with a hairpad in distal third, but seminal groove unexpectedly terminating subapically.

Remarks. This remarkable species somewhat bridges the former Haplodesmidae and Doratodesmidae . Hence the quotation marks which are used for “haplodesmids” and “doratodesmids” above and hereafter. In addition to showing the tergal trichome of peculiar, bisegmented setae and the unusually simple gonopods so characteristic of Cylindrodesmus (both features partly shared also with several true “doratodesmids”), it also, most importantly, has the body only capable of incomplete volvation, due to the relatively very short paraterga. Moreover, the ozopores are borne on small porostele-like tubercles, a feature characteristic of most “haplodesmids”, but only rarely encountered among “doratodesmids”. At least the incomplete volvation and the simple biramous gonopods seem to be relatively primitive characters amongst the more advanced “doratodesmids” in which volvation is already perfect.

The new species especially resembles the similarly tuberculate-setose Dyomerothrix gremialis Hoffman, 1982 or Parapauroplus monodentus Zhang in Zhang & Wang, 1993 , which also show rather simple gonopods ( Hoffman 1982a; Zhang and Wang 1993).

Figures

Figure 1. Eutrichodesmus basalis sp. n., ♀ paratype; A, habitus, lateral view; B, anterior part of body, lateral view; C, midbody segments, lateral view; D, posterior part of body, lateral view; E, midbody segments, dorsal view; F, posterior part of body, dorsal view. − Scale bars: A, 0.5 mm, B, C, D & F, 0.1 mm & E, 0.2 mm.

Figure 2. Eutrichodesmus basalis sp. n., ♀ paratype; A, anterior part of body, frontodorsal view; B, head, front view; C, antenna; D, cross-section of a midbody segment, caudal view; E, posterior part of body, ventral view; F, legs, ventral view. − Scale bars: A, B, D, E, 0.1 mm & C, F, 0.05 mm.

Figure 3. Eutrichodesmus basalis sp. n., ♀ paratype; A, enlarged paraterga with ozopores, lateral view; B, bisegmented seta; C, tegument texture; D, limbus and adjacent parts; E, claw. − Scale bars: A, 0.05 mm, B, D, E, 0.01 mm, C, 0.02 mm.

Figure 4. Eutrichodesmus basalis sp. n., ♂ paratype; A, leg 9, caudal view; B & C, left gonopod, mesal and lateral views, respectively (dp = distofemoral process). − Scale bar: A, 0.2 mm, B, C, 0.1 mm.