Retrodesmus cavernicola, Golovatch, Sergei I., Geoffroy, Jean-Jacques, Stoev, Pavel & Spiegel, Didier Vanden, 2013

Golovatch, Sergei I., Geoffroy, Jean-Jacques, Stoev, Pavel & Spiegel, Didier Vanden, 2013, Review of the millipede family Opisotretidae (Diplopoda, Polydesmida), with descriptions of new species, ZooKeys 302, pp. 13-77 : 34-37

Retrodesmus cavernicola sp. n. Figs 14-16

Type material.

Holotype ♂ (NMNHS), Papua New Guinea, Western Prov., Finim tel Plateau, Peep Hole Cave, 18.08.1975, leg. P. Beron (British Speleological Expedition).

Paratypes: 1 ♂, 1 ♀, 1 ♂ (incomplete), 5 juv. (17 segments) (NMNHS), 1 juv. (17 segments) (ZMUC), 1 ♀ subadult (19 segments) (MNHN JC 338), Papua New Guinea, Western Prov., Telefomin, Cave Bem Tem (No. 1), 31.07.1975, leg. British Speleological Expedition; 1 ♀ subadult (19 segments) (ZMUM), 1 ♀ subadult (19 segments) (SEM), 1 juv. (17 segments) (NMNHS), Finim tel Plateau, Upper Bitip Cave, west chamber, 21.11.1975, leg. British Speleological Expedition, FT-11; 1 ♀ (fragments) (NMNHS), Finim tel Plateau, bottom of a 150 m shaft near Girtoil, 08.08.1975, leg. British Speleological Expedition; 1 ♀ (fragments) (NMNHS), Chimbu Prov., Goglme Village, Cave Ogon I, 1975, leg. P. Beron (British Speleological Expedition).

Diagnosis.

Differs readily from Retrodesmus dammermani Chamberlin, 1945, the only other known species of Retrodesmus , by the particularly broad paraterga, several clearly troglomorphic features such as especially long and slender antennae, legs and metatergal setae, the latter also being very dense, the subcaudal position of the ozopores, and the shape and ornamentation of the gonopod apex.

Name.

To emphasize the obvious troglomorphic traits strongly suggesting obligate cave-dwelling; a noun in apposition.

Description.

Length of adults of both sexes ca 12 (♂) or 16 mm (♀), width of midbody pro- and metazona 0.95-1.0 and 2.0 mm (holotype and ♂ paratype) or 1.5 and 2.8 mm (♀ paratypes), respectively. Coloration in alcohol from uniformly pallid to light yellowish.

Body with 19 (♂) or 20 (♀) segments. Tegument mainly dull, at most slightly shining, texture very delicately alveolate. Head densely pilose throughout; epicranial suture superficial and thin; isthmus between antennae about twice the diameter of antennal socket. Antennae very long and slender, reaching behind segment 2 when stretched dorsally, geniculate between antennomeres 5 and 6, each latter with an apicodorsal group of tiny sensilla; antennomere 7 with a tiny mid-dorsal knob; antennomeres 2-6 subequal in length (Fig. 15A).

In width, collum << head <segment 2 <3 = 4 <5 (6) =15 (♂, ♀), thereafter body gradually tapering towards telson. Paraterga very strongly developed, starting from collum, invariably slightly to clearly upturned, set high, but always lying slightly below a faintly convex dorsum, with shoulders frontolaterally (Figs 14 A–C). Caudal corner of postcollum paraterga invariably spiniform, pointed, extending increasingly behind rear tergal margin. Lateral edge of paraterga with 2 or 3 clear and deep seti gerous indentations in poreless and poriferous segments, respectively. Pore formula normal; ozopores evident, round, flush open on dorsal surface, located very close to caudal margin at bottom of caudalmost lateral incision (Fig. 14J), lateral tooth being considerably shorter than medial one. Collum and each following metatergum with mostly 3+3 long, nearly pointed, but ribbed and subbacilliform setae arranged in three transverse, rather regular rows and borne on small stalks; polygonal bosses very flat; both rear rows of setae more irregular, placed very close to each other (Figs 14 A–E, H). Stricture between pro- and metazona wide, shallow and smooth. Limbus very fine, microspiculate, the spikes mostly being rather sparse and irregular. Pleurosternal carinae absent (Figs 14D, E). Epiproct short, conical, directed caudoventrally; pre-apical papillae small (Figs 14C, E, G). Hypoproct trapeziform (Fig. 14G), setiferous papillae at caudal corners very small and well separated.

Sterna without modifications, rather broad, strongly setose (Fig. 14G). Epigynal ridge very low. Legs very long and slender, growing slightly slenderer towards telson (Figs 15B, 16A), ca 1.5 (♂) times as long as midbody height; femora and tarsi longest, subequal in length; sphaerotrichomes missing.

Gonopod aperture evident, transversely oblong-oval, taking up most of ventral part of metazonite 7. Gonopods (Figs 15C, D, 16B, C) with globose, medially fused coxae carrying a few setae on ventral face and a normal cannula mesally. Telopodite nearly straight, unipartite, rather short and stout. Distal part of telopodite split into a shorter frontal stump (s) (= solenomere?) beset with bacilliform ornamentations and a quite complex, subtriangular, pointed, caudal branch (b) with a spine (sp) at base. Seminal groove terminating near base of both s and b, with neither a distinct solenomere nor a hairy pulvillus, but with a small accessory seminal chamber.

Remarks.

Because of several apparent troglomorphic traits,this species seems to be a troglobite. Surprisingly, it appears to be rather widespread in western Papua New Guinea, occurring in places like Finim tel and Goglme which are separated from each other by>200 km.

It is the gonopod conformation, not the location of the ozopores, that clearly indicates the true affinities of Retrodesmus cavernicola sp. n. to Retrodesmus dammermani , despite the great geographical gap between Java and New Guinea that also separates these species.