Thalassisobates emesesensis, Enghoff, 2013

Enghoff, Henrik, 2013, New montane, subterranean congeners of a littoral millipede, genus Thalassisobates (Diplopoda: Julida: Nemasomatidae), Journal of Natural History 47 (23 - 24), pp. 1613-1625 : 1614-1620

Thalassisobates emesesensis sp. nov.

( Figs 1A–E , 2A–B , 5A )

Material studied

Male holotype, SPAIN, Canary Islands, La Gomera, Reventón Oscuro , 28 ◦ 07 ′ N, 17 ◦ 12 ′ W, 6 August 2003, mesovoid shallow stratum, P. Oromí leg. ( DZUL). 1 male, paratype, data as holotype ( ZMUC), 1 female paratype, data as holotype ( DZUL) .

Diagnosis

A blind species of Thalassisobates . Differs from the other blind congener, T. almeriensis , in being more slender, and in having fewer setae on the anterior gonopod coxal processes.

Derivatio nominis

Named after its habitat, the mesovoid shallow stratum, MMS (em-em-es).

Description

Male holotype 33 + 2 + T, length 81 / 2 mm, height 0.58 mm; male paratype 27 + 2 + T, length 7 mm, height 0.52 mm; female paratype 32 + 2 + T, length 81 / 2 mm, height 0.60 mm .

Colour of preserved specimens uniform white.

Head: No eyes. Four frontal setae (only two setae seen in one of the males which was later dissected such that a re-count became impossible). Clypeus tridentate, a row of marginal clypeal setae; four supralabral setae. Antennae: length 178–194% of body height, with four apical sensilla, relative length of antennomeres 2–8 (8 = apical sensilla) 17/19-20/17-18/17-21/15-16/6-7/3, apical sensilla 3.9–4.7 times longer than wide. Mandibles ( Figure 2A, B ): Cardo with one, stipes with one or two setae, gnathal lobe: external tooth with ca. two accessory anterior cusps (cf. Enghoff 1979) and a single accessory posterior cusp; internal tooth with ca. six cusps, the posteriormost cusp smaller than the second; four rows of pectinate teeth, posteriormost teeth with two or three finger-like branches. Gnathochilarium: each stipes with three setae, each lamella lingualis with three setae, promentum fully separating lamellae linguales, lingual lobe without a deviating sensillum. Epipharynx and hypopharynx of the non-juloid type (cf. Enghoff 1981).

Collum with a whorl of eight setae about one-third collum length in front of posterior margin.

Body rings ( Figure 1A ) with marked constriction at about mid-length; prozona with scale-like microstructure; metazona dorsally smooth, ventrally with longitudinal striae; ozopores placed about in middle of metazona; a whorl of setae just in front of posterior margin, length of setae c.0.25 × body height. Sterna ( Figure 1B ) of the type unique for Nemasomatidae : (secondarily) free from pleuroterga and with anterior, wing-like expansions.

Legs ( Figure 5A ): length 101% of body height in male, 92% of body height in female, relative length of podomeres (prefemur-claw) 14-16/20/12-13/12-14/24/15. Claw very slender, length/height ratio 8–10; no accessory claw.

Telson: Preanal ring without a projection, with a marginal whorl of setae and four additional dorsal setae in a transverse row in front of marginal whorl. Anal valves each with two setae, subanal scale with two setae.

Male sexual characters

Mandibular stipites not expanded. First pair of legs with a long, backward-directed spine on tibia, otherwise unmodified. Femur, post-femur and tibia of following legs with ventral soft areas ( Figure 1C ). Coxa of second pair of legs ( Figure 1D, E ) with a small pore-field opening in a shallow pocket near lateral margin of anterior side, near mid-length.

Anterior gonopods ( Figure 3A ). Coxal processes each with two setae placed at c.0.4 of the process’s length from its basis and with very large apical hooks. Flagella well-developed. Telopodites about two-thirds as long as coxal processes, each with two apical setae.

Posterior gonopods ( Figure 3C ) very simple, flagellum-conducting flange with about five denticles.

Female sexual characters

Second pair of legs unmodified: coxae neither fused to sternum, nor to one another. Vulvae ( Figure 3D ) pyriform, situated in short invaginations confined to body ring 3. Operculum slightly longer than bursa, with two longitudinal rows of three setae each apically on oral surface. Bursa with one seta on mesal valve. Posterior field (“cimier” of Brolemann 1923) covering apical half of aboral surface of bursa, its margin reinforced by horseshoe-shaped structure. Receptaculum seminis long, slender, claviform.

Habitat

The type locality is situated in well-preserved laurel forest in the Garajonay National Park at> 650 m above sea level in the centre of La Gomera, the mesovoid shallow stratum is a colluvial slope covered by thin soil, the trap was set at 25–70 cm deep underground. The new species was found together with three widespread, probably introduced millipede species: Blaniulus guttulatus Fabricius, 1798 , Brachydesmus superus Latzel, 1884 and Brachydesmus proximus Latzel, 1889 , as well as the Gomeran endemic Glomeris gomerana Attems, 1911 . Thalassisobates emesesensis sp. nov. seems to be rare: despite many months of trapping (see Material and methods) only three specimens were found although numerous other millipedes entered the traps.

Notes

Whereas T. emesesensis clearly differs from T. littoralis in a number of characters, including absence of eyes, it is extremely similar to T. almeriensis sp. nov. The only clear difference concerns body size: males of T. emesesensis being more slender (0.52–0.58 mm for 27–33 podous body rings) than T. almeriensis (0.87 mm for 38 body rings). In juliformian millipedes, size differences should always be expressed in terms of body diameter and number of body rings ( Enghoff 1992). In the case of the two new Thalassisobates species , only a few individuals are available, but although the unique male specimen of T. almeriensis has more podous body rings than either of the two males of T. emesesensis , the difference in diameter seems significant. The other apparent differences between the two species: more slender coxal processes and more setae on the coxal process in T. almeriensis may, on the other hand, be functions of size and therefore not very reliable.

Figures

Figure 1. (A–E) Thalassisobates emesesensis sp. nov. (A) Midbody ring; (B) anterior sternum of leg-bearing body ring; (C) tibia of midbody male leg, showing striate ventral soft area; (D) second pair of male legs showing coxal pore group; (E) close-up of pore group. (F) Thalassisobates littoralis, detail of left second male coxa, showing inconspicuous pore group (encircled). Scanning electron micrographs, scale bars 0.1 mm (A, B); 0.01 mm (C, D, F); 0.001 mm (E). ms: metazonital setae, oz: ozopore, pg: coxal pore group.

Figure 2. (A, B) Thalassisobates emesesensis sp. nov. (A) Gnathal lobe of right mandible; (B) close-up of teeth from posterior part of distalmost pectinate lamella. (C, D) Sinostemmiulus simplicior Chamberlin & Wang, 1953, left mandible. Scanning electron micrographs, scale bars 0.01 mm. il: largest cusp of internal tooth, is: small posterior cusp of internal tooth, pl: pectinate lamellae (encircled), xm: main cusp of external tooth, xs: small posterior cusp of external tooth.

Figure 3. (A,C,D) Thalassisobates emesesensis sp. nov., (B) Thalassisobates littoralis. (A, B) Anterior gonopods, posterior view; (C) posterior gonopods, anterior view; (D) right vulva. Scale bars 0.05 mm. bu: bursa, cph: apical hook of coxal process, cps: setae of coxal process (encircled), ff: flagellum-conducting flange with spines, fl: flagellum, mcx: intercoxal muscle, mf: flagellar muscle, op: operculum, rs: receptaculum seminis.

Figure 5. Thalassisobates spp., midbody legs. (A) Thalassisobates emesesensis; (B) Thalassisobates almeriensis (with sternum); (C) Thalassisobates littoralis. Scale bars 0.1 mm (B), 0.05 mm (A, C).