Trilacuna Tong and Li, 2007

Grismado, Cristian J., Deeleman, Christa, Piacentini, Luis N., Izquierdo, Matías A. & Ramírez, Martín J., 2014, Taxonomic Review Of The Goblin Spiders Of The Genus Dysderoides Fage And Their Himalayan Relatives Of The Genera Trilacuna Tong And Li And Himalayana, New Genus (Araneae: Oonopidae), Bulletin of the American Museum of Natural History 2014 (387), pp. 1-108 : 26-30

Trilacuna Tong and Li

Trilacuna Tong and Li, 2007: 333 (type species by original designation Trilacuna rastrum Tong and Li, 2007 ).

DIAGNOSIS: This genus resembles Dysderoides and Himalayana by the chelicerae abruptly narrowed in the distal part, the deeply incised labium, and the genitalic morphology; it differs from Dysderoides in having normally developed eyes and in lacking macrosetae on legs III and IV, and from both by the long female postepigastric scutum, covering almost the whole ventral abdomen (as in figs. 29B, 32B, 49B). Males of Trilacuna also can be separated from those of Himalayana by lacking the prolateral dorsal acute projection in the copulatory bulb characteristic of that genus, and also by lacking the furrow connecting the posterior tracheal spiracles.

DESCRIPTION: Male: Cephalothorax: Carapace orange, without any pattern, anteriorly narrowed to 0.49 times its maximum width or less, with rounded posterolateral corners, posterolateral edge without pits, posterior margin not bulging below posterior rim, anterolateral corners without extension or projections, surface of elevated portion of pars cephalica smooth, sides smooth or granulated, thorax without depressions, fovea absent, without radiating rows of pits; lateral margin straight, rebordered; posterior margin of pars thoracica with stout setae with enlarged bases, without plumose setae; nonmarginal pars cephalica setae needlelike, in U-shaped row. Clypeus margin unmodified, sinuous in front view, vertical in lateral view, high, ALE separated from edge of carapace by their radius or more. Chilum absent. Eyes six, well developed. Sternum uniform, not fused to carapace, usually covered with numerous rounded pits (except in T. aenobarba , T. bangla , and T. hazara ; see below); at least in T. meghalaya , these pits have a central pore (fig. 24H); median concavity absent, radial furrow opposite coxae III absent, sickle-shaped structures absent, anterior margin unmodified, anterior corner unmodified, distance between coxae approximately equal, precoxal triangles absent, without posterior hump; setae dark, needlelike, originating from surface, usually without hair tufts (although T. mahanadi have a more dense patch on the central area, fig. 37E; see also T. kropfi, Eichenberger and Kranz-Baltensperger, 2011 : fig. 15D, F). Mouthparts: chelicerae straight, anterior face usually with prominent basal processes (fig. 23G); fangs without toothlike projections, directed medially, shape normal, tip unmodified; retromargin with one tooth (as in T. meghalaya , fig. 17C) or a patch with small teeth ( T. bangla , as in fig. 42E); setae needlelike, evenly scattered; paturon inner margin with pairs of enlarged setae, distal region abruptly narrowed, promargin unmodified, inner margin unmodified, laminate groove absent. Labium triangular, usually not fused to sternum, anterior margin deeply incised (fig. 30E), same as sternum in sclerotization; with six or more setae on anterior margin, subdistal portion with unmodified setae. Endites mesodistally excavated, serrula as a single row, posteromedian part unmodified, same as sternum in sclerotization. Abdomen: Ovoid, without long posterior extension, rounded posteriorly, interscutal membrane without rows of small sclerotized platelets; dorsum soft portions white, without color pattern. Book lung covers large, without setae, anterolateral edge unmodified. Posterior spiracles usually not connected by a groove (see figs. 23B, 31B), but a shallow groove is present in T. aenobarba and T. bangla (figs. 41B, 47B, 51B). Pedicel tube medium sized, usually ribbed, scutopedicel region unmodified, scutum extending far dorsal of pedicel, matted setae on anterior ventral abdomen in pedicel area absent, cuticular outgrowths near pedicel absent. Dorsal scutum strongly sclerotized, without color pattern, covering full length of abdomen, not fused to epigastric scutum, middle surface smooth, sides smooth, anterior half without projecting denticles. Epigastric scutum strongly sclerotized, surrounding pedicel, small lateral sclerites absent. Postepigastric scutum strongly sclerotized, long, semicircular, fused to epigastric scutum, anterior margin unmodified. Supraanal scutum absent. Setae of dorsal, epigastric, and postepigastric areas needlelike. Males of some species (such as T. mahanadi , T. aenobarba , and T. bangla ) have a conspicuous set of enlarged and stout setae behind the epigastric furrow (figs. 38B, 41B, 47A–C, 51B). Dense patch of setae anterior to spinnerets absent. Interscutal membrane with setae. Colulus represented only by setae. Legs: Orange or pale orange (in some species the legs III–IV are paler, almost white); without color pattern; femur IV not thickened, same size as femora I–III, tibia I unmodified, tibia IV specialized hairs on ventral apex absent, tibia IV ventral scopula absent, metatarsi I and II mesoapical comb absent, metatarsi III and IV weak ventral scopula absent. Leg spines: legs I–II with four ventral pairs of spines on tibiae and two on metatarsi; legs III–IV without spines, except an occasional ventral apical spine on tibiae IV. Tarsi I–IV without inferior claw. Trichobothria examined with SEM only in T. meghalaya and T. bangla ; tibiae: each with three; metatarsi: each with one; base longitudinally narrowed, hood covered by numerous low, closely spaced ridges (figs. 26C–G, 46G–O). Tarsal organ with three sensilla visible on legs I–II, two on legs III–IV and palp (as in fig. 46P–T); distal sensilla on legs I and II very small. Genitalia: Epigastric region with sperm pore small; furrow without Ω- shaped insertions. Palp normal size, not strongly sclerotized, right and left palps symmetrical, proximal segments pale orange; embolus light, prolateral excavation absent; trochanter normal size, unmodified; femur normal size, two or more times as long as trochanter, without posteriorly rounded lateral dilation, attaching to patella basally; patella shorter than femur, not enlarged, setae unmodified; tibial trichobothria (at least in T. meghalaya and T. bangla ) with structure similar to those of the legs; cymbium pale orange, ovoid in dorsal view, not fused with bulb, not extending beyond distal tip of bulb; bulb pale orange; embolus flanked with at least three laminar structures bearing filiform projections; internally (fig. 47J–L) there is a tortuous, thin tube, presumably the duct of a gland, discharging in the area of the filiform projections.

Female: As in male except as noted. Cephalothorax: Sternum setae sparse, evenly scattered. Endites anteromedian tip unmodified. Palp without claw, spines absent, tarsus unmodified. Claws of legs IV with a notably enlarged distal tooth on the internal row, appearing as bifid (at least in T. meghalaya and T. bangla , figs. 19C–D, 44D). Abdomen: Epigastric scutum not protruding, without lateral joints. Postepigastric scutum long, not fused to epigastric scutum. Spinneret scutum present, incomplete ring. Epigastric area setae uniform. Genitalia: The copulatory opening is a small slit situated posteriorly and separated from the epigastric furrow, in the middle of the transverse plates (figs. 22A, B, D, 45C, G, H; Eichenberger and Kranz-Baltensperger, 2011: fig. 18B, E); between the plates lies a field of papillae (as in fig. 45E, F). The opening leads to a posterior receptacle of variable shape (rounded to worm shaped), which extends to the vicinity of the epigastric furrow. It reaches the final part of the uterus externus through a rounded orifice (figs. 22E, F; 45C–E). The T-shaped anterior structure (here called ‘‘anterior sclerite’’; figs. 22C, 45B, C) apparently lacks a lumen, and has conspicuous anterolateral bars for muscle attachments; these muscles are connected with the ventral transverse plates, and presumably serve as a locking mechanism. The transverse plates have two long lateral apodemes projecting posteriorly, which serve as attachment for other muscles.

NOTE: The Himalayan species described in this paper have a relatively simpler set of paraembolic elements than those of the Chinese and Southeast Asian species (see Tong and Li, 2007; Eichenberger and Kranz-Baltensperger, 2011).

COMPOSITION: Sixteen species, six of them here described.

DISTRIBUTION: Members of this genus are known from the Himalayan range in Pakistan, Nepal, Bhutan, and northern India, to China, Thailand, Sumatra, and Malaysia ( Tong and Li, 2007; Eichenberger and Kranz-Baltensperger, 2011).

MONOPHYLY AND INTRAGENERIC RELATIONSHIPS: So far the only clear synapomorphy for Trilacuna seems to be the loss of the furrow connecting the posterior tracheal spiracles in males. The remaining characters that have been used to define the genus are variable through the species now included (e.g., pitted sternum, modified endites in males, thickness of male palpal femur), or define more inclusive groups (incised labium, cheliceral, and genitalic characters). Three species from Nepal, northern India, and Pakistan ( aenobarba , bangla , and hazara ) are probably basal in the genus, as they have a shallow groove connecting the spiracles in males, and lack the pitted texture on the sternum, widespread in other congeners. Two species described by Eichenberger and Kranz-Baltensperger (2011), T. werni and T. diabolica , have a well-developed furrow, and their placement should be reconsidered.