Tricellina Forster & Platnick, 1989

Rix, Michael & Harvey, Mark, 2010, The spider family Micropholcommatidae (Arachnida: Araneae: Araneoidea): a relimitation and revision at the generic level, ZooKeys 36 (36), pp. 1-321 : 34-35

Genus Tricellina Forster & Platnick, 1989

Tricella Forster & Platnick, 1981: 266 (name preoccupied in Diptera ). Type species by original designation Tricella gertschi Forster & Platnick, 1981 . Brignoli, 1983: 696.

Tricellina Forster & Platnick, 1989 in Platnick, 1989: 166 (replacement name for Tricella Forster & Platnick, 1981 ). Platnick, 2009.

Affinities. The genus Tricellina appears to be the sister-lineage to Austropholcomma from Australia ( Fig. 4 ).

Diagnosis. Tricellina gertschi can be distinguished from all other Micropholcommatini by the presence of an extremely long (length >> 5× width), bifurcate embolus with a complex trajectory around the entire pedipalpal bulb ( Fig. 45 ). Other diagnostic characters include the presence of a concave male clypeus in lateral view (Fig. 41A), and the retention of a five-segmented female pedipalp ( Fig. 43C ).

Description. Very small, entelegyne Araneoidea ; total length 1.00 to 1.10. Cephalothorax: Carapace without glandular depressions above maxillae; cuticle without glandular pits ( Fig. 42E ); margins fused to sternum via pleural sclerites; clypeus of male concave in lateral view (Fig. 41A). Eight eyes present on anterior margin of pars cephalica (Fig. 41); AME smallest. Chelicerae with bulging anterior projections in males; promargin with true teeth, a pair of fused setal sockets adjacent to base of fang and single peg tooth in males ( Fig. 43F ); proximal peg tooth-like seta of fused setal sockets modified in males, proximally-flattened ( Fig. 43F ); ectal stridulatory ridges present in males.

Legs and female pedipalp: Legs three-clawed ( Fig. 44D ), covered with smooth or serrate hair-like setae. Trichobothria present on tibiae and metatarsi of legs; tibiae each with two (legs I–III) or three (leg IV) trichobothria; metatarsi (legs I–III) each with single trichobothrium ( Fig. 44C ). Female pedipalp entire, five-segmented; claw absent ( Figs 43 C–D).

Abdomen: Abdomen oval; anterior sclerite present around epigastric region and petiole; large dorsal scute present on males (Fig. 41A), absent on females ( Fig. 40B ); lateral sclerotic strips present on males; posterior sclerotic ring surrounding spinnerets and colulus. Six spinnerets situated posterior to fleshy colulus ( Figs 23 G–H); PMS with single medial AC gland spigot and apparently without anterior CY gland spigot; PLS with complete triad. Anterior tracheal system with multiple anteriorly-directed tracheae; posterior tracheal spiracle absent.

Genitalia: Male pedipalp ( Fig. 45 ) relatively large; trochanter with modified prolateral seta forming stridulatory ‘tooth’; patella with broad, distally-directed, flang- ed ligulate retrolateral apophysis; tegulum smooth, with curved, evaginated tegular ridge; embolus exposed, very long (length >> 5× width), with looped proximal portion and bifurcate distal portion which winds in a complex trajectory around the entire pedipalpal bulb. Female genitalia ( Fig. 33D ) with pair of separate, globular anterior spermathecae; insemination ducts coiled around fertilisation ducts, with sclerotised proximal portion and expanded, membranous distal portion; fertilisation ducts bent, posteriorly-directed.

Distribution. Southern Chile, in Región de la Araucanía (Cautín and Malleco provinces) and Región de los Lagos (Chiloé, Llanquihue, Osorno and Palena provinces) (Fig. 212).

Composition. Only the type species Tricellina gertschi ( Forster & Platnick, 1981) .

Figures

Figure 4. Optimal cladogram for the Micropholcommatidae under equal and implied weights, and one of six equally parsimonious trees recovered from an equal weights analysis of the ‘new’ matrix (length = 135; see Appendix II). With the exception of the highlighted (*) node ‘Patelliella adusta + Micropholcommatini’, all clades shown were recovered in all iterations of an implied weights analysis (K=1–6); the phylogenetic position of P. adusta changed to ‘P. adusta + Textricellini’ under K-values 1–5. Unambiguous character optimisations are shown for each node, and bold species are newly described, with generic type species highlighted (*).

Figure 23. Scanning electron micrographs of posterior median spinnerets of female (left) and male (right) Micropholcommatini: A–B Micropholcomma bryophilum (Butler) from near Marysville, Victoria (WAM T94453) C–D Pua novaezealandiae Forster from the Makarora Valley, New Zealand (AMNH) E–F Austropholcomma florentine sp. n. from the Florentine Valley, Tasmania (FMC) G–H Tricellina gertschi (Forster & Platnick) from near Chaitén, Chile (AMNH). Note the apparent loss of the anterior CY gland spigot in female Austropholcomma and Tricellina. Arrows denote the anterior, mesal direction.

Figure 33. Austropholcomma, Tricellina species, female cleared receptacula, dorsal view: A–B, paratype A. florentine sp. n. from the Florentine Valley, Tasmania (FMC) C paratype A. walpole sp. n. from Walpole-Nornalup National Park, Western Australia (WAM T94440) D T. gertschi (Forster & Platnick) from south of Chaitén, Chile (AMNH). Arrows indicate the trajectory of insemination ducts. Scale bar = 0.065 mm (65 µm).

Figure 40. Tricellina gertschi (Forster & Platnick) from south of Chaitén, Chile (AMNH): A male habitus, dorsal view B female habitus, dorsal view C male pedipalps, ventral view D female abdomen, ventral view.

Figure 42. Scanning electron micrographs of Tricellina gertschi (Forster & Platnick) from near Chaitén, Chile (AMNH): A male eyes and clypeus, frontal view B female sternum, ventral view C female abdominal cuticle D male epigastric furrow, showing the absence of epiandrous gland spigots E female pars thoracica, lateral view F female chelicera and labrum.

Figure 43. Scanning electron micrographs of Tricellina gertschi (Forster & Platnick) from near Chaitén, Chile (AMNH): A female right chelicera (left removed), frontal view B female cheliceral promargin C female pedipalp, frontal view D tip of female pedipalp E male right chelicera (left removed), frontal view F male cheliceral promargin.

Figure 44. Scanning electron micrographs of female Tricellina gertschi (Forster & Platnick) from near Chaitén, Chile (AMNH): A leg I tarsal organ B leg I lyriform organ C leg I metatarsal trichobothrium D leg II claws.

Figure 45. Scanning electron micrographs of pedipalp of male Tricellina gertschi (Forster & Platnick) from near Chaitén, Chile (AMNH). B simplified illustration of (A) showing the complex trajectory of the embolus.