Aetius decollatus O. Pickard-Cambridge, 1896

Figs 1–8

Aetius decollatus O. Pickard-Cambridge, 1896: 1006, plate LII, figs 1, 1a–e; Petrunkevitch, 1928: 178; Reimoser, 1934: 491; Majumder & Tikader, 1991: 161, figs 338–342; Deeleman-Reinhold, 2001: 336, figs 496–501; Dankittipakul & Singtripop, 2013: 582.

Type material. Holotype female from Sri Lanka, O. Pickard-Cambridge leg., 1896, deposited in OUMNH, EXAMINED.

Additional material examined. INDIA: Kerala: Wayanad, Wayanad Wildlife Sanctuary, Kurichiad Range, 11°45ʹ55.3ʹʹN 76°14ʹ57.4ʹʹE, 843 m, P.P. Sudhin leg., 16.VI.2014, by hand, 1♂ (CATE 090101 A); Bathery Range, 11°40ʹ48.3ʹʹN, 76°20ʹ38.1ʹʹE , 850 m, P.P. Sudhin leg., 17.VI.2015, by hand, 1♀ (CATE 090101 B). INDIA: Tamil Nadu: Coimbatore, Pollachi, Angalakurichi, 10°30ʹ42.5ʹʹN, 76°59ʹ21.4ʹʹE, 300 m, K.S. Nafin leg., 14 & 28.X.2015, from bark of Tamarindus indica, by hand, 5♂, 3♀ (CATE 090101 C).

Diagnosis. Both males and females of A. decollatus can be separated from the only congener, A. nocturnus by the following combination of characters: carapace reddish-orange with black cephalic region (carapace in A. nocturnus uniformly dark chestnut brown), abdomen with anterior reddish-orange, inverted U-shaped patch (abdomen in A. nocturnus without such patch), abdomen with two tufts of long white hairs at the posterior (single tuft in A. nocturnus), posterior obtuse prolongation over the pedicel less prominent (prominent in A. nocturnus), embolus thick with corkscrew appearance (embolus in A. nocturnus thin and spiniform), sperm duct with sharp apical twist (sperm duct in A. nocturnus with less prominent apical twist), spermathecae II circular with moderately long spermathecae I (spermathecae II ovate with short spermathecae I in A. nocturnus) and funnel-like copulatory openings ( A. nocturnus with semi-circular copulatory openings) (compare Figs 1A–D, 3D–E, 4B, 5B,F, 8B with Deeleman-Reinhold 2001: figs 503, 504 and Dankittipakul & Singtripop 2013: figs 1–2, 12, 16, 18).

Description. Male (CATE 090101 C) (Figs 1A–C, 2A–C, 3A, E): Measurements: Body length 7.30. Carapace length 3.20, width (at middle) 1.83, carapace index 57.18. Sternum length 1.74, width 1.30, sternum index 74.71. Pedicel length 0.39, width 0.33. Abdomen length 3.71, width (at middle) 1.41, abdominal index 38. Dorsal sclerite length 3.48, width 1.61, dorsal sclerite index 46.26. Epigastric sclerite length 0.97, width 1.25. Ventral sclerite length 1.84, width 1.03. Inframamillary sclerite length 0.46, width 0.72. Eye sizes and interdistances: ALE 0.08, AME 0.12, PLE 0.07, PME 0.09; AME–ALE 0.05, AME–AME 0.15, AME–PME 0.13, PME–PLE 0.27, PME–PME 0.27. Clypeus height at AME 0.29, at ALE 0.21. Length of chelicerae 0.83. Measurements of palp and legs: Palp 2.48 [0.71, 0.34, 0.27, 1.16], Leg I 5.31 [1.47, 0.59, 1.20, 1.20, 0.85], Leg II 5.34 [1.57, 0.62, 1.23, 1.10, 0.82], Leg III 5.03 [1.48, 0.64, 1.20, 1.07, 0.64], Leg IV 6.49 [1.88, 0.65, 1.70, 1.49, 0.77]. Leg formula: 4213. Spination. Palp: femur do 2, patella pl 1 do 1, tibia pl 2 do 1, tarsus pl 1; Legs: Femur I pl 1 do 2, II do 2, III pl 1 do 2, IV pl 1 do 3; Patellae I–IV spineless; Tibiae I–II plv 3 rlv 3, III plv 2 rlv 2, IV plv 3 rlv 3; Metatarsi I–II plv 2 rlv 2, III rl 1 plv 1 rlv 1 vt 1, IV pl 1 rl 2 plv 1 rlv 1 vt 1; Tarsi I–IV spineless.

Carapace sub-pentagonal, widest at midline, rugous, reddish-orange with black cephalic region, suffused with black feathery setae situated on minute elevations; thoracic region with pair of discontinuous transverse white bands medially, white spots laterally at coxae II and III, and median stripe from midpoint to posterior margin, all formed by white feathery setae; carapace narrowed posteriorly, forming extension over pedicel. Eye field black; AER slightly procurved, half the width of the cephalic region; PER strongly recurved; MOQ trapezoid. Fovea broad, forming shallow depression, faint striae radiate from fovea to lateral margins. Chelicerae, maxillae, labium dark reddish-orange. Chelicerae vertical, provided with fringe of stiff serrated setae antero-basally to the fangs; cheliceral promargin with two teeth, distal tooth largest; retromargin with two teeth of equal size lying close to each other. Labium broader than long. Sternum reddishorange, shield-shaped, with precoxal triangles, covered with numerous colourless and few long black setae; lateral margins contiguous with intercoxal sclerites between all coxae except I and II; intercoxal sclerites fused with pleural bars; posterior sternal margin forming long, narrow, digitiform projection between coxae IV. Abdomen oblong, with medial constriction dorsally and laterally (Figs 2A, C); blackish, with a reddish-orange inverted U-shaped marking anteriorly (Fig. 2A); anterior half with four discontinuous transverse white bands of white feathery setae, fourth one extending ventrally; dorsal scutum covering entire dorsal surface, provided with median longitudinal row of paired long, stiff, spine-like setae that extend over carapace; posterior with two tufts of long white setae, second tuft lying close to spinnerets (Fig. 3E); epigastric sclerite reddish-orange, with short pedicel collar; ventral sclerite heavily sclerotised, situated between epigastric furrow and inframamillary sclerite; inframamillary sclerite short, broad, concave. Spinnerets orange-brown. Leg segments light reddish-orange, with black shades on all femora, and tibia IV; legs with patches of white feathery setae, mostly on femora, leg IV banded with white setae; tarsus II apically with cluster of ventral bristles, tarsi III and IV ventrally with row of paired short spine-like setae (Fig. 5G); tarsi with claw tufts.

Palp (Figs 4A–E, 5A–F). Femur dark, rest of the segments light reddish-orange; tibia with deep ventral depression, with small prolateral elevated ridge, prolaterally with pair of long dark setae; retrolateral tibial apophysis digitiform, curved inwardly (Figs 4B–C, 5C); cymbium elongate distally, with single long dark seta prolaterally, baso-retrolateral excavation forming semi-circular notch (Figs 4C, 5C); tegulum pyriform with prolateral bulge. Part of subtegulum visible apico-retrolaterally; sperm duct with proximal convolutions, with sharp apical twist before entering embolus (Figs 4A–B, 5A–C); embolus thick, straight, corkscrew-like, sclerotised, bluntly pointed, almost reaching apex of cymbium (Figs 4A, C–D, 5A–F).

Redescription. Female (CATE 090101 C) (Figs 1B–D, 3B, D, 5G, 6A –F, 7A–D, 8A–C): Measurements: Body length 8.83. Carapace length 3.78, width (at midline) 2.18, carapace index 57.67. Sternum length 1.74, width 1.30, sternum index 74.71. Pedicel length 0.58, width 0.41. Abdomen length 4.47, width (at midline) 2.39, abdominal index 53.46. Dorsal sclerite length 3.60, width 1.85, dorsal sclerite index 51.39. Epigastric sclerite length 1.32, width 1.67. Inframamillary sclerite length 1.67, width 1.07. Eye sizes and interdistances: ALE 0.10, AME 0.14, PLE 0.12, PME 0.11; AME–AME 0.20, AME–ALE 0.06, AME–PME 0.19, PME–PME 0.35, PME–PLE 0.43. Clypeus height at AME 0.40, at ALE 0.28. Length of chelicerae 1.17. Measurements of palp and legs: Palp 3.00 [0.84, 0.42, 0.56, 1.18], Leg I 8.57 [2.43, 1.03, 1.96, 1.78, 1.37], Leg II 8.78 [2.59, 1.07, 1.97, 1.81, 1.34], Leg III 8.08 [2.45, 1.02, 1.87, 1.75, 0.99], Leg IV 12.84 [3.58, 1.36, 3.31, 3.05, 1.54]. Leg formula: 4213. Spination. Palp: femur do 1, patella pl 1 do 2, tibia pl 1 do 1 plv 1, tarsus pl 1; Legs: Femur I pl 1 do 1, II do 2, III pl 1 do 2, IV pl 1 do 3; Patellae I–IV spineless; Tibiae I–II plv 3 rlv 3, III plv 2 rlv 2, IV plv 3 rlv 3; Metatarsi I–II plv 2 rlv 2, III rl 1 plv1 rlv 1 vt 1, IV pl 1 rl 2 plv 1 rlv 1 vt 1; Tarsi I– IV spineless.

In all details like male except the following: Carapace slightly concave. Abdomen without lateral constrictions. Dorsal scutum 5/6th abdomen length. First tuft of white setae lying adjacent to the posterior border of dorsal scutum. Ventral sclerite restricted to posterior half of venter.

Epigyne (Figs 7A–D, 8A–C). Epigyne represented by median part of epigastric sclerite, heavily sclerotised, on elevated circular mound. Copulatory openings funnel-like, lying mediolaterally to posterior margin of epigynal plate (Figs 7A, 8A, C). Copulatory ducts short, heavily sclerotised (Figs 7C, 8B). Spermathecae II circular in outline, spermathecae I narrow, straight and moderately long, contiguous medially, without distinct bursae (Figs 7C, 8B). Fertilization ducts short, curved, acuminate, posterior to spermathecae (Figs 7C, 8B).

Female HOLOTYPE (Figs 6A–B, 7D): Same as the fresh female, except the following: Slight variation in body pattern (Figs 6A–B; Majumder & Tikader 1991: fig. 338); O. Pickard-Cambridge (1896) reported a single tuft of long white hairs on the posterior abdomen. However, the holotype specimen was found to lack this tuft, which was probably lost due to the long period of preservation in alcohol. Epigyne (Fig. 7D) structure the same as in the fresh material. For body measurements see Majumder & Tikader (1991).

Variations. Body length: Male: 7.30–8.66 (n=6). Female: 8.33–8.81 (n=3). Variation can also be observed in the colour pattern of the carapace and abdomen. The anterior half of the abdomen of specimens collected from Wayanad Wildlife Sanctuary were prominently reddish-orange in colour, compared to that of the specimens collected from Pollachi, which had reddish-orange inverted U-shaped pattern, even though both have a similar colour pattern on the carapace (Figs 3A–B, 6C–E). The inverted U-pattern also varies, from a perfect U-shape to nearly broad triangular patch. Unlike the holotype, which had a broad transverse band of nearly iridescent greenish scales lying immediately behind the median abdominal constriction (O. Pickard-Cambridge 1896; Majumder & Tikader 1991), all specimens examined here possess a band of white feathery hairs. The holotype also differed from the specimens examined here by having comparatively broad lateral black carapace margins, and the anterodorsal abdominal reddish-orange pattern that appears as paired curved stripes (Figs 6A,B; see also Majumder & Tikader 1991: fig. 338).

Cymbial semi-circular notch (Figs 4C–E, 5C–E). The males of the Aetius spp. are characterised by the presence of a cymbial semi-circular notch of unknown function, which is located baso-retrolaterally on the cymbium, facing opposite to the retrolateral tibial apophysis (Figs 4C–E, 5C–E; Dankittipakul & Singtripop 2013: figs 14–15); this structure is only known from the genus Aetius (Dankittipakul & Singtripop 2013) . While studying the male specimens, we observed that one of the male specimens (CATE 090101 C) had both the palps in an expanded state, with the bulb twisted towards the retrolateral side in such a way that the tegular neck was inserted into the cymbial semi-circular notch (Figs 4D–E, 5D–E). It was also observed that once inserted into the cymbial semi-circular notch, the tegular neck was flanked on its opposite side by the inwardly curved retrolateral tibial apophysis, preventing further free movements of the bulb (Figs 4D–E, 5D– E). Orientation change in the palpal bulb towards the retrolateral side has already been recorded in various genera of the subfamily Castianeirinae (Raven 2015; Murthappa et al. 2016). However, none of these genera were known to have cymbial modifications as seen in Aetius spp., indicating that the cymbial semi-circular notch might be derived feature for increasing the male efficacy in mating.

Note. Mating plugs are known to occur in many spider families and are supposedly functioning as paternity protection or sperm leakage prevention or sperm desiccation prevention mechanism (Uhl et al. 2010; Herberstein et al. 2012). Mating plugs are reported in 10 genera and 12 species of the Corinnidae, including species of Castianeira Keyserling, 1879, Copa Simon, 1886 and Myrmecium Latreille, 1824 belonging to the Castianeirinae (Uhl et al. 2010; Marusik et al. 2015). A mating plug was found blocking the right copulatory opening of one of the females of A. decollatus studied (Figs 7B, 8C). The plug is probably made of an amorphous material (secretory mating plug) of unknown origin. The plug was dissolved in 10% Potassium Hydroxide while clearing the epigyne. The frequency of occurrence of mating plugs in the species could not be accessed due to the low number of females collected.

Habitat. Aetius decollatus is known from moist deciduous forests of Kerala and the bark of Tamarindus indica trees in Tamil Nadu (Figs 9A–B).

Natural history. A. decollatus specimens collected from Tamil Nadu State were found to live in sympatry with the worker ants of Tetraponera rufonigra Jerdon, 1851, a large arboreal ant species that nests in the barks of dead and living trees (Majumder & Tikader 1991). Both the adults and juveniles have bi-coloured appearance similar to the worker ants, indicating that these spiders may be batesian mimics of T. rufonigra (K.S. Nafin, in preparation). Distribution. India (Kerala [new record]), Tamil Nadu (Reimoser 1934) and Sri Lanka (O. Pickard-Cambridge 1896) (Fig. 10).