Revalidating the taxonomic position of the Indian Ischnocolus spp. (Araneae: Theraphosidae)
Wildlife Information Liaison Development Society, 9-A, Lal Bahadur Colony, Gopalnagar, Peelamedu, Coimbatore, Tamil Nadu 641004, India
Tikader (1977) reported the genus Ischnocolus Ausserer, 1871 for the first time from India with the description of two new species I. decoratus Tikader, 1977 and I. khasiensis Tikader, 1977. The known distribution of this genus is mainly in the Mediterranean countries and nearby countries like Ethiopia, Cameroon and Congo in Africa; and in other parts of the world such as Brazil and India. Siliwal et al. (2005) commented that the report of Ischnocolus from India could be a case of misidentification.
The subfamily Ischnocolinae differs from rest of the subfamilies of the family Theraphosidae by the absence of stridulating organ (Smith 1987, 1990, 1994). Spiders belonging to the closely related subfamily Selenocosmiinae differ in having stridulatory organ in the form of numerous bacilliform setae on the prolateral surface of maxillae and short spike setae on the retro-margin of the chelicerae; legs are without spines; and metaspines are present (Pocock 1900; Raven 1985; Smith 1987).
In order to verify its status, the type specimens of Indian Ischnocolus spp. were examined at the Zoological Survey of India collection in Kolkata. On detailed examination of the types, the following were noted in both Ischnocolus decoratus and I. khasiensis types: (i) presence of the stridulating organ on the chelicerae; (ii) presence of enlarged paddle setae in the maxillary lyra and short thorn setae on retro-lateral side of the chelicerae.
While the presence of stridulatory organ places the taxa in the subfamily Selenocosmiinae (Pocock 1900; Raven 1985; Smith 1987), the paddle setae in the maxillary lyra and short thorn setae on the chelicerae confirms its identity as genus Chilobrachys Karsch, 1891 (Pocock 1900; Raven 1985). I therefore transfer the two described species of Ischnocolus from India to the genus Chilobrachys Karsch, 1891 (Images 1-2, 4-5).
Further, on examining the female genitalia of the types of I. decoratus (Image 3), all were found to be immature due to the conspicuous absence of spermathecae or seminal receptacles. The author may have probably confused the very prominent stiff epigastric fold dorsally due to hardening of the preserved specimens to be the spermathecae (Image 3) and named it a new species. The type specimens of I. decoratus from Borivali National Park resemble Chilobrachys fimbriatus Pocock, 1899 in stridulatory structure and dorsal patterns on the abdomen (chevron marking), and therefore are juvenile specimens of C. fimbriatus.
I place Ischnocolus decoratus Tikader, 1977 as a synonym under Chilobrachys fimbriatus Pocock, 1899, and transfer Ischnocolus khasiensis Tikader, 1977 to Chilobrachys khasiensis (Tikader, 1977).
Material examined: Ischnocolus decoratus Tikader, 1977, holotype, female, Borivali National Park, Bombay, Maharashtra, viii.1975, coll. J.S. Serrao, registration number not provided, Zoological Survey of India, Kolkata. Paratype: 1 female, Medtedi, near Mahabaleshwar, Satara District, Maharashtra, India, 29.v.1976, coll. B.K. Tikader, registration number not provided, Zoological Survey of India, Kolkata; 1 female, Borivali National Park, Bombay, Maharashtra, viii.1976, coll. S.R. Nayak, registration number not provided, Zoological Survey of India, Kolkata.
Ischnocolus khasiensis Tikader, 1977, holotype, female, Umshining, Khasi and Jaintia Hills, Meghalaya, India, 24.vii.1969, coll. B. Dutta, registration number not provided, Zoological Survey of India, Kolkata.
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