Stenochilidae

Stenochilidae is a distinct family of araneomorph spiders originating from Southeast Asia, notable for their production of ecribellate silk. First formally described by Tamerlan Thorell in 1873, the family currently encompasses thirteen recognized species distributed across two genera.

Distribution and Habitat

The geographical range of Stenochilidae is notably restricted, primarily within the Oriental realm. Their distribution extends from India in the west, through Southeast Asia, and reaches as far east as Fiji. Specific locations where they have been recorded include India, Sri Lanka, Myanmar, Cambodia, Thailand, Malaysia, Singapore, China, the Philippines, Borneo, Bali, New Guinea, and Fiji. An unusual westernmost record has been noted from Iraq.

Morphology and Characteristics

Stenochilidae spiders are generally small, measuring between 3.5 to 10 mm in total length. They are readily identifiable by their unique, diamond-shaped carapace, which is widest behind the second pair of coxae and exhibits extensive tuberculation. The carapace varies in outline, being simpler in the genus Colopea and more undulated in Stenochilus. Unlike most spiders, they possess two thoracic grooves: typically an anterior groove and a posterior pit. Their eye arrangement is also distinctive, with the eyes of each side forming a single, continuous, gently curved row. In many species, the posterior median eyes are notably elongated, twice the size of the other eyes. A key diagnostic feature is the presence of only two large spinnerets, accompanied by remnants of four posterior spinnerets. In males, these remnants are nonfunctional, but in females, they are larger, functional, and fused into a platelike structure resembling a cribellum. The leg formula follows the pattern 1243, with legs I and II being enlarged and bearing divided prolateral scopulae on the metatarsi. The opisthosoma is pale yellow, marked with two brown oblique dorsal muscle impressions, and covered in dark, spine-like setae.

Taxonomy and Evolution

The taxonomic history of Stenochilidae involves its initial description as a family by Thorell in 1873, followed by its reclassification as a subfamily of Palpimanidae by Simon in 1893. Platnick and Shadab's comprehensive revision in 1974 re-established Stenochilidae as a distinct family, citing numerous morphological differences from Palpimanidae, including features of the carapace, thoracic grooves, eye pattern, chelicerae, labium, abdominal scutum, spinnerets, leg segment lengths, and genitalia. The family's diversity was further explored by Pekka Lehtinen in 1982, who described new species and provided detailed morphological analyses.