Typhloperipatus is a genus of velvet worm in the family Peripatidae, containing the sole species Typhloperipatus williamsoni.[1] This genus is notable for containing the only species in the phylum Onychophora found in South Asia.[2] This species is also striking in that this velvet worm shows no external trace of eyes,[3] although rudimentary optical vesicles are present internally.[4]
The species was discovered in the foothills of the Himalayas in northeastern India in 1911 and first described by Stanley Kemp in 1913. The species is named for Noel Williamson, a political officer at Sadiya who was murdered in 1911 along with his travelling companion Dr J.D. Gregorson, a physician working on a tea plantation. These murders led to a punitive military expedition being organized by the British Indian government to the Abor region; Kemp, then an assistant superintendent at the Indian Museum at Calcutta was a zoologist assigned to this expedition.[5]
Kemp's assistant found the first three specimens in December 1911 near Rotung and the Dihang River gorge, where workers soon collected many more. Although the nearest known velvet worm species, from the Malay Peninsula, are typically found in dead wood, these were found mainly under large stones near the roots of trees. Subsequently some more specimens were found at the mouth of the Sireng stream and another specimen was found by the 32nd Sikh Pioneers while working between Upper Rotung and Rengin. Kemp did not designate a holotype, but syntypes are deposited in the Natural History Museum of London.
This species is blind and has no eyes, an unusual trait for a velvet worm. The colour of the upperside is a deep umber brown with the tips of the antennae slightly paler brown. The papillae on the skin have pale tips and the underside is pale brown. Some individuals have a dark dorsal stripe. The inner jaw has a serrate edge.
Females have 20 pairs of oncopods (legs); males usually have 19 pairs, but Kemp found one male with 20 pairs. The oncopods have coxal glands, four complete spinous pads on all but the last two pairs of legs (only two pads on the last pair and three on the penultimate pair), and fine setae on all pads. The feet have two distal papillae, one anterior and one posterior.[6] The minimum number of oncopod pairs found in this species (19) is the lowest number recorded in any member of the family Peripatidae.[7] [8]
Although Kemp suggested that Typhloperipatus was closer to Neotropical species than to Southeast Asian species, more recent studies place Typhloperipatus close to the genus Eoperipatus of Southeast Asia.[9] Like Eoperipatus, Typhloperipatus exhibits lecithotrophic ovoviviparity; that is, mothers in both genera retain yolky eggs in their uteri. Furthermore, a study of the fossil species Cretoperipatus burmiticus, embedded in Burmese amber from 100 million years ago, finds two distal foot papillae, one anterior and one posterior, placing Cretoperipatus among the Asian Peripatidae (Typhloperipatus and Eoperipatus) and distinguishing this group from all other extant Peripatidae.[10] This study also identifies Typhloperipatus as the closest extant relative of Cretoperipatus.