Onychophora: India
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Onychophora
Introduction
We are often able to arrange existing organisms in progressive series, of which the extremes are connected by intermediate forms. Not only are all the connecting links found between closely related species, but sometimes between the larger groups of the animal kingdom also.
The Onychophora (Peripatus and its allies) are in some. respects annectent between the Annelida and Arthropoda but the reason for their inclusion in the latter phylum is not evident from superficial examination. They perhaps evolved from Pol'ychaete ancestors which had forsaken a marine habitat and became terrestrial. Parapodia are consequently no longer present as swimming organs, but have become modified for locomotion on land without having acquired the jointed arthropod character.
The integument is soft, though it contains chitin and the excretory organs take the form of metamerically repeated coelomoducts. Ar~opodan features are exhibited in the possession of tracheae, salivary glands and the tenninal claws to the appendages. The presence of jaws of an appendicular" nature, the paired ostia to the heart, the pericardium, the heamocoelic body cavity and the reduced coelom are further important characters, allying them with that phylum.
Historical Resume
The discovery of a species of Onychophora from 'the north-east frontier of India at the foot of the Eastern Himalaya, must be reckoned as one of the most iilteresting zoological results of the Abor expedition (1911-1912). The single species found was highly peculiar in many respects. Though it showed traces of alliance with Eoperipatus, which occurs in Sumatra and the Malay Peninsula, differed sufficiently .in regard to th~.characters employed by Bouvier, Evans and other workers to entitle it to a separate genus. In the absence of any• external trace of eyes it appeared to be unique~
For the Abor species the name Typhloperipatus williamsoni was suggested by Kemp in 1913. It was given in honour of the late Mr. Noel Williamson, one time Assistant Political Officer at Sadiya, who was treacherously murdered by Minyong Abors on March 30th, 1911, at Komsing, a village not many miles distant from the spot where the-specimens were obtained.
The specimens were all found under stones, and this is a .point of some interest seeing that all the Malayan species were found in dead wood. the majority of the specimens were" found in chinks and crannies under comparatively large stones among the roots of jungle plants. Solitary individuals were occasionally met with, but more us~ally two to four adults accompanied by a number of young (one time as many as six) were collected together. Some of these specimens are preserved and kept in the N~tional collection of the Zoological Survey of India.
The area in which the great majority of the specimens was obtained was very limited in extent, being about 200 yds. in length by 100 yds. in breadth. Subsequently a close search in a somewhat similar locality, situated in the N .E. near the mouth of the S ireng stream, resulted in the discovery of a few more individuals.
When touched, the specimens, as is usual in the Onychophora, ejected a semi-transparent viscous fluid from the oral papillae. The viscous fluid rapidly solidified and formed long strings of rubber-like consistency which adhered to everything with which they came in contact. That they never stuck to the animal itself was doubtless due to the special skin processes which, in'life gives it such a deep velvety appearance.
When moving the antennae diverged and were held in the same horizontal plane as the body with the tips flexed a little outwards. The fllst four ot five pairs of limbs are rather irregular in their motions. That of the flISt.pair are frequently held clear of the ground and this is generally the case with those of the last two pairs. Affinities
The principal characters of the genus Typhloperipatus may be thus summarized :
Number of legs, 19 or 20, variable in the same species; Inner jaw with a diastema and saw of denticles; Legs with four complete spinous pads; Nephridial openings of the fourth and futh legs situated on the third pad; Feet with two distal papillae, one anterior, one posterio~; Genital opening between the legs of the penultimate pair; Receptacula seminis present, with two ducts opening into the oviducts; Receptacula ovorum present; Ovaries completely fused, with a single cavity. They lie closely pressed against but not directly atta9hed to the floor of the pericardium, to . which, however, they are connected posteriorly by means of a funiculus; The ovary is exogenous, i.e. it is studded with follicles in which the maturing ova lie; The ova are large and heavily charged with food-yolk: they measure about 1.5 mm in their long~st diameter; Embryo without a trophic vesicle; Uterine embryos of about the same age; Unpaired part of vas diferens of very great length; Spermatophores long, with horny coat and cap; Skin-pigment brown, disappearing in course of time in alcohol; Legs with well-developed coxal glands; A single crural gland in the male in each of the two pre-genital pairs of legs;
The accessory glands of the male open separately on the ventral surface between the genital opening and the anus. To these it must be added that there is no external trace of eyes and that there is a patch of highly modified scales, probably sensory in function, on the lower surface of each antenna. The absence of eyes and the curious modifications in the antennae are doubtless to be regarded as evidence of specialization. They are not shared by any other genus of Onychophora.
It is clear that the affinities of Typhloperipatus are primarily with its nearest geographical neighbour, Eoperipatus, with which, except for the unique characters mentioned above, it agrees in all important structural details but four viz. (i) the position of the renal openings of the fourth and fifth legs which, as in most genera of Onychophora, are situated on the third pad, (ii) the presence of a horny coat, as well as a cap, on the spermatophore, (iii) the separation of the openings. of the male accessory glands, and (iv) the similarity in 'age between the embryos found in a single female. It may also be noted that in Typhloperipatus the oviducts are united for a long distance in front of the ovary and that in the male there is' only a single crural gland in each of the two pre-genital pairs of limbs in place of the two found in Eoperipatus. In the number and position of the leg papillae and in the complete fusion of the ovaries, the Abor genus agrees with Eoperipatus and differs from all other known forms.
It can scarcely be doubted that Typhloperipatus is an off-shoot from the original Malaysian stock and that it is, on the whole much more highly specialized than its allies in the Malay Archipelago and in Sumatra.
As the question stands at present the evidence for a neotropical connection seems to outweigh that for a migration from the Australasian region, and if we accept the view that the former has occurred, some support is given by what is known of the structure of the tropical African Mesoperipatus, which both Evans and Bouvier associate with Peripatus and Eoperipatus. A further study of the tropical African species may be expected to prove of considerable interest from this point of view and if any Onychophore should be discovered in S. India or Ceylon results of great importance may be anticipated.
In spite of further surveys this species has not been encountered till now. It is to be hoped that interested persons can be found to carry on the search.
Reference
Kemp, S. 1914. Onychophora : Zoological Results of the ABOR EXPEDITION. Rec. Indian Mus., 8 (6) : 471-492.
