Kinorhyncha: India
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Kinorhyncha
Introduction
Kinorhyncha forms one of the most interesting groups of invertebrate animals in. marine meiobenthos. They are microscopic, spiny, segmented and worm-like creatures living in marine and esturarine sediments. They are generally less than 1 mm in length and mostly brown in colour. Their body is covered with thick cuticle devoid of any cilia and divided into 13 segments or zonites. Head constituting the frrst zonite is spherical and eversible with several rows of curved spines called scalids. The terminal mouth cone is surrounded by 9 oral styles.
Head can be retracted into the few succeeding zonites. The animal moves and feeds in sediment like a worm by averting and withdrawing its head, when the scalids gain hold on the solid substratum. The second zonite is largely plated and forms the neck. Rest of the 11 zonites comprise the trunk bearing lateral, dorsal and terminal spines, which sometimes exceed the length of the specimen. The trunk segments are often subdivided longitudinally into a series of separate plates. Some sand-living forms in exposed beaches have lateral adhesive organs which help them to adhere to substratum and withstand sever wave action. Sexes are sepm:ate.
All the kinorhynchs are free-living and harmless, mostly inhabiting the .upper few millimeters or centimeters of the fine organically rich marine sediments in shallow coastal waters. Occasionally they are also seen associated with littoral algae and a variety of invertebrate animals. Ecologically, they are eurybenthic occurring from the exposed intertidal upto 5000 m or more in the abyss, euryhaline tolerating a wide range of salt concentration from 7 to 60 parts per 1000 and eurythermic withstanding termeraturcs varying between -20°C and 40°C. These worms penetrate deep into the coarse intertidal sediments upto 1 m below surface. They are omnivorous, largely feeding on fine organic detritus and microscopic plant and animal matter. Quantitatively, their densities in marine sediments are known to range from few individuals to few hundreds of specimens per 10 cm2 of the substrate. IGnorhynchs are quite susceptible to ecological stress in the environment due to effect of organic pollution, which largely affects their population density and diversity.
Historical Resume
The ,published records indicate that Kinorhynchs were first discovered in the collections of intertidal meiofauna made from algae on the French Nonnandy coast (Dujardin, 1851), the same subsequently resulting in the description of the frrst species Echinoderes dujardini by Claparade (1863). Since then, the slow and steady research on this group resulted in the description of about 100 species from different parts of the world, in addition to a larg~ number of unreliable descriptions made based on juvenile specimens (Zelinka, 1928; higgins, 1988).
But, nothing was known of this group in the Indian fauna until Krishnaswamy (1957) reported their occurrence from Madras coast while studying the sand-living harpacticoid copepods. Later, Ganapati and Rao (1962) recorded kinorhynchs from the interstitial fauna ofWaltair coast and subsequently reported 3 species, viz., Echinoderes bengaiensis (Timm), Cateria styx Gerlach, Cateria sp. from the area (1966, 1968). As part of his studies on Indian Ocean Kinorhyncha, Higgins (1968, 1969a, b) described 4 new species viz., Caleria gerlachi, Condyloderes paradoxus, Sphenoderes indicus and Neocentropohyes satyai from meiodbenthos at different localities in the seas around India. Four more species were subsequently reported from Andaman Islands (Higgins and Rao, 1978),ofwhich one species Echinoderes andamensis was described as new to science. The genus Pycnophyes was also recorded by them for the fust time from the Indian Ocean. In the Arabian Sea, 3 Kinorhynchs viz., Echinoderes ehlersi Zelinka, Echinoderes sp., and Cateria gerlachi Higgins, w.ere recently reported from the littoral sediments on Lakshadweep (Rao, 1990).
Estima tion of Taxa
The phylum Kinorhyncha was earlier referred as Echinodcra, the name being based on the recurved spines on the eversible head of these animals. Although Kinorhyncha was treated earlier as a class of the phylum Aschelminthes, due to its distinguishing characters it was recently raised to the status of a phylum. The structure of oral styles, eye-spots, number.and disposition of plates, spines, adhesive tubes, etc., are largely taken into consideration for their classification. the phylum is divided into two main orders, the Cyclorhagida and Homalorhagida based on the number of neck plates. The Cyclorhagida is again divided into 3 suborders based on the structure of the closing apparatus, the Cyclorhagae, Conchorhagae and Cryptorhagae. The Cycloraghae has two families, the Echinoderidae with a single genus Echinoderes (42 species) and the Centroderidae with 3 genera, Condyloderes (2 species), Campyloderes (3 species) and Centroderes (2 species). The Conchorhagae represents a single family, the Semnoderidae with 2 genera Simnoderes (3 species) and Sphenoderes (1 species). The Cryptorhagae has a single family Cateriidae with the single aberrant genus Cateria (3 species).
The order Homalorhagida consists of a single suborder Homalorhagae with two families. the Neocentrophyidae include two genera, Paracentrophyes (2 species) and Neocentrophyes (1 species). The Pycnophyidae includes two genera Pycnophyes (23 species) and Kinorhynchus (17 species) All the six known families of the phylum Kinorhyncha are represented in littoral sediments in the seas around India But, out of the 11 known genera, only 5 were hitherto encountered, namely Echinoderes, Condyloderes, Sphenoderes, Cateria, Neocenlrophyes and Pycnophyes, representing the 10 species given below.
A perusal of the data presented here shows that despite their weak powers of locomotion many of these kinorhyoch species are widely distributed in the seas around India, although their present endemism to the Indian Ocean is yet to be confIrmed with intensive exploration of other areas.
Current Studies
Kinorhynch research at the global level received very little attention from the beginning and this holds true even to this day. Very few workers are presently engaged in their study. The research probably received a major set-back due to the microscopic size of these worms and the difficulty of their separation from muddy sediments. Further, because of their morphological similarity, kinorhynchs are often mistaken as copepods in the meiofauna collections. However,
Map showing the areas on Indian Coast where Kinorhyncha were collected, studied and reported. Numbers indicate the species recorded.
many areas on the Indian coast still remain unexplored or under explored for collection of these worms. At present G. C. Rao is working on the taxonomy of this group in the Zoological Survey of India based on the stray collections made during the general faunistic survey on Indian coasL On the global level, R. P. Higgins is the only active worker and world "authority on this group, having made a valuable contribution to the knowledge of these worms from different seas. He has also re-described several of the little known species. As no detailed investigations were hitherto made on the biology, ecology distribution and population dynamics of Kinorhyncha anywhere in the world, the phylum offers ample scope for researchers.
Expertise India
G. C. Rao, Zoological Survey of India, Middle Point, Port Blair.
Abroad
S. A. Gerlach, Institue fur Meereskunde; Dustembrookerweg 20, 0-2300 Kiel, Germany.
R. P. Higgins, Department Invertebrate Zoology, National Museum Natural History, Smithsonian Institution, Washington D. C. 20560, U.S.A.
P. Schmidt, Zoologisches Institute der Universitat Gottingen, Gottingen, Germany.
Selected References
Claparede, E. 1863. Beobachtungen uher Anatomie und Entwicklungsgeschichte wirbelloser Tiere und der Kuste der Normandie angestellt. 120 pp. Leipsig, Wilhelm Engelmann.
Higgins, R. P. 1988. Kinorhyncha. In : Introduction to the study of meiofauna. Smithsonian Institution, Washington. pp. 328-331.
Higgins. R. P. &Rao, G. C. 1919. Kinorhynchs from the Andaman Islands, Zool. J. Unn. Soc., 67(1): 75-85.
Remane, A. 1936. Gastrotricha und Kinorhyn~ha. In : G. G. Bronns, editor, Klassen "nd Ordnungen des Tierreichs, 4: 1-242. Zelinka, C. 1928. Monographie der Echinodera. 396 pp. Leipzig: Wilhelm Engelmann.
