BIODIVERSITY AND DISTRIBUTION OF FRESHWATER ROTIFERS (ROTIFERA: EUROTATORIA) OF TAMIL NADU

Taxonomic studies on freshwater Rotifera of Tamil Nadu were initiated by Edmondson and Hutchinson (1934); about two dozen papers published during the time span of more than seven decades indicate that their faunal diversity is still inadequately explored. A large number of earlier works, however, deal with scattered reports of various taxa or record only planktonic species. The detailed faunal surveys from this state are yet lacking while samples from certain districts are examined by Daisy (2001) and Sivakumar and Altaff (2001). Raghunathan and Suresh Kumar (2006) compiled a list of the rotifers reported from Tamil Nadu based on the published literature; it reflects several nomenclatural anomalies, incorrect family allocations, obsolete names and records requiring confirmation and, hence, requires a critical analysis.


INTRODUCTION
Taxonomic studies on freshwater Rotifera of Tamil Nadu were initiated by Edmondson and Hutchinson (1934); about two dozen papers published during the time span of more than seven decades indicate that their faunal diversity is still inadequately explored.A large number of earlier works, however, deal with scattered reports of various taxa or record only planktonic species.The detailed faunal surveys from this state are yet lacking while samples from certain districts are examined by Daisy (2001) and Sivakumar and Altaff (2001).Raghunathan and Suresh Kumar (2006) compiled a list of the rotifers reported from Tamil Nadu based on the published literature; it reflects several nomenclatural anomalies, incorrect family allocations, obsolete names and records requiring confirmation and, hence, requires a critical analysis.
The present study, a part of our investigations on Fauna volume of Indian Freshwater Rotifera, documents 139 species (149 taxa) belonging to 38 genera and 20 families from Tamil Nadu and, includes 38 new records from this state and 20 new reports from the southern India.This study raises the micro-faunal diversity of Tamil Nadu Rotifera to 177 species (188 taxa); an up-dated systematic inventory is presented and, various interesting species are briefly diagnosed and illustrated.Remarks are made on nature and composition of the rotifer fauna of Tamil Nadu as well as on the biodiversity observed in the collections examined by the authors.In addition, comments are made on biogeographic ally important elements, occurrence and distribution of interesting species, taxonomic status of several taxa and validity of various earlier records.

MATERIALS AND METHODS
A total of 248 plankton samples collected from the following localities, spread over nine districts, of Tamil Nadu (Fig. 1, A-B All the measurements were given in micrometers (/lm).

SYSTEMATIC ACCOUNT
One hundred seventy-seven species (188 taxa) of Rotifera, belonging to 56 genera and 25 families are recorded presently from Tamil Nadu.Of these, 139 species (149 taxa), spread over 38 genera and 20 families, are observed in the collections examined by the authors.A detailed systematic list of the recorded taxa is presented in Table 1 and their family-wise break-up is indicated in Table 2.
Remarks: This species is reported first time from Tamil Nadu.
Characters: Body ovoid, truncate anterior at end and rounded posteriorly.Dorsal plate arched in cross-section, with anterior margin raised in middle into a small arched and non-retractable semicircular plate.Venter membranous, its posterior portion stiffened.Lateral sulci absent.Toes long.Slender, cylindrical, slightly broad at base and with tips curved outwards.Mastax modified malleate type.
Elsewhere : Endemic to India.
Remarks: This species is reported first time from Tamil Nadu.(Hauer, 1936) Material examined: not observed in the examined collections.

Lecane (Monostyla) bulla diabolica
Characters : Lorica smooth, egg-shaped, without clear distinction between dorsal and ventral plates and with dorsal plate with a pair of characteristic anteriorly directed spines.Toe long, parallelsided; claw relatively long.
Elsewhere : Endemic to India.Remarks : This species is reported first time from southern India.

DISCUSSION
Plankton samples examined presently from Tamil Nadu reveal 139 speCIes (149 taxa) of Eurotatoria and, hence, reflect their speciose and diverse taxocoenosis.Besides, our collections exhibit 38 new records from the state and 20 taxa are new records from southern India.The present findings notably raise the faunal diversity of freshwater Rotifera from Tamil N adu to 177 species (188 taxa) which, in tum, represents the richest biodiversity of the Phylum known till date from any state of India and, is reasonably greater than the highest published report of 148 species from West Bengal (Sharma, 1998b).The overall richness currently documented from Tamil Nadu comprises about 47 % of the Indian Rotifera and it presents a notable increase over 120 species recognized by the authors following a critical review of earlier taxonomic works published from the state.The rotifer fauna of Tamil Nadu as well as species examined by the authors exhibit 53.4% and 55.3% community similarities (vide Sorenson's index) respectively with the fauna of Sri Lanka (vide Fernando, 1980), thereby, indicating significant divergence in their faunal diversity in spite of the geographical proximity with the island country.On the other hand, the rotifer fauna of Tamil Nadu shows 61.5 % similarity with the fauna of West Bengal (vide Sharma, 1998b) and 66.2% similarity with the fauna of Orissa (vide Sharma and Sharma, 2005b).
The rotifer fauna of Tamil Nadu is characterized by greater higher diversity.This generalization is endorsed by the fact that out of 67 genera of the Phylum recorded so far from India, 56 genera (83.6%) and all (25) families of Eurotatoria known from this country are represented in Tamil Nadu.The salient features of the rich species, generic and family diversity attach special biodiversity importance to the studied fauna and, reflect greater environmental heterogeneity as well as microhabitat diversity of the aquatic environs of this state.The stated remarks are also endorsed by 139 species (149 taxa) examined by the authors from Tamil Nadu which, in tum, represent 20 families (80%).On the contrary, the relatively lower generic diversity (38 genera, 67.9%) noticed in our collections in general and lack of the representatives of five families namely Proalidae, Atrochidae, Collothecidae, Adinetidae and Habrotrochidae deserves comment and may be attributed to the planktonic and littoral-periphytonic nature of the presently observed collections.
2. Oriental endemics: Brachionus donneri, Keratella edmondsoni and Lecane acanthinula.Amongst the members of the first category, Pseudoeuchlanis longipedis deserves special mention; this endemic Indian genus of the Euchlanidae is represented by only one species described from Andhra Pradesh (Dhanapathi, 1978).Raghunathan and Suresh Kumar (2006) listed its occurrence of Pseudoeuchlanis sp. in Tamil Nadu and thus did not indicate any species determination.Pseudoeuchlanis was, however, included under the list of invalid Rotifera genera recognized by Segers (2002) while Segers (2007) subsequently considered it to be valid taxon.This rare and interesting euchlanid is not observed in our collections and, hence, its report still requires confirmation but the original description given by Dhanapathi (op cit.) indicates the need for its possible re-examination or re-description.Asplanchnopus bhimavaramensis, another interesting Indian endemic, was also described from Andhra Pradesh (Dhanapathi, 1975) and its distributional range is now extended to Tamil Nadu.In addition, Lecane bulla diabolica was described by Hauer (1936) from Almati reservoir, Chennai as a form of L. bulla and is not known so far elsewhere in India.The last two, nevertheless, are valid taxa but are not noticed in our collections.
Referring to the Oriental endemics, Brachionus donneri was described by Brehm (1951) based on the material examined from Almati reservoir, Chennai.Sharma andSharma (2001, 2005a) considered it to be a Pantropical species while Segers (2007) believed it to be an Oriental element though there is single unconfirmed record of this brachionid from Panama canal waters (? introduction).This species is so far known in India from N. E. region (Assam, Meghalaya, Manipur, Tripura), West Bengal and Tamil Nadu.Keratella edmondsoni, another interesting Oriental endemic, was described from Tamil Nadu (Ahlstrom, 1943) as K. quadrata var.edmondsoni and was subsequently treated as a distinct species by Nayar (1965).It is now recorded from Rajasthan, Tamil Nadu, Northeast India and Northeast Thailand.Lecane acanthinula, a possible vicariant of L furcata, is reported in this country from Assam, Tripura, Kerala and Orissa and its distribution is presently extended to Tamil N adu.The stated Oriental species are, however, observed in our collections and so far exhibit disjunct occurrence in India.
All palaeotropical species, except Encentrum longipes are observed by the authors in the samples from Tamil Nadu.Of these, Lecane braumi, L. eswari, L. la tera lis, L. simonneae merit special global biogeographical interest.The first species, an erstwhile endemic to the floodplains of the river Niger (Segers et al., 1993) is subsequently reported from Indonesia and Papua New Guinea.that no such valid species is listed in the global review of genus Trichocerca (refer Segers, 2003), the second species is a synonym of P. vulgaris (refer Koste, 1978) while the last species is a synonym of Lecane depressa (refer Segers, 2007).The authors, however, desire confirmation of earlier records of Lecane depressa, L. elasma and L. thalera from Tamil Nadu.
Latitudinal variations in the distribution of Rotifera, directly or indirectly induced by climatological factors, are reported by Green (1972), Pejler (1977), De Ridder (1981) Dumont (1983), Segers (1996Segers ( , 2008)).Segers (2001) stressed the role ofthermophiles in the rotifer fauna of Southeast Asia and indicated the qualitative significance of two 'tropic-centered' genera namely Lecane and Brachionus.The biodiversity importance of these two genera is distinctly observed in the rotifer taxocoenosis of Tamil Nadu.Lecane (40 species, 22.6%) is the most speciose genus; its richness represents about 50% of total species so far known from India.In general, the lecanid dominance compares well with the reports of Segers et al. (1993, 1998), Sanoamuang (1998), Jose de Paggi ( 2001), Sharma and Sharma (2001, 2005a, 2008) and Sharma (2005).Among about two dozen Brachionus spp.known from the Indian inland waters (Sharma, 1983(Sharma, , 1998a)), 17 species are recorded from Tamil Nadu while 16 species are observed in our collections; their richness corresponds with the report of 17 species from West Bengal (Sharma, 1998b) while it is marginally higher than 13 species each recorded from Orissa (Sharma and Sharma, 2001) and Assam (Sharma, 2005).
The qualitative significance of 'tropic-centered' Lecane and Brachionus as well as wider representation and distribution of several pantropical and cosmotropical species impart a 'tropical character' to the rotifer fauna of Tamil Nadu.This generalization concurs with the composition of the tropical faunas from different parts of the globe (Green, 1972;Pejler, 1977;Fernando, 1980;Dussart et al. 1984;Segers, 2001;Sharma and Sharma, 2008).In addition, our observations show rich diversity of Lepadella (15 species) > Trichocerca (12 species).Hence, the mentioned five monogonont genera comprise the bulk of the reported species (92 species, 52.0 %); this salient feature corresponds with the remarks of (Sharma and Sharma, 2005a).Interestingly, the richness of the 'temperate-centered' Keratella is noteworthy and requires explanation while Euchlanis, Filinia, Ephiphanes and Asplanchna, together include 18 species.In general the most diverse genera, except Brachionus and to lesser degree Keratella and Filinia, include mainly the littoralperiphytonic taxa.
Twenty six species namely Brachionus durgae, B. leydigii, B. donneri, Keratella edmondsoni, The scattered plankton samples examined by the authors as well as our limitations to the extent of extensive collections do not warrant comments on latitudinal and longitudinal variations of various taxa.Nevertheless, the present observations significantly enrich the status of faunal diversity of Tamil Nadu Rotifera and, provide useful information on biogeographically interesting elements and on status and validity of various species.Our results exhibit rich and diverse spectrum of monogonont rotifers in general and planktonic and semi-planktonic or the littoral-periphytonic elements in particular but still reflect certain lacunae with special reference to benthic, sessile, colonial and bdelloid taxa.The fauna, therefore, has scope for its up-dating based on analysis of specific communities involving special sampling techniques as well as emphasis on collections from different ecosystems.Our conservative estimate, however, expects occurrence over 250 species of Rotifera in Tamil Nadu.
Fig. 1 : A (inset) : Map of India indicating location of Tamil Nadu; Fig. 1, B : Map of Tamil Nadu indicating sampled localities.

Table 1 :
Systematic list of reported Rotifera taxa

Table 2 :
Family-wise break-up of the Rotifer fauna of Tamil Nadu.