Deepor Beel revisited: new records of rotifers (Rotifera: Eurotatoria) with remarks on interesting species

Plankton samples collected (April 2009 - March 2010) from Deepor Beel, a Ramsar site, revealed 21 species of the Phylum Rotifera belonging to 12 genera and eight families as new records. Amongst these, Brachionus durgae is a new record for northeastern India. The recorded species included the Australasian Brachionus dichotomus reductus and Notommata spinata; two Oriental endemics, namely, Keratella edmondsoni and Lecane blachei while Lecane lateralis, L haliclysta, Lepadella benjamini, Platyias leloupi, Mytilina acanthophora, Macrochaetus longipes, Trichocerca bicristata and T. flagellata are examples of regional distribution interest. The present report increases the number of species recorded from this important wetland of northeastern India to 134 species which, in turn, is the richest rotifer diversity known till date from any aquatic ecosystem of South Asia.

Deepor Beel, a Ramsar site of India and an important floodplain lake of northeastern India, is an interesting 'hot-spot' for its aquatic biodiversity.This largest wetland of the Brahmaputra River basin of Assam is under severe environmental stress because of general habitat degradation and various anthropogenic activities.The authors conducted a limnological survey of this beel during November 2002 -October 2003 and reported (Sharma & Sharma 2005) 110 species of Phylum Rotifera, while (Sharma & Sharma 2010) added three species to the earlier list based on samples collected in 2006.
During the course of our recent limnological reconnaissance of Deepor Beel (April 2009-March 2010), the authors initiated work on invertebrate faunal diversity and documented 116 species of Rotifera, including 21 species as new records from this Ramsar site with one new record from northeastern India.Various new records are briefly diagnosed and comments are made on occurrence of biogeographically interesting elements.
Qualitative plankton samples were collected by towing a nylobolt plankton net (No. 25) from different parts of this Ramsar site and were preserved in 5% formalin.The samples were screened for rotifers and the species were isolated and mounted individually in polyvinyl alcohol-lactophenol mixture.The species were identified following Koste (1978), Segers (1995), Sharma (1998), and Sharma & Sharma (1999, 2000, 2008).Photographs were taken with a Leica DM 1000 image analyzer.Segers (2002) is followed for the recent system of nomenclature of Rotifera and remarks on the distribution are made vide Segers (2007).The reference materials are deposited in the holdings of Freshwater Biology Laboratory, Department of Zoology, North-Eastern Hill University, Shillong.
Distribution: Australasia.India: Assam, Meghalaya and Tripura.Our report includes a number of biogeographically interesting rotifers.Amongst these, the Australasian elements Brachionus dichotomus reductus and Notommata spinata deserve special mention.Their occurrence highlights the affinity of Assam Rotifera with those of Southeast Asia and Australia confirming the earlier generalization of Sharma (2005).Referring to the former brachionid, Segers (2001) commented on the occurrence of the reductus vicariant of B. dichotomus outside Australia, hypothesizing the recent expansion of these populations to Southeast Asia with Australia as possible origin of this taxon.The record of disjunct populations of the reductus vicariant from Deepor Beel lends support to Segers's hypothesis.Interestingly, both Australasian elements show a distribution restricted to northeastern India; the former is known from Assam, Meghalaya and Tripura while the later is known only from Assam.
The occurrence of two Oriental endemics i.e., Keratella edmondsoni and Lecane blachei is another salient feature of the present study.The former was described originally from Tamil Nadu (Ahlstrom 1943) as K. quadrata var.edmondsoni while Nayar (1965) subsequently proposed it to be raised to the status of a distinct species.Besides the Indian records from Assam, Rajasthan, Orissa and Tamil Nadu, K. edmondsoni is known from northeastern Thailand.Lecane blachei, described as a new species from Cambodia (Berzins 1973), was also recorded from Thailand while its occurrence in India is confined to Assam, West Bengal and Delhi.
Amongst other interesting species, Brachionus durgae, Lecane lateralis, L haliclysta, Lepadella benjamini, Platyias leloupi, Mytilina acanthophora, Macrochaetus longipes, Trichocerca bicristata and T. flagellata are examples of regional distributional interest.Of these, the cosmo (sub)-tropical B. durgae was described as a new species from Andhra Pradesh (Dhanapathi 1976) while its current distribution extends to African, Neotropical, Oriental and Palearctic regions (Segers 2007).Besides the type-locality, the Indian reports of this brachionid are from Orissa while Sharma & Sharma (2009) recently recorded it from Tamil Nadu.Sharma (1978) described Lecane lateralis from West Bengal as an Indian endemic; Savatenalinton & Segers (2005) categorized it as an Eastern Hemispheric rotifer while this lecanid is now considered as palaeotropical element (Sharma & Sharma 2008).This species is known to occur in the Indian inland waters from Assam, Meghalaya, Tripura, West Bengal, Orissa and Tamil Nadu.Lepadella benjamini, a cosmopolitan species, is examined from the state of Manipur (Sharma 2007) from the Indian subcontinent.Besides, it is reported from China and Thailand among the Asian countries.Besides, Lecane haliclysta, Platyias leloupi and Macrochaetus longipes are so far known from northeastern India while Mytilina acanthophora, Trichocerca bicristata and T. flagellata show disjunct populations in India.
To sum up, the present report of 21 new records of Rotifera from Deepor Beel raises the number of species known from this important floodplain lake of northeastern India to 134 and, hence, adds to the relevance of Deepor Beel as a Ramsar site.The richness is higher than the 120 species examined from Loktak Lake (Sharma 2009) -another Ramsar site of India as well as the 106 taxa from Thale-Noi Lake, a Ramsar site in Thailand (Segers & Pholpunthin 1997).However, we should caution against over-emphasizing the importance of the present record as Dumont & Segers (1996) argued that lakes in the tropics could contain 210+ species of rotifers.Sampling intensity and methodology can vastly influence the diversity encountered: the total species reported for Deepor Beel incidentally coincides with the report obtained from two samples only from a non-descript Laotian rice field and adjacent pond (Segers & Sanoamuang 2007).Nevertheless, the qualitative features of the rotifer fauna of Deepor Beel hint at a high biodiversity value.A more extensive, sampling campaign, focusing in particular on quantitative aspects of the fauna of this Ramsar site may corroborate these initial findings.

Image 4 .Image 5 .Image 6 .Image 7 .Image 8 .
Lepadella benjamini (ventral view) 50µm Lecane blachei (dorsal view) ovate; anterior dorsal margin concave and anterior ventral margin with a shallow sinus flanked by undulating sides.Ventral plate with characteristic postero-lateral extensions.Toes long, parallel-sided along ¾ of their lengths, then tapering and terminating into stout claws; each claw with one basal spicule.Distribution: Palaeotropical.India: Assam, Meghalaya, Orissa, Tripura and West Bengal.slender and elongated; with two characteristic distinct keels extending unto 2/3 the length of dorsum, separated by wide depression of dorsum.Left toe longer than body, right toe reduced; sub styles present.50µm Lecane haliclysta (ventral view) 50µm Lecane lateralis (dorsal view) Trichocerca bicristata (lateral view) Distribution: Cosmopolitan.India: Assam, Bihar and Orissa.Trichocerca flagellata Hauer, 1937 (Image 9) Characters: Body ovoid and head indistinctly demarcated.Keel high vaulted with wide striated area extending to the beginning of the short foot opening.Left toe longer and slightly sigmoid, right toe reduced and stylet present.Distribution: Tropicopolitan.India: Assam, Meghalaya and Tamil Nadu.Trichocerca iernis (Gosse, 1887) Characters: Body elongate, slightly curved and with a short spine at anterior margin of lorica.Striated keel extending from anterior margin to end of abdomen.Left toe nearly ¾ of body length, right toe short, basal stylet present.Distribution: Cosmopolitan.India: Assam and Kashmir.Trichocerca pusilla (Jennings, 1903) Characters: Body cylindrical; anterior end straight but with longitudinal folds.Toes unequal; left toe long and ventrally directed, right toe very small.laterally expanded into two distinct alae and without dorsal hump.Lateral tip of each ala armed with stout triangular cusp.Trophi modified virgate, asymmetric.Distribution: Australia.India: Assam.Dicranophoroides caudatus (Ehrenberg, 1834) Characters: Body cylindrical.Trunk with lateral sulci and longitudinal folds.Tail prominent.Toes long and terminating into acute tips.Trophi large and stout.Distribution: Cosmopolitan.India: Assam.Remarks A total of 116 species of Rotifera, belonging to 35 genera and 19 Eurotatorian families, are documented from plankton samples collected from Deepor Beel during April 2009 -March 2010.Of these, 21 species belonging to 12 genera and eight families are new additions to our earlier species inventory (Sharma & Sharma 2005) from this wetland while Brachionus durgae is a new record for northeastern India.