Deepor Beel revisited: new records of rotifers (Rotifera: Eurotatoria) with remarks on interesting species
B.K. Sharma 1 & Sumita Sharma 2
1 Freshwater Biology Laboratory, Department of Zoology, North-Eastern Hill University, Permanent Campus, Shillong, Meghalaya 793022, India
2 North Eastern Regional Centre, Zoological Survey of India, Risa Colony, Fruit Gardens, Shillong, Meghalaya 793003, India
Email: 1 email@example.com (corresponding author), 2 firstname.lastname@example.org
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.
Materials and Methods
The present study is a part of limnological survey, undertaken during April 2009 - March 2010, in Deepor Beel (910 35’-91043’E & 26005’-26011’N; area 40km2; elevation 42m), located in the Kamrup District of lower Assam, India. This floodplain lake is covered with various aquatic macrophytes namely Hydrilla verticillata, Eichhornia crassipes, Vallisneria spiralis, Utricularia flexuosa, Trapa bispinosa, Euryale ferox, Najas indica, Monochoria hastaefolia, Ipomea fistulosa, Hygrorhiza aristata, Polygonum hydropiper and Limnophila sp.
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.
Systematic list of new records of Rotifera from Deepor Beel
1. Anuraeopsis navicula Rousselet, 1911
2. Brachionus dichotomus reductus Koste & Shiel, 1980
3. B. durgae Dhanapathi, 1974
4. Keratella edmondsoni Ahlstrom, 1943
5. Platyias leloupi Gillard, 1957
6. Mytilina acanthophora Hauer, 1938
7. Macrochaetus longipes Myers, 1934
8. Colurella sulcata (Stenroos, 1898)
9. Lepadella benjamini Harring, 1916
10. L. eurysterna Myers, 1942
11. Lecane arcula Harring, 1914
12. L. blachei Berzins, 1973
13. L. doryssa Harring, 1914
14. L. haliclysta Harring & Myers, 1926
15. L. lateralis Sharma, 1978
16. Notommata spinata Koste & Shiel, 1991
17. Trichocerca bicristata (Gosse, 1887)
18. T. flagellata Hauer, 1937
19. T. iernis (Gosse, 1887)
20. T. pusilla (Jennings, 1903)
21. Dicranophoroides caudatus (Ehrenberg, 1834)
Various interesting species observed presently are briefly diagnosed below:
Anuraeopsis navicula Rousselet, 1911
Characters: Lorica boat-shaped and granulated; dorsal plate with two longitudinal ridges running parallel to each other and then united at the posterior end to form a single ridge.
Distribution: Pantropical. India: Assam, Gujarat, Orissa, Meghalaya, Tripura and West Bengal.
Brachionus dichotomus reductus
Koste & Shiel, 1980
Characters: Lorica dorso-ventrally compressed, stippled, and with maximum width in its posterior region. Anterior occipital margin with distinct median spines. Posterior spines moderately long and divergent.
Distribution: Australasia. India: Assam, Meghalaya and Tripura.
Brachionus durgae Dhanapathi, 1974
Characters: Lorica almost oval, smooth, compressed dorso-ventrally. Anterior occipital margin with six saw-tooth like spines of nearly equal length. Foot-opening situated ventrally in posterior region.
Distribution: African, Neotropical, Oriental and Palearctic regions. India: Andhra Pradesh, Orissa and Tamil Nadu.
Keratella edmondsoni Ahlstrom, 1943
Characters: Lorica elongated and granulated; with six anterior occipital spines, median occipitals longest and curved. Dorsum with characteristic pattern of carinal plaques. Posterior spines equal and divergent.
Distribution: Oriental region. India: Assam, Orissa, Rajasthan and Tamil Nadu.
Platyias leloupi Gillard, 1957
Characters: Lorica broadly circular, granulated and moderately compressed. Anterior dorsal margin with two blunt spines, posterior end with two long and parallel spines. Dorsum with distinct keel under the triangular frontal dorsal plaque.
Distribution: Tropicopolitan. India: Assam.
Mytilina acanthophora Hauer, 1938
Characters: Lorica granulated, dorsally arched and laterally compressed; anterior ventral corners with triangular cusps. Toes long and ending into acute points.
Distribution: Pantropical. India: Assam, Punjab and West Bengal.
Macrochaetus longipes Myers, 1934
Characters: Lorica shield-shaped, with serrate external margins and dorsum with 12 long spines. Head protruded. Anal segment flanked by long spines. Toes long and pointed.
Distribution: Cosmopolitan. India: Assam and Meghalaya.
Colurella sulcata (Stenroos, 1898)
Characters: Lorica elongated, with a longitudinal cleft; anterior margins of lorica rounded, posterior angles not produced. Foot and toes directed forwardly; toes long.
Distribution: Cosmopolitan. India: Assam, Gujarat, Meghalaya, Orissa, Tripura and West Bengal.
Lepadella benjamini Harring, 1916
Characters: Lorica broadly oval, with maximum width in its middle region. Head aperture with ventrally directed rim; anterior dorsal margin nearly straight and ventral margin with U-shaped sinus. Posterior end of lorica slightly concave. Foot-groove with divergent sides. Distal foot-segment elongated and projecting beyond lorica. Toes long, pointed and gently ventrally curved.
Distribution: Cosmopolitan. India: Manipur.
Lepadella eurysterna Myers, 1942
Characters: Lorica almost oval in outline; dorsal plate moderately arched. Posterior margin of lorica convex in the region of its foot-opening. Toes elongated and pointed.
Distribution: Cosmopolitan. India: Assam, Delhi and Meghalaya.
Lecane arcula Harring, 1914
Characters: Lorica small, elongate-oval; with straight and coincident anterior margins. Ventral plate elongated. Antero-lateral occipital spines distinct. Toes parallel-sided; claw small.
Distribution: Tropicopolitan. India: Assam and Meghalaya.
Lecane blachei Berzins, 1973
Characters: Lorica oval, anterior dorsal margin nearly straight, ventral margin with a shallow median sinus flanked by undulating sides and blunt external angles. Dorsal plate with distinct surface markings. Toes fused partly at base, claws with distinct basal spines.
Distribution: Oriental region. India: Assam, Delhi and West Bengal.
Lecane doryssa Harring, 1914
Characters: Lorica with few surface markings; anterior occipital margins straight and coincident. Toes slender and with pointed and undifferentiated claws.
Distribution: Tropicopolitan. India: Assam and Meghalaya.
Lecane haliclysta Harring & Myers, 1926
Characters: Lorica elongate-oval; anterior ventral margin with small spines at external angles. Dorsal and ventral plates with surface markings. Toes parallel-sided for more than 3/4 of their length and then terminating into small undifferentiated pointed claws.
Distribution: Tropicopolitan. India: Assam and Meghalaya.
Lecane lateralis Sharma, 1978
Characters: Lorica 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.
Trichocerca bicristata (Gosse, 1887)
Characters: Lorica 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.
Distribution: Cosmopolitan. India: Assam, Bihar and Orissa.
Trichocerca flagellata Hauer, 1937
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.
Distribution: Cosmopolitan. India: Bihar, Meghalaya, Orissa, Tripura and West Bengal.
Notommata spinata Koste & Shiel, 1991
Characters: Body 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.
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.
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.
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