Testate amoebae ( Protozoa : Rhizopoda ) of Deepor Beel ( a Ramsar site ) , Assam , northeastern India

Testate amoebae or testaceans, a group of freeliving Protozoa belonging to the superclass Rhizopoda, form an important micro-faunal component of aquatic, semi-aquatic and soil communities and provide integral links of the food chain in their respective environments. Taxonomic studies on Indian freshwater Rhizopoda were initiated by Naidu (1966) and followed by Mahajan (1971), Nair et al. (1971) and Mishra et al. (1977). In addition, certain contributions under the state fauna series (Das et al. 1993, 1995, 2000, 2003, 2004) dealt with limited freshwater collections. In spite of these studies freshwater Rhizopoda from different states of India are poorly documented, while their ecosystem diversity is practically neglected except for the works of Sharma & Sharma (2008), Bindu (2010) and Bindu & Das (2010). Our study on the Rhizopoda

of Deepor Beel, a Ramsar site and an important floodplain lake of the Brahmaputra River basin of Assam, merits biodiversity interest in view of the stated lacunae.The listed species are briefly diagnosed and comments are made on the nature and composition of the Rhizopoda fauna.

Arcella hemispherica Perty, 1809
Characters: Test yellow, distinctly hemispherical and circular in lateral and front views.Surface of test with more or less fine areoles.

Arcella vulgaris Ehrenberg, 1830
Characters: Test light yellow, discoid or hemispherical in front or lateral views; height about half of its diameter; test surface with large areoles.Mouth circular and central.

Centropyxidae 4. Centropyxis aculeata (Ehrenberg, 1830)
Characters: Test brownish, cap-shaped; encrusted with quartz crystals and sometimes with admixture of diatoms and sand particles.Fundus obtusely rounded and usually with 4-6 divergent spines at the border, arranged in a single and somewhat regular row.

Centropyxis ecornis (Ehrenberg, 1843)
Characters: Test large, discoid or elliptical; without any spine and covered with quartz grains.Dorsal surface slightly arched and more elevated at posterior part.Oral aperture circular and much eccentric.

Centropyxis orbicularis Deflandre, 1929
Characters: Test almost circular in ventral view and semi-circular in lateral view, ventral surface flat; oral aperture semi-circular, plagiostomic; test with large stony particles.

Difflugidae 9. Difflugia acuminata Ehrenberg, 1838
Characters: Test cylindrical, with pointed 'horn' like extension; horn straight and differentiated from the base.Quartz crystals big; some even projecting out of the margin.

Difflugia corona Wallich, 1864
Characters: Test broadly spherical, slightly narrow near oral aperture; with 5-10 smooth test spines formed by quartz crystals.Oral aperture wide and crenulated.

Difflugia oblonga Ehrenberg, 1838
Characters: Test typically oblong, with smooth margins and rounded base; composed of big angular quartz crystals.Oral aperture circular and without any lobe.

Difflugia tuberculata (Wallich, 1864)
Characters: Test ovoid, with wide base; oral aperture hexagonal and surrounded by a short collar; test covered with tubercles and small platelets uniting the tubercles.

Difflugia urceolata Carter, 1864
Characters: Test ovoid-spherical, composed of angular quartz crystals and diatoms.Oral aperture circular; its collar around re-curved or rolled towards exterior.

Assulina seminulum (Ehrenberg, 1848) Leidy, 1879
Characters: Test yellow or brown, pyriform or ovoid, compressed and composed of imbricate oval or elliptical siliceous platelets.Aperture terminal, oval and bordered by a thin chitinous membrane with irregularly dentate margin.

Euglypha laevis (Ehrenberg, 1845)
Characters: Test oviform, glabrous and elliptical or sub-circular; aperture elliptical or sub-circular, bordered by a single row or platelets pointed terminally.Test platelets oval.

Discussion
Our collections show 14 species of Lobosea and seven species of Filosea, the L/F ratio of 2 is close to the 3.0 reported by Sharma & Sharma (2008) from various floodplain lakes of Assam but exceeds the range of 0.5-1.4 reported for moss-dwelling rhizopods (Chattopadhyay & Das 2003).
The total Rhizopoda richness of Deepor Beel is higher than the 16, 12, 7 and 19 species examined from the freshwater biotopes of Meghalaya (Das et al. 1995), Tripura (Das et al. 2000), Sikkim (Das et al. 2003) and Manipur (Das et al. 2004) respectively.Further, the richness is higher than the reports of 16 species from Loktak Lake -a Ramsar site ( refer Das et al. 2004); 10 species from Melghat Wildlife Sanctuary (Bindu 2010), Maharashtra; 13 species from Pench National Park, Maharashtra and also 7-16 species listed from 15 floodplain lakes of the Brahmaputra river basin of Assam (Sharma & Sharma 2008).However, we caution against over-emphasizing the importance of these comparisons without considering sampling intensity and the nature of different ecosystems.In analyzing the comparative species-richness of our and other communities, it also needs to be emphasized that the number of species recorded to date are yet provisional and these may well be revised in light of future research.
Whilst Centropyxis orbicularis and Cyphoderia ampulla currently exhibit restricted occurrence in India with reports from Sikkim and Uttarakhand respectively, their distribution ranges were extended recently to Assam (Sharma & Sharma 2008).The mossdwelling Cyphoderia ampulla was recently observed in freshwater from Assam (Sharma & Sharma 2008) and Maharashtra (Bindu 2010); the present report re-affirming its occurrence in freshwater environs merits ecological interest.Our report also endorses an identical report (Sharma & Sharma 2008) of Cyclopyxis eurystoma which was known from soil and mosses in India (Chattopadhyay & Das 2003).Arcella hemispherica, Centropyxis cassis, Difflugia corona, D. tuberculata, D. urceolata, Cyclopyxis eurystoma, and Euglypha laevis comprise examples of local or regional distributional interest.Further, these species exhibit rare occurrence in our collections.On the other hand, Arcella discoides, A vulgaris, Centropyxis aculeata, C. ecornis, Difflugia acuminata, D. oblonga, Euglypha acanthophora and E. tuberculata exhibit relatively frequent occurrence.
The present report raises the total number of Rhizopoda so far known from different ecosystems of Assam to 49 species, affirming the biodiversity value of this Ramsar site.The observed association of Rhizopoda with different aquatic macrophytes merits future interest, and studies of this and other ecological aspects have been initiated by the authors.

14. Lesquereusia spiralis (Ehrenberg, 1830)
Characters: Test transparent, semi-spiral and composed of closely arranged vermiform pellets; neck continued in a straight line down to mouth.Oral aperture circular.Distribution: India -Assam, Meghalaya, Manipur, West Bengal and Andhra Pradesh.