On the Occurrence of Four Diatom Taxa from Eastern India with a Taxonomic Note

Diatoms were collected from the Kotulpur area of West Bengal. Four diatom taxa, namely, Eunotia minor (Kützing) Grunow, Achnanthidium minutissimum (Kützing) Czarnecki, Lemnicola hungarica (Grunow) Round and Basson, and Navicula radiosa Kützing were observed using scanning electron microscopy (SEM) and identified in light of modern diatom taxonomic trends. Except Eunotia minor, all these taxa are new records to Eastern India. A note on the taxonomy of Achnanthes pseudobiasolletiana as described by Gandhi and Eunotia serrata var. diadema (Ehr.) R. M. Patrick as reported by Dwivedi and Misra has been added.


Introduction
Diatoms are a very important group of algae as they are the most common producers of organic matter in water bodies.According to Prygiel et al. [1] diatoms are good bioindicators responding quickly to environmental changes.During the 19th century, diatoms were studied for the first time in India by Ehrenberg [2].Subsequent notable works were made by Skvortzow [3], Biswas [4], Krishnamurthy [5], Venkataraman [6], and Sarode and Kamat [7] as well as 34 papers with a book on diatom taxonomy by Gandhi [8].
Though several hundreds of papers dealing with diatom taxonomy of Indian regions were published, most of them are limited to line drawings or bright field microscopic images, which have limited information on the ultrastructural details of diatoms.Further, some of the taxa have broad species concepts and follow an old classification system.The main reason behind these taxonomic identification problems was the scarcity of ultramodern scanning and light microscopes and up to date scientific literature.
The main purpose of this study was to examine the diatom diversity of eastern India in light of current systematic trends.Since diatom studies in eastern India were done very sporadic (Skvortzow [3], Prasad et al. [19], and Roy and Keshri [18]), this study adds new information on the diversity and taxonomy of this group in this part of the globe.

Study Area and Sample Collection.
The study area covered small ponds of Kotulpur from Bankura district in West Bengal, India.Kotulpur is situated at 23.0125 ∘ N latitude and 87.5936 ∘ E longitude.Diatom materials were collected from Kotulpur on 24.10.2014.Epiphytic, epilithic, and episammic materials were collected and preserved in 70% ethanol.

Cleaning
Techniques and Microscopy.Subsamples were cleaned using 30% hydrogen peroxide solution for removal of organic coatings.These procedures are modified from the techniques of Krammer and Lange-Bertalot [20], Taylor et al. [21], and Karthick et al. [22].Cleaned samples were then centrifuged at 3000 rpm and alternatively rinsed with distilled water 3-4 times to remove of traces of hydrogen peroxide from samples.The standard protocol was followed for light microscopic and scanning electron microscope (SEM) studies.SEM studies were carried out using a LEO 430 SEM located at the Birbal Sahani Institute of Paleobotany, Lucknow.
The collected preserved materials, along with the permanent slides made up with diatom mounting medium, were stored in the Herbarium of Phycology laboratory in the department of Botany, The University of Burdwan for future study and reference purpose (BURD-JPK 2066 dated: 24.10.2014).

SEM Morphology.
Valves with bilateral symmetry.Valves are linear-lanceolate with rounded, subrostrate apices.Heterovalves flexed across the transapical axis.Raphe system present only on one valve.Raphe valves with narrow, linearlanceolate axial area broadening in the center to form a transverse irregularly shaped central area.Raphe filiform, straight, with proximal raphe ends dilated and distal raphe endings subtly unilaterally curved.Striae moderately radiate on both valves with two shortened striae on either side of central area.Striae composed of up to 6 areolae per stria.Sometimes slit-like areola present on the valve margins.Valve length: 15.9 m, valve breadth: 3.3 m, and striae density: 32-34/10 m (RV).
It is a common and widely spread taxon but reported for the first time from Eastern India.

Discussion
Except for the work of Skvortzow [3] no significant contribution has been published on the freshwater diatoms of Eastern India.To some extent the research on the freshwater diatoms of Gujarat and Maharashtra as done by Gandhi [8] and Sarode and Kamat [7] could be mentioned, but this was limited in taxonomic scope.Since the advent of SEM that changed diatom taxonomy radically, notable contributions have been very few , Karthick et al. [12][13][14], Alakananda et al. [15,16], Wojtal et al. [17] and Roy and Keshri [18]).In this light the four taxa as observed under SEM from Eastern India appear to be significant because except E. minor, all the taxa are new records to Eastern India.From this study it also appears that the distributional records of diatoms are to be checked in light of modern diatom taxonomy, since several diatom taxa show endemism.Notably our knowledge of the diatoms of South East Asia is very poor as the published literature shows.Moreover the existing knowledge of diatoms of India should be re-evaluated in above mentioned perview.This is because in many papers, mere listing has been done, and in several other cases identifications have been done very reluctantly.This has created confusion in actual biodiversity records.
It also appears that there is the need for taxonomic revisions in many taxonomic groups.For example Gandhi [49] in his paper reported a new taxon to science as Achnanthes pseudobiasolletiana but from the camera lucida drawings, description, and measurements it is none other than A. minutissimum as appears in the light of modern taxonomy.Similarly there is confusion regarding the taxonomy of Achnanthidium minutissimum sensu lato as available in the literature of the works of Indian authors and abroad.A. minutissimum sensu stricto nowadays has a better circumscription with finer ultrastructural details, and more detailed study of Indian populations may show new taxa distinctly different from A. minutissimum.In one paper of Dwivedi and Misra [50] they identified taxa as Eunotia serrata var.diadema (Ehr.)R. M. Patrick but in the photographic girdle view image the taxa looks like a rectangular box which is one of the characteristic feature of E. minor (Karthick et al. [25]), so we propose it should be considered as E. minor.