Indian Hydrobiology, 19(1&2): 77–96, 2020 Diversity of Freshwater Diatoms from the World Heritage Mamallapuram region of Tamil Nadu, India Bakthavachalam Babu* and S. Pauline Gifty Department of Botany, Madras Christian College (Autonomous), Chennai – 600 059 (Affiliated to the University of Madras) *Corresponding Author – babu@mcc.edu.in Abstract Diatoms are abundant and ubiquitous, autotrophic eukaryotic organisms, responsible for one fourth of photosynthesis on the Globe. They are ecologically and economically very important organisms. The present study was aimed at documenting such significant freshwater diatoms from six different sites located in and around the places of heritage site, Mamallapuram, Chengalpattu District, Tamil Nadu, India. A total of 45 species were documented in the present study, which comprises 24 genera belonging to 18 families. Sellaphora hustedtii (Krasske) Lange-Bertalot and Werum is recorded for the first time in India and also 13 species were recorded for the first time from Tamil Nadu. This result indicates the significance of systematic studies of freshwater diatoms in Tamil Nadu and in India. Key words: Bacillariophyceae; Centric and Pennate Diatoms; Sellaphora hustedtii. Introduction Diatoms are microscopic organisms that constitute a major group of algae that belong to the division Bacillariophyta. Diatoms are primary producers which play a major role in aquatic ecosystems and contribute to about a quarter of global primary production and 43% of primary production in the oceans (Treguer et al., 1995). These siliceous bodies have a long history of exploit and acquire many features valued in ecological indications and extended their uses in various fields (Stevenson, 2014). In India, diatoms are not much researched. The first systematic account of freshwater diatoms from Tamil Nadu was provided by West and West (1907), followed by Venkataraman (1939) and Krishnamurthy (1954). Despite an early begin, such documentation works were not consistently carried out. This created a huge knowledge gap on freshwater diatoms in Tamil Nadu and also in India. Recently, Karthick et al. (2009), Venkatachalapathy and Karthikeyan (2012, 2013) and Karthikeyan et al. (2018) contributed valuable information to the diatom flora of Tamil Nadu. Babu and Pauline (2018) have worked on certain sites situated in the East Coast regions of Kanchipuram District where they have documented 28 taxa of which 78 15 taxa were recorded for the first time from Tamil Nadu. More studies should be carried out on the biology and the application of these simple yet significant organisms. The main objective of this work is to document the diatom flora in various regions of Tamil Nadu and to add new reports to the Tamil Nadu Diatom flora to bridge the gap of lacking data. This study also lays a foundation for further research to be carried out in the application aspect of these diatoms. Material and methods Mamallapuram (Mahabalipuram) (12.62°N, 80.20°E) is situated along the coast of the Bay of Bengal. It is culturally significant as it is one of the UNESCO World Heritage Site in the country. This site that has got a lot of attention for its aesthetics and tourism has now attracted the diatomologists for the documentation of the bacillariophytes growing here. Diatom samples for the present taxonomic studies were collected on 23rd January and 11th February 2015 from six different water bodies Viz., Thirukullam Pond, Kulupakuttai Pond, Pond near Chariot beach resort, Poonjeri Lotus Pond, Karukathamman Temple Tank and Kaaliamman Temple Tank in and around Mamallapuram. A portion of the collected diatom samples was preserved in 1% Lugol’s Iodine Solution. The remaining portion of the sample was treated and processed by the hot digestion method suggested by Wu and Wang (2009). The processed samples were then mounted on micro slides for observation. A Zeiss – Axiostar (Carl Zeiss, Halbergmoos, Germany) fitted with a Canon EOS 500D DSLR Bakthavachalam Babu and Pauline Gifty camera was used for the imaging. The measurements of the diatoms were carried out using the AxioVision LE software. Identification of the diatom species was carried out using standard monographs (Krammer, 1997, 1997a, 2000, 2002, 2003; Lange–Bertalot 2001; Lange-Bertalot and Metzeltin 1996; Levkov 2009; Reichardt 1999; Wu et al., 2011, 2011a) along with various research articles. The collected samples and processed slides were deposited in the Phycology Laboratory, Department of Botany, Madras Christian College (Autonomous), Chennai, Tamil Nadu. Result A total of 45 species belonging to 24 genera were documented in the present study (Plates 1–3). The species were arranged in systematic position according to Round et al. (1990) classification. Among the 45 species, Sellaphora hustedtii is reported for the first time from India, which is denoted by double asterisks (**). In addition to this, 13 species such as Fragilaria gracilis, Eunotia bilunaris, Eunotia flexuosa, Eunotia incisa, Cymbopleura cuspidate, Pinnularia biceps, Pinnularia brauniana, Pinnularia brevicostata, Pinnularia viridis, Hantzschia amphioxys, Nitzschia fossilis, Nitzschia subacicularis and Tryblionella apiculata were reported for the first time from Tamil Nadu, which are denoted by an asterisk (*). Cyclotella atomus Hustedt 1937 (Fig. 1) Frustules slightly rectangular and eccentrically undulate in girdle view. Valves 4–12 μm in diameter, valve shows Diversity of Freshwater Diatoms from the world heritage Mamallapuram region 79 Plate 1: 1 – Cyclotella atomus, 2 – Cyclotella meneghiniana, 3 – Aulacoseira granulata, 4 – Fragilaria capucina, 5 – *Fragilaria gracilis, 6 – Ulnaria ulna, 7 – *Eunotia bilunaris, 8 – *Eunotia flexuosa, 9 – *Eunotia incise, 10 – Anomoeoneis sphaerophora, 11 – *Cymbopleura cuspidata, 12 – Encyonema silesiacum, 13 – Gomphonema affine, 14 – Gomphonema augur [(* denotes the species reported for the first time from Tamil Nadu); Scale bars: Figs. 1–5, 9–12 = 5 μm; Figs. 6–8, 13 & 14 = 10 μm]. smooth central zone and a single stigma near the marginal zone. The marginal zone shows thick costae and radial striae 11–21 in 10 μm. Epiphytic and free floating form collected from Kaaliamman Temple Tank, Karukathamman Temple Tank, Poonjeri Lotus Pond. 80 Cyclotella meneghiniana Kützing 1844 (Fig. 2) Synonym: Cyclotella kuetzingiana Thwaites; Surirella melosiroides Meneghini; Cyclotella operculata var. rectangula Kutzing; Cyclotella rectangular Brebisson in Rabenhorst; Cyclotella laevissima Van Goor. Frustules drum shaped, 10–36 μm in diameter. Valve disc shaped, central zone flat or tangentially undulated, mostly structures less or rarely with radial bands. Central zone shows distinct one to four fultoportulae. The marginal zone contains radial striations, 6–11 in 10 μm and interstriae with distinct fultoportula. Valve margins with ring of spines and a single marginal rimoportula. Epiphytic or free floating forms collected from Thirukulam Pond and Kaaliamman Temple Tank. Aulacoseira granulata (Ehrenberg) Simonsen 1979 (Fig. 3) Basionym: Gaillionella granulata Ehrenberg Synonym: Gaillionella decussata Ehrenberg; Melosira granulata (Ehrenberg) Ralfs; Melosira punctata var. granulata (Ehrenberg) Cleve & Möller, Melosira lineolata Grunow in Van Heurck; Lysigonium granulatum (Ehrenberg) Kuntze; Orthoseira granulata (Ehrenberg) Schonfeldt; Melosira polymorpha subsp. granulata (Ehrenberg) H. Bethge Frustules cylindrical and form long filaments, predominately observed in girdle view. Valves measure 5–12 µm diameter and mantle 6–19 µm long. Valve mantle with short marginal connective spines and 1–3 separation spines measure 2–8 µm in length. Separation spines very long and almost equal in length to the valve mantles. Valve mantle coarsely punctuate, Bakthavachalam Babu and Pauline Gifty areolae square and arranged parallel to axis or slightly curved; striae 6–13 in 10 µm, punctae 7–16 in 10 µm Free floating and epiphytic form collected from Kaaliamman Temple Tank and Poonjeri Lotus Pond. Fragilaria capucina Desmazières 1825 (Fig. 4) Synonym: Fragilaria capucina var. lanceolata Grunow in Van Heurck; Fragilari capucina f. lanceolata (Grunow) Hustedt; Fragilaria capucina f. lanceolata (Grunow) Skabichevskii Valves linear to linear lanceolate and apices cuneate or slightly rostrate with single rimoportula. Valve 12–140 µm in length, 4–8 µm in breadth. Central area distinct and reaches to the valve margins or central area one-sided. Epiphytic and free floating form collected from Kulupakuttai Pond. *Fragilaria gracilis Østrup 1910 (Fig. 5) Synonym: Fragilaria capucina var. gracilis (Oestrup) Hustedt Valves narrowly linear to linear lanceolate and apices acute to subcapitate. Valve length 40–110 μm and 3–5 μm breadth. Axial area narrow and linear, distinct central area reaching to the valve margins. Striae parallel, 13–18 in 10 μm and Spines absent. Single transapically orientated rimoportula present at each apex of the valve. Epiphytic and free floating form collected from Kulupakuttai Pond. Ulnaria ulna (Nitzsch) Compère 2001 (Fig. 6) Basionym: Bacillaria ulna Nitzsch Synonym: Frustulia ulva (Nitzsch) Agardh; Frustula ulna (Nitzsch) Agardh; Diversity of Freshwater Diatoms from the world heritage Mamallapuram region Exilaria ulna (Harvey) Jenner; Fragilaria ulna (Nitzsch) Lange –Bertalot; Ulnaria ulna (Nitzsch) compere Valves linear with attenuate rostrate ends. Valves 70–150 μm in length and 4–15 μm in breadth. Central area rectangular, striae coarse, parallel 8–13 in 10 µm, pseudoraphe linear, narrow and same breadth throughout the valve. Epiphytic and free floating form collected from Karukathamman Temple Tank and Poonjeri Lotus Pond. *Eunotia bilunaris (Ehrenberg) Schmidt 1881 (Fig. 7) Basionym: Synedra bilunaris Ehrenberg Synonym: Synedra lunaris Ehrenberg; Synedra lunaris var. bilunaris Brun; Synedra ulna var. bilunaris (Ehrenberg) Brun; Eunotia lunaris (Ehrenberg) Grunow in Van Heurck; Eunotia lunaris var. bilunaris (Ehrenberg) Grunow in Van Heurck; Eunotia curvata (Kutzing) Lagerstedt; Pseudo-eunotia lunaris var. bilunaris (Ehrenberg) De Toni; Eunotia bilunaris (Ehrenberg) Mills. Frustules transapically symmetrical and rectangular in girdle view. Valves dorsiventral, narrowly linear shows convex dorsal and concave ventral margins with rounded to rostrate apices. Valves 47–185 μm in length and 2–7 μm in breadth. Raphe curved strongly on valve mantle and restricted to the apices. Striae parallel extend across entire valve face, 14–23 in 10 μm. Free floating and epiphytic form collected from Pond near Chariot beach resort and Kulupakuttai Pond. 81 *Eunotia flexuosa (Brébisson in Kützing) Kützing 1849 (Fig. 8) Basionym: Synedra flexuosa Brebisson in Kützing Synonym: Eunotia flexuosa var. pachycephala Grunow; Eunotia flexuosa var. eurycephala Grunow; Eunotia mesiana Cholnoky Valves linear slightly arched more or less capitate apices and measure 85–260 μm in length and 3–9 μm in breadth. Raphe extends toward the center of the valve from the dorsal margin of the terminal nodules. Terminal nodules distinct on the ventral margins. Striae parallel 14–21 in 10 μm. Free floating and epiphytic form collected from Poonjeri Lotus Pond and Pond near Chariot beach resort. *Eunotia incisa W. Smith in Gregory 1854 (Fig. 9) Synonym: Himantidium veneris Kutzing; Eunotia veneris (Kutzing) De Toni; Eunotia veneris (Kutzing) Berg. Valves linear with ventral margin straight and dorsal convex margin; acute or rounded apices. Valve 40–55 μm in length and 9–15 μm in breadth. Raphe occurs at apices, terminal ends visible and proximal ends slightly expanded as notch at the ventral margin. Striae parallel and more widely placed at the center than at the apices, 12–17 in 10 μm. Free floating and epiphytic form collected from Pond near Chariot beach resort and Kaaliamman Temple Tank. Anomoeoneis sphaerophora (Ehrenberg) Pfitzer 1871 (Fig. 10) Synonym: Navicula sphaerophora Kützing; Navicula amphisbaena var. sphaerophora (Kützing) Rabenhorst 82 Valves elliptic to elliptically lanceolate with rostrate to sub-capitate apices and measure 25–70 µm in length and 14–22 µm in breadth. Raphe straight filiform and axial area linearly narrow. Central area elliptical or extend unilaterally to valve margins and striae irregular13–18 in 10 µm. Free floating form collected from Thirukullam Pond, Pond near Chariot beach resort, Kaaliamman Temple Tank, Kulupakutttai Pond and Karukathamman Temple Tank. Bakthavachalam Babu and Pauline Gifty 20–46 μm in length and 10–18 μm in breadth. Single stigma present on the dorsal side of the central area. Raphe straight, proximal and distal raphe ends deflected dorsal and ventral sides, respectively. Striae radial, fine 13–21 in 10 μm. Free floating and epiphytic form collected from Pond near Chariot beach resort, Kulupakuttai Pond and Poonjeri Lotus Pond. Gomphonema affine Kützing 1844 (Fig. 13) *Cymbopleura cuspidata (Kützing) Krammer 2003 (Fig. 11) Basionym: Cymbella cuspidata Kutzing Synonym: Cymbella meniscus Heribaud; Cymbella ovum Heribaud Valve slightly dorsiventral ellipticlanceolate with apiculate or cuspidate apices. Valves 30–65 μm in length and 11–16 μm in breadth. Raphe filiform, straight, distal raphe ends deflected dorsally and comma shaped. Axial area narrow linear; central area round or asymmetric and expanded on ventral side. Striae radial and convergent towards the apices, 9–15 in 10 µm. Free floating form collected and reported from Pond near Chariot beach resort. Synonym: Gomphonema dichotomum var. affine (Kutzing) Rabenhorst; Gomphonema lanceolatum var. affine (Kutzing) CleveEuler; Gomphonema lanceolatum var. affine (Kutzing) Cleve-Euler. Valves heteroploar, club shaped with constricted head pole and narrowly blunt rounded tail. Valves 30–95 μm in length and 8–14 μm in breadth. Raphe slightly undulated; axial area linear and narrow and central area small, extend to one side or indistinct. Single stigma present on one side of the central area. Striae radial and extend up to the valve mantle 12–18 in 10 μm. Epiphytic and free floating forms were collected from Thirukullam Pond, Pond near Chariot beach resort, Kulupakuttai Pond, Karukathamman Temple Tank and Poonjeri Lotus Pond. Encyonema silesiacum (Bleisch) Mann in Round et al. 1990 (Fig. 12) Gomphonema augur Ehrenberg 1840 (Fig. 14) Basionym: Cymbella silesiaca Bleisch Synonym: Cymbella ventricosa var. silesiaca (Bleisch) A. Cleve-Euler; Cymbella minuta var. silesiaca (Bleisch) Reimer in Patrick & Reimer. Valves dorsiventral with rounded to rostrate apices, valve measure Synonym: Gomphonema apiculatum Ehrenberg Valve heteroploar, head pole wider than the tail and rostrate to capitate apices. Valves 30–120 μm in length, 14–22 μm in breadth. A single stigma present on one side of the central area. Raphe Diversity of Freshwater Diatoms from the world heritage Mamallapuram region slightly sinuous and undulate. Striae coarser often with one shorter stria in the central area, 12–18 in 10 μm. Epiphytic and free floating forms collected and reported from Pond near Chariot beach resort and Poonjeri Lotus Pond. Gomphonema gracile Ehrenberg 1838 (Fig. 15) Synonym: Gomphonema lanceolatum Ehrenberg; Gomphonema grunowii Patrick Valves lanceolate with narrowly rounded apices and measures 40–180 μm in length, 8–13 μm in breadth. A single stigma present on one side of the central area. Raphe slightly sinuous. Striae coarser with one shorter stria in the central area, density 11–18 in 10 μm. Epiphytic and free floating forms collected from Pond near Chariot beach resort, Kaaliamman Temple Tank, Kulupakuttai Pond and Poonjeri Lotus Pond. Gomphonema lagenula Kützing 1844 (Fig. 16) Synonym: Gomphonema parvulum var. lagenula (Kutzing) Frenguelli; Gomphonema parvulum var. lagenula (Grunow) Hustedt. Valves lanceolate to clavate with constricted subcapitate head pole and slightly protruded tail. Valves 22–35 μm in length and 6–10 μm in breadth. Raphe filiform and straight; axial area narrow linear. Central area unilateral with an isolated stigma at the opposite side. Striae radial 10–16 in 10 μm. Epiphytic and free floating forms collected and reported from Kaaliamman Temple Tank and Karukathamman Temple Tank. 83 Gomphonema parvulum (Kützing) Kützing 1849 (Fig. 17) Basionym: Sphenella parvula Kutzing. Synonym: Sphenoneis parvula (Kützing) Trevisan; Gomphonella parvula (Kützing) Rabenhorst; Gomphonema parvulum (Kützing) Van Heurck. Valves linear-lanceolate with rostrate to subcapitate apices, measure 13–44 μm in length, 6–11 μm in breadth. Raphe slightly sinuous and straight; axial area narrow and linear, central area small and expended on one side. One short stria occurs opposite to the central stigma. Striae parallel, 8–22 in 10 μm. Epiphytic and free floating forms collected from Thirukulam Pond. Lemnicola exigua (Grunow) Kulikovskiy, Witkowski & Plinski in Plinski and Witkowski 2011 (Fig. 18) Basionym: Achnanthes exigua Grunow Synonym: Achnanthes exigua var. exigua Grunow; Achnanthes exigua var. heterovalva Krasske; Microneis exigua (Grunow) Comber; Achnanthidium exiguum (Grunow) Czarnecki. Valves linear to broadly elliptical with parallel margins and rostrate to subcapitate apices. Valves 9–22 μm in length and 4–9 μm in breadth. Raphe valve, central area rectangular and extended up to valve margin, axial area linearly lanceolate, raphe straight, filiform, terminal raphe ends deflected in opposite directions. Striae radial, 23–27 in 10 μm. Araphe valve, raphe sternum narrow and lanceolate, Axial area linear to lanceolate and central area small or absent. Striae 19–24 in 10 μm. 84 Bakthavachalam Babu and Pauline Gifty Plate 2: 15 – Gomphonema gracile, 16 – Gomphonema lagenula, 17 – Gomphonema parvulum, 18 – Lemnicola exigua, 19 – Lemnicola hungarica, 20 – Diadesmis confervacea, 21 – Halamphora veneta, 22 – Neidium affine, 23 – Fallacia pygmaea, 24 – **Sellaphora hustedtii, 25 – Sellaphora laevissima, 26 – Pinnularia acrosphaeria, 27 – *Pinnularia biceps, 28 – *Pinnularia brauniana, 29 – *Pinnularia brevicostata, 30 – Pinnularia laterea, 31 – *Pinnularia viridis [(*denotes the species reported for the first time from Tamil Nadu; **from India); Scale bars: Figs. 16–21, 23–25, 27, 28, 30 = 5 μm; Figs. 15, 22, 26, 29, 31 = 10 μm]. Epiphytic and free floating forms were collected from Kulupakutttai Pond, Karukathamman Temple Tank and Poonjeri Lotus Pond. Lemnicola hungarica (Grunow) Round and Basson 1997 (Fig. 19) Basionym: Achnanthidium hungaricum Grunow Diversity of Freshwater Diatoms from the world heritage Mamallapuram region Synonym: Achnanthes hungarica (Grunow) Grunow; Achnanthidium hungaricum Grunow; Microneis hungarica (Grunow) Cleve Valves linear-elliptic to linearly lanceolate with subcuneate to subrostrate apices. Valve 6–16 µm in length and 5–11 µm in breadth. In raphe valve, axial area linear, central area broad, widening and asymmetrical, stauros form expanded to one or both margins of valve. Proximal raphe ends eye drop like and distal raphe ends turned toward opposite sides. Araphe valves show linear axial area and small, asymmetrical central area. Striae radial, biseriate, 18–25 in 10 µm. Free floating and epiphytic forms were collected from Pond near Chariot beach resort. 85 Halamphora veneta (Kützing) Levkov 2009 (Fig. 21) Basionym: Amphora veneta Kützing. Valves dorsiventral, linear lanceolate to lanceolate with apices rostrate and ventrally curved. Valves show strongly arched dorsal margin and straight or slightly concave ventral margin, valves measure 15–39 µm in length and 3–7 µm in breadth. Raphe straight or slightly curved and placed near ventral margin. Proximal raphe ends straight or slightly deflected towards dorsal side, fascia absent. Axial area linear; dorsal striae radial and convergent towards apices, striae radial, 20–30 in 10 μm. Free floating and epiphytic forms were collected from Pond near Chariot beach resort, Kulupakuttai Pond and Poonjeri Lotus Pond. Diadesmis confervacea Kützing 1844 (Fig. 20) Neidium affine (Ehrenberg) Pfitzer 1871 (Figs. 22) Synonym: Diadesmis peregrina W. Smith; Navicula confervacea (Kutzing) Grunow in Van Heurck; Navicula confervacea var. hungarica Grunow in Van Heurck; Navicula confervacea var. peregrina Grunow in Van Heurck. Valves elliptic to broadly lanceolate with obtuse or apiculate apices and measure 13–22 µm in length and 5–10 µm in breadth. Axial area linear at apices and widening towards center; central area rounded to rhomboid with nodular thickening. Raphe straight, simple proximal raphe ends and distal ends slightly broader or slightly T-shaped. Striae radial, 17–27 in 10 µm. Epiphytic and free floating forms collected from Thirukullam Pond, Pond near Chariot beach resort and Kaaliamman Temple Tank. Basionym: Navicula affinis Ehrenberg. Valves linear to linear elliptic with blunt and rostrate apices, measure 21–80 μm in length, 6–18 μm in breadth. Raphe straight, filiform, proximal raphe ends deflected opposite directions and distal raphe ends forked. Axial area linear and straight; central area small, round or elliptic. Striae slightly radial at the center and parallel towards the apices, 17–33 in 10 μm. Epiphytic and free floating forms collected from Pond near Chariot beach resort. Fallacia pygmaea (Kützing) Stickle & Mann in Round et al., 1990 (Fig. 23) Basionym: Navicula pygmaea Kutzing 86 Synonym: Navicula minutula Smith; Navicula rotundata Hantzsch fide Grunow in Van Heurck; Navicula hudsonis Grunow in Cleve; Diploneis hudsonis Cleve. Valves lanceolate to elliptical with blunt round apices measure 12–34 μm in length, 9–13 μm in breadth. Axial area narrow and linear. Lyre-shaped non-ornamented area presents on either side of axial area and jointed to form small rounded central area. Striae radial and finely punctate 23–32 in 10 μm. Epiphytic and free floating forms collected from Thirukullam Pond. **Sellaphora hustedtii (Krasske) LangeBertalot & Werum in Werum and Lange-Bertalot 2004 (Fig. 24) Basionym: Navicula hustedtii Krasske Valves elliptically lanceolate with protruded, constricted capitate apices measure 9–18 μm in length and 3–6 μm in breadth. Raphe filiform and straight; axial area narrow, central area small and transverse. Striae radial at the center and parallel, convergent at the apices, 15–20 in 10 μm. Epiphytic and free floating forms collected from Pond near Chariot beach resort. Sellaphora laevissima (Kützing) Mann 1989 (Fig. 25) Basionym: Navicula laevissima Kutzing. Synonym: Sellaphora bacilliformis (Grunow) Mereschkowsky; Navicula wittrockii (Lagerstedt) Cleve-Euler; Navicula laevissima var. perhibita (Hustedt) Lange- Bertalot. Valves linearly lanceolate with broad rounded apices with small polar bars. Bakthavachalam Babu and Pauline Gifty Valves 21–68 μm in length and 8–12 μm in breadth. Raphe straight, central, proximal raphe ends expanded and deflected; distal raphe ends hooked. Axial area narrowly linear and central area rhomboid to square. Striae distinct, slightly radial, 16–21 in 10 μm. Epiphytic and free floating forms collected from Pond near Chariot beach resort. Pinnularia acrosphaeria W. Smith 1853 (Fig. 26) Valves linearly lanceolate measure 50–85 µm length and 8–13 µm breadth. Axial area broad, one-third as wide as the valve and central area asymmetric surface of both areas mottled. Proximal raphe ends slightly expanded and deflected same side. Distal raphe ends sickle shaped. Striae slightly radiate at the center and parallel towards the apices, 10–14 in 10 µm. Free floating and epiphytic forms were collected from Pond near Chariot beach resort and Kulupakuttai Pond. *Pinnularia biceps Gregory 1856 (Fig. 27) Synonym: Pinnularia termes Ehrenberg; Pinnularia interrupta W. Smith; Navicula mesolepta (W. Smith) Grunow; Navicula bicapitata var. crucifera O’Meara; Navicula termes (Ehrenberg) O’Meara; Navicula interrupta (W. Smith) Schmidt; Pinnularia stauroptera var. interrupta (W. Smith) Brun; Navicula nivalis var. interrupta (W. Smith) Heribaud; Pinnularia interrupta f. biceps (Gregory) Cleve; Navicula interrupta f. biceps (Gregory) Fricke; Pinnularia bicapitata var. interrupta (W. Smith) Diversity of Freshwater Diatoms from the world heritage Mamallapuram region Dippel; Pinnularia interrupta var. biceps (Gregory) Meister; Navicula interrupta var. termes (Ehrenberg) Prochazka; Navicula interrupta var. biceps (Gregory) Prochazka; Pinnularia gibba var. interrupta (W. Smith) Woodhead & Tweed; Pinnularia bicapitata (Langerstedt) Cleve. Valves linear with parallel to slightly convex or very slightly triundulate margin and capitate apices. Valves 38–80 µm in length and 5–12 µm in breadth. Axial area linearly lanceolate and central area rhomboidal or square. Fascia formed due to absence of one or more striae on one or either sides of central area. Raphe straight and slightly lateral. Striae radial at the center and convergent towards the apices, 10–19 in 10 µm. Epiphytic and free floating forms collected from Pond near Chariot beach resort and Karukathamman Temple Tank. *Pinnularia brauniana (Grunow) Studnicka 1888 (Fig. 28) Basionym: Navicula brauniana Grunow Synonym: Navicula braunii Grunow; Pinnularia braunii (Grunow) Cleve; Schizonema braunii (Grunow) Kuntze; Navicula interrupta f. braunii (Grunow) Fritsch; Pinnularia interrupta f. braunii (Grunow) Mills. Valves linear lanceolate margins slightly convex with small capitates apices. Valves 24–48 μm in length and 5–10 μm in breadth. Axial area broadly lanceolate and widening towards center of the valve; central area broad with transverse fascia. Raphe filiform, proximal raphe ends deflected 87 unilaterally and hooked distal raphe ends. Striae radiate at the center and convergent towards the end, 9–15 in 10 μm. Epiphytic and free floating forms collected from Karukathamman Temple Tank. *Pinnularia brevicostata Cleve 1891 (Fig. 29) Synonym: Schizonema brevicostatum (Cleve) Kuntze; Navicula brevicostata (Cleve) Fricke; Pinnularia brevicostata var. leptostauron Cleve; Navicula brevicostata var. leptostauron (Cleve) Fricke Valves linear with parallel margins and apices bluntly rounded. Length 65–95 μm, breadth and 16–21 μm. Raphe slightly undulates, proximal raphe ends large, «comma» shaped and distal raphe ends sickle shaped. Axial area very broad, 1/4–1/2 breadth of valve. Central area a narrow bilateral fascia. Striae slightly radiate at the center, parallel to slightly convergent at the apices, 7–9 in 10 µm. Epiphytic and free floating forms collected from Pond near Chariot beach resort and Kulupakuttai Pond. Pinnularia laterea Krammer 2000 (Fig. 30) Valves linear with capitates and distinctly protracted apices. Valves 40–55 µm in length and 7–10 µm in width. Raphe straight, proximal ends tear-drop shaped bent to the one direction and distal raphe ends hook shaped. Axial area widely lanceolate continuous with large central area that reaches the valve margins. Striae small and mostly marginal, radial at the center and convergent towards the apices, 8–12 in 10 µm. 88 Free floating and epiphytic forms were collected from Pond near Chariot beach resort. *Pinnularia viridis (Nitzsch) Ehrenberg 1843 (Fig. 31) Basionym: Bacillaria viridis Nitzsch. Synonym: Navicula virdis (Nitzsch) Ehrenberg Valves linear, margins parallel or slightly convex or triundulate with rounded apices measure 76–180 μm in length and 15–28 μm in breadth. Raphe lateral, undulate, proximal raphe ends deflected one direction with distinct round pore and distal raphe ends broadly hooked. Axial area narrow near apices and widening towards center, central area asymmetric, round or elliptical. Striae slightly radiate at center and parallel at the apices, 6–11 in 10 μm. Epiphytic and free floating forms collected from Pond near Chariot beach resort. Caloneis bacillum (Grunow) Cleve 1894 (Fig. 32) Basionym: Stauroneis bacillum Grunow. Synonym: Navicula fasciata Lagerstedt; Caloneis bacillaris (Gregory) Cleve. Valves linearly lanceolate to lanceolate with parallel margins and blunt rounded apices measure 17–45μm in length and 6–11 μm in breadth. Raphe straight with distal ends hooked to one side. Axial area narrows, central area extend to the margin. Striae fine, parallel to slightly radial towards apices, 18–32 in 10 μm. Epiphytic and free floating forms collected from Thirukulam Pond, Pond near Chariot beach resort, Poonjeri Lotus Pond. Bakthavachalam Babu and Pauline Gifty Navicula rostellata Kützing 1844 (Fig. 33) Synonym: Navicula rhyncocephala var. rostellata (Kutzing) Cleve & Grunow; Navicula viridula var. rostellata (Kutzing) Cleve. Valves linear to lanceolate with slightly convex or parallel margins and protracted to subrostrate apices. Valves 32–55 μm in length and 8–14 μm in breadth. Raphe straight, proximal raphe ends slightly dilated and bent and distal raphe ends hooked. Axial area narrow; central area orbicular. Striae radial at the center and parallel to convergent at the apices, 8–14 in 10 μm. Epiphytic and free floating forms collected from Kaaliamman Temple Tank, Kulupakuttai Pond, Karukathamman Temple Tank. Gyrosigma acuminatum (Kützing) Rabenhorst 1853 (Fig. 34) Basionym: Frustulia acuminata Kützing Synonyms: Navicula acuminata (Kützing) Kützing; Pleurosigma acuminatum (Kützing) Grunow. Valves slender, sigmoid with tapering to acutely rounded apices. Valves 70–145 µm in length and 12–18 µm in breadth. Raphe central, sigmoid shape, proximal raphe curved in opposite directions. Central area small, elliptic and axial area narrow. Transverse and longitudinal striae fine and resolvable. Transverse striae slightly radial and perpendicular to the raphe. Longitudinal striae 18–23 µm in 10 µm and transverse striae 17–20 µm in 10 µm. Free floating and epiphytic forms collected from Thirukulam Pond, Karukathamman Temple Tank, Poonjeri Lotus Pond. Diversity of Freshwater Diatoms from the world heritage Mamallapuram region 89 Plate 3: 32 – Caloneis bacillum, 33 – Navicula rostellata, 34 – Gyrosigma acuminatum, 35 – Craticula ambigua, 36 – Craticula cuspidata, 37 – *Hantzschia amphioxys, 38 – Hantzschia elongata, 39 – *Nitzschia fossilis, 40 – Nitzschia intermedia, 41 – Nitzschia obtusa, 42 – Nitzschia perminuta, 43 – *Nitzschia subacicularis, 44 – *Tryblionella apiculata, 45 – Tryblionella calida [(* denotes the species reported for the first time from Tamil Nadu); Scale bars: Figs. 32–45 = 10 μm]. Craticula ambigua (Ehrenberg) Mann in Round, Crawford and Mann 1990 (Fig. 35) Basionym: Navicula ambigua Ehrenberg Valves elliptic to lanceolate with protracted rostrate apices and measure 55–80 µm in length and 11–19 µm in breadth. Raphe filiform straight with slightly expanded proximal raphe ends and deflected distal raphe ends. Central area small or absent and axial area narrow linear. Striae parallel or slightly 90 radiate and convergent towards the apices, 13–22 in 10 µm. Free floating and epiphytic forms were collected from Thirukulam Pond, Kaaliamman Temple Tank, Poonjeri Lotus Pond. Craticula cuspidata (Kützing) Mann in Round, Crawford and Mann 1990 (Fig. 36) Basionym: Frustulia cuspidata Kutzing Synonym: Navicula cuspidata (Kutzing) Kutzing; Vanheurckia cuspidata (Kutzing) Brebisson; Schizonema cuspidatum (Kutzing) Kuntze Valves rhomboidal to lanceolate with rostrate or sub-capitate apices. Valve 75–148 µm in length and 16–27 µm in breadth. Raphe filiform, proximal raphe ends expanded slightly and slightly hooked. Distal raphe ends deflected towards one side. Axial area narrow linear; striae transverse, parallel, 13–24 in 10 µm. Free floating and epiphytic forms collected from Pond near Chariot beach resort and Kulupakuttai Pond. *Hantzschia amphioxys (Ehrenberg) Grunow in Cleve and Grunow 1880 (Fig. 37) Synonym: Eunotia amphioxys Ehrenberg Valves asymmetrical with arched apices, 20–52 μm in length and 4–9 μm in breadth. Raphe contained within a canal and eccentrically placed on the valve margin. Proximal raphe endings bent towards opposite sides. Fibulae in the middle clearly more spaced, 7–12 in 10 µm. Striae uniseriate, slightly radiate in the middle and parallel towards the apices, 21–28 in 10 µm. Free floating and Epiphytic forms collected from Kulupakuttai Pond. Bakthavachalam Babu and Pauline Gifty Hantzschia elongata (Hantzsch) Grunow 1877 (Fig. 38) Basionym: Nitzschia vivax var. elongata Hantzsch Synonym: Hantzschia amphioxys var. elongata (Hantzsch) Protic Valves slightly arched with sub capitate to capitate apices; valves constricted in the middle of the raphe keel. Valves 160–330 in length, 8–15 µm breadth, The two middle fibulae placed apart from each other than the rest; fibulae 7–11 in 10 µm. Striae, parallel at apices and slightly radial at the center, 12–19 in 10 µm. Free floating and epiphytic forms collected from Kaaliamman Temple Tank, Kulupakuttai Pond and Poonjeri Lotus Pond. *Nitzschia fossilis Grunow in Cleve and Grunow 1880 (Fig. 39) Basionym: Nitzschia amphibia var. fossilis Grunow Valves linearly lanceolate with parallel margins and apices rostrate to subcapitate. Valves 30–80 μm in length and 3–7 μm in breadth. Raphe fibulate, marginal and distal raphe fissures slightly hooked. Fibulae square shaped, 7–10 in 10 μm. Central pair of fibulae more widely separated than the others; Striae distinct, 18–23 in 10 μm. Epiphytic and free floating forms collected from Kulupakuttai Pond and Poonjeri Lotus Pond. Nitzschia intermedia Hantzsch in Cleve and Grunow 1880 (Fig. 40) Synonym: Nitzschia subtilis var. intermedia (Hantzsch) Schonfeldt Diversity of Freshwater Diatoms from the world heritage Mamallapuram region Valves linear to linearly lanceolate with constricted subcapitate rounded apices. Valves 55–145 μm in length and 4–7 μm in breadth. Raphe eccentric and marginal, Raphe fibulate, 10–12 fibulae in 10 μm, small. Striae fine but distinct, 25–30 in 10 μm. Epiphytic and free floating forms collected and reported in Kaaliamman Temple Tank. Nitzschia obtusa W. Smith 1853 (Fig. 41) Synonym: Bacillaria obtusa (W. Smith) Elmore Valves linear, slight or strongly sigmoid with curved cuneiform apices, measure 110–340 μm in length and 8–17 μm in breadth. Raphe marginal, fibulat; fibulae short, transverse ribs like in girdle and valve view, fibulae 4–7 in 10 μm. Striae distinct, 20–32 in 10 μm. Epiphytic and free floating forms collected from Karukathamman Temple Tank. Nitzschia perminuta (Grunow) Peragallo 1903 (Fig. 42) Basionym: Nitzschia kuetzingiana var. perminuta Grunow Synonym: Nitzschia frustulum var. minutula Grunow; Nitzschia frustulum var. perminuta (Grunow) Grunow; Nitzschia hiemalis Hustedt; Nitzschia minutula Grunow Valves linear to lanceolate with slightly constricted central region and apices rostrate or sub-rostrate. Valves 15–20 µm in length and 2–4 µm in breadth. Raphe marginal, fibulate and widely placed, fibulae 10–14 in 10 µm. Striae parallel; 21–33 in 10 µm. 91 Epiphytic and free floating forms collected from Kaaliamman Temple Tank and Poonjeri Lotus Pond. *Nitzschia subacicularis Hustedt in A. Schmidt 1922 (Fig. 43) Synonym: Nitzschia subrostrata Hustedt Valves lanceolate or linearly lanceolate, central part of the valve with parallel or very slightly convex margins. Valves 28–90 μm in length, 2–5 μm in breadth. Raphe system fibulate and marginal. Fibulae small, more or less square. Central pair of fibulae not widely separated than the others, fibulae 9–14 in 10 µm. Striae distinct, 26–36 in 10 μm. Epiphytic and free floating forms collected and from Karukathamman Temple Tank. *Tryblionella apiculata Gregory 1857 (Fig. 44) Synonym: Synedra constricta Kutzing; Nitzschia constricta (Kutzing) Ralfs; Nitzschia dubia var. constricta (Kutzing) Carruthers; Homoeocladia apiculate (Gregory) Kuntze; Tryblionella constricta (Kutzing) Poulin; Nitzschia apiculata (Gregory) Grunow. Valves linear, slightly concave in the center with narrow to cuneiform or slightly rounded, subrostrate to rostrate apices. Valves 17–60 μm in length and 4–10 μm in breadth. Transverse striae prominent 17–20 in 10 μm. A longitudinal sternum present, extending from pole to pole. Raphe system fibulate and marginal. The fibulae appear faint due to every transapical rib bearing a fibula. Central raphe endings present, detectable as 92 a slight thickening of the wall of the subraphe canal at the center. Epiphytic and free floating forms collected and from Kulupakuttai Pond. Tryblionella calida (Grunow) Mann in Round, Crawford and Mann 1990 (Fig. 45) Basionym: Nitzschia calida Grunow in Cleve & Grunow. Synonym: Nitzschia umbilicata Hustedt. Valves linear, slightly concave at the center and protracted at the ends into short, narrow rostrate or subcapitate apices. Valves 20–49 μm in length and 5–11 μm in breadth. Raphe eccentric, slightly constricted at the middle portion of valve; fibulae narrow, apically elongated, interspaces small, rounded; fibulae 6–12 in 10 μm. Transapical costae prominent, slightly sinuous, 15–24 in 10 μm; transapical striae 15–38 in 10 μm. Epiphytic and free floating forms collected from Thirukullam Pond. Discussion Diatoms are one of the most important and interesting groups of phytoplankton. They dwell in almost all kind of aqueous and semi-aqueous environment and it also occurs on extreme environmental conditions commonly known as extremophiles. Study on such an important group of phytoplankton is meager in India, especially in Tamil Nadu. In the present study, six locations were selected from in and around Mamallapuram, a heritage site situated in the district of Chengalpattu and documented a total number of 24 genera and 45 species. Such a large Bakthavachalam Babu and Pauline Gifty number of diatoms were previously recorded by Venkataraman (1939) and Krishnamurthy (1954). Recently, Karthick et al. (2009) recorded 98 taxa from the wetlands of Coimbatore, Tamil Nadu. In the present study, Sellaphora hustedtii (Krasske) Lange-Bertalot & Werum is recorded for the first time from India and also 13 species were recorded for the first time from Tamil Nadu which indicates the significance of this study. The same authors, Babu and Pauline (2018) have already reported 28 species from the Kancheepuram district out of which 15 species were reported for the first time from Tamil Nadu. The result indicated that the pinnate group of diatoms dominated the centrales group in the studied area, where only three species (viz., Aulacoseira granulata, Cyclotella atomus and C. meneghiniana) were recorded. Among the 24 genera, Pinnularia dominated the other genera by representing 6 species out of which 4 species are new to Tamil Nadu followed by Gomphonema and Nitzschia represented by 5 species each. The assemblage of diatoms reveals the quality of the aquatic environments. Karthick et al. (2009) monitored the wetland aquatic system using diatoms as a pollution indicator. The water quality of the River Cauvery was evaluated based on the diatom indices (Venkatachalapathy and Karthikeyan, 2012, 2013; Karthikeyan et al., 2018). Result of the study showed that cosmopolitan and pollution tolerant species such as Diadesmus, Nitzschia, Pinnularia, Gomphonema, Encyonema, Eunotia, Ulnaria etc. were dominant in Diversity of Freshwater Diatoms from the world heritage Mamallapuram region various localities which indicated that these species can be used as a pollution indicators to monitor and evaluate the lotic and lentic water bodies present in India. These organisms not only used as pollution indicators but also can be used in the field of phyco-remediation, biofuel production and used as a model in Nanotechnology. Since the freshwater diatom flora of Tamil Nadu is poorly documented, the species richness observed in the present and previous studies by the same authors (Babu and Pauline, 2018) indicated that more studies on the diatom flora of Tamil should be carried out to document many more new species and new reports. 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