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Identification And Morphological Characterization of Rotifera (Zooplankton); A Review Sukh Sandan and Rina Chakrabarti Aqua Research Lab, Department of Zoology, University of Delhi, Delhi 110 007, India Abstract Identification key to the species of genus Brachionus • Two posterior spines are present which are divergent………………………………………………………………………………………………………………………………………………………. Brachionus caudatus (Fig. 27). Zooplankton are free swimming minute organisms, found in marine as well as freshwater bodies. They vary in size from microscopic to larger such as jelly fish. They are • Absence of posterior spines…….………………………………………………………………………………………………………………………………………………………………..………….………….. Brachionus angularis (Fig. 28). heterotrophic in nature and feeds on phytoplankton. Zooplankton are considered as important natural basic diet for many fish and shrimps as they are serving as an • Smooth, transparent lorica, posterior lorica circular……………………………………………………………………………………………………………………………………………………..…. Brachionus calyciflorus (Fig. 29). intermediary species in food chain that transfers energy from small planktonic algae to larger fish who in turn feed on them. Identification of the planktonic organisms is a • Length of spines of posterior lorica is unequal, right spine longer than left spine………………………………………………………..…………………………………………….….… Brachionus diversicornis (Fig. 30). very important step. The organisms are classified either on the basis of morphological features or molecular markers. DNA barcoding is the most widely used molecular • Length of spines of posterior lorica is less equal, inward curved …………………………………………………………………………………………………………………………….………..Brachionus forficula (Fig. 31). technique for plankton identification. This technique used short sequences of one or a few genes in order to classify known organisms and use this information to detect new • Absence of spines in posterior lorica, halophilic species…………………………………………………………………………………………………………………………………………………. Brachionus plicatilis (Fig. 32). ones. The morphological approach is simple and less expensive than molecular approach. In this study some important freshwater zooplankton are characterized on the basis • Presence of two large spines in posterior lorica …................................................................................................................................................................. Brachionus donneri (Fig. 33). of their morphological features and some identification keys are also specified to identify them. • Antero-median and antero-lateral spines are smaller then antero- intermediate spines, which is larger one, posterior 2 long spines are present……….. Brachionus falcatus (Fig. 34). • Lateral posterior side has no spines……………………………………………………………………………………………………………………………………………………………………….……... Brachionus urceolaris (Fig. 35). Introduction • Lateral posterior side with spines, anterior median spine is longer and curved than other spines………………………………………….…..………….…………………... Brachionus quadridentatus (Fig. 36). Identification key to the species of genus Keratella The live feed zooplankton are playing a key role in the growth and nutritional quality of fish, especially for larvae. Live feed is essential feed for growth of fish larvae as they • Margin of posterior lorica with 2 different spines, one line in dorsal plate has five pieces with longitudinal dorsal………………………………………………..….. Keratella tropica (Fig. 37). are easily ingested and digested (Kinne, 1997), and they do not affect the water quality (Watanabe et al., 1978). Live feeds are higher nutritional prey for many aquaculture • Margin of posterior lorica with 1 spine, characterised by a median line in dorsal plate extending longitudinally from behind the median frontal area to the base of the posterior species (Drillet et al., 2006; Hagiwara et al., 2001). Many studies are carried out on various aspects of zooplankton viz., their ecological diversity, population dynamics, spine………………………….………….………………………………………………………………………………………………………………… Keratella cochlearis (Fig. 38). genome sequencing and much more molecular work. To interpret and use these studies, a very important first step is the proper identification and nomenclatural Identification key to the family of order Flosculariaceae determination of all zooplankton. The morphological identification is one of the most common and useful approach in this area, though DNA barcoding is another molecular • Presence of six arm like appendages in body….. Family Hexarthridae (Fig. 39). • Presence of foot……………………………………………… Family Conochilidae (Fig. 40). based approach to identify and classify zooplankton. The present review is based on the morphological identification of some Rotifera (zooplankton) commonly used in • Loricate body…………………………………………….……. Family Testudinellidae (Fig. 41). aquaculture. • Absence of foot………………………………….…………… Family Trochosphaeridae. Identification key to the species of genus Filinia Rotifera • Presence of 2 unequal seate in caudal…………………… Filinia opoliensis (Fig. 42). Rotifera is a group of microscopic invertebrates, primarly freshwater, are tiny, free living zooplankton (Balian et al. 2008). The word “Rotifera” is derived from the latin word • Presence of 1 seate in caudal……………………………….. Filinia camasecla (Fig. 43). which means “wheel-bearer”. This name is given on the basis of the crown of cilia present in the mouth region that appear as wheel. General characters of Rotifera (Fig. 1) • Transparent body, elongated, relatively cylindrical and bilateral symmetrical. • Non segmented body and body cavity is pseudoceolomic. • The Epidermis has fixed small number of nuclei that are strengthened into a distinctive armor, called “Lorica”. • The body is divided into 3 parts; head, trunk and foot. • Head bears a crown of cilia often called “corona”, the most distinctive feature of Rotifera, organized as two-wheel like cilliary organ, from which the name of group is derived. • Mouth is ventral and opens into pharynx called the “mastax”, the second important distinctive feature of the rotifers. The mastax has powerful walls and contains small jaw like structures called “trophy”, helps to bite and chewing the prey. The shape of Trophi varies from species to species. • Trunk is the major part of the body and encloses most of the internal organs. • The foot projects from the posterior part of the trunk and are usually narrow that appear as tail. The foot may be retractile partially or wholly into the trunk. It may be reduced or totally absent in free swimming species. Figure 4. Colurella uncinata, a: lateral view, b: dorsal view • Respiratory organ and Circulatory system are absent. • The rotifers are either dioeceous or parthenogenetic females. The dioeceous rotifers have always smaller males then females and males are often with degenerated sex organs. Classified Rotifera species Their taxonomy is still in the state of flux. Rotifers may be classified into two superclasses - Pararotatoria and Eurotatoria. Pararotatoria are the most primitive rotifers and exclusively marine. It includes only one family; Seisonidae. Eurotatoria is further divided into two classes; Monogononta and Bdelloidea (Digononta). Previously, Acanthocephala was also included under Eurotatoria. The exact relationship between Acantocephala and other rotifers is still not clear. Family Seisonidae includes only 2 genera and 3 species (Paraseison annulatus, Seison nebaliae, Seison africanus) and are exclusively marine, they are not discussed here. Strictly speaking, Rotifera phylum is confined to Monogononta and Bdelloidea. Phylum Rotifera comprises of 2030 species. Monogononta is the largest group with 1570 species. Bdelloidea includes 461 species. The detailed classification of phylum Rotifera with some important species is given below based on the study of Cuvier 1798. Identification keys Identification key to the class of the phylum Rotifera • Two ovaries present………………………………….Class Bdelloidea, Order Bdelloida, Family Philodinidae, Genus Rotaria(Fig. 2). • One ovary present ……………………………………………………………………………………………………………………………Class Monogononta Identification key to the order of the class Monogononta (Fig. 3) • Trophi types are forcipate, incudate, malleate or virgate…………………………………………………………………………………………………………………………………….………….Order Ploima. • Trophi type is ramate, elliptical to round corona, horseshoe-shaped or four-lobed, heart-shaped, without long setae ……………………………………Order Flosculariaceae. Identification key to the families of order Ploima • Trophi incudate……………………………………………………………………………………………………………………………………………………………………………………………….……….Family Asplanchnidae. • The body is more or less asymmetrical. Very asymmetrical Trophi, asymmetry refers to all components of trophies. Foot terminally, a short single pseudosegment with many bristles and elongated spine-like toe, unequal in length.………………………………………………………………………………………………………..…………………………..Family Trichocercidae. • Trophi symmetrical, toes missing or present of similar length, a single toe, rarely. Shape of body is sacciform, fusiform, conical, never with dorsal crest…Family Synchaetidae. • Decreased number of unci teeth, normally composed of 3 stout subequal fused teeth. Foot short, a single pseudosegment inserted ventrally on the ventral plate. Toes 2 or fused (partially or entirely) to 1. Usually loricate with dorsal and ventral plate separated by lateral furrows (sulci)……………………………………………..…………………Family Lecanidae. • Presence of head shield may be retractile or non retractile….………………………………………………………………………………………………………………………………..Family Lepadellidae (Fig.

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