B-3759 [1-5] Indian J. Anim. Res., AGRICULTURAL RESEARCH COMMUNICATION CENTRE Print ISSN:0367-6722 / Online ISSN:0976-0555 www.arccjournals.com Histological Investigation of the Digestive System and SEM Study of Radula in Fusinus nicobaricus (Gastropoda: Fasciolariidae) P. Subavathy* PG and Research Department of Zoology, St. Mary’s College (Autonomous), Thoothukudi Affiliated to Manonmaniam Sundaranar University, Abishekapatti, Tirunelveli-627 012, Tamil Nadu, India. Received: 26-11-2018 Accepted: 15-10-2019 ABSTRACT In the present study, histological studies of the digestive system and SEM study of radula of Fusinus nicobaricus was evaluated. The digestive system contains proboscis, oesophagus, stomach, hepatopancreas, intestine, rectum and anus. The digestive tract of Fusinus nicobaricus encloses a buccal mass at the anterior region which contains a chitinous radula. The oesophagus leaved the buccal mass dorsally and passed the food into an extensible stomach. A pair of salivary gland lied with mid-oesophagus region. Digestive gland secreted digestive enzymes into the lumen of the stomach into mid region. Intestine was thin walled, usually long and possess loop through the digestive gland tissue and leaves as short rectum. Hepatopancreas was also implicated in storage and excretion of inorganic reserves, lipids and carbohydrate metabolites. Radula, a specific character and part of the appendices of digestive system of majority of molluscs. It was observed that the type of radula in F.n is rachiglossate with radular formula of 1+R+1. Key words: Fusinus nicobaricus, Hepatopancreas, Oesophagus, Radula, Rectum. INTRODUCTION in a longitudinal ribbon of transverse rows (Ramesh and Marine fauna comprises of several phyla, orders, Ravichandran, 2008). classes, families, genera and species. Among the various Scanning electron microscope is the powerful tool phyla represented in the marine environment, the phylum in radular study. Research on functional morphology of Mollusca is the second largest phylum in the animal kingdom molluscan radula has focussed attention on the obvious food next to Arthropoda (Abbott, 1954). Gastropods evolved on preparing and food-gathering operation of teeth and their rocky marine bottoms but have radiated into a wide variety relationship. The scanning electron microscope permits the of other habitats. Fusinus nicobaricus comes under the family examination of radula with higher magnification without fasciolariidae and sub-family fusininae. They are carnivores, elaborate preliminary preparation and without squashing or feeding on worms and clams. fragmentation. A clear picture of three-dimensional Virtually every possible feeding mode is found in morphology can therefore be obtained, which enlightens gastropods and the morphology and physiology of the more mundane methods of observation. The radula has been digestive system vary widely (Hyman, 1967).The gastropoda frequently investigated because of its importance as a tool are remarkable for their feeding mechanisms and for the wide in supraspecific systematics to diagnose the species. The variety of food they subsist. The feeding habits and food shape of the radula teeth is directly related to the kind of preference do not form a distinctive part of a particular group. food, which the animals eat and the way in which it is Thus, the prosobranchia in particular, displays almost every manipulated. The length of the radula also appears to be conceivable food preference. related to the quantum of work, which has to be done in Another peculiar feature of mollusc is the presence feeding (Reid and Mak, 1999). In the present study an attempt of a chitinous radula. Purchon (1977) stated that the adaptive was made to elucidate the histological studies of digestive radiation of the gastropoda is principally based on system and anatomy of the radulae of Fusinus nicobaricus adaptations of the buccal mass and radula to meet the from the Gulf of Mannar region. problems faced in feeding in various ways on a wide variety MATERIALS AND METHODS of food substances. In most gastropods the radula is a highly Specimens of Fusinus nicobaricus used in the developed feeding organ that acts as a grater, rasp, brush present study were collected during low tides from the sea cutter, grasper, harpoon or conveyor. Total number of teeth in their natural habitat that is intertidal zone, from reefs by varies from 16 to thousands and is almost always arranged divers and from trawl nets used for crab fishing from Gulf *Corresponding author’s e-mail: [email protected] 2 INDIAN JOURNAL OF ANIMAL RESEARCH of Mannar coastal region. They were brought to the electron microscope specimen chamber and heating the laboratory and maintained under laboratory conditions for conductive metal (gold) to the point of vapourization. A small further observations. Preserved specimens were not used for part of the cloud of metallic vapour hits the surface of the anatomical study of digestive system as they lose their object and sticks to it so as to provide a thin metallic coating original colour due to preservation. Additionally, the organs over it. Continuous tiltation and rotation of the specimen may show considerable shrinkage. Freshly killed specimens ensures that the metallic vapour covers all sides of the were used for the study of digestive system. Measurements specimen. Then the specimens were mounted to SEM stub were made using ocular and stage micrometers. Camera and the observations were made with different magnifications lucida drawings were made with the help of a stereo-zoom for making the electron micrographs by using JEOC JSM microscope. 35CF scanning electron microscope (Annamalai University, Histological studies of the digestive system: For Chidambaram). histological studies, the tissue samples were taken from RESULTS AND DISCUSSION proboscis, oesophagus, stomach, hepatopancreas, intestine Histological studies of the digestive system of Fusinus and rectum. These different soft tissues were fixed in aqueous nicobaricus: The digestive system of Fusinus nicobaricus Bouins and Zenker’s solution. Sections of 6-8mthickness contains proboscis, oesophagus, stomach, hepatopancreas, were made from different organs and stained in delafield intestine, rectum and anus.The general organization of hemotoxylin with eosin as a counter stain. digestive system of Fusinus nicobaricus, follow the same SEM study of radula: For scanning electron microscope general pattern of neogastropod. The cellular organization study of radula, the anterior portion of the proboscis was of the various body parts of Fusinus nicobaricus, excised, the radula with adjoining tissues were removed from histologically proved the same functional significance as the proboscis and boiled with alkaline iodide solution until encountered in other Fasciolarids.The digestive system in the dissolution of all the muscle fibers attached to the radula. the Fasciolaria Fusinus nicobaricus begun with the The radula thus obtained was then dehydrated by immersing pleurembolic type of proboscis and the rachiglossate type them in increasing concentration of alcohol (50, 70, 90 and of radula (Fig 1-3) similar to that of Thais sp, Muricanthus 100%). Then the dehydrated radula was prepared with sp, Uro sucpinx sp (Kool,1993). coating for making it suitable for scanning electron Proboscis: The most conspicuous features of the digestive microscopical observation. system was the massive proboscis. In Fusinus nicobaricus Principally coating of the radula consists of placing the proboscis was a large, yellowish organ and of the specimen in a vacuum evaporator pumping the chamber pleurembolic type in which the basal part was invaginable down to a vacuum level equivalent to that in the scanning (Fig 1a). When the proboscis invaginated, it retracted the (a) (b ) (c) Fig 1: (a) Proboscis – Cross section through proboscis of Fusinus nicobaricus showing the histological organization of columnar ciliated cells, radula tooth and odontophore (4x). (b) Oesophagus – Cross section through the oesophagus of Fusinus nicobaricus showing the histological organization of ciliated columnar epithelium, lumen and basement membrane (4x). (c) Stomach – Cross section through the stomach of Fusinus nicobaricus showing the histological organization of ciliated columnar epithelium and connective tissue (4x). Vol. Issue , () distal part into a proboscis sheath. The mouth lied at the and muscle fibres were embedded in the stomach of Fusinus anterior end of the proboscis. The odontophore and the radula nicobaricus (Fig 1c). sac lied within the proboscis.The proboscis of Fusinus Intestine: The intestine was a tubular structure arised from nicobaricus was similar to the description of the proboscis the distal part of the stomach. The intestine had a wall of its of Thais species by Tagore (1989), Rapana rapiformis by own, till it enters the mantlle cavity. It ran forward adjacent Rajakumar (1995), Babylonia spirata by Thilaga (2005) and to the kidney. It was attached to the mantle as it nears the Chicoreus virgineus by Sharmila (2009). mantle cavity and was surrounded by connective tissue. The Oesophagus: The oesophagus which followed the buccal intestine was smooth leading out from stomach. mass was long in Fusinus nicobaricus. The oesophageal Histologically the intestine showed finger-like projections region was complicated and divided into anterior, mid and inside the intestinal wall lined by ciliated cells and glandular posterior oesophagus. A pair of salivary glands were cells