Anatomy of soft body of Pugilina cochlidium (Linnaeus, 1758) and P. erecta (Vermeij & Raben, 2009) (Neogastropoda: Melongenidae) from Thondi Coast-Palk Bay in Tamil Nadu, India

The species of Pugilina cochlidium (Linnaeus, 1758) and P. erecta (Vermeij & Raben, 2009) has been studied in the present study. The female can be differentiated from the male by the absence of the cephalic penis and a complicated genital aparatus visible through the mantle skirt in both the sexes. In other aspects of the external features of female are quite to males. In both species the digestive system was similar with few differences in structure between each other. It consists of buccal mass, proboscis, salivary glands, accessory salivary glands, oesophagus, stomach, intestine, rectum and anus. The nervous system in both P. cochlidium and P. erecta is constituted by six ganglia which forms the circumoesophgeal ganglionic ring. Among the neogastropods there is a similarity in the organization of the reproductive systems. The female reproductive system is more complicated than that of male. The sexes are separated in these two species. The gross morphology of the reproductive system of P. cochlidium and P. erecta was almost similar. The present study aims to describe the digestive system, nervous system and reproductive system of two gastropods species P. cochlidium and P. erecta.


Introduction
The phylogenetic analyses of the higher classification of neogastropoda have been studied based on the anatomical characters of the digestive system especially on the foregut (Andrews, 1991;Ball et al., 1997;Benny et al., 1996;Brown, 1969;Carriker et al., 1963Carriker et al., , 1967Carriker and Williams, 1978;Carriker, 1981;Chétatl and Fournié, 1969;Greene and Köhn, 1989;Harasewych, 1984;Hou et al., 1990;Kantor and Taylor, 2002;Kantor, 1996;Kantor and Harasewych, 1994;Lus, 1981;Marcus and Marcus, 1962a, b;McLean, 1971;Merdsoy and Farley, 1973;Nylen et al., 1969;Person et al., 1967;Taylor et al., 1993). It is generally accepted the evolution of the order, as well as that of other caenogastropods, was determined mainly by the changes in the anatomy of the digestive system (Kohn, 1983) while similarity of shells is often the result of convergence. Ponder (1973) studied the anatomy of the digestive system of neogastropoda. Buccinoidea is one of the generally accepted monophyletic groups in neogastropods. Six families are usually included into this superfamily: buccinidae, fasciolariidae, nassariidae, melongenidae, columbellidae and colubrariidae. Carriker (1943) has studied the structure and function of the proboscis in the common oyster drills Urosalpinx cinerea (Say, 1822). Ward (1965) has described the digestive tract and its relation to feeding habits in the stenoglossan prosobranch Coralliophila erosa (Röding, 1798). Houston (1976) has studied the structure and function of neogastropod reproductive systems with special reference to Columbella fuscata G.B. Sowerby, 1832. The anatomy of the various proboscis types has been investigated by Greene and Kohn (1989) and Medinskaya (1992). Medinskaya (1992) has investigated the anatomy of the proboscis walls in neogastropods and its connection with diets and feeding mechanism. Medinskaya (1992) has investigated the anatomy of the proboscis walls in Neogastropods and its connection with diets and feeding mechanism. Taylor et al. (1993) has studied the foregut anatomy, feeding mechanisms, relationships and classification of the Conoidae. Ball et al. (1997) has studied the ontogeny of the pleurembolic proboscis in Nucella lapillus. Numerous studies have been made on various aspects of the digestive system by Fretter and Graham (1962), Wu (1965a), Bhanu et al. (1981), Tagore (1989), Guohua et al. (1990), Andrews (1991), Jaramillo (1991) and Middlefart (1992a, b). Smith (1967Smith ( , 1980Smith ( , 1981 studied the neogastropod stomach, with notes on the digestive diverticula and intestine. Ponder (1968Ponder ( , 1970 studied the anatomical notes on two species of the colubrariidae. Medinskaya (1993Medinskaya ( , 1999 studied the anatomy of the stomach of some neogastropoda from the offshore zone of the Japan sea. Taylor (1978) and Taylor et al. (1980Taylor et al. ( , 1993 studied the foregut anatomy, feeding mechanisms, relationships and classification of Conoidea (Gastropoda). Tan and Phuah (1999) observed the diet and feeding habits of P. cochlidium (Linnaeus, 1758) (Neogastropoda: Melongenidae) in Singapore. Kantor and Tursch (2001) have been observed the feeding of Oliva genus. Kantor and Taylor (2002) studied the foregut anatomy and relationships of raphitomine gastropods. In neogastropod there is a similarity in the organization of the reproductive systems. The works carried out on the reproductive system are the following: Fretter (1941), Fretter and Graham (1962), Purchon (1968), Stephen and Blaber (1970), Houston (1971), Bhanu et al. (1981Bhanu et al. ( , 1982, Hawkins and Hutchinson (1988), Gallardo and Garrido (1989), Hou et al. (1990), Cantillanez et al. (2011), Cantillanez andAvendaño (2013) The present study aims to describe the digestive system, nervous system and reproductive system of two species P. cochlidium and P. erecta (Vermeij & Raben, 2009) that are a very important fisheries resources in local fisheries in Thondi Coast-Palk Bay in Tamil Nadu, India (De los Ríos et al., 2020).

Material and Methods
Collected specimens were obtained from Thondi Coast-Palk Bay in Tamil Nadu, India (9°44' N; 79°19' E) in January 2009. For anatomical studies, the soft body, inside the shell was obtained by cracking open the shell. The animal was kept for relaxation in 75% magnesium chloride. Dissections were made in seawater in a dissecting dish under a stereo zoom binocular microscope. The reproductive system was studied mostly in fresh animals as the genital ducts and genital complex are more readily visible. Measurements were made with ocular and stage micrometers and the drawings were made obtained at laboratory. Only preserved animal were used to study the diminute nerves stood out prominently after fixation under direct illumination. The mean size of P. cocchlidium specimens were 98.71 mm and 114.29 mm for male and female respectively, whereas the for P. erecta were 94.28 mm and 106.70 mm for male and female respectively, 30 specimens for each sex for each species (60 specimens for species) were studied.

Digestive system
The present study in both species the digestive system was similar with few differences in structure between each other. It consists of buccal mass, proboscis, salivary glands, stomach, intestine, rectum and anus. The digestive system of P. cochlidium and P. erecta is shown in (Figure 1). The proboscis in the present study, these two species showed the most conspicuous feature of the digestive system in the massive proboscis of pleuroembolic type, which is oval with two folded lips ( Figure 1). In both the species the oesophagal region is extremely long and completed ( Figure 1). The salivary gland in both species the salivary gland is a white mass, which surrounds the organ of oesophagus. In both the species the salivary glands are bilobed in structure. Each lobe is of the compound acinous type (Figure 1).
The stomach for both the species P. cochlidium and P. erecta the stomach is almost similar in structure. It is pale brown in colour. In two species the length and width of the stomach was measured about 53 to 60 mm in length in P. cochlidium and 75 mm to 80 mm in P. erecta. Internally the stomach is a simple sac with two folds. The stomach is very small, tubular, simple and U-shaped. The oesophagus is broad, opening ventrally into the posterior part of the stomach. A posterior mixing area is absent. The posterior oesophagus is lined with well-developed longitudinal folds. The folds on the dorsal side of the oesophagus are continuous with longitudinal folds on the outer stomach wall. The gastric chamber is subdivided into dorsal and ventral channels by a distinct and tall longitudinal fold on the inner stomach wall. The ventral channel is represented by the oesophageal groove, occupying a mid-ventral position which is continuous with the rather deep intestinal groove that is lined with tall, longitudinal, but narrow folds. The dorsal channel of the gastric chamber is lined with oblique, longitudinal folds that are much larger and more raised on the outer stomach wall (Figure 1).
The digestive gland for both species P. cochlidium and P. erecta the digestive gland is a brown coloured mass which surrounds the stomach all its length except its dorsal surface. In the two species it coils in a counter clockwise direction together with the stomach and the gonad. The duct of the digestive gland is of dichotomous branching type and opens into the stomach by way of the two apertures ( Figure 1). The intestine for two species, P. cochlidium and P. erecta the intestine leaves the stomach at the end of the style sac region and the colour of the intestine is pale brown. It leads posterior to the oesophagus and ventrally to the heart and dorsoventrally compressed rectum. The intestinal wall is smooth bearing the major and minor typhlosoles leading out from the stomach. These are prominent features in the proximal portion of the intestine only and thereafter they gradually disappear (Figure 1). The rectum begins where the intestine is dorsoventrally flattened in both species P. cochlidium and P. erecta. The wall of the rectum is longitudinally folded. The anus opens into the right corner of the mantle cavity and terminates in a papilla like projection. The wall of the anus is distinctly folded into ridges and grooves. A dark brown coloured rectal gland is present near the anus (Figure 1).

Nervous system
The nervous system in both P. cochlidium and P. erecta is constituted by six ganglia which forms a ring the circumoesophageal ganglionic ring. The central nervous system of P. cochlidium and P. erecta consists of an oesophageal nerve ring, a visceral ganglion and two pleurovisceral connectives. The oesophageal nerve ring is formed by the fusion of several ganglia, including a pair of cerebral ganglia, pleural ganglia, pedal ganglia, buccal ganglia and a supra oesophageal ganglia. These ganglions are connected by commissures and connectives. However, the other ganglionic inner nerves were not able to be traced ( Figure 2).

Reproductive system
Among the neogastropods there is a similarity in the organization of the reproductive systems. The reproductive system of various members of family melongenidae has been the subjects of several studies by virtue of their diverse modes of reproduction. The female reproductive system is more complicated than that of male. The sexes are separated in these two species in the gross morphology of the reproductive system of P. cochlidium and P. erecta. (Figure 3).

Male reproductive system
The male reproductive system consists of the following parts: Testis, vesicular seminalis, vas deferens, prostate gland and penis. The male reproductive system of P. cochlidium and P. erecta (Figure 3). Testis (Figure 3) in these two  species, testis lies on the ventral surface of the visceral mass, where its tubules form a compact mass and do not ramify through the digestive gland. In fully matured condition, the colour of the testis is brick red in P. cochlidium and P. erecta. During the breeding season the testis occupies a greater part of the visceral mass. The testis is made up of numerous follicles, and small duct lets, which join to form a genital duct called vas deferens. The vas deferens is thrown into numerous convolusions and coils, which serve as vesicular seminalis. The noticeable differences between two species were that the testis appears to be small and shorter in P. cochlidium and in P. erecta it appears large and elongate. In both species, the vesicular seminalis is formed by the union of several duct lets from the globules of testis, which serves as to store the sperms during breeding season. For this purpose, it is thrown into numerous convolutions. When the sperm is packed into the vesicular seminalis, which is dull brick red in colour.
The vas deferens is situated from the testies, on the columellar side of the visceral mass in both species P. cochlidium and P. erecta the coiled vas deferens which passes anteriorly in a superficial position leads to the gut and the pericardium of the right posterior corner of the mantle cavity and it opens into the prostate gland. At this point the vas deferens lies embedded in the penis, which is situated just posterior to the right cephalic tentacles (Figure 3). The prostate gland commences at the posterior end of the pallial cavity in both species P. cochlidium and P. erecta receives in the vas deferens. Size of the prostate gland depends on the reproductive stage of the animal and it is well developed in matured animal in its breeding season (Figure 3). The vas deferens opens at the posterior end of the prostate gland which runs through it as a slit like lumen and the width of the prostate gland is uniform throughout the length until the region where it joins the vas deferens. It is well known that the prostate gland provides a liquid medium for the spermatozoa so that it could be transferred from male to female (Figure 3). In the present study, the penis is noted to be slightly flattened dorso ventrally and its duct is not centrally placed but lies towards the outer edge. In two species P. cochlidium and P. erecta it has a strong broad base with round coiled proximal end. The pallial vas deferens which enters the penis and its base runs through the penis towards its tip on the outer edge. The male reproductive system of P. cochlidium differs from that P. erecta in the following aspects. In P. cochlidium the length of the vas deferens which starts from the vesicular seminalis is slightly longer than that of P. erecta. The size and shape of the prostate gland is narrow and elongated in P. cochlidium whereas in P.erecta it is broad and short. The penis is more dorsoventrally flattened in P. erecta than in P. cochlidium (Figure 3).

Female reproductive system
In two species P. cochlidium and P. erecta the ovary lies in the upper part of the visceral coil, intermingling with the digestive gland. In a fully matured animal the ovary occupies 1/3 of the visceral coil. The structure, position and colour of the ovary are similar in P. cochlidium and P. erecta (Figure 3). In both species the oviducts spreads over the surface of the digestive gland in the visceral mass and from it, a thin walled oviduct leads forwards and ventrally on the right side of the viscera. The junction of oviduct with the albumen gland is characterized with the presence of another duct called the gonopericardial duct. The gonopericardial duct opens into the wall of the pericardium and near the opening, it is thick and muscular. The oviduct in two species joins with the albumen gland on its ventral aspects (Figure 3). In two species albumen glands, P. cochlidium and P. erecta the first and posterior most part of the pallial oviduct has an albumen gland into which the visceral oviduct opens. The albumen gland is an inverted 'U' shaped loop like structure with the two arms close to each other. It is pale yellow in colour. The oviduct opens into the first distal limp of the capsular gland and its opening is guarded by sphincter muscles which may regulate the passage effects. The albumen gland opens into the posterior ventral wall of the capsule gland on the right side of the ventral channel (Figure 3). In between the intestine gland a thick blackish brown colour strip like structure is present which is called ingesting gland. This gland communicates with the ventral canal. In P. erecta, this gland occupies more area than in P. cochlidium. In P. erecta, the dorsal part of this gland is more elevated, and its base is narrow, whereas in P. cochlidium there is a broad base and not that much elongated dorsal part (Figure 3). In two species the capsular gland leads forward on the right side of the mantle cavity and on dissection it can be seen as an opaque white or yellowish mass which is divided into right and left glandular lobes. These lobes are joined dorsally and ventrally by a comparatively thin and narrow wall forming a dorsal and ventral suture. Throughout the length of the capsular gland a channel called ventral channel runs on the ventral aspects of the ventral channel gland which is a closed duct. Posteriorly the ventral channels lead to the duct of the ingesting gland and receptaculum seminalis and anteriorly to the bursa copulatrix (Figure 3). In general, organization of the male and female reproductive system of P. cochlidium and P. erecta follows the same general neogastropod pattern. The bursa copulatrix is in the proximal part of the pallial oviduct situated ventrally. It is a pouch like structure which receives the sperm along with prostatic secretion during copulation. It is connected with the ventral channel on its posterior end.

Digestive organs
The mouth is over hung by the outer muscular rim of the peristomal rim, which is very similar to U. cinerea (Carriker, 1943). In P. cochlidium the proboscis measures about 8 to 10 cm in length and 0.2 to 0.5 cm in width and in P. erecta it was measured about 7 to 10 cm in length and 0 .3 to 0 .5 mm in width. In both forms the colour of the proboscis is white. The odontophore and radular sac lies within the proboscis. The odonotophore is composed of the retractor muscles, cartilaginous rod and the radular sac. The proboscis in P. cochlidium and P. erecta are similar to the description of the proboscis and this similar observation has been made by Tagore (1989) in Thais species and Thais haemastoma (Linnaeus, 1767) by Roller et al. (1984).
It is most conveniently divided into 3 parts, the anterior, mid and posterior oesophagus (Graham, 1941(Graham, , 1949. The anterior oesophagus begins above the opening of the radular sac. Its dorsal folds are the continuations of the prominent dorsal folds of the wall of the buccal cavity. The mid oesophagus can be subdivided into two portions on the basis of structural differences in the organ of nerve ring portion and the convoluted portion. Posterior and mid oesophagus becomes extremely narrow and slightly turned to the left side of the median axis (Figure 1). The posterior oesophagus is slender and long. The junction where the mid oesophagus joins with the posterior oesophagus is marked by a constriction along with the reduction in diameter of posterior oesophagus. These glands of paired salivary gland and accessory salivary gland are associated with the oesophagus, which opens into the mid oesophagus.
The position and shape of the lobes are closely related to the Muricid gastropod Druparicina (Wu, 1965a(Wu, , b, 1973. The ducts of salivary glands are dichotomously branched and all the branches united to form a single tube. The stomach was similar with descriptions of Thais sp. by Tagore (1989), in C. ramosus by Middlefart (1992a, b) and Stella (1995) in Chicoreus species and Ravichandran (2012) in Ch. ponderosus. The openings of the ducts of the digestive glands are large and oval. The anterior opening is located just anterior and ventral to the transverse fold, while the posterior one lies at the entrance of the oesophagus into the stomach. Duct pouches are not prominent and the typhlosoles are poorly defined. Tan and Phuah (1999) examined the feeding of the species of P. cochlidium in Singapore. The observations of digestive organs, are similar with descriptions of Thais sp. by Tagore (1989), in C. ramosus (Linnaeus, 1758) by Middlefart (1992a, b) and Stella (1995) in Chicoreus species and Ravichandran (2012) in C. ponderosus, P. tupiniquim (Abbate and Simone, 2015), Thaisella guatemalteca (Simone, 2017), and Tudicla spirillus (Linnaeus, 1767) (Harasewych, 2018).
The male and female reproductive system of two species agree well with the description given by Fretter (1941) for N. lapillus, Tagore (1989) for Thais sp. and Stella (1995) for Chicoreus sp and Ravichandran (2012) in C. ponderosus P. tupiniquim (Abbate and Simone, 2015), T. guatemalteca (Simone, 2017), and Tudicla spirillus (Linnaeus, 1767) (Harasewych, 2018). In male, the prostate gland is a closed one which is slightly broader in diameter in P. cochlidium and in P. erecta. In these two species it is basically organized on the same plan. In female the capsular gland is obvious because of the similar mode of reproduction and production of attached egg capsule.
In summary, the exposed results of soft body anatomy of P. cochlidium and P. erecta is similar to other gastropods species, and these results would be important for other basic and applied studies about both species that are an important fisheries resource.