1. A large number of guanine plates are present on the inner surface of the choroid layer which is called tapetum lucidum. Alternation of Generations: Life Cycle of Angiosperms 6. The entire body is covered by an exoskeleton of placoid scales. It eats small pelagic schooling and bottom living bony fishes, including anchovies, codlet (Bregmacero-tidae), burrowing gobies (Tripauchenidae) and Bombay ducks (Harpadontidae) as well as shrimps and cuttle fish. The species is abundant in Indian and Pakistani waters. The optic chiasma is formed by the decussation of the nerve fibres of two optic nerves (Fig. The retinal layer consists of rods and cones. (b) The efferent branchial arteries which origi­nate from gills and convey the oxygenated blood to the different parts of the body (Fig. In addition to short longitudi­nal connectives connecting the four loops, these are further connected with each other by a network of longitudinal commissural vessels called the lateral hypobranchial chain. The pupil is a vertical slit and it cannot be dilated or con­tracted. It is bounded by upper and lower jaws, each is beset with one or two rows of sharply pointed and backwardly directed teeth (Fig. The birds have a spindle-shaped body to offer less air resistance during flight. The hypochordal lobe is flexible and the epichordal part is rigid. The pit organs occur on the lateral and dorsal sides of the head. A small outgrowth often called ‘blind sac’ is present at the junction of the cardiac and pyloric limbs. 6.18E). By this way of cleavage, a blastodisc is separated from a layer of periblast cells. In Shark 3 pair of internal ears are present. The afferent spiracular artery after originating from the middle of the hyoidean efferent, proceeds for­ward as the spiracular epibranchial artery and enters the cranial cavity. 6.13). A tubular caecal or rectal or digit form gland opens into the rectum. The posterior rectus muscle runs backwards and is attached with the posterior surface of the eye ball. This yolk stalk connects the intestine of the embryo with the yolk sac. A small opening called the neuropore is present on the mid-ventral surface of the cerebrum. This canal communicates to the exterior by minute pores. The subclavian vein also opens to each side of the ductus Cuvieri. The number of embryos present inside one uterus varies greatly in different species of Scoliodon. Both sexes mature between 1-2 years old and the males reach largest size at the age of about 5 years and females reach largest size at the age of 6 years. The auricle communi­cates with the ventricle through a slit-like auriculoventricular aperture guarded by two lipped valves. The utriculus together with the semicircular canals is responsible for the orientation and acce­leration, while the sacculus is meant for hea­ring. Each lateral cutaneous vein ultimately opens into the brachial vein. 6.12). 102 Algae and Microbiology : C 45+5 4 3 hrs. Q.5. After this stage, the cleavage plane is irregular. The cerebral hemisphere is relatively larger than that of other fishes. The trunk is more or less oval in transverse section. In addition to their trademark hoods, cobras have round pupils and smooth scales.Colors vary widely from species to species. 6.10). The abdominal pores are paired structures and situated on elevated papillae to communicate the coelom to the outside. The contractility of the myotomes thus causes the bending of the body. The third ventricle is extended forward about half the length of the cerebral hemispheres. The anterior cardinal sinus enters the ductus Cuvieri. The body is divisible into head, trunk and tail. In the head region, the muscles do not exhibit any sign of segmentation and have become specialised to control the movement of the jaws, pharynx and eyes. To study the structure, functional organization, adaptation and the economic importance of lower and higher chordates. At the anterior portion of each oviduct there is a dilated shell gland which has but little signifi­cance in Scoliodon. The basal plate as well as the dentine of the spine is the derivatives of the mesoderm. The fourth ventricle is large and extends dorsally into the cerebellum and is continuous behind with the cavity of the spinal cord. The sperm cells escape by vasa efferentia into the vas deferens which becomes extremely coiled in the anterior por­tion of the kidney. The nature of enamel is controversial. Throughout its length, the renal portal vein receives small parietal veins. The kidneys are extremely elongated structures extending from the root of the liver to the cloacal region. The internal ear is a complex structure. The phylum is "chordate" because the frogs are vertebrates, as opposed to invertebrates. Physiologically each nasal opening is divided by three muscular nasal valves into a median ex-current siphon and a lateral incurrent siphon. (b) A pair of small subcla­vian arteries arise from near the origin of the fourth epibranchial arteries. Aedes. Sharks can rouse fear and awe like no other creature in the sea. The typical Indian genus, Scoliodon is described below. The canal opens to the exterior by minute pores at intervals. From the anterior end of cerebral hemisphere arise two stout olfactory peducles, each termi­nates into a large bilobed olfactory lobe (Fig. Pronunciation of scoliodon with 3 audio pronunciations, 1 meaning and more for scoliodon. It is called the fibro dentine, because it is formed as the calcification of the fibrous material between the dentine and the enamel organ. It is present in the auditory capsule of the cranium. The pericardial artery gives off the com­mon epicoracoid artery which in turn divides into left and right epicoracoid arteries each joining one subclavian artery. Two great veins, the ductus Cuveiri, open into the sinus venosus, one on each late­ral side. 6.2D). The cleavage is restricted to a small germinal disc which floats on the top of the yolk mass (Fig. The enamel is derived from the ectodermal enamel organ. It has two rows of homodont or polyphyodont teeth, which are homologous to the placoid scales covering the body. 6.10). The blastocoel lies between the ectoderm (epiblast) and the inner hypoblast (mesendoderm). It has two rows of homodont or polyphyodont teeth, which are homologous to the placoid scalescovering the body. (i) The brachial nerves supplying the gills. There are ten pairs of cra­nial nerves in all the fishes. One of the branches unites with its fellow from the opposite side and other branch unites with the stapedial. (f) A pair of iliac arteries extend to the pelvic fin as femoral arteries. The brain lies in a bony cranium. The olfactory lobes lie close to the olfactory capsules. The iter (i.e., the communicating duct between the third and the fourth ventricles) is wider. The basipterygium is attached anteriorly to the pelvic girdle. The buccal cavity possesses no such glands that can be compared with the salivary glands of higher vertebrates. 2. Geographical Distribution 4. An oval depression between the two capsules is called the pari­etal fossa. What are the general characters of bryophytes? A pair of epigonial organs is pre­sent between the ovary and the rectal gland. Our mission is to provide an online platform to help students to share notes in Biology. The distribution of the appendicula in the placental cord varies in different regions. The inner mucous mem­brane of the pharynx is raised to form longi­tudinal folds. The lumen of the conus arteriosus is provided with two transverse rows of semi-lunar valves. The Wolffian duct in males, becomes the vas deferens which is connected with the vasa efferentia from the testis. Placoid scale has dual source of origin and develops partly from epidermis and partly from dermis. They con­tain sea-water and help in the expulsion of the sperms through the clasper groove. The median ventral fin is located in the mid-ventral line and just anterior to the caudal fin. Arteries from the first efferent branchial (hyoidean efferent) are: (c) The hyodean epibranchial which in turn receives a branch from dorsal aorta. Each egg gets a coating of albumen during its transit down the oviduct. Privacy Policy3. Enumerable pores on the dorsal and the ventral sides of the head lead into a long tube which terminates into radially arranged ampullary sacs (see Fig. Habit and Habitat of Scoliodon 3. Each eye is provided with movable upper and lower eyelids. The dorsal root bears a ganglionic swelling. The seminal vesicles open into the urinogenital sinus which in turn opens into the cloaca. The cloaca is a common cham­ber, into which anus, urinary and genital aper­tures open. When reproducing, the female Scolion laticuadus has a minimum of 8 to a maximum of 19 embryos when conceiving. Development. The cerebral hemi­spheres contain narrow lateral ventricle. The ventral aorta is situated on the ventral surface of the pharynx and extends up to the posterior bor­der or the hyoid arch. Scoliodon possesses well-developed exoskeletal and endo-skeletal structures. The optic chiasma lies in front of the infundibulum. 6.8B shows the organisation of gill-pouch of Brachaelurus, a related genus of Scoliodon. Scoliodon has an elongated, spindle-shaped body tapered at the ends, making it a very fast swimmer. The centra are reinforced by calcified fibrocartilage which forms four wedges and traverse the body of the centrum as a cross. The medulla controls res­piration. The hepatic por­tal vein receives the lienogastric vein and anterior and posterior gastric veins. The olfactory sense organs are greatly developed in Scoliodon. The roof of the medulla oblongata is non-nervous and bears the posterior choroid plexus. b) Bilobed. The brain lies in a cartilagenous cranium. The pancreatic juice is poured into the intestine by pancreatic duct situated opposite to the aperture of the bile duct. Biology, Phylum Chordata, Fishes, Dogfishes, Scoliodon. The heart is situated on the ventral side of the body between two series of gill-pouches. The endoskeleton embraces the axial and appen­dicular skeleton. The controlling factors governing such con­traction of muscles are not fully known. (c) The middle region of the skull is composed of orbit. Each appendicularium is made up of a central core of loose connective tissue surrounded by several layers of epithe­lial cells. The siphons are not connected with the genital system. Just before its entry into the cranial cavity it sends a great oph­thalmic artery to the eye ball. With the expansion of the blastocoel the blastodisc becomes multi- layered. The spinal nerves arise from the spinal cord. The eighth cranial nerve is called auditory which gives the vestibular and saccular branches to the inter­nal ear. The conus arteriosus is a stout median muscular tube arising from the ventricle. These nerves supply branches to the pharynx, pharyngeal muscles and the mucous membrane surroun­ding the first gill-slit. They are called gill or branchial slits. Immediately after the entry to the cranium it joins with a branch from the internal carotid to form the cerebral artery. The yolk sac contains yolk material which pro­vides nutrition for the developing embryo. How to say scoliodon in English? There are two blind sac-like olfactory organs situated in front of the mouth. Principles of Taxonomy and Phylogeny 9. 6.18B). (b) The appendicular skeleton consisting of the pectoral and pelvic girdles and the skeleton of the fins. The dorsal surface of the cerebellum produces many irregular convolutions. This page was last edited on 5 February 2020, at 15:28. Files are available under licenses specified on their description page. Caudal fin is supported by the extensions of the neural and haemal spines. The cerebellurp is divided into three lobes by two well-marked transverse furrows. Welcome to BiologyDiscussion! The spine is composed of dentine coated externally with enamel. The alimentary canal starts with the mouth and ter­minates in the anus. The peri­cardial coelom houses the heart. The first pair of the visceral arches give rise to the jaws, the second pair to the hyoid arch and the rest of them support the gills. manoj kumar adaptations ADHATODA VASICA agarose agarose gel electrophoresis. The blastopore is separated into two (embry­onic and vitelline blastopores) by the fusion of the edges of the yolk sac. The stratum laxum is the outer layer and lacks fibres. The ventricles of the brain are moderately developed (Fig. 3. The neural canal is enclosed by neural arch which contains a short blunt neural spine. The hind- brain controls swimming movements. The fins under this category include two dorsals, one caudal and one ventral fin. Arterial System 14. The medulla oblongata is triangular and the anterior end gives a pair of hollow corpora restiformia with trace of con­volutions in adults. The teeth are similar in both the jaws. Skeletal Structures 8. Answer and Explanation: 75. 6.2E). Accessed at https://animaldiversity.org. Each olfactory sac is … All structured data from the file and property namespaces is available under the Creative Commons CC0 License; all unstructured text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. 0. The haemal arch gives a haemal spine to support the ventral lobe of the caudal fin. It is covered by cartilaginous labyrinth. To cite this page: Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. […] The endoderm is differentiated by cellular proliferation from the underside of the hypoblast. The teeth of Scliodon are modified scales. There are several genera of dogfishes available in the different parts of the earth. 6.18A). The major digestive gland is the liver which is a massive yellowish gland and con­sists of two lobes. The Scoliodon genus of sharks has been found mainly in the Indo-West Pacific oceans from the west coasts of Africa to South of Japan. TOS4. (d) defensive adaptation of skin against ultraviolet radiations. 6.14). Content Guidelines 2. (With Methods)| Industrial Microbiology, How is Cheese Made Step by Step: Principles, Production and Process, Enzyme Production and Purification: Extraction & Separation Methods | Industrial Microbiology, Fermentation of Olives: Process, Control, Problems, Abnormalities and Developments, The best answers are voted up and rise to the top. The oesophagus dilates posteriorly to form a large stomach. The gill- pouches are separated by inter-branchial sep­tum which projects beyond the branchial lamellae (Fig. The dorsal horns are united to form a single broad region, as a result the grey matter assumes a shape of an inverted ‘T’. The eye is kept in its position in the orbit by six extrinsic eye muscles. The distal ends of the somactidia bear double series of the ceratotrichia or horny fin-rays. Digestive System of Scoliodon at July 06, 2014. Each testis is attached to the dorsal body wall by peritoneal membrane called mesorchium and posteriorly attached by ordinary tissue with the caecal gland. The shape, size and colour of the ovaries vary greatly according to the age of the individual. The conus arteriosus is continued forward as the ventral aorta. The ventri­cle has a very thick muscular wall, the inner surface gives many muscular strands, thus giving it a spongy texture (Fig. Mammalia. It excretes urine from the cloaca in the form of urea. OR . Such a type of the heart is designated as the venous or branchial heart, because only the deoxygena­ted blood circulates through its different parts. The arterial system of Scoliodon is divided into two distinct categories of arteries. (iii) A dorsolateral artery to the dorsal muscula­ture. Select the amphibious adaptation of frog. The third eyelid or nictitating membrane can cover the whole eye in emer­gency. Short notes/sketch and label (4 marks each). The ampullae get the names according to their location. 6.6) and opens to the exterior through a pair of abdominal pores. Somactidia are absent in the caudal fin. Two hepatic sinuses enter the sinus venosus posteriorly. Type study: Scoliodon - external characters, … 6.3E). Similarly a postorbital process emerges from the side forward along the upper margin of the orbit. The venous system is extremely compli­cated and is described under the following heads: The blood from the anterior region of the body is returned to the heart by paired jugular and anterior cardinal sinuses. The anterior dorsal is larger and situ­ated at about the middle of the body. The middle and external ears are absent. The internal ear or the mem­branous labyrinth of Scoliodon is a closed ectodermal sac. The pyloric valve, at the end of the pylorus, guards the entrance of it into a thick-walled small chamber called the bursa entiana. Reproductive strategy of spadenose shark, Scoliodon laticaudus Muller and Henle, 1839 along north‐eastern Arabian Sea. Mouth is bounded by upper and lower jaws each bearing 1 or 2 rows of sharply, pointed and backwardly directed teeth. Generally, there are two types of flight adaptations in birds: Morphological Adaptations. Where are the pollen grains formed in the flower? (c) A large coeliacomesenteric artery ari­ses just behind the origin of fourth epibranchial artery. On either side of the pharynx there lie the inter­nal openings of the spiracles and five branchial clefts. The class Elasmobranchii embraces a large variety of cartilaginous fishes. They have an excellent sense of smell and night vision. The neuromast organs help to orient the body in relation to currents and waves and are designated as rheoreceptors. The dorsal one is named as Wolffian duct and the ventral one is the Mullerian duct. Above this foramen there is a median ridge, called the occipital crest. The trunk and tail are laterally compressed, while the head region is dorsoventrally compressed. In this article we will discuss about Scoliodon:- 1. On each side of the cloaca lies the abdominal pores. 2. The margin between the roof of the cra­nium and the orbit is marked by the supra­orbital ridge. Clasper is rod-like in appearance having a dorsal groove leading to a siphon at its base. The membranous labyrinth of Scoliodon performs three functions: (a) It helps in orientation in relation to gravity, (b) It accelerates in changing the direction during swimming and. pp. Alimentary canal of Scoliodon. Each half of this arch divides into two parts, the upper part is called palatopterygoquadrate which forms the upper jaw and the lower part is known as Meckel’s cartilage which forms the lower jaw. The entrance of the oesophagus into the stomach is provided with a crescentic fold which serves as the valve. The muscle fibres run parallel to the length of the body in each myotome. The ventral parietal gives renal branches to the kidneys. The lateral line, also called lateral line system (LLS) or lateral line organ (LLO), is a system of sense organs found in aquatic vertebrates, used to detect movement, vibration, and pressure gradients in the surrounding water. Important body features of scoliodon are given below: 1. The sixth cranial nerve is the abducens which supplies the posterior rectus muscle of the eye ball. Each inferior jugular sinus is formed by the union of the sub-mental sinus from the lower jaw, the hyoidean sinus and the ventral nutri­ents from the gills. The sinus venosus opens into the auricle by sinuauricular aperture which is guarded by a pair of valves. Then the water rushes in to fill the greatly expanded buccal cavity. A trunk ver­tebra has a centrum that encloses the notochord. Name the types of nitrogenous bases present in the RNA. (d) A lienogastric artery originates posterior to the coeliacomesenteric artery and gives off. The Mullerian duct becomes the oviduct in females. What is its function? The lens is kept in position by suspensory lig­ament which extends from the margins of the lens to the ciliary processes. The teeth are very sharp and are obliquely placed (see Fig. 4. The superior rectus mus­cle runs outwards and upwards and is inserted on the dorsal side of the eye ball. The spinal cord in Scoliodon shows definite advancement towards the plan of higher vertebrates, The spinal cord is pro­vided with pia mater only. Genus Scoliodon. The tail is also oval in cross-section (Fig. What is a mushroom shaped gland? This video is unavailable. Name the ten Cranial Nerves found in Scoliodon In FAO species catalogue, Sharks of the World, Compagno (1984) used Rhizoprionodon (Carcharias) acutus instead of S. sorrakowah as law of priority. The two dorsal fins and the ventral fin are pro­vided with series of cartilaginous rod-like structures, called the pterygiophores or somactidia. The mucous membrane of the pharyngeal wall contains numerous der­mal denticles. The pectoral fins also help to maintain stability in the vertical plane. Scoliodon is a genus of requiem sharks in the family Carcharhinidae. The pos­terior dorsal is comparatively small and occu­pies a median position between the first dorsal and the tip of tail. The mesoderm produces a prechordal plate. Two corpora restiformia are connec­ted by the transverse nerve band. Distally the groove ter­minates into a sharp style which is enclosed by two sheathing plates. Scoliodon is an ureotelic animal. Definition of Scoliodon in the Definitions.net dictionary. Felis. During respiration the floor of the buccal cavity is lowered and the mouth is opened. In amphibians, reptiles and mammals the terminal nerve is intimately associated with the vomeronasal organ (Jacobson’s organ). A common tropical shark of continental and insular shelves close, frequently in rocky areas. Another nerve called ophthalmicus profundus becomes secondarily associated with the trigeminal to supply nerves to the eye ball and the dorsal surface of the snout (Fig. Nervous System 16. The last branchial arch is gill-less. To avoid confusion which would result if the long established nomenclature and symbols of other cra­nial nerves were altered, this newly reported cranial nerve was named terminal nerve or cranial nerve ‘0’. From the gills the blood is collected by efferent branchial arteries (Fig. (i) Holobranch or complete gill when a branchial arch bears two sets of gill lamellae and. The optic lobes are situated behind the diencephalon. The genus Scoliodon is distinguished from other dogfishes by having an elongated snout, depressed head and a compressed body. The radials at the distal ends contain small carti­lages bearing the ceratotrichia. The lateral line sense organs lie inside the lateral line canal. The superior orbital artery gives a large buccal artery which runs as the maxil­lonasal artery. The sclera is cartilaginous. The space between the membranous labyrinth and the auditory capsule is filled with the perilymph. 6.2C) to catch the slip­pery prey. The appendicularia help in the absorption of nutrients secreted from the uter­ine wall of the mother. The lobes are united ante­riorly. Posteriorly the vas deferens becomes very much dilated to form the semi­nal vesicle. The head region gets the blood supply from the first efferent branchial artery and partly from the proximal end of the dorsal aorta. Two kinds of corpuscles are encoun­tered; the RBC (or erythrocytes) and the WBC (or leucocytes). The middle and external ears are absent. A faint lateral line is present. The egg, particularly in oviparous forms, is enclosed by horny shell which is oblong in shape. A new cra­nial nerve was first recorded in 1894 which con­nects the anterior end of cerebral hemispheres. The sec­ond pair of cranial nerves are the optic nerves which, after the origin from the optic thalami, form the optic chiasma and supply the eyes. It is claimed that during copulation the claspers are introduced into the cloacal aperture of the female for the transmission of spermatozoa. During for­ward progression the contraction of the myotomes occurs along the anteroposterior direction in such a way that the waves of cur­vature pass down each side of the body alter­nately from the head to the tail. (a) The afferent branchial arteries arising from the ventral aorta which bring the deoxy­genated blood to gills for oxygenation and. There are numerous myotomes which are separated from one another by partitions made up of tough connective tissue called the myocommata. This system of veins returns blood from the head region and consist of a pair of internal jugular veins. The branchial slits lead into the gill-pouches which in turn open into the pharyngeal cavity. The sec­ond arch is called hyoid arch which consists of three parts—a ventral basihyal, a lateral ceratohyal and a dorsal hyomandibular. After reading this article you will learn about: 1. The lobi inferiors are the centres for gustation and smell. Besides the eye muscles there are an optic nerve and a carti­laginous optic pedicle (Figs. Presence of two chambered heart . A long and slen­der tube, the pineal organ or epiphysis cerebri projects from the roof of the diencephalon up to the membrane covering the anterior frontanella. With the formation of placenta, the yolk stalk is lost and the blood vessels of the yolk stalk form the placental cord. An outer thick dura mater, and inner thinner piamater protects the brain so there are two meninges (membranes) 3. The first eight arteries form a series of four com­plete loops around the first four gill-slits and the ninth efferent branchial artery collects blood from the demi branch of the fifth gill- pouch and from where blood is poured into the fourth loop. Such centra are generally called asterospondylous types. The sacci vasculosi is believed to be a centre for reception of the pressure of cerebrospinal fluid and at the same time they produce cerebrospinal fluid. 6.12C). The Schneiderian folds are composed of olfactory sense cells and supporting cells. The posterior vertebrae contain haemal arch which is present on the ventral side of the centrum. Email This BlogThis! Circulatory System of Scoliodon: The circulatory system consists of: (a) The circulatory fluid, called blood, (b) The heart, (c) The arteries and (d) The veins. The mouth leads into a spacious buccal cavity which is lined with mucous membrane. The body of the embryo is constricted from the blastodisc and the tail fold is differentiated and extended backward. There are nine pairs of efferent branchial arteries and these are equally distributed on each side. The rest of the visceral arches are known as branchial arches which support the pharynx and the gills. The sacculus gives a posterior outgrowth called the lagena. The posterior region of the blastodisc grows faster than the other regions and is raised from the yolk mass to become a double- layered germ ring. d) Four lobed. The vertebral column is composed of a chain of cartilaginous verte­brae. The head is dorsoventrally flattened and terminates anteriorly into a dorsoventrally compressed snout. Share to Twitter Share to Facebook Share to ... 2012 4TH LARVAL AND PUPAL STAGES. Male Scoliodon species mature at a length of 33cm while female Scoli… Two types of cells are encountered in the ampullae—glandular cells and sensory cells. When the yolk is fully exhausted the yolk sac becomes folded and becomes anchored with the uterine wall of the mother as the yolk-sac placenta. The kidney tubules have the peculiar property of reabsorbing urea. The erythrocytes are oval bod­ies containing a nucleus. Above the centrum there is a neural canal through which the spinal cord passes down. The epider­mis is composed of epithelial cells inter­mixed with numerous unicellular mucous glands. The testes are paired elongated organs (Fig. The two olfactory capsules are separated by internasal septum. The excretory organ consists of a pair of elongated kidneys. 6.18D). Scoliodon is possibly colour-blind (Fig. This germ ring is raised pos­teriorly to form a blastopore (Fig. A hollow infundibulum is given off from the floor of the diencephalon. Presence of hair. 6.8A). 6.2B) and bears a heterocercal type of caudal fin, i.e., the posterior end of the vertebral col­umn is bent upwards and lies in the dorsal or epichordal lobe. 61-76. The sinus venosus is a thin-walled tubular chamber. The periblast cells form a syncitial layer over the yolk mass. To keep the valves in position the free ends of the valves are attached to the ventricular wall by fine tendinous threads, called chordae tendinae. In the phylogenetic history of the fishes, the fins were primarily employed to raise the body off the bottom, but these become secondarily used in swimming by producing undulatory movements. This system con­sists of a dorsal, a ventral and two paired lat­eral cutaneous veins. This condi­tion is not observed in Scoliodon but is observed in case of oviparous sharks. The visceral skeleton consists of seven half-hooped cartilaginous structures that encir­cle the buccal cavity and the pharynx. The dorsal fins are triangular in outline. The entire surface of the body is covered by oblique rows of placoid scales or odontoids (Fig. The first visceral arch is the mandibular arch. The most important adaptation of the Hispaniolan solenodon is its ability to secrete venomous saliva. The anterior rectus muscle runs out­wards and downwards and is attached to the ventral surface of the eye ball. A typical pla­coid scale has a basal plate made up of calcified tissue which remains embedded in the skin and a backwardly directed spine projecting out of skin. The dorsal fin is well-developed and helps to restore stability and helps in the restoration of equilibrium, if there is any devi­ation along the vertical axis of the body.
2020 adaptation of scoliodon