Long, laterally compressed spindle shaped body tapering at both ends. 30 to 60 cm in length.
Body surface is rough due to backwardly directed spines of placoid scales embedded in the dermis.
Divided into head, trunk and tail. But there are no distinct boundaries between these regions.
Head is strongly compressed dorso-ventrally and is produced in front into a wedge shaped snout or rostrum.
Trunk is almost elliptical in transverse section. Gradually tapers into the tail.
Tail is laterally compressed and bent upwards at a small angle and has a caudal fin — heterocercal fin.
Fins — Flattened extensions of the skin supported by cartilaginous rods and horny fin rays.
Median Fins: Unpaired fins, both dorsal fins. Ventral/Anal Fin and a Caudal Fin.
Lateral Fins: Paired pectoral and pelvic fins.
Eye: Each eye has two poorly formed immovable eye lids and a nictitating membrane. Pupil is narrow
and vertical.
Body Apertures
Mouth: On the ventral side, wide crescent shaped mouth. Bounded by Upper and Lower jaws each with sharp backwardly directed teeth.
Nostrils lead to olfactory sacs. Small fold of skin covers each nostril. Nostrils have only olfactory and no respiratory function.
Gill Clefts: Behind the eyes, series of apertures that lead into gill pouches and hence the pharynx. Respiratory in function.
Cloacal Aperture: Elongated median opening at the root of the tail between two pelvic fins. Intestinal, urinary and genital ducts open here.
Abdominal pores on either side of cloaca.
Lateral Line: Faint one that runs on either side of the body from the head to the posterior of the tail. It marks the position of an underlying canal which runs along each side of the body and contains special receptor organs.
Skin contains outer ectodermal epidermis and inner mesodermal dermis.
Scoliodon (external features):
Male Indian dogfish in ventral view