Sunday, 27 April 2014 01:49

Grey Nurse Sharks - Anatomy, Teeth & Description Of Species

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General Description

The Grey Nurse is a distinctive fish, which is usually grey-brown on top and a dirty white underneath. A distinctive character of this species is that both dorsal fins and the anal fin are of a similar size. Many sharks have a tail with a long dorsal (upper) lobe and a shorter ventral (lower) lobe. This type of tail is described as heterocercal. When a shark swims the large upper lobe of the tail tends to push the snout of the shark down. This is balanced by the lift produced by the pectoral fins and the ventral surface of the snout.

The tail of the Grey Nurse Shark is heterocercal and has a characteristic subterminal notch. You can see this in the image above.

For a more unusual look at the anatomy of the Grey Nurse Shark, you can have a look at the Autopsy Images we have from a autopsy done on a male grey nurse shark that died in an aquarium in 2000.

Colouration

Grey Nurse Sharks are counter shaded, the dorsal (upper) part is dark, mostly a grey to bronzy colour whereas the ventral (lower) part of the body is pale. Juveniles have reddish or brownish spots on the posterior (back) half of the body and tail. These spots generally fade as the Grey Nurse matures, but are sometimes still visible on adults.

Skin

Sharks do not have scales like bony fish but instead have rough skin. Their skin is covered with tiny sharp teeth called dermal denticles. These teeth can scrap the skin off your hand if you rub it the wrong way, which is from tail to head. When rubbed from head to tail sharks feel smooth (with the exception of a few species). The denticles are there to make the shark move silently, and for protection.

Skeleton

The internal skeleton of a shark is made of cartilage and connective tissue making the shark very flexible and light. The shark has no rib cage, so when it is on land its own weight can literally crush its body.

Teeth

In Africa, the Grey Nurse Shark is known as the Raggy Tooth Shark. The reason for this name is obvious. This species has fang-like teeth which are visible when the shark's mouth is closed. The teeth of the Grey Nurse Shark are constantly being replaced. This means that older, damaged, or blunt teeth on the exterior surfaces of the jaws are replaced by new teeth. In the whaler sharks, family Carcharhinidae, each tooth is replaced every eight to fifteen days. The  front teeth of the Grey Nurse Shark are lanceolate (long) with a lateral cusplet (small barb) on each, whereas those at the back of the jaw are smaller and lack cusps.

Description Of Species

The Grey Nurse Shark, also known in the USA as the sand tiger shark and in South Africa as the spotted ragged-tooth shark, is one of four species belonging to the family Odontaspididae. The species has a large, rather stout body and is coloured grey to grey-brown dorsally, with a paler off white under belly. Reddish or brownish spots may occur on the caudal fin and posterior half of the body, particularly in juveniles.

The species has a conical snout, long awl-like teeth in both jaws (with single lateral cusplets), similarly sized first and second dorsal fins and an asymmetrical caudal fin. Grey Nurse Sharks grow to at least 360 cm total. The Grey Nurse Shark is a slow but strong swimmer and is thought to be more active at night.