Sharks are fish; the term refers to a group of around 465 species (Elasmo-research.org).. Scientifically, they are classified in the order Seachimorpha, subclass Elasmobrancii and class Chondrichthyes. Sharks have an exoskeleton composed of cartilage; which makes it flexible and light enough for ease in swimming (Elasmo-research.org).
Size and body structure
They grow to averagely 4.6- 6m long. Due to the large number of shark species, their size vary, ranging from 1 centimeters to as long as 12 meters (Elasmo-research.org).They have 7 gills through which they breathe; the gills are located on both sides of the body. Their teeth are 300 in 7 rows and very sharp to allow tearing. The teeth fall off and grow back throughout their lifetime. They camouflage from the upper dark body and lower dark body to blend in with the see above and below.
Habitat
Sharks live in the sea and the oceans averagely at a depth of 2000 meters. They have a protective cover that protects them from parasite and preserves their skin; this is made of dermal denticles (Elasmo-research.org). Some shark prefer shallow waters while the big ones like the dog fish have been seen to live in areas as deep as 3700 meters.
Feeding
Most sharks feed on smaller sea animals like fish, mollusks, crustaceans, krill, and other sharks. Their feeding mechanisms include, suction, ram feeding and gill racking (Elasmo-research.org).A shark’s jaw can dislocate to allow it to grab its prey. They attack swiftly in as fast as 1/10 of a second.
Sharks take a long time to digest their food, with food moving slowly from the mouth to the digestion track. Undigested and indigestible food are often expelled through the mouth by vomiting and they mostly never travel the entire digestive track (Elasmo-research.org).. Their intestines are shorter than most animals.
Senses
Sharks have extremely sensitive sense of smell that can detect objects from up to 200 miles away. They are able to smell 1/1,000,000 of blood in water (Elasmo-research.org).. They are also able to follow the source of smell from a long distance away. Their eyes have the tapetum lucidum tissue which reflects light, adapting it to seeing well in darkness and in the water (Elasmo-research.org).. Some species have nictitating membranes in the eyes which acts as protection like eyelids do in mammals (Pradel et al., 8).
Behavior
Shark behavior largely depends on the species. Most of them are social, hunting in groups and frequently swimming in couples. There are some species that prefer a solitary life, hunting in the deep seas at night. However, these solitary sharks become social during breeding seasons. Some stay in large schools for protection and display swimming tactics to threaten intruders (Etymonline.com).
Movement
The swim fast at averagely 8km/hr and 18 plus km/hr when chasing prey or when under threat (Etymonline.com). However, some shark species like the marko and white sharks can travel at speeds above 50km/hr (Pradel et al., 8). The shark’s intelligence is like that of other fish, occasionally exhibiting a sense of curiosity (Etymonline.com). The sharks are said to sleep swim, where they use their spinal cord to coordinate their movement while their brain rests.
Reproduction
Sharks exhibit internal fertilization like mammals. The males have clappers that introduce the sperm into the female shark. Bites are often seen in females which result from the courting process or injury during mating. Sharks deliver their young in three ways: by laying eggs in the water like other fish, by remaining attached to the placenta and delivering a live young one, or by the egg hatching within the female shark. These are referred to as viviparity, oviparity and oviviparity respectively (Elasmo-research.org).
Works Cited
Elasmo-research.org,. "Sharks". N.p., 2016. Web. 2 Mar. 2016.
Etymonline.com,. "Online Etymology Dictionary". N.p., 2015. Web. 2 Mar. 2016.
Pradel, Alan et al. "A Palaeozoic Shark With Osteichthyan-Like Branchial Arches". Nature 509.7502 (2014): 608-611. Web.
