Subscribe
the Legacy continues…………………….
Gregory R. Mann, Ph.D. {ret.}

ELASMOBRANCHS

Pronounced: E·las·mo·branchs      ( Ih-las-muh-brangks )

The name Elasmobranch represents any of numerous cartilaginous fishes of the subclass Elasmobranchii, having 5 to 7 gill slits on each side, dermal denticles for scales and a small respiratory opening called a spiracle behind each eye. The pectoral fins of Elasmobranchs are often greatly enlarged. The term Elasmobranch refers to the cartilaginous fish family of sharks, rays, chimaras and skates. Their upper jaws are also fused with their skull and instead of the replaceable rows of teeth they have three pairs of large grinding tooth plates. They usually live in the deep ocean and very little is known about their biology.sharks1

sharks


Elasmobranch Senses

shark-anatomy-ampullae-of-lorenzini-1

“Ampullae of Lorenzini”

Ampulla-of-Lorenzini-w

2000px-Electroreceptors_in_a_sharks_head


Elasmobranchs are renowned for their highly tuned senses, which make them incredibly successful in their environment. Their sense of smell is very sensitive and most species have large nostrils that allow a large volume of water to flow continually over their olfactory organs. Surprisingly, hearing is also a very important sense to Elasmobranchs and they have well-developed ears. There is no external sign of this except for two tiny holes behind the eyes. Hearing is often the first sense to detect prey at long distances and it is used in conjunction with a special sensory organ called the lateral line which is a line of pressure detectors that runs down each side of their body. These detect changes in water pressure that might result from struggling prey. Around their snout and mouth are more special sense organs known as the “Ampullae of Lorenzini” which detect electric fields given off by prey. Many sharks also have very good eye-sight and the Great White can even see when its head is out of the water. When combined, all these sense make Elasmobranchs extremely good hunters and helps explain how they have managed to survive for 400 million years.

All Elasmobranchs unlike bony fish, practice internal fertilization when reproducing. Therefore they occur as either male or female. Female sharks have no obvious external reproductive structures, whilst males have two extensions of the pelvic fin known as claspers. These claspers are used by males during reproduction to internally fertilize the female sharks. Some sharks and all skates lay egg cases on the sea bed or wrapped around seaweed. This is called oviparity and the Elasmobranchs are renowned for their highly tuned senses, which make them incredibly successful in their environment. Their sense of smell is very sensitive and most species have large nostrils that allow a large volume of water to flow continually over their olfactory organs. Surprisingly, hearing is also a very important sense to Elasmobranchs and they have well-developed ears. There is no external sign of this except for two tiny holes behind the eyes. Hearing is often the first sense to detect prey at long distances and it is used in conjunction with a special sensory organ called the lateral line which is a line of pressure detectors that runs down each side of their body. These detect changes in water pressure that might result from struggling prey. Around their snout and mouth are more special sense organs known as the “Ampullae of Lorenzini” which detect electric fields given off by prey. Many sharks also have very good eye-sight and the Great White can even see when its head is out of the water. When combined, all these sense make Elasmobranchs extremely good hunters and helps explain how they have managed to survive for 400 million years.


Reproduction

Elasmobranchs unlike bony fish, practice internal fertilization when reproducing. Therefore they occur as either male or female. Female sharks have no obvious external reproductive structures, whilst males have two extensions of the pelvic fin known as claspers. These claspers are used by males during reproduction to internally fertilize the female sharks. Some species of shark such as the Spotted Dogfish and all skates lay egg cases on the sea bed or wrapped around seaweed. This is called oviparity and the young develop within the egg cases whilst being nourished by a ball of yolk. These egg cases are often found washed up on beaches and are common known as a “mermaid’s purse”. By recording where these egg cases are found, we can get important information on the distribution of skates. In all other sharks and “true” rays, the young develop inside the mother in much the same way as in mammals. This is known as viviparity and the young may stay in the mother for anywhere up to two years depending on the species. This form of reproduction can be further divided into two categories, the first is aplacental viviparity whereby the developing young are nourished either by a yolk ball, by absorbing secretions from the mother (histotrophy), by eating extra eggs (oophagy) or even by eating their siblings (embryophagy). The other form is placental viviparity, whereby after using up their yolk ball the young develop a placental connection with the mother. Some species of shark have been shown to return to the same areas where they were born to give birth similar to the way salmon return to their native river to spawn. They may also have specific nursery areas where young can safely grow up away from other major predators. These areas can be very important for the survival of species but very little is known about them for most species.


Repro1-300x175

Elasmobranch Female Reproductive system

reproduction-fig3-eng

x3690e00

male

Elasmobranch Male Reproductive system

il-shark-anatomy


Special Adaptations

Elasmobranchs have many extra special adaptations for living and hunting in the sea. The rough skin which is characteristic of the group is due to a covering of hard tooth-like scales called dermal denticles. These vary in shape and size between species and help reduce drag and resistance in the water.


shark_06_1

Sharkskin2

1370529935


115c

Shark Jaws (1)

Megalodon-Shark-Teeth-2

Megalodon Shark Tooth with Great White Shark Teeth


Megalodon_tooth_great_white_shark_teeth

Megalodon Shark Tooth with Great White Shark Teeth


Shark teeth are highly adapted for the type of prey that the particular species eats. For example the starry smooth-hound (Mustelus asterias) is a specialist and feeds solely on crabs therefore it doesn’t need shark teeth and has flat crushing type teeth instead. The Porbeagle Shark only eats fish therefore it has long sharp-pointed teeth that are ideal for piercing and catching fish. The Bluntnose Sixgill Shark is a deep-sea shark that has a wide variety of prey species and is probably just an opportunistic feeder. They eat mollusks, crustaceans and also fish therefore they have a mixture of shark teeth and also serrated cutting teeth so they can eat anything they find.

24tendua-foie_requin

 

Advertisements