Yeily Hernandez

Prof. Frolich

Zoo3021

• Cartilaginous fish are part of the class Chondrichthyes, divided into two subclasses Elasmobranchii and Holocephali.
  • We will focus on the subclass Elasmobranchii which branches off into two super orders Selachii (sharks) and Batoidea (rays).
• In a sense they are living fossils, many of the living species are assigned to the same genera as species that swam the Cretaceous seas over 100 mya.
• There are more than 400 species of sharks and about 500 species of rays
• Members of Elasmobranchii are jawed vertebrates with paired fins, paired nares, scales, a heart with its chambers in series, no swim bladders and their skeletons are made of cartilage rather than bone.
• All sharks are carnivorous and, with a few exceptions, have broad feeding preferences, governed largely by the size and availability of the prey.
• The danger some sharks and stingrays present to humans makes these animals fascinating and, at the same time, fearsome.
• The majority of sharks and rays are marine fishes, but many enter estuaries; some travel far up rivers, and a few are permanent residents of fresh water.
  • Most species live in the relatively shallow waters of continental margins or around offshore islands; a few roam far out in the vast spaces of the oceans. Some live at great depths, in midwaters or on the bottom; others are surface swimmers or inhabit the bottom in shallow waters

• The figure shows a cladogram of fishes, showing the probable relationships of major fish taxa.

• Kingdom: Animalia
• Phylum: Chordata
• Subphylum: Vertebrata
• Infraphylum: Gnathostomata
• Clade: Eugnathostomata
• Class: Chondrichthyes
  • Subclass Elasmobranchii (sharks, rays and skates)

Superorder Batoidea (rays and skates)

• Generally flattened in shape due to their enlarged pectoral fins (or wings). They have 5 pairs of gills on the underside of the body rather than on the side as with sharks.
  • Order Myliobatiformes (common sting rays and relatives)
    • Family Plesiobatidae (deepwater stingray)
    • Family Hexatrygonidae
    • Family Dasyatidae (stingrays)
    • Family Urolophidae (round stingrays)
    • Family Gymnuridae (butterfly rays)
    • Family Myliobatidae (eagle rays)
  • Order Rajiformes (Guitarfishes and skates)
    • Family Rhinidae
    • Family Rhinobatidae (guitarfishes)
    • Family Rajidae (skates)
  • Order Pristiformes (Sawfish)
    • Family Pristidae (sawfishes)
  • Order Torpediniformes (electric rays)
    • Family Torpedinidae (electric rays)
    • Family Narcinidae

Superorder Squalomorphii

• Order Hexanchiformes: containing 5 extant species within 2 families:
• As the name suggests these sharks have 6 pairs of gills. Yet to add confusion some have 7. Unlike most other sharks which have 5.
  • Hexanchidae(cow shark)
  • Chlamydoselachidae (frilled shark)
• Order Squaliformes: containing 80 species divided into 3 families:
• Have a short mouth with a long snout and 5 pairs of gills.
  • Echinorhinidae(Bramble Sharks),
  • Squalidae (Dogfish sharks)
  • Oxynotidae (Roughsharks).
• Order Pristiophoriformes: containing 5 species within a single family:
• have a long saw-like snout, which they use to stun prey and defend themselves against predators. They have either 5 or 6 pairs of gills.
  • Pristiophoridae(sawsharks).
• Order Squatiniformes: containing 13 species in 1 family,
• Have flattened body that resemble more rays than sharks, but their gills are on the side of their body.
  • Squatinidae (Angel sharks).

Superorder Galeomorphii:

• Order Heterodontiformes: 8 species in 1 family,
• Have 5 pairs of gills and fin spines
  • Heterodontidae (bullsharks).
• Order Orectolobiformes: 7 families are found within this order:
• Have a short snout and 5 pairs of gills. Most have barbels near their mouth, which they use to taste food under the seabed
  • Brachaeluridae (blind catsharks and blind sharks),
  • Ginglymostomatidae (nurse sharks),
  • Hemiscylliidae(bamboo sharks and longtailed carpetsharks),
  • Orectolobidae (wobbegongs),
  • Parascyllidae (collared carpetsharks),
  • Rhincodontidae (Whale sharks)
  • Stegostomatidae(zebra sharks).
• Order Carcharhiniformes: this is the largest order containing approximately 200 species within 8 families:
• Have a wide mouth with sharp-edged teeth and 5 pairs of gills. They also have a movable membrane over their eyes to protect them when they're feeding.
  • Carcharhinidae (requiem sharks),
  • Hemigaleidae (weasel sharks),
  • Leptochariidae(barbeled houndsharks),
  • Proscylliidae (finback catsharks),
  • Pseudotriakidae(false cat sharks),
  • Scyliorhinidae (cat sharks),
  • Sphyrnidae(bonnethead sharks, hammerhead sharks, and scoophead sharks),
  • Triakidae (houndsharks, smooth-hounds, topes, and whiskery sharks).
• Order Lamniformes: known as mackerel sharks, this order contains 7 families and 16 species:
• Have a long snout and mouth, with 5 pairs of gills
  • Alopiidae (thresher sharks),
  • Cetorhinidae (basking sharks),
  • Lamnidae (mackerel sharks, porbeagles, and white sharks),
  • Megachasmidae (megamouth sharks),
  • Mitsukurinidae (goblin sharks),
  • Odontaspididae (sand sharks and sand tiger sharks) and
  • Pseudocarchariidae (crocodile sharks)

Elasmobranchii

Body

• Five to seven pairs of gill clefts opening individually to the exterior.
• Have rigid dorsal fins
• Small placoid scales also called dermal dendrites which are homologous with vertebrate teeth which can also be in the form of modifies teeth, such as the spine of the stingrays, dorsal spines of dogfish, and defensive spines in the skates
• Teeth are arranged in rows in the mouth, they are not firmly attached to the jaws but are embedded in a fibrous membrane lying over the jaws. When a tooth becomes broken, worn, or lost, it is replaced by one moving forward from the next row behind; at the base of the innermost row are rudimentary teeth and tooth buds that develop and move forward as needed.
• Their upper jaw it not fused with the cranium while the lower jaw is articulated with the upper which allows for flexibility.

Batoidea

• They differ from sharks:
  • Have flattened disk-like bodies bodies with the exception of guitarfish and sawfish, enlarged pectoral fins that are fused to the head. Gills and mouth placed on ventral surface while their eyes and nares are located on the dorsal surface. Their mouth can protrude upper jaw away from cranium to capture prey.
  • Have absent anal fin and tails.

Digestion/ Excretion

• The intestines of sharks and rays are much shorter that those of mammals. They have compensated for this problem by having spiral valves. Spiral Valve extends through the intestines it is the corkscrew-shaped, lower portion of the intestine, internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption.
  • The spiral valve constricts the lumen of the ileum, thus sharks cannot pass large hard objects (such as bones) through their lower intestine. Such objects remain in the stomach until sufficiently broken down for passing through the valve region, or are regurgitated.
  • By keeping digestible materials in the ileum for an extended period, maximum nutrient absorption is ensured. For this reason, many sharks and rays feed very infrequently.
  • The food passes into the comparatively short colon of the shark almost fully digested, and then out the cloaca and vent which excrete both urine and feces.
  • They are able to reabsorb most of their nitrogenous waste products (urea and trimethylamine oxide) in the renal tubules and accumulate these products in their tissues and blood, an ability termed the urea retention habitus. Allowing the concentration of salt within the body to exceed that of the surrounding seawater, thus, water moves into the body with no expenditure of energy. When any of these fishes moves into fresh water, as many do, the urine flow to the outside increases; hence, the concentration of urea in the blood decreases.

Circulation/ Respiration

• Lack bone marrow, thus blood is produced in the spleen, in epigonal organs near the gonads, and in some cartilaginous species in specialized cells called Leydig's organs.
• The respiration and circulation process begins when deoxygenated blood travels to their two-chambered heart. Here they pump blood to their gills via the ventral aorta artery where it branches into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses. From there blood enters the heart ventricle and the cycle repeats.
• Spiracle lies just behind the eye which assists the shark and rays with taking in water, it is a key factor in bottom dwellers- take in water through the spiracles and passing it outward through the gills. While in motion, water passes through the mouth and over the gills in a process known as "ram ventilation" and while at rest, most pump water over their gills to ensure a constant supply of oxygenated water.
• Cartilaginous fish lack swim bladders but keep their buoyancy with enlarged livers filled with light viscous oils. In many deep water sharks the body cavity is often greatly elongated to accommodate the huge, oily liver, which reduces the specific gravity of the shark to neutral buoyancy,allowing it to swim and hover off the bottom without having to generate lift from its fins and body. When nutrients are depleted they may use the oils stored in their liver as backup.

Reproduction

• Fertilization is internal.
  • All species of sharks, and rays produce large yolk-rich eggs.
  • Males have claspers in the inner margin of their ventral surface for the transmission of sperm. Each consisting of a groove for guidance of sperm.
    • The male grasps one of the female’s pectoral fins with his teeth to hold her in position as he inserts a clasper through a cavity (cloaca) and into a tube (oviduct).
    • Males of most species probably use only one clasper at a time. The sperm travel to the anterior end of the oviduct, where they fertilize the eggs.
    • The eggs then move down the oviduct past the shell gland, where they are covered by a shell or capsule.
  • Development is usually live birth (ovoviviparous species) but can be through eggs (oviparous). Some rare species are viviparous.
    • Most sharks are ovoviviparous, meaning that the eggs hatch in the oviduct within the mother's body and that the egg's yolk and fluids secreted by glands in the walls of the oviduct nourishes the embryos. The young continue to be nourished by the remnants of the yolk and the oviduct's fluids.
    • Some species are oviparous, laying their fertilized eggs in the water. In most oviparous shark species, an egg case with the consistency of leather protects the developing embryo(s). These cases may be corkscrewed into crevices for protection. The egg case is commonly called a mermaid's purse.
    • Viviparity is the gestation of young without the use of a traditional egg, and results in live birth. Viviparity in sharks can be placental or aplacental. Young are born fully formed and self-sufficient
  • There is no parental care after birth; however, some do guard their eggs.
  • Some sharks and rays move close inshore to drop their young, then depart these `pupping grounds' after giving birth. Young may stay in food-rich `nursery areas' for some time while growing, then migrate out of these areas. Some newborn sharks, faced with large predatory sharks and even cannibalistic adults of their own species, seek dense cover such as mangrove roots or eelgrass to hide and feed until they reach sufficient size to range open areas.

Nervous system/ Senses/ Movement

• The eyes have a tapetum lucidum - is a layer of tissue in the eye of many vertebrates. Lying immediately behind the retina, it is a retro-reflector. Even though their eyes are structurally and functionally adapted for seeing, it is believed that their visual acuity in distinguishing the form and color of an object varies between species.
  • Fast predatory sharks tend to have more acute vision, and in some deep-diving species the eyes are well developed to maximize detection of ambient light.
• Nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves.
• Have Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors. These ampullae are sensitive to electrical fields, and provide a means for cartilaginous fishes to locate potential prey or one another by sensing the electrical fields produced by muscles and nerves. The ampullae may also function in navigation; cartilaginous fishes, moving through the water, produce electric fields that vary directionally according to the position of the cartilaginous fish relative to the Earth's electromagnetic field. These localized electrical fields can be detected by the ampullae and may provide directional information for long-distance navigation without visual, olfactory, or other sensory cues.
• The sense of smell is well-developed, which have large nostrils and olfactory organs. Some sharks can detect attractive substances at over one part per million parts of sea water, and are able to follow scent trails directionally and from great distances. Such sharks will swim against a current, tracking the scent trail to its source. Olfactory cues may play some role in orientation of cartilaginous fishes, perhaps in finding receptive mates or other members of their species, or locating specific areas, but this needs further research.
• Taste buds are well-represented in the mouths of cartilaginous fishes; some sharks are very selective on potential food items, swallowing or disgorging them after taking them into their mouths.
• Their inner ears consist of 3 large semicircular canals which aid in balance and orientation. Their sound detecting apparatus has limited range and is typically more powerful at lower frequencies. The hearing apparatus, located in the auditory capsule of the cranium, includes a system of semicircular canals, which are responsible for maintaining equilibrium. No cartilaginous fishes are known to produce underwater sounds, unlike many bony fishes.
• Related to sound reception is the lateral line canal system, a network of tubes below the skin, with several branches on the head but with a single line, the lateral line proper, running along the body on both sides and extending to the caudal fin. These canals have short tubes with external pores opening at frequent intervals to the outside, and have sensory cells that are responsive to low-frequency, close-range water vibrations. These can aid in avoidance of obstacles, location of prey, and detection of low-frequency sound. A similar function has been suggested for the pit organs, blind subdermal pockets with similar sensory cells as in lateral line canals, and with pores connecting to the surface. Pit organs are scattered along the body and may be very numerous in some large sharks such as hammerheads.
• Sharks and some rays use their strong tails and caudal fins to swim with, but skates and stingrays, with reduced tails and large pectoral disks, use their pectoral fins as propellers, and can achieve fine control by differential undulation of these fins. Some bottom sharks such as the bullhead sharks and various carpet sharks have muscular pectoral and pelvic fins, and use them to walk on rocks and coral. Other sharks and rays swim in midwater and at the surface, and the peak of their prowess is seen in highly advanced types such as the mackerel sharks and devil rays, which are extremely active, cruise for long distances, and can jump high out of the water.

External/ Internal anatomy of Selashii

Habitat/ behavior

• The ecology of cartilaginous fishes is not well known since most cartilaginous fish researchers have concentrated on other aspects of their biology. Most marine community studies are focused on bony fishes or invertebrates while overlooking the importance of cartilaginous fishes to these very same communities.
• Most sharks and rays do not school
• Mainly solitary and usually come together only to exploit food resources or to mate. During these encounters, some species may show dominance, usually based on size to protect smaller individuals from larger ones.
• They are among the top predators and among among them there exists a hierarchy, having many species at or near the apex of the food pyramid, some species being prey to others.
• Most cartilaginous fishes are slow growing and long-lived, with some species requiring up to 20 years or more to reach adulthood and with a maximum age of 75 years.
• Most have symbiotic relationships with Remora fish. The Remora fish attaches to them and catches a rid, feeding on their leftover food. Sharks allow this kind of behavior due to the fact that while it eats its leftovers it is also riding it of parasites, cleaning their teeth and skins.
• Communicate using their senses, such as the sense of smell and electrical fields.
• Batoidea
  • Most species live on the sea floor, in a variety of geographical regions — mainly in coastal waters, although some live in deep waters to at least 3,000 metres (9,800 ft). Batoids prefer tropical and subtropical marine environments, although there are temperate and cold-water species. Only a few species, like manta rays, live in the open sea, and only a few live in freshwater, while some Batoids can live in brackish bays and estuaries. Manta rays swim mostly at or near the surface, progressing by flapping motions of the pectoral fins. Even the largest often leap clear of the water.
  • Most sting rays and eagle rays swim gracefully, with motions of the broad winglike pectoral fins. Some species, especially the eagle rays, frequently swim near the surface and even jump clear of the water, skimming a short distance through the air.
• Selashii
  • Most are marine and generally do not live in fresh water. Few exceptions such as the bull shark and the river shark can swim both in seawater and freshwater.
  • Sharks are common down to depths of 7,000 ft, and some live even deeper, but they are almost entirely absent below 10,000 ft. The deepest confirmed report of a shark is a Portuguese dogfish at 12,100 ft

Symbiotic relationship with Remora fish

• Batoidea
  • The majority are bottom dwellers preying on other animals on or near the seafloor
    • Guitarfishes, butterfly rays, eagle rays, and cow-nosed rays feed on invertebrates, principally mollusks and crustaceans.
    • Whip-tailed rays use their broad pectoral fins to dig shellfish from sand or mud.
    • Skates lie on the bottom, often partially buried, and rise in pursuit of such active prey as herring. Trapping their victims by swimming over and then settling upon them, a practice facilitated by their habit of hunting at night.
    • Electric rays feed on invertebrates and fish, which may be stunned by shocks produced from the electric organs. They are capable of taking very active fishes, such as flounder, eel, salmon, and dogfish. Shallow-water electric rays have been observed to trap fishes by suddenly raising the front of the body disk while keeping the margins down, thereby forming a cavity into which the prey is drawn by the powerful inrush of water.
    • Mantas moves through masses of macroplankton or schools of small fish, turning slowly from side to side and using the prominent cephalic fins, which project forward on each side of the mouth, to funnel the prey into the broad mouth.
• Selachii
  • Experiments on several species of large sharks indicate that they do discriminate food types—preferring tuna, for example, to other fish species. Under some conditions, they become less fastidious, going into a feeding frenzy in which they attack anything, including others of their own kind. In most cases, sharks locate food by smell.
  • All sharks are carnivorous
  • Few exceptions, have broad feeding preferences which are governed largely by the size and availability of the prey.
  • Many bottom-dwelling sharks, such as the smooth dogfishes take crabs, lobsters, and other crustaceans, as well as small fishes.
  • The three largest sharks, the whale shark , the basking shark, and the megamouth shark resemble the baleen whales in feeding mode as well as in size. They feed exclusively or chiefly on minute passively drifting organisms (plankton). To remove these from the water and concentrate them the basking shark and the megamouth shark have modified gill rakers, the whale shark elaborate spongy tissue supported by the gill arches. The whale shark also eats small, schooling fishes.
  • The saw sharks have a specialized mode of feeding that depends on the use of their long blade-like snout, or “saw.” Snout is equipped with sharp teeth on its sides, the saw is slashed from side to side, impaling, stunning, or cutting the prey fish.
  • Thresher sharks feed on open-water schooling fishes, such as mackerel, herring, bonito, and on squid. The long upper lobe of the tail, which may be half the total length of the shark, is used to herd the fish (sometimes by flailing the water surface) into a concentrated mass convenient for feeding. Thresher sharks have also been observed to stun larger fish with a rapid strike of the tail.

Predators/ Human interaction

• Depending on the species, sharks and batoids have several predators, including other sharks, elephant seals, and killer whales.
• Human Interaction
• Vulnerable to overfishing.
  • Slow-growing and a single female produces only a few hundred pups or less in a lifetime, depleted populations may take years or decades to recover.
  • Recreational and commercial shark harvesting has increased in the past several years due to an increased demand for sharks and shark products.
• Medicinally, used for hemorrhoid treatments, vitamin supplements, artificial skin to treat burn patients, acne medication, anti-clotting blood compounds, and human cornea transplants.
• A substance called squalamine, found in the liver, stomach, and gall bladder of some dogfish, is believed to slow the growth of human brain tumors.
• Shark cartilage is also being tested for treatments against the growth of tumor cells.
• No part of the shark, however, is as economically valuable as their fins.
  • Shark finning is the practice where the fins are removed from the shark and the rest of the shark is simply discarded.
    • Shark fins can be worth up to $25 per pound
      • The fins are used primarily to make shark fin soup, a delicacy in Asia.
      • A bowl of shark fin soup can cost as much as $150 a bowl.

• Earliest fossils too fragmentary to permit precise tracing of origin
• Ancestral forms found at the end of the Ordovician Period (455 mya) in upper reaches of streams
• End of Silurian and beginning of Devonian periods
  • Appearance of armor-plated fish with jaw-like structures, paired fins, and bony skeletal tissue (Placoderms)
• Devonian period (about 400 mya)
  • Placoderms reach their peak most die out
  • Only few linger another 10 my into Carboniferous period ( about 350 mya)
• Placoderms gave rise to both bony fish and cartilaginous fish
• Lines remain to be discovered
• Clear the two groups evolved independently
• Invaded sea perhaps in response to arid Devonian climate

Fish family tree

• Shows the evolution of major groups through geological time.
• The widened areas in the lines of descent indicate periods of adaptive diversification and the relative number of species
• Sharks and rays diversified during the Carboniferous period, declined during the Permian period, and then diversified again during the Mesozoic era

References

• https://sharkresearch.rsmas.miami.edu/assets/pdfs/learning-tools/high-school/MODULE%202%20Ichthyology%20-%20SECTION%204%20Cartilaginous%20Fishes.pdf
• https://en.wikipedia.org/wiki/Chondrichthyes
• https://www.britannica.com/animal/chondrichthian
• http://www.newworldencyclopedia.org/entry/Chondrichthyes
• http://www.mesa.edu.au/fish/fish03.asp
• https://giphy.com/gifs/week-shark-genYkph5NoJbO
• http://www.biodiversityexplorer.org/chondrichthyes/behaviour.htm