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CHORDATA |
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TUNICATA |
Tunicates bear no resemlance to other chordates. A few are free-living, but most, after a short larval stage attach themselves to rocks, shells, wharf pilings or ship hulls. They are solitary or colonial or with many individuals grouped under a common covering.
They vary in size from microscopic forms to others that are 30cm in diameter. About 2000 species are known and only their larvae bear chordate similarities. Tunicates are usually hermafroditic, but methods of reproduction are varied (some asexual through budding others sexual). The group name refers to the self-secreted tunic, or sacklike covering, over the body. Three classes are recognized, the best known being the sea squirts or ascidians (Ascidiacea). Thaliacea and Larvacea are very small groups. |
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ASCIDIACEA | Sea squirts |
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While sea squirts might appear featureless they are in actuallity highly advanced and closely related to the vertebrates. These similarities are most noticable in the larvae (tadpole-like creatures with a primitive backbone, nerve cord and tail). All these are missing in the adult which becomes sessile, sac-like animals topped by a pair of tubular siphons and enclosed in a cellulose casing or test. Water is sucked into the inhalant siphon and is then filtered through an enlarged shieve-like pharynx and is then expelled through the exhalant siphon. |
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| A sagittal section through an ascidian. |
Most of the larger ascidians are solitary animals, but many of the smaller species are colonial either consisting of numerouse tiny individuals (zooids) that are embebded in a shared mass of jelly-like tissue or many individuals that are branching from one common base. These individuals may have seperate siphons or they may share common exhalant siphons. Ascidieans are very common on most of the rocky shores and reefs.
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VERTEBRATA |
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The classes Clyostomata to Mammalia constitute for the major part of the phylum. The characteristic and diagnostic features for the subphylum Vertebrata being the enlarged brain, encased in the brain case, or cranium, and a segmental spinal column of vertebrae that becomes the axial support of the body. Typically the body comprises a head, neck, trunk and tail. These classes show a progressive series of structural and functional advances in all organ systems besides the features of the notochord, nerve cord, and gill slits. Characteristics: 1. The body covering is a stratified epithelium of epidermis and dermis with many mucous glands in aquatic species. Most fishes are covered with protective scales. The exterior is conified on land dwellers, with scales on reptiles, feathers on birds and hair on mammals (feathers and hair form insulated body coverings). 2. The internal and jointed skeleton is of cartlage in lower vertebrates and of bone in higher forms. The skeleton supports and protects the various organs of the body. The cranium houses the brain and has special paired capsules for the sensory organs. A series of visceral arches supports the gill region, and certain arches become the jaws and other structures of the head region. The vertebral column (spine) extends from the base of the cranial cavity to the end of the tail and has neural arches dorsally to house the nerve cord. Two pairs of appendages (the fins of fishes and the limbs of tetrapods, with jointed skeletal supports) are articulated with the vertebral column though limbgirdles. 3. On the skeleton are muscles that move its parts and provide functionality and movement. 4. The complete digestive canal is ventral to the vertebral column. The mouth contains a tongue and usually has teeth. The liver and the pancreas are two large digestive glands that pour their secretions into the digestive canal through ducts that are joined to the intestine. The anus opens at the end of the trunk. 5. The circulatory system includes a well-developed, muscular heart, with two, three or four chambers, that lies ventral to the digestive canal. The contractions of the heart propels the blood through a closed system of arteries, capillaries and veins the flow being anteriorly on the ventral side, and posteriorly in the dorsal arteries. The blood plasma contains both white and red corpuscles. The red contain hemoglobin as a respiratory pigment. A system of lymph vessels is present. Paired aortic arches transport blood from the heart to the gills in lower vertebrates. The progresive separation of the respiratory (pulmonary) and systemic blood paths through the heart contributes to regulated body temperature in the warm-blooded (endothermic) birds and mammals. 6. Respirationin the lower forms is by paired gills. Terrestrial species have lungs developed from outpocketings of the digestive canal. 7. The paired excretory organs (kidneys) discharge through ducts opening near or through the anus. In the lower forms the organs are of segmented form and drain wastes from both the blood and the coelom. In higher forms they are nonsegmental and drain only from the blood. a bladder for the storage of urine is located in many. 8. The brain becomes regionally differentated as to structure and function. The cerebral hemispheres and cerebellum are enlarged, especially in the higher forms. There are ten to twelve pairs of cranial nerves in the head that serve for both motor and sensory function, including the paired organs of special sense (smell, sight and hearing + equalibration). From the nerve cord a pair of spinal nerves serve each primitive body segment. An autonomic nervous system regulates involuntary functions of internal organs. 9. A series of endorine glands(thyroid, pituitary, etc.) provide hormones, transported by the bloodstream, that regulate bodily processes, growth and reproduction. 10. With very rare exeptions the sexes are separate, and each has a pair of gonads that discharge sex cells through ducts opening into or near the anus. 11. A well developed perivisceral coelom is present. |
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PISCES |
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There are over 22 000 species of fish the World over including more than 50% of all the vertabrates. Fish originated over 480 million years ago. Fish evolved in fresh water the chondrichthyes made their move to the sea early in evolutionary cycle, while the bony fishes went through most of their evolutionary developments in fresh water and
spread to the seas only at a much later stage. Fish are the dominant, free swimming
animals of the seas. The structure of a fish's body is designed for comfortable movement. Their ability to move about with ease and without having to rely on the water currents to carry them about, has enabled fishes to exploit most parts of the world's oceans, and this is reflected in great variety of sizes and shapes. Fish are found in both fresh and salt water worldwide, and are a very important food source for many nations.
Fish are usually cold-blooded, finned aquatic vertebrates. They are mostly scaled and breathe by passing water over gills. Modern fish are divided into three classes. |
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AGNATHA | Hagfish & Eels |
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Eels have a snake-like body which is long and cylindrical. It has a smooth skin with no scales and is without pelvic fins.The Hagfish also lacks true jaws or paired fins. The skeleton is cartliginous with gills in pouches (5 to 16 pairs). Heart 2-chambered. There are around 50 species. |
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| Structure of the anterior of a lampray. |
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Characteristics: 1. Body long, slender and cylindrical with the tail region compressed. Median fins supported by cartiliginous fin rays. A soft and smooth skin with many unicellular glands. No scales, no true jaws or paired fins. 2. Mouth is situated ventroanteriorly, suctorial in lampreys, eversible and biting in hagfish. Olfactory organs are paired but with a single median opening on snout. 3. Skull and visceral arches (branchial basket) cartiliginous. A notochord is present. Vertibrae are represented by small and imperfect neural arches (arcualia) over notochord. 4. Heart two-chambered, with atrium and ventricle. Multiple aortic arches in the gill region. Blood with leukocytes and erythrocytes. Multiple hearts. 5. Gills in lateral saclike pouches of pharynx. 5 to 16 pouches in hagfish. 6. Brain is differentiated with eight or ten pairs of cranial nerves. Each "ear" with a semicircular canal. 7. Mesonephric kidneys with ducts to urogenital papilla. Pronephros persists in adult hagfishes. Nitrogenous wastes are chiefly ammonia. 8. Body temperature variable(ectothermal). 9. single, large, without duct. Fertilization occurs externally. Development is direct. |
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CHONDRICHTHYES |
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(Greek.chondros=cartilage + ichthys=fish The sharks, rays and chimaeras are the lowest of the living vertebrates with complete and separate vertebrae, movable jaws and paired appendages. Characteristics: 1. Skin tough, covered with minute placoid scales and having many mucous glands. Both median ond paired fins present, all supported by fin rays. Pelvic fins with claspers in males. Heterocercal tail. 2. Mouth ventral, with enamel-capped teeth. Nostrills two or one, not connected to mouth cavity. Both lower and upper jaws present. Intestine with spiral valve. |
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| The Spiral valve in the intestine of a dogfish (squalus). |
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3. The skeleton is cartilaginous, no true bone. Cranium joined by paired sense capsules. Notochord persistent. Vertebrae many, complete and seperate. Pectoral and pelvic girdels present. 4. Heart two chambered (one atrium one ventricle), with sinus venosus and conus arteriosus, contains only venous blood. Several pairs of aortic arches. Some veins expand as sinuses. Red blood cells are nucleated and oval. 5. Respiration by gills attached to opposing walls of gill pouches, each pouch with its own slitlike opening. No swim bladder. 6. Ten pairs of cranial nerves. Each "ear" with three semicircular canals. 7. Excretion by mesonephric kidneys. Urea chief nitrogenous waste. 8. Body temperature variable (ectothermal). 9. The sexes are seperate. Gonads are typically paired. Reproductive ducts discharge into cloaca. Fertilization occurs internally. oviparous or ovoviparous. The eggs are large with much yolk, segmentation meroblastic. No embryonic membranes. Development direct, no metamorphosis. |
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ELASMOBRANCHII | Sharks, rays |
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| The visceral organs of a dog fish (squalus). |
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| The great white shark ( Carcharodon carcharias). |
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| A tropical spotted eagle ray (Aetobatis narinari). |
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HOLOCEPHALI | Chimaeras |
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OSTEICHTHYES | Bony fishes |
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These fish have bony skeletons, are covered by dermal scales, usually have spindle-shaped bodies, swim by movements of the body and fins, and breathe by means of gills. |
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| The visceral organs of a bony fish. |
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Characteristics: 1. Skin with many mucous glands,usually with embedded bony scales of mesodermal origin (cycloid, ctenoid, sometimes ganoid). Some are scaleless. A few with enamel-covered scales. Both median and paired fins are present (some exceptions), supported by fin rays of cartilage or bone. 2. Mouth usually terminal and with teeth. Jaws well developed and articulated to the skull. Two olfactory sacs which are usually not connected to the mouth cavity. The eyes are usually well developed with no lids. 3. Skeleton chiefly made up of bone (cartlige in sturgeons and some others). Vertebrae many and distinct. Tail usually homocercal in advanced forms. Relics of notochords often persist. 4. Heart two pumping chambers (one atrium one ventricle), with sinus venosus and conus arteriosus, contains only venous blood. Four pairs of aortic arches. Red blood cells are nucleated and oval. 5. Respiration by pairs of gills on bony gill arches in a common chamber at each side of the pharynx, covered by a bony opperculum. Usually with a swim bladder, sometimes with a duct to the pharynx, and lunglike in Dipnoi and some others. 6. Brain with optic lobes and cerebellum well developed. Ten pairs of cranial nerves. 7. Exretion by mesonephric kidneys. Chief nitrogenous wate of larvae is ammonia. Of most adults its urea. 8. Body temperature variable(ectothermal). May be metabolically elevated in large, active fishes. 9. Gonads are typically paired. Usually oviparous (some ovoviviparous or viviparous). Fertilization occurs externally (some exceptions). The eggs are minute to 25mm,yolk various in amount. Segmentation usually meroblastic. No embryonic membranes. Early young (postlarvae) are sometimes quite unlike the adults. |
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TETRAPODA |
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AMPHIBIA | Frogs |
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(Greek.amphi = dual + bios = life) The Amphibia comprise of the Characteristics: 1. The skin is moist and glandular with no external scales. 2. Two pairs of limbs for walking or swimmimg (no paired fins). Toes four to five or fewer (no limbs on caecilians, no hind limbs on Sirenidae). Any median fins lack fin rays. 3. Nostrils two, connected with the mouth and valves that exclude water and aid respiration through lungs. Eyes often poses movable lids. Eardrums external on toads and frogs. Mouth usually with small teeth and a tongue that is often protrusible. 4. Skeleton mostly bony. Skull with two optical condyles. Ribs, if present, not attached to the sternem. 5. Heart tipically three chambered (two atria and one ventricle), but atrial septum incomplete in salamanders, which lack or have reduced lung function. One or three pairs of aortic arches. Red blood cells are nuclated and oval. 6. Respiration through lungs, gills, skin or mouth lining (separatly or in combination), but gills are present at some stage in the life cycle. Frogs and toads poses vocal chords. 7. Brain with ten pairs of cranial nerves. 8. Excretion by mesonephric kidneys. Urea is usually the chief nitrogenous waste of the transformed individuls. 9. Body temperature variable (ectothermic). 10. Fertilization occurs externally or internally. Mostly oviparous. Eggs with some yolk and enclosed in gelatinous coverings. The cleavage is holoblastic, but unequal. No extraembryonic membranes. Usually in aquatic larval stage with metamorphosis to adult form. |
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REPTILIA |
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Turtles spened virtually all their adult life at sea, and their legs are modified into flat flippers for swimming. Their bodies are enclosed in a hard, bony "shell" (carapace). Turtles nest on sandy beaches, returning instinctivaly to the same beach year after year. Temperature controls the sex of the offspring. Eggs kept at 20 - 29oC hatch as males. Those that are kept at temperatures of above 29oC will be female. Turtles are vulnurable to several human activities including disturbances at their nesting beaches, their capture for meat, strangulation in shark nets and death due to the ingestion of plastic or tar balls.
A very few snakes are completely marine.
Characteristics: 1. Reptiles are amniotes and have developed a cleidoic egg. 2. Ectothermic. Maintain a high body temperature by controlling their exposure to the sun. 3. Poses scales or plates that cover the body surface. A few cutaneous glands are present. 4. Well ossified and strong skeleton. Two sacral vertebrae support the pelvic griddle. 5. A tympanic ear has evolved in most reptiles independantly from the amphibians. It has been secondarily lost in some. 6. Cutaneos breathing is negligable. The surface of the lung area is increased. The lungs are ventilated by changing the size of the body cavity. 7. There is a more complete division, in the heart, between the heart ventricle and conus arterious that prevents the mixing of oxygen-rich and oxygen-depleted blood when the lungs are in use (the lungs can be bypassed during prolonged periods of apnea. 8. Nitrogen wastes are excreted in the form of uric acid, therefore conserving water. 9. Fertilization occurs internally. Most reptiles are oviparous, but some species brood their young internally. |
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CHELONI | Turtles |
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SQUAMATA | Snakes & lizards |
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AVES | Birds |
| Many birds depend on the sea, but the focus here falls on the birds which are associated with the open coast. Penguins (Spheniscidae) are found only inthe southern hemisphere. They are all flightless but they use their wings for swimming underwater in a way that resembles flying. Their feathers are modified into scaly cover that traps a layer of air when the bird submerges and then helps to insulate the body from the cold water. Pelicans (Pelecanidae) are characterized from the pouch that hang from their lower jaw and that is used to scoop up fish. Flamingoes (Phoenicopteridae) have extraordinarily long legs and necks and also a bent bill used to sieve food particles from the water. Gannets (Sulidae) are closely related to cormorants, and have large bodies, heavy, sharply-pointed bills, and short, web-footed legs. Cormorants (family Phalacrocoracidae) are mostly black with, short legs and with webbed feet. Their feathers get wet whenever they enter the water and they can often be seen while they are spreading their wings to dry them. They mainly hunt under water, propeled swiftly by their webbed feet. The Herons & Egrets belong to a family (Ardeidae)that are closely related to the Cormorants. They are tall and slender birds, with pointed bills and long thin toes. They frequently wallow in the shallow waters. Waders and Wagtails are common on beaches, rocky shores and estuaries. All the species are associated with shallow waters and their diets consist of small invertebrates. Several species breed in the Arctic and then they migrate to the lower part of the southern hemisphere for the (southern) summer. Gulls (family Laridae) are boisterous scavengers, common around ships, harbours and landfills. The are rather large birds with long slender wings. They poses webbed feet and robust, pointed beaks. The oystercatchers (family Haematopodidae) are the largest of the waders with bills that are considerably flattened from side to side an adaption that assists in prying open mussels. They have short legs with only three toes. Terns (family Sternidae) have slender, pointed bills and more delicate bodies than gulls. Their tales are long and often forked. Most feed on fish, diving from considerable heights to to capture them. |
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| The major internal organs of birds. |
Characteristics: 1. Endothermic. 2. scales on feet, feathers cover the rest of the body. Cutaneos glands are absent except for the presence of a uropygeal (oil) gland. 3. The bones the skeleton comprises of are extremly light and usually pneumatic.
The pectoral appendeges are modified into wings. The sternum is broad and usually keeled. The redused number of caudal vetebrae fuse to form the pygostyle. |
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| The basic skeletal structure of birds. |
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4. The visual centers in the brain and the eyes are enlarged and of great importance. The inner ear comprises a cochlea but it is not long and coiled. 5. The narrow jaws form a horn-covered beak in the contemporary species. There are no teeth. Villi occurs in the small intestine. 6. The lungs are relatively small, but the unusual patterns of air passages and air sacs produce a very efficient one-way passage of air across the respiratory surfaces. 7. The atrium and ventricle of the heart are completely divided so that the mixing of oxygen-rich and oxygen-depleted blood is prevented. 8. Nitrogenous wastes are eliminated primarily in the form of uric acid. The urinary bladder is not present. 9. Birds are oviparous. One of the ovaries and oviducts are lost during the development. The eggs are cleidoic with large amounts of yolk. Albuminous materials and a calcareous shell are secreted around the egg as it passes through the oviduct. |
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MAMMALIA |
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Characteristics: 1. Endothermic. 2. They poses hair and subcutaneous fat to form a layer for insulation. Cutaneous glands are abuntant and they have the jobs of secreting sweat, oil and pheromones. 3. The appendages of mammals are caried to a lesser or greater degree beneath the body. The skull is of type synapsid with a relatively large braincase.The joint of the jaw lies between the squamosal (temporal) bone of the skull and the dentary bone of the lower jaw. 4. Three auditary ossicles occur in the middle ear with a spiral cochlea in the inner ear. 5. A large cerebrum is has a gray cortex. Large cerebellar hemispheres are present. 6. The teeth are heterodont and have a precise occlusion. Their replacement is limited. The small intestine possesses numerous multicellular intestinal glands and microscopic villi. Most of the species lack a cloaca. 7. The digestive and respiratory passages are almost completely seperated by a secondary pallate in the oral phyrangeal areas. Numerous aveoli greatly increase the surface for respiration in the lungs. The diaphragam and a muscular rib cage play a fundemental role in the ventalation of the lungs. 8. Oxygen-depleted and oxygen rich blood run through the heart completely seperated. 9. Nitrogenous wastes are eliminated primarily as urea by metanephric kidneys. The long loops of Henle in the renal tubules makes the production of a urine hyperosomatic to the blood possible. 10. The testis of most mammals are either situated permanently in a scrotum or descend to a scrotum during the breading season. Males possess a penis and fertilzation occurs internally. 11. Except for primitive egg-laying mammals the ovaries are small and produce few eggs. Very little yolk is deposited in the eggs. The oviducts have differentiated into vaginal, uterine, and uterine tube regions. 12. Monotremes are oviparous, other animals are viviparous. The uterine lining and certain extraembryonic membranes unite to form a plasenta. Mammary glands are always present in females. |
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CETECEA | Whales, Dolphins |
| Highly specialized, whales and dolphins have lost their hind limbs and have engineered their fore limbs into flippers for stabilaty and steering with their horizontal tail-flukes providing propulsion. There are two groups: the toothed Odontoceti and the Mysticeti that have comb-like baleen plates, instead of teeth, through which they force water to extract plankton. Some of the larger species were once hunted, for their meat and oil, and their numbers were heavily depleted. Strict protection have ensured that the numbers of certain species have recovered, but the numbers of most previously exploited species are still small. All of the cetaceans are air-breathers and must frequently surface to breath, expelling then a spout of air and watervapour as they do so. Dolphins navigate by echolocation (emitting high-frequency clicks that bounce off solid objects and then back to them. |
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PINNIPEDIA | Seals |
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Seals are adapted to swimming. They have sleekly streamlined bodies that are covered with a layer of insulating blubber and a thick fur to reduce the loss of heat. Their limbs are modified into flippers. The seals are divided into two main families : Fur seals (Otariidae) poses external ears and their hind limbs can be rotated forwards to allow them to walk and run on land. Harbour & Elephant seals (family Phocidae ) have no external ears and their hind limbs can not be turned forward for support in walking and subsequently they have to wriggle their way through life while they move on land. |
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CARNIVORA | Otters |
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SIRENIA | Manatees and Dugongs |
| Manetees and Dugongs are marine herbivores. They have pectoral paddle-like limbs, while their pelvic limbs are lost. Their large horisontal tail is used for propultion |
