Terms in this set (30)

located in the pharyngeal part of the digestive tract behind the oral cavity and anterior to the esophagus. The visceral clefts appear as several pairs of pouches that push outward from the lateral walls of the pharynx eventually to reach the surface to form the clefts. Thus the clefts are continuous, slit-like passages connecting the pharynx to the exterior.
The soft and skeletal tissues between adjacent clefts are the visceral arches. The embryonic fate of the clefts and slits varies greatly depending on the taxonomic subgroup. In many of the non-vertebrate chordates, such as tunicates and cephalochordates, the clefts and arches are elaborated as straining devices concerned with capture of small food particles from water.
In typical fish-like vertebrates and juvenile amphibians the walls of the pharyngeal clefts develop into gills that are organs of gas exchange between the water and blood.
In adult amphibians and the amniote tetrapods (= reptiles, birds and mammals) the anteriormost cleft transforms into the auditory (Eustachian) tube and middle ear chamber, whereas the other clefts disappear after making some important contributions to glands and lymphatic tissues in the throat region.
The skeleton and muscles of the visceral arches are the source of a great diversity of adult structures in the vertebrates. For example, in humans (and other mammals) visceral arch derivatives include the jaw and facial muscles, the embryonic cartilaginous skeleton of the lower jaw, the alisphenoid bone in the side wall of the braincase, the three middle ear ossicles (malleus, incus and stapes), the skeleton and some musculature of the tongue, the skeleton and muscles of the larynx, and the cartilaginous tracheal rings.
The Ascidiacea are the Sea Squirts or Tunicates and they make up the bulk of the species found within the Urochordata.
They are all sessile (non-moving or staying in one place) as adults. Most species are common coastal animals occurring in rock pools and out into deeper water to about 400 meters depth, though there are species which have been found living ad depths up to 5,000 meters. They can be either solitary or colonial and the colonial species may share a common exhalent siphon.
Many species are translucent or whitish in color but some species are much more colorful and can be red, brown, yellow and even blue. The name Tunicates arises from the existence of the tunic.
The larvae resemble tadpoles and are far more obvious members of the phylum Chordata than the adults. The larvae swim towards light and thus the surface of the sea at first then after a short while they reverse direction and swim down towards the sea floor, often in less than one day.
Tunicate larvae do not feed and are essentially a dispersal form. Soon they find a suitable spot on the sea floor and the settle in a head down, tail up position. They attach themselves to the sea floor (substrate) using special adhesive glands in the front of their head. Once settled they undergo an amazing metamorphosis during which the symbols of the phylum Chordata, the post-anal tail and the notochord it contained are lost. The remainder of the body twists through 180 degrees in order to become a small tunicate. Most tunicates are thought to live about one year as adults.
Carilaginous fishes
Bony Teeth
leathery protective skin
gills (some must swim to circulate water)
internal fertilization
eggs or live birth
Sharks, skates, rays, and even stranger fish make up the Chondrichthyes, or "cartilaginous fish." First appearing on Earth almost 450 million years ago, cartilaginous fish today include both fearsome predators and harmless mollusc-eaters (harmless, that is, unless you are a mollusc). A number of shark and ray species are fished, commercially or for sport.
Members of the Chondrichthyes have a skeleton made of cartilage. Only their teeth, and sometimes their vertebrae, are calcified; this calcified cartilage has a different structure from that of true bone. Thus, preservation of the whole body of a cartilaginous fish only takes place under special conditions.

Not only does this class have internal fertilization and a reproduction strategy that reminds about what is seen in amniotes, they have also a relative brain development of its major divisions which reminds about what is found in birds and mammals. Their relative brain weight comes close to that of mammals, and is about ten times of bony fishes at the same size. There are not surprisingly some exceptions; the bony fishes mormyrids have a relative brain size to be compared with the brain size of humans, while the primitive Megamouth have a brain of only 0.002 percent of its body weight.
Digestive system - Their digestive systems are unique due to spiral valves, and with the exception of Holocephali they also have a cloaca

Because they don't have any bone marrow, the RBC must be produced somewhere else. The spleen and special tissue around the gonads is where we can find the production of red blood cells, as well as a special organ called Leydig's Organ and is only found in cartilaginous fishes, even if some have lost it. Another unique organ is named epigonal organ, and has probably a role in the immune system.
A spiracle is found behind each eye on most species. Their tough skin is covered with dermal teeth, also called placoid scales or dermal denticles, making it feel like sandpaper.
1 . Sharks typically have a fusiform body (rounded and tapering at both ends). This body shape reduces drag and requires a minimum of energy to swim.
2. Sharks are generally drably countershaded. Countershading is a type of camouflage in which the dorsal side is darker than the ventral side. The result is that predators or prey do not see a contrast between the countershaded animal and the environment.
3. Fins - Fins are rigid, supported by cartilaginous rods. Sharks have five different types of fins.
a. Paired pectoral fins lift the shark as it swims.
b. Paired pelvic fins stabilize the shark.
c. One or two dorsal fins stabilize the shark. In some species, dorsal fins have spines.
d. A single anal fin provides stability in species where it is present; not all sharks have an anal fin.
e. The caudal fin propels the shark.
4. Head.
a. Eyes -are lateral on sharksSome species have an eyelidlike structure called a nictitating membrane. The nictitating membrane protects the eye from being injured by thrashing prey while the shark is feeding.
b. Nostrils - Sharks have ventral external nostrils. Some species have nasal barbers, sensory projections near the nostril
c. Mouth. - the mouth is usually ventral. The mouth may have labial folds or furrows. Teeth are modified, enlarged placoid scales. Sharks have numerous rows of teeth attached at their bases by connective tissue. Several rows of replacement teeth continually develop behind the outer row(s) of functional teeth. As the functional teeth fall out, replacement teeth take their place. Some species of sharks may shed as many as 30,000 teeth in a lifetime.
5. Gill slits - Sharks have five to seven pairs of lateral gill slits.
6. Spiracles - Some species of elasmobranchs have small openings called spiracles behind the eyes at the top of the head. These openings bring oxygen-carrying water into the gill chamber. Spiracles originate from rudimentary first gill slits and are reduced or absent in active, fast-swimming sharks.
7. Scales -Sharks have placoid scales, also called dermal denticles Placoid scales have the same structure as a tooth, consisting of three layers: an outer layer of vitro-dentine (an enamel), dentine, and a pulp cavity. Placoid scales are arranged in a regular pattern in sharks and an irregular pattern in batoids.
Unlike other types of scales, placoid scales do not get larger as the fish grows. Instead, the fish grows more scales.
- Like teeth, the shape of the scales is variable among species and can be used to identify the species.
- Placoid scales gave rise to teeth, stingrays'spines, and the dorsal spines of horn sharks (Heterodontus spp.) and dogfishes (family Squalidae).
- As a shark or batoid swims, placoid scales may create a series of vortices or whirlpools behind each scale. This enables a shark to swim efficiently.
- European cabinetmakers used the rough skin of a shark as sandpaper, called shagreen. With the denticles removed, shark skin is also used for leather.
Must spend part of their early development in water
limbs extend laterally
lungs and skin for gas exchange (moist skin)
external fertilization
metamorphosis found in some species
Some of the physical features of amphibians, like the scales of gymnophions, suggest their fish ancestry. Other characteristics are more clearly related to those of their descendants--the reptiles, birds, and mammals. Amphibians are unlike fishes in that most types have limbs instead of fins and generally breathe through lungs and skin instead of through gills. Unlike reptiles, amphibians lack a scaly or armored covering and take in water and oxygen through their skin. Amphibians have developed in many different ways in order to survive in areas with widely varying climates, dangers, and food sources.
Most amphibians are relatively small animals. Except for the salamander of Japan, the giants among them became extinct long ago. They vary in length from less than 2/5 inch (1 centimeter) to over 60 inches (150 centimeters). The West African Goliath frog grows to more than 1 foot (30 centimeters) in length and may weigh as much as a full-grown house cat. Most of the species have four limbs. The hands generally end in four fingers, and the feet in five toes. Although the limbless gymnophions crawl, most amphibians with legs move by jumping, climbing, or running.
The skulls are usually flat and wide, and the teeth, which grow in the jawbones and roof of the mouth, lack roots and are replaced intermittently. Amphibians do not chew with these teeth. They use their long, flexible tongues to capture their prey, which they then swallow whole.
The moist, supple skin of most amphibians provides protection and absorbs water and oxygen. The upper skin layer, called the epidermis, is regularly shed in a process called molting. The skin usually comes off in one piece and is then eaten by the animal.
The lower skin layer, called the dermis, of the typical amphibian often includes mucous and poison glands. The mucous glands help provide essential moisture to the body. The protective poison glands are quite often located in different places on different species--by the ears in certain toads, and behind the eyes of salamanders. These glands produce poisons that are toxic to natural enemies, such as birds and small mammals, but that rarely harm humans.
These glandular secretions give some amphibians distinct odors. The spotted salamander and the common toad smell of vanilla. Some frogs smell of onion, and the fire-bellied toad smells of garlic.
The skin's protective properties include the ability to change color so that the animal can hide when an enemy is nearby. Certain cells under the skin alter the color so that the amphibian can blend into its surroundings. Sometimes parts of the skin become brightly colored. The amphibian displays these colors to enemies to warn them to keep away.
The sense organs vary greatly, depending on the order and the species. The eyes are virtually useless in underground amphibians but are well-developed in other species. The sense of smell is generally good. Hearing ability varies according to the species. Some amphibians also have pores on their bodies, called lateral line organs, that are sensitive to vibrations in the water.
internal fertilization
deeper skull
long and flexible neck
scales to prevent water loss
the shelled amniote egg
efficient lungs and circulatory system
further development of limbs and skeleton
1. Reptiles have tough, dry, scaly skin offering protection against desiccation and physical injury. The skin consists of a thin epidermis, shed 3'l periodically, and a much thicker, well-developed dermis (Figure 3a). The dermis is provided with chromatophores, the colour-bearing cells that give many lizards and snakes their colourful patterns.
The characteristic scales of reptiles are formed largely of keratin. Scales are derived mostly from the epidermis; they are not homologous to fish scales, which are bony, dermal structures. In some reptiles, such as alligators, the scales remain throughout life, growing gradually to replace wear. In others, such as snakes and lizards, new scales grow beneath the old, which are shed at intervals. Turtles add new layers of keratin under the old layers of the platelike scutes, which are modified scales. In snakes the old skin (epidermis and scales) is turned inside out when discarded; lizards split out of the old skin leaving it mostly intact and right side out or it may slough off in pieces.
2. The shelled (amniotic) egg of reptiles contains food and protective membranes for supporting embryonic development on land. Reptiles lay their eggs in sheltered locations on land. The young hatch as lung- breathing juveniles rather than as aquatic larvae. The appearance of the 34- shelled egg (Figure 3b) widened the division between the evolving amphibians and reptiles and, probably more than any other adaptation, contributed to the evolutionary establishment of reptiles.
3. Reptilian jaws are efficient for crushing or gripping prey. The jaws of fish and amphibians are designed for quick jaw closure, but once the prey is seized, little static force can be applied. In reptiles jaw muscles became larger, longer, and arranged for much better mechanical advantage.
4. Reptiles have some form of copulatory organ, permitting internal fertilization. Internal fertilization is obviously a requirement for a shelled egg, because the sperm must reach the egg before the egg is enclosed. The glandular walls of the oviducts secrete albumin (source of amino acids, minerals, and water for the embryo) and shells for the large eggs.
5. Reptiles have a more efficient circulatory system and higher blood pressure than amphibians. In all reptiles the right atrium, which receives unoxygenated blood from the body, is completely partitioned from the left atrium, which receives oxygenated blood from the lungs. Crocodilians have two completely separated ventricles (Figure ); in other reptiles the ventricle is incompletely separated. Even in reptiles with incomplete separation of the ventricles, flow patterns within the heart prevent admixture of pulmonary (oxygenated} and systemic (unoxygenated} blood; all reptiles therefore have two functionally separate circulations.
6. Reptilian lungs are better developed than those of amphibians. Reptiles depend almost exclusively on lungs for gas exchange, supplemented by respiration through the pharyngeal membranes in some aquatic turtles. Reptiles suck air into the lungs by enlarging the pleural cavity, either by expanding the rib cage (snakes and lizards} or by movement of internal organs (turtles and crocodilians}. Reptiles have no muscular diaphragm, a structure found only in mammals. Cutaneous respiration (gas exchange across the skin), so important to amphibians, has been completely abandoned by reptiles.
7. Reptiles have efficient water conservation. All amniotes have a metanephric kidney which is drained by its own passageway, the ureter. However, the nephrons of the reptilian metanephros lack the specialized intermediate section of the tubule, the loop of Henle that enables the kidney to concentrate solutes in the urine. To remove salts from the blood, many reptiles have salt glands located near the nose or eyes (in the tongue of saltwater crocodiles) which secrete a salty fluid that is strongly hyperosmotic to the body fluids. Nitrogenous wastes are excreted by the kidney as uric acid, rather than urea or ammonia. Uric acid has a low solubility and precipitates out of solution readily, allowing water to be conserved; the urine of many reptiles is a semisolid suspension.
8. All reptiles, except the limbless members, have better body support than the amphibians and more efficiently designed limbs for travel on land. Nevertheless, most mode~ reptiles walk with their legs splayed outward and their belly close to the ground. Most dinosaurs, however, (and some modern lizards) walked on upright legs held beneath the body, the best arrangement for rapid movement and for the support of body weight. Many dinosaurs walked on powerful hindlimbs alone.
9. The reptilian nervous system is considerably more complex than the amphibian system. Although the reptile's brain is small, the cerebrum is larger relative to the rest of the brain. Connections to the central nervous ( system are more advanced, permitting complex kinds of behaviour unknown in amphibians. With the exception of hearing, sense organs in general are well developed. Jacobson's organ, a specialized olfactory chamber present in many tetrapods, is highly developed in lizards and snakes. Odours are carried to Jacobson's organ by the tongue
4 chambered heart
7 cervical vertebrae (neck bones)
Most are viviparous though some are oviparous
teeth embedded in the jaw bone
Well developed brain
Possess hair which is made of keratin. The evolution of mammalian keratin is believed to be independent of reptilian keratin. Hair provides insulation . Endothermic. The majority of the heat energy is used to maintain their high body temperature. 4 chambered heart. Mammary glands are used to produce milk to nourish their young. Female glands are the only functional glands. The diaphragm is a muscle that separates the thoracic cavity from the abdominal cavity. 7 cervical vertebrae (neck bones) are present in most mammals. Most are viviparous though some are oviparous. An extended gestation period (uterine development) is common in most placental mammals. Teeth are imbedded in the jaw bone and come in a variety of forms. Well developed brain.

Although mammals share several features in common (see Physical Description and Systematics and Taxonomic History), Mammalia contains a vast diversity of forms. The smallest mammals are found among the shrews and bats, and can weigh as little as 3 grams. The largest mammal, and indeed the largest animal to ever inhabit the planet, is the blue whale, which can weigh 160 metric tons (160,000 kg). Thus, there is a 53 million-fold difference in mass between the largest and smallest mammals! Mammals have evolved to exploit a large variety of ecological niches and life history strategies and, in concert, have evolved numerous adaptations to take advantage of different lifestyles. For example, mammals that fly, glide, swim, run, burrow, or jump have evolved morphologies that allow them to locomote efficiently; mammals have evolved a wide variety of forms to perform a wide variety of functions.