Origin And Characteristics Of Vertebrates

Comparative Anatomy of Vertebrates Characteristics and Origin Prepared by Mr. Ian Kenneth M. Cabrera

Objectives • To identify the three important characteristics of chordates and the over-all characteristics of vertebrates. • To know the features, i.e. structure and form, of lower chordates. • To describe similar morphological characteristics between lower and higher vertebrates. • To know the taxonomic hierarchy and classification of vertebrates.

General Chordate Characteristics • The wall of the pharynx of the embryo or adult is pierced by openings, the gill slits or pharyngeal slits which probably served as a food catching device. • A notochord is present in the embryo or adult. The notochord is a rod lying dorsal to the intestine, extending anteroposteriorly, and serves as a support. • The presence of a dorsally located, hollow neural tube containing a single continuous cavity.

Characteristics of Vertebrates • The morphological characteristics of vertebrates are the following: • Animals with bilateral symmetry, internal heteronomous segmentation, and high degree of cephalization. • With two pairs of locomatory appendages in the form of fins or limbs. • Skin separable from the rest of the body wall commonly producing protective structures such as scales, feathers, hair, etc. • With an internal skeleton made up of either cartilage or bone consisting of a skull and gill supports in the head, vertebral column, ribs and breastbone in the trunk and support for the appendages. • Digestive tract giving rise to two equally important digestive glands, the liver and the pancreas.

• Nervous system consisting of the brain, much enlarged, encased within the skull, and the spinal cord protected by a highly metameric vertebral column. • Head with three pairs of senese organs: eyes, ears and nose. • The pharynx is intimately connected with the respiratory tract. • Heart always ventral in the body. • Genital and excretory systems closely related. The excretory ducts generally serving as genital ducts. • Viscera supported by mesenteries. • Circulatory system generally closed, always with a median dorsal artery, the aorta, and with one or two portal systems.

Esssential Features of Lower Chordates Phylum Hemichordata •

Members are marine, worm-like organisms. • With apparent links to chordates and to echinoderms • Chordate features include the presence of pharyngeal slits and the embryonic invagination of the neural tube. • Some species pass through a small planktonic stage called tornaria larva which is equipped with cilia running along its body surface and has a simple gut. These features resemble that of echinoderms’ auricularia larva.

 The body is divided into 3 distinct regions: proboscis, collar, and trunk. - the proboscis is the elongated, conical structure located at the anterior end of the animal. It is used for burrowing into the sand. - the collar is a band encircling the body posterior to the proboscis. The proboscis is attached to the collar by a slender proboscis stalk. A permanently open mouth which leads to a buccal cavity is located ventrally. - the trunk is further divided into 3 regions: the branchiogenital (also known as thoracic region), forms the first part of the trunk and contains the gonads; the hepatic region, where the intestines are located and usually bears a paired series of lateral pouches called hepatic caeca; the abdominal region, forms the last portion of the trunk which bears the remainder of the tubular intestine and terminates at an opening , the anus.

Subphylum Urochordata •

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Generally show all chordate characteristics at some point in their life histories: notochord, pharyngeal slits, tubular nerve cord, and even the presence of a post-anal tail especially during their larval stage. All species are marine. Adult forms are sessile, juvenile form – free swimming. They are specialists at feeding suspended matter. The name literally means “tail backstring”, a reference to the notochord. Also known as tunicates, referring to the outer body covering of the animal in the sessile, adult form – tunic (also known as test).

 The lower end of the animal serves  

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as an attachment to any substrate on the ocean floor. Hardly recognizable as an animal. The opposite end bears two openings, the siphons. - the upper siphon, oral or incurrent siphon; the lower one, atrial or excurrent siphon. Tunic or test, the outer covering is secreted by the underlying epithelial tissue Some tunicates have transparent tests.

Subphylum Cephalochordata •

Occurs in warm temperature and tropical seas. • Body is slender and fish-like, pointed at each end and compressed laterally. • The more blunt end is the anterior and the more pointed end is the posterior.

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Ventral portion of the head – oral hood – expanded membrane, enclosing a cavity the vestibule. At the bottom of which is the mouth located. Tentacles or cirri – form the borders of the oral hood. Metapleural folds or lateral fins – extends posteriorly from the oral hood forming the ventro-lateral fin of the animal. Muscle segments or myotomes – longitudinal V-shaped muscles visible through the transparent epidermis. Each separated from one another by connective tissue partitions – myosepta.

*note: other internal structures and cross-section of the animal will be dealt in the laboratory.

Classification of Vertebrates •

Subphylum Vertebrata or Craniata. all chordates with an endoskeleton consisting of cartilage or bone or a combination of both. Fish and fish-like animals Superclass Agnatha. are fish-like animals with no jaws with poorly developed fins Class Myxini. the hagfishes Class Cephalaspidomorpha Order Petromyzoniformes. the lampreys. Superclass Gnathostomata. fish with jaws and apparently a full-sized hyoid gill slits, with pectoral and pelvic fins, body covered with scales, with cartilage or bone as skeleton. Includes some extinct species Class Placodermi. extinct fish with jaws. Class Chondrichthyes Subclass Elasmobranchii Order Selachimorpha. Sharks. Order Batidoidimorpha. Rays and skates. Subclass Holocephali. The chimereas

Examples of lower forms of fishes. from top (clockwise), hagfishes, lampreys, and two examples of extinct placoderms.

Class Chondrichthyes.

From upper l-r. Great White shark, Ray-shark; from bottom l-r. Hammer-head shark, skate.

Class Osteichthyes. The bony fishes. Skeleton partly or largely ossified, body clothed in dermal scales or rhomboid plates, gills covered with bony operculum, with air or gas bladders, nostrils double, no claspers. Order Acipenseriformes. Sturgeons, paddlefishes Order Lepisosteiformes. Gars. Order Amiiformes. Bowfins Superorder Dipnoi. The lungfishes. Subclass Actinopterygii or Teleostomi. Order Chondostrei Order Holostei Order Teleostei. Typical bony fishes. Class Amphibia Order Gymnophiona or Apoda. The coecilians or blindworms. Vermiform amphibians without limbs or limb girdles. Vertebrae amphicoelus with persistent notochord. Order Urodela or Caudata. Newts and salamanders. Naked tailed amphibians, with or without external gills, with two pairs of limbs. Order Salientia or Anura. Frogs and toads. Naked, tailless amphibians, with external gills, with typical vertebrae, caudal vertebrae fused into one elongated piece, with two pairs of limbs.

Class Amphibia top: Coecilian, a blindworm middle: newts bottom left: salamander, Salamendra terrestris bottom right: Yellow tree frogs

Class Reptilia. Cold-blooded aquatic or terrestrial tetrapods; naked, scaly or with bony plates, breathing exclusively by lungs, skeleton completely ossified, heart with sinus venosus, ventricles partially or completely divided by a partition, embryo provided with embryonic membranes. Subclass Anapsida Order Testudinata Suborder Chelonia. The turtles. Superorder Lepidosauria. Order Rhynchocephailia. Order Squamata. Lizards and snakes. Long tailed reptiles covered with scales, quadrate movable, teeth set in sockets, vertebrae usually procoelus, abdominal ribs wanting or ruminary. Suborder Lacertilia. The lizards. With limbs and limb girdles. Suborder Ophidia. The snakes. Limb and limb girdles absent. Superorder Archosauria. Skull diapsid with two temporal openings, tending to bipedal gait, also includes flying forms, birds (Aves) stem from this group. Order Crocodylia. Alligators, crocodiles and caimans. Large aquatic or amphibous reptiles, with bony plates underneath horny skin thickenings, teeth in sockets, ribs double-headed, heart with two ventricles.

Class Reptilia

Class Aves. The birds. Warm blooded, oviparous tetrapods with feathers; one occipital condyle, forelimbs modified into wings, heart with two ventricles, embryo with membranes. Subclass Sauriurae Infraclass Archeornirthes. The Archaeopteryx. Infraclass Neornithes. Tail feathers arranged in a fan-like manner around tail stump, metacarpals fused, teeth present only in extinct forms. All present birds. Superorder Palaeognathae. Ostritches, emus, rheas, cassowaries, kiwis and other flightless birds. Superorder Neognathae. Order Falconiformes. Falcons, hawks Order Galliformes. Grouse, pheasants Order Sphenisciformes. Penguins Order Anseriformes. Ducks, geese Order Strigiformes. Owls Order Psittaciformes. Parrots Order Apodiformes. Hummingbirds

Class Mammalia. The mammals. Warm blooded; nearly always viviparous, aquatic or terrestrial tetrapods clothed with hair, wool or fur, some naked or with sparse hair; skull with zygomatic arch, two occipital condyles, teeth in sockets, with muscular diaphragm, young nourished with milk secreted by the mammary glands, embryo with membranes. Subclass Prototheria. Oviparous mammals, mammary glands without nipples, with cloaca. Infraclass Monotremata. The monotremes, which includes the duckbill platypuses and Echidna the spiny anteater. Subclass Theria Infraclass Metatheria, also Didelphia or Marsupialia. Viviparous mammals with an abdominal skin pouch called a marsupium, wherein the very fragile young are kept; teats opening into the marsupium, no cloaca, vagina double. Order Marsupialia. Kangaroos, wallabies, wombats, koalas, and opossums, and others.

From clockwise (l-r): duckbilled platypus, kangaroo and koala

Infraclass Eutheria, Monodelphia or Placentalia. The placental mammals. Viviparous mammals with an allantoic placenta, without marsupium, one vagina, no cloaca. Order Edentata. The edentates. Anteaters and sloths. Order Insectivora. The insectivores. Shrews and moles. Order Chiroptera. The flying mammals. Bats Order Dermoptera. Flying squirrels. Order Primates. Lemurs, monkeys, apes and man Order Carnivora. The carnivores Suborder Fissipedia. The typical, terrestrial carnivores. Cats, lions, tigers, dogs, wolves, civets, foxes, hyeanas, cheetahs, racoons, bears, otters, weasels, etc. Suborder Pinnipedia. Aquatic carnivores. Seals, sea lions, and walruses. Order Perrisodactyla. Odd-toed ungulates. Horses, asses, and zebras Order Artiodactyla. Even-toed ungulates. Pigs, hippopotamuses, camels, deers, antelopes, cattle, sheep, goats, giraffes, etc. Order Proboscidea. The elephants. Order Sirenia. Dugong, manatees Order Rodentia. The rodents. Rats, mice, squirrels, prairie dogs, guinea pigs, porcupines,etc. Order Lagomorpha. Hares and rabbits.

• It should be noted that these are just some of the hundreds of different classes, orders, suborders in the entire animal kingdom. • The groups that you have seen here are just the common ones, most familiar to you, non-biology and non-zoology majors. Hopefully. • It should also be understood that you must be able to differentiate each of the different groups you’ve seen here. • Take note of the diversity of the animal world. As well as of the Earth millions of years ago.

References Hyman, L.H. Comparative Vertebrate Anatomy. The University Chicago Press. 2nd ed. 1963. Kardong, K. Vertebrates Comparative Anatomy, Function, and Evolution. McGraw-Hill.2nd ed. 1998.

The End Thank you for listening And have a nice day!

…sed libera nos a malo