AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

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AP Inter 1st Year Zoology Notes 4th Lesson Animal Diversity-II: Phylum Chordata


→ Atrium : One of the chambers of the heart; the tympanic cavity of ear; the spacious ectodermlined cavity, enclosing the pharynx in most tunicates and cephalochordates.

→ Creatine phosphate : A high-energy phosphate compound, found in the muscles of vertebrates and some invertebrates, used to regenerate ATP.

→ Endostyle : Mucous secreting longitudinal ciliated groove present on the ventral wall of the pharynx of tunicates, cephalochordates and larvae of the jawless fishes, useful for accumulating and moving food particles to the oesophagus.

→ Filter feeding : Any feeding process by which particulate food is filtered by the ciliary action from the water in which it is suspended. e.g.: Protochordates, Sponges and Bivalves.

→ Mesonephron: It is the functional kidney of the adult fishes, amphibians and the embryos of the ‘amniotes’.

→ Pelagic animals : Animals living in open oceans or seas.

→ Portal system : A system of large veins beginning and ending in a plexus of capillaries, e.g. : Hepatic and renal portal systems of vertebrates.

AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

→ Retrogressive metamorphosis : Metamorphosis of a larva with advanced characters into a degenerate adult, e.g. : Ascidians, Sacculina.

→ Solenocyte : It is a tubular terminal flame cell like structure of a protonephridium. It has one or more flagella, which drive the excretory fluid along the tubule. They are found in cephalochordates.


→ Acrodont: Having teeth attached to the edge of the jawbone without sockets.

→ Claspers : They are formed from the posterior portion of pelvic fins in male cartilaginous fish. They serve as intromittent organs used to channel semen into the female’s cloaca during mating.

→ Coelacanth : An ancient, extant bony fish of the group Rhipidistia which was thought to be extinct until 1938, but was rediscovered in 1938, off the coast of South Africa. At present, there are two living species of the genus Latimerial.

→ Ctenoid scale : A fish scale having marginal projections that resemble the teeth of a comb, found in many teleost fishes.

→ Cycloid scale : A fish scale which is thin and shows concentric lines of growth, without serrations on the margin, found in lung fishes and some teleost fishes. .

→ Dipnoi : They are a group of fishes commonly known as ‘lung fishes’, their lungs are being modified air bladders, e.g. : Protopterus, Neoceratodus and Lepidosiren.

→ Ganoid scales : Thick, bony scales of some primitive bony fishes such as Acipenser.

AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

→ Ostracoderms : Extinct palaeozoic fish like jawless vertebrates, characterized by a heavily armoured body; considered the ancestors of the jawed fishes.

→ Placoid scales : The type of scales found in cartilaginous fishes, with a basal plate of dentine embedded in the skin and a backward-pointing spine, tipped with vitrodentine.

→ Polyphyodont: A type of dentition in which the teeth are naturally shed many times and replaced during the lifetime of vertebrates.

→ Ray finned fishes : They are a highly diverse group of aquatic vertebrates. Over half of all living vertebrate species are ray finned fishes.


→ Alveolus : A small cavity or pit, such as a microscopic air sac of the lungs, terminal part of an alveolar gland, or bony socket of a tooth in the jaws of mammals and crocodiles.

→ Amplexus : The copulatory embrace of frogs or toads during which the male and female shed their gametes.

→ Chyme : Semifluid mass of partly digested food formed in the stomach.

→ Columella auris : A small rod like bone in the middle ear of frogs, reptiles and birds that transmits sound to inner ear; homologous to the mammalian stapes (modification of the hyomandibula of the fishes).

→ Conus arteriosus : It is a single, wide arterial vessel leaving the ventricle and passing ventrally over the right atrium. It is absent in the amniotes.

→ Dura mater: It is the outermost, tpughest and the most fibrous of the three membranes (meninges) covering the brain and the spinal cord.

AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

→ Harderian gland : A gland associated with eye; the fluid it secretes varies in different groups of animals. In some animals it acts as an accessory gland to the lacrimal gland; secreting a fluid that lubricates the nictitating membrane.

→ Labyrinthodontia : A group of extinct amphibians typically resembles heavy-bodied salamanders and crocodiles. They have folded enamel and dentine at the base of conical teeth, e.g. : Eryops.

→ Lacrimal glands : These are paired glands, one in each eye. They secrete watery fluid (tears), which contains lysozyme.

→ Opisthocoelous vertebra : In this type, the centrum is convex at the anterior face and concave at the posterior face; found in the urodeles.

→ Piamater : It is the delicate, inner most and vascularized membrane (meninx) enveloping the brain and spinal cord. It forms the choroid plexuses.

→ Sinus venosus : An enlarged region between the vena cavae and the right atrium. In the heart of frog, the pacemaker is the sinus venosus, (the ‘SA node’ in the heart of a mammal is believed to be an evolutionary remnant of the sinus venosus.)


→ Allantois : It is one of the four extra embryonic membranes of the amniotes. It participates in respiration and excretion in sauropsids and also in the formation of placenta in most of the therians.

→ Amnion : It is the innermost of the extra embryonic membranes. It is a fluid-filled sac enclosing the embryo in the amniotes. It is protective in function (protection from shock and desiccation).

→ Chorion : It is the outermost extra embryonic membrane that surrounds the embryo of amniotes. It participates in the formation of placenta along with allantois in the placental mammals.

AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

→ Hemipenis (plural : hemipenes) : It is one of the pairs of intromittent organs of male squamates (snakes and lizards)

→ Meroblastic cleavage : It is a partial cleavage which occurs in the megalecithal eggs. The cleavages are restricted to a disc like cytoplasmic area near the animal pole. e.g. : Sauropsids and mono tremes.

→ Metanephros : It is the functional kidney of adult amniotes. It is the most efficient type of kidney,

→ Sauropsida : It is a group of amniotes, which includes all extinct and living reptiles and birds.

→ Temporal fossae : These are shallow depressions in the temporal regions of the skull of many reptiles, which provide space for the insertion of muscles.


→ Altricial hatchling : It is the hatchling of carinate bird which is ‘incapable of moving around on its own soon after hatching.

→ Carinate birds : These are the birds with a ‘keeled sternum’ for the insertion of flight muscles, e.g.: Flying birds.

→ Heterocoelous vertebra : It is the type of vertebra in which the articulating surfaces of the vertebral centrum are ‘saddle-shaped’.

→ Pecten : It is a pigmented, vascular and comblike process that projects Into the vitreous humour from the retina at the point of entrance of the optic nerve in the eyes of birds and some reptiles.

AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

→ Precocial young : It is the hatchling of a ratite bird, which is ‘capable of moving around on its own soon after hatching.

→ Theropods : The extinct bipedal carnivorous dinosaurs that gave rise to birds at the beginning of the Jurassic period.

→ Vitreous humour : It is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates.


→ Cochlea : A tubular cavity of the inner ear containing the essential organs of hearing; occurs in crocodiles, birds and mammals. In the eutherians, it is spirally coiled with ‘organ of Corti’ – a specialized region for sound perception.

→ Diphyodont dentition: It is the type of dentition in which two sets of teeth are formed. They are deciduous and permanent sets of teeth which are formed successively.

→ Heterodont dentition : It is the type of dentition in which the teeth are differentiated into cutting, tearing and grinding teeth.

→ Malleus : The outer ear ossicle which is attached to the tympanum in the middle ear of mammals (modification of the articular bone of the ancestors).

→ Placenta : The vascular structure, formed from embryonic and maternal tissues, through which the embryo and foetus are nourished while in the uterus.

→ Sebaceous glands : These are a type of mammalian epidermal glands associated with the hair follicles. They secrete ‘sebum’ which keeps the skin and hair smooth and lustrous.

AP Inter 1st Year Zoology Notes Chapter 4 Animal Diversity-II: Phylum Chordata

→ Stapes : Stirrup-shaped, inner most ossicle of the middle ear in mammals (modification of hyomandibula); Smallest bone in the body of a mammal.

→ Sudoriferous glands : These are epidermal glands of the skin whose secretion (sweat) helps in excretion and thermoregulation; found only in mammals.

→ Therapsids : These are mammal-like extinct reptiles that gave rise to mammals during the ‘Triassic period’. ‘

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