Chacta - (plural chaetae), Bristle, especially of annelid worms.

Chactognatha - A small phylum of marine, coelomate animals including sagitta, the common planktonic arrow worm. The relationships of this group are not clear.

Chemoreceptor - Sense organ reacting to chemical stimulation (e.g) organs of taste and smell.

Chemotaxis - Movement of an organism in response to chemical stimulation. Flatworms and many other creatures move instinctively towards food but away from acids and other harmful substances.

Chilopoda - Centipedes; sub class of Myriapoda.

Chiroptera - Order of mammals containing the bats the only truly flying mammals and the limbs are modified accordingly. The wings are elaborate folds of skin supported by the enormously elongated finger bones (other (than that of the first digit or thumb). the rest of the arms, the sides of the body, and the legs and tail. Compare this arrangement with the wings of the birds and the pterosaurs the only other vertebrates to have taken to the air. The most amazing thing about bass is their 'radar' system of echo location. A bat's eyes are almost useless and it finds its way about by sending out series of high pitched sounds (much too high for human ears to detect). These sound waves bounce back from nearby objects and the echoes are picked up by the bat's large ears. This all happens so quickly that the bat can detect and avoid an obstacle even when flying at high speed. The 'radar' is so sensitive that the bats can use it to detect and catch the flying insects on which they feed. Apart from their modifications for life in the air, the bats closely resemble the insectivores.

Chitin - Horny, nitrogen containing material which makes up most of the external skeleton (cuticle) of arthropods and also the chaetae of annelid worms. It is very tough and resistant to a wide range of chemicals.

Chitons - (See Mollusca).

Choanae - (=Internal Nares). The internal openings of the nasal cavity possessed by all land living vertebrates, Lung-fishes have internal nares but other fishes do not: their organs of smell are situated in pits at the front of the head but the pits do not open into the mouth cavity.

Cholinesterase - A very important enzyme that destroys acetylcholine in the nervous system.

Chondrichthyes - (=Elasmobranchii).

Chondrostei - Order of fishes of the class Actinopterygii (q.v.) in which there is a reduction of bone so that most of the skeleton is of cartilage. Bony plates on the head and other features however, show that they are descended from bony ancestors and are not related to the cartilaginous sharks and rays. The order contains the sturgeons and the strange paddlefish Polyodon.

Chordata - Large phylum including all the back boned animals (sub phylum Vertebrata) and a number of other creatures; the sea' squirts (sub phylum UrocllOrdata); acorn worms and their relatives (HemichordoTa); and Amphioxus and its relatives (Cephalochordata). The diagnostic characteristics of the phylum are the possession at some stage in the life history of gill slits, a flexible skeletal called the notochord, and a hollow dorsal nerve cord. These features are present in the embryos of all vertebrates but in the higher forms the gill slits disappear and the notochord is replaced by the vertebral column, leaving the hollow, dorsal nerve cord as the only connection between the vertebrates and the invertebrate chordates.

Chorion - An embryonic structure; the outer wall of the sac containing the embryo of reptiles, birds, and mammals. The amnion is the inner wall.

Choroid - Pigmented layer outside the retina of vertebrate eye. Contains blood supply for retina.

Chromatid - One of the two strands of a chromosome.

Chromatophore - Cell containing pig ment. In many animals the cells, or the pigments within them, can expand and contract and thus bring about a colour change in the animal. The chromatophores are controlled by nerves or hormones.

Chromosome - Double thread like structure which can be seen in cell nuclei when the cells are undergoing division. In normal body cells the chromosomes occur in pairs the number of pairs depending on the species. The members of each pair (except sex chromosomes, look exactly alike and are said to be homologous. Chromosomes are composed mainly of nucleo proteins and they carry the genes that control the features of the cell and, indeed, of the whole body. When, for example, a skin cell divides, it is essential that the new daughter cells are identical with the parent. During the division of the nucleus the chromosomes all divide along their length, each producing two identical daughter chromosomes. One daughter from each new cell, carrying identical instructions, so that the .new cells will be exactly alike. This process is called mitosis.

Although the body cells contain pairs of chromosomes (diploid condition), the sex cell, i.e. sperms and ova, contain only half the normal number, one of each pair (haploid condition). A special form of cell division known as metiosis (q.v.), gives rise to the sex cells; the bomologous chromosomes come together and they separate, one going to each new cell. At fertilisation, a sperm and an egg cell join and so produce the diploid number of chromosomes again.

Chrysalis - Pupa or resting stage between larva and adult insect of butterfies, moths and some other insects.

Chyme - Partly digested food in stomach.

Cilliary Body - Outer part of iris of vertebrate eye.

Ciliated - Covered with minute hairs (cilia) e.g. ciliated epithelium.

Ciliophora - A class of protozoans all of which possess cilia at some stage in their lives Most of them (e.g. Paramoecium) retain the cilia but some such as Acineta lose them as adults and replace them by suction pads on small tentacles.

Cilium (plural cilia) - Very short, fine 'hair' projecting from the cell surface of certain types of cell. There are always many and they beat with a definite rhythm. They are found in most animal groups and their function is to move the animal through the water (e.g. Paramoecium) or to move liquids along inside the animal. The lining of man's nose is covered with cilia which beat and sweep out mucus and any dust that it traps.

Cirripedia - Barnacles a sub class of the Crustacea although because of their fixed mode of life they are very unlike typical crustacenas. .

Class - A category used in the classification, of living organisms.

Classification - There are over a million known kinds or species of animals and zoologists must be able to refer to any of these by a definite name so they will be understood by other zoologists no matter what language they speak. For this, reason living things are named in Latin. Sevenspoted ladybird' means nothing to a Russian zoologist but if he reads Coccinella septemunctata, he knows exactly what creature is being referred to All organisms are given two mames: the first is the generic name, indicating the genus to which the creature belongs, and the second is the specific name indicating the exact species within the genus a genus being a group of closely related species.

The double name therefore gives a better idea of the relationships of a creature than a single name could do. Linnaeus was the fist to use this binomial system on any wide scale. Classification, however, means more than merely dividing creatures into genera and the genera into species; these are merely the finest divisions. The animal kingdom is in fact divided into about twenty major groups called phyla. Each phylum contains animals with certain basic similarities. Within each phylum some animals are more alike than others and these ate separated into Classes, may be subdivided into sub classes, these into orders, orders into sub orders, sub orders into families, families into genera and genera into species.

The members of a large division, therefore, have fewer characters in common than those in a sub division.

For example, mammals and bony fishes are vertebrates, that is they have a backbone and a hollow dorsal nervous system, part of which forms a brain that is protected by a braincase. However, mammals have hair, suckle their young, have limbs and are warm blooded. Fishes lack hair and have a scale covered body, they have fins and not limbs, the young generally hatch from eggs which are laid, and they' are cold blooded. Both are placed in separate sub groups of the Vertebrata.

If we classi man starting with his mammal grouping (Class Mammalia) we can see how his genus and species rankings are arrived at. He is a placental mammal (sub class: Placentalia) which is based on a number of characters. He belongs to the Order Primates along wth the tarsiers, lemurs, apes and monkeys all animals with binocular vision, similar skeletons, etc. Only the apes and monkeys are included with man in the sub order Anthropoidea and only fossil man is in the same family, Hominidae. His gemus Homo is the same for Neanderthal man, but the latter's species is neanderthalensis, while man's is sapiens,

Man's classification as described here may be summarised as:
Class : Mammalia
Subclass: Placentalia
Order : Primates
Suborder: Anthropoidea
Family : Hominidae
Genus : Homo
Species : Sapiens

Man is a backboned animal (i.e. a vertebrate) with places him in the sub-phylum Vertebrata. Above this, his phylum ranking is the Chordata (all animals that at some stage in their life possess gill slits and an elastic supporting rod or notochord and always have a hollow dorsal nervous system, i.e. one in the back).
Vertebrata and Chordata would be placed above class Mammalia in a fuller classification.