ZOO506 Handouts by VUBuddy

Topic no 1 to 59 mid term and 60 to 134 final term syllabus · 1-Relationship of insects with other animals · Groups of animals

Among the larger groups of animals now recognize~ by science, the one known as the Chordata is naturally the most familiar Including the mammals, birds, reptiles and fishes, besides numerous forms less well known Another group, also familiar, called the Mollusca, includes the snails, clams, etc The starfish and sea urchin, often seen at the seashore, belong with other similar animals to a third group called the Echinodermata A multitude of tiny beings, almost all too small to be seen without the aid of a microscope, are included 'in the group Protozoa A fifth large group is composed mainly of soft, jellylike animals, the more common larger members being called jellyfish, and to this group the name Coelenterata is applied.

Several other groups including various kinds of worms and less familiar forms are also known Arthropoda

The largest group of all, however, is the Arthropoda

Its members found in the seas, in fresh water, on land or even flying freely

A group with remarkable differences of structure, and so abundant that all the other animals taken together are less than one-sixth as many as the arthropods

Well-known members of this group are

The lobsters, cray fish and crabs

Scorpions, spiders, mites, ticks

The centipedes and millipedes

Last, and most abundant of all, the insects

2-Characteristics of Arthropod

No one feature will serve to separate the arthropods from' all other animals

But the possession by an animal of several of those here described will enable the observer to determine in each case whether he is examining one of this group.

In arthropods the body is composed of a series of more or less similar pieces or segments

Placed one behind another, the line of attachment of these to each other being usually somewhat evident on parts of the body at least

This character is also shown, and indeed more clearly, in some worms, such as the common earthworm Another character of the arthropods is the presence of jointed legs (or appendages of some kind), as is indicated by the name of the group, and these are not possessed by worms

The surface of the body is covered by a secretion which hardens on exposure to the air, forming an outside shell or external skeleton called exoskeleton There being practically no internal structures supporting the soft organs within this shell except as ingrowths from the outside

Distinctive Characters of Arthropods Groups

3-Characteristics of Arthropod II

In the possession of this external skeleton these animals have a seeming resemblance to the shells (Mollusca) But the materials of which the skeleton is composed are quite different Being largely calcium carbonate in the Mollusca And chitin which somewhat resembles horn in its nature, sometimes with calcareous salts·deposited in it, in the Arthropoda .The simple members of arthropod have bilaterally symmetrical body, though this condition is concealed somewhat by secondary changes in many of the group .The possession of a bilaterally symmetrical body consisting of a series of segments, an exoskeleton of chitin and the presence of jointed legs are, then, distinctive features of the arthropods .To separate the various groups of arthropods, other characters must be Used Aside from several small sections not often seen, there are five large and important divisions which call for recognition

Groups of Arthropods

1. The Crustacea, including the lobster, crab, beach flea, sowbug and many Others
2. The Diplopoda or millipedes
3. The Chilopoda or centipedes
4. The Hexapoda or insects
5. The Arachnida, including the scorpions, pseudo-scorpions, spiders, mites, ticks, etc.

4-Crustacea

The Crustacea are mainly water-inhabiting animals which breathe either by gills or, in the smaller forms, through the surface of the body In those cases where its members live on land the gills are still present, though in a somewhat modified condition.

They have numerous pairs of legs and generally two pairs of antennae (jointed "feelers")

Often some of the bug; body segments are fused with the head to form a crustacean cephalothorax

5-Diplopoda

The Diplopoda are land animals breathing by air tubes opening on the sides of the body, these tubes carrying the air into all the internal parts of the animal

The head bears a pair of antennae and is followed by a series of segments all practically alike and each, except the first three, with two pairs of legs

The reproductive organs open far forward on the body

In most of the more common members of this group the body is quite cylindrical, and when disturbed the animal usually curls up in a sort of close spiral

Small diplopods about the diameter of the lead of a pencil and gray in color are often found boring into potatoes and roots in the ground In the fall and are sometimes wrongly called wireworms

The Common name, millipede, refers to the large number of legs possessed by these animals

6-Chilopoda

The Chilopoda are also land animals

Like the diplopods they have antennae and breathe by air tubes, and the body segments are practically all alike