In the Pedipalpida, two median eyes are large and six small eyes are placed along the margin. In all Ar­thropods, excepting Insects, the circulatory system performs this dual role. Your IP: 207.180.199.176 Of these three kinds of salivary glands, usually only one kind is functional and other two are degen­erated. Phylum Arthropoda contains more species than any other phylum. True salivary glands originating from the pharyngeal system open within the pharynx. In arthropods, the muscles are striated. Jointed foot:They are commonly called Arthropods, Word “arthro” means “joined” and “pod” means “feet”. In Scorpionids, the hindgut is the straight continuation of the midgut and is called rectum. In Stomatopoda, these digestive glands are ar­ranged in ten metameric pairs. Segmentation: Their body is segmented. Some of the walking legs being chelated can grab the food. Majority of the arthropods are ovipa­rous and it is curious enough that in most of them there are certain devices for internal fertilization. In the thorax are longitudinal muscles are present as a pair of dorsal and a pair of ventral bundles. In all the Crustaceans (excepting Cirripedia, Malacostraca and some Cladocera) both the sexes have reproductive openings in the same segment. The larvae of a Dipteran insect, Master can pro­duce eggs which develop parthenogenetically. Body has more than two cell layers, tissues and organs. The eye stalk is usually jointed but in many Branchiopods the stalk is unjointed. The eye may be single or paired. In some Crustacea, paired ganglia of each segment are fused; in others the ventral nerve cord is reduced. Some of these somatic muscles can work at astounding speed, e.g., wing muscles of insects, muscles operating the stridulating organs in various arthro­pods. The Myriapods have powerful mandibles for capturing and cutting the food. The young resembles the adult but many adult structures are lacking. But in advanced groups the appendages are differentiated to capture food. The diverticula of the midgut produce digestive juices. Mouth is placed at the ventral and terminal end of the head. • Why don't libraries smell like bookstores? In Scolopendra, it is enclosed within a cardiac diaphragm. The hindgut is considerably long and in some (Julidae) is subdivided into three parts. Privacy Policy3. In certain Crustaceans, e.g., Palaemon, Argulus, larva does not come out of the egg. Such her­maphrodites are called protandrous because in them male reproductive organs appear first and then the female organs. In Insecta, three sets of glands—labial glands, maxillary glands and mandibular glands are often referred together as salivary glands, which secrete digestive juices. The mouth in gen­eral is ventrally placed and some distance away from the anterior end. In Arachnids, the presence of haemo­globin in blood plasma has given red colour to the blood. In all arthropods, the integument consists of: (i) An innermost extremely thin stellate cell layer, called basement membrane, (ii) A monolayer of closely packed hexagonal cells, hypodermis (epidermis) and. In Limulus, similar disposition of eyes is marked but the median eyes are com­pound in nature. In Xiphosura, the short tubular rectum has folded walls. In Diplopods, a pre- oral cavity is present in front of the mouth and it leads to a pharynx of varied length. The inner side of the base of the first maxilla possesses a pit with profuse lining of setae. Round eggs may have varied concentra­tions of yolk. Many insects lay their eggs directly within the body of some other insects. What are the general characters of pteridophytes? In Insects, the blood is usually colourless. The reproductive organs in both the sexes are hollow and are usually united either completely or incompletely above the ali­mentary canal. Each joint is provided with two sets of muscles, one of which is antago­nistic to the others. Their body has jointed appendages which help in locomotion. But in Malacostraca, the next part, stomach is also included within foregut. The Crustaceans exhibit an evolutionary trend in the food-getting devices. It is called mixocoel and as blood flows through it, this is also referred to as haemocoel. Here fertilization and major part of the develop­ment take place within a special chamber, called ‘uterus’. This organ has a fluid-filled vesicle inside to act as membranous laby­rinth. The Phylum Arthropoda Etymology: From the Greek Arthron a joint and Pous for foot. These sense organs co-ordinate joint movement and work as vibration receptors. Thus transformation occurs internally and a young resembling the adult is hatched out. It is called mixocoel and as blood flows through it, this is also referred to as haemocoel. Body Cavity of Arthropods: In Arthropoda, true coelom appears as pouches in the embryonic stage In course of development its walls are used up in the formation of organs and the space becomes continuous with the blastocoel. A general survey of life history in the different groups of Arthropods reveals the existence of three categories of development: From the egg hatches out an individual, which resembles the adult in all respects except the size. Reproductive System 8. They show following characters. These setae work for receiving smell and are distributed over the antennae.

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