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Segmentation in biology is the division of some animal and plant body plans into a linear series of repetitive segments that may or may not be interconnected to each other. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda , Chordata , and Annelida .
Arthropod heads are typically fused capsules that bear a variety of complex structures such as the eyes, antennae and mouth parts. The challenge that the arthropod head problem has to address is to what extent the various structures of the arthropod head can be resolved into a set of hypothetical ancestral segments.
Arthropod eyes Head of a wasp with three ocelli (center), and compound eyes at the left and right. Most arthropods have sophisticated visual systems that include one or more usually both of compound eyes and pigment-cup ocelli ("little eyes"). In most cases, ocelli are only capable of detecting the direction from which light is coming, using ...
The development of distinct tagmata is believed to be a feature of the evolution of segmented animals, especially arthropods. In the ancestral arthropod, the body was made up of repeated segments, each with similar internal organs and appendages. One evolutionary trend is the grouping together of some segments into larger units, the tagmata.
Heteronomous annulation is a characteristic of some arthropods. It means that segments are differentiated from one another, each having different form so as to serve a different function – for instance, using some limbs for walking and others for feeding. The trait is first observed in the armoured lobopods. [1]
As in all arthropods, the chelicerate body has a very small coelom restricted to small areas round the reproductive and excretory systems. The main body cavity is a hemocoel that runs most of the length of the body and through which blood flows, driven by a tubular heart that collects blood from the rear and pumps it forward.
The arthropod exoskeleton is divided into different functional units, each comprising a series of grouped segments; such a group is called a tagma, and the tagmata are adapted to different functions in a given arthropod body. For example, tagmata of insects include the head, which is a fused capsule, the thorax as nearly a fixed capsule, and ...
The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. [1] In insects, it contains most of the digestive tract, respiratory system, and circulatory system, and the apical segments are typically modified to form genitalia.