Question

what are body tissues of Echinodermata?

Answer 1

Echinoderms are exclusively marine animals that literaly means 'spiny or prickly skinned'. They possess an endoskeleton of calcareous ossicles, embedded in the skin. The adult forms are pentamerous radially symmetrical but their larvae are bilaterally symmetrical. They possess the organ-system level of organisation and are triploblastic animals having the germ layers viz. ectoderm, mesoderm and endoderm. The different structural aspects of echinoderms and their body tissue organisation are as follows:

(i) The endoskeleton of calcareous ossicles (small bones) embedded in the skin comprised the epithelial tissue elements. Many echinoderms on the body surface bear a number of calcareous spines, they are also called as tubercle which are epidermal in origin. Between the spines, there are pincer like structures called as pedicellariae which are made up of three calcareous plates. Finger like processes called dermal branchiae are also present between the spines that help in respiration.

(ii) Echinoderm has a undefined musculature resembling those with smooth muscles of vertebrates. The visceral musculature is composed of coelomic epithelium or mesothelium which is modified into an unique circulatory system called water vascular system consisting of a system of canals which are filled with watery fluid. It consists of madreporite or sieve plate, stone canal, ring canal, radial canals and tube feet. This water vascular system perform several functions like locomotion, capture and transport of food, respiration, etc. Echinoderms possess catch connective tissues or mutable collagenous tissues that contain large amount of extracellular matrix mainly composed of collagen, proteoglycans and microfibrils. The fluid connective tissue comprised of haemal and perihaemal systems which are of coelomic origin. So the so called circulatory system is open type and the so called blood is often without a respiratory pigment and there is no heart as well.

(iii) Echoinoderms possess nervous tissue that build up the nervous system which include a nerve ring at the center with five radial nerves extending outward along the arms. There is no structure analogous to brain is present.

(iv) Echinoderms have histologically similar muscular tissue as those present in vertebrates. In most echinoderms, they consist of individual bundles of smooth muscle fibres embedded in the extracellular matrix of connective tissue. Muscles present in tube feet namely ampulla and podia helps in locomotion.