Echinodermata PDF

# Invertebrates ZOO 232 ## Phylum Echinodermata - Sea stars (Pisaster ochraceus) surrounded by green algae at low tide. ## Echinodermata Characteristics - Echinoderms have a combination of characteristics found in no other phylum: - an endoskeleton of large plates or small scattered ossicles...

# Invertebrates ZOO 232 ## Phylum Echinodermata - Sea stars (Pisaster ochraceus) surrounded by green algae at low tide. ## Echinodermata Characteristics - Echinoderms have a combination of characteristics found in no other phylum: - an endoskeleton of large plates or small scattered ossicles, - a water-vascular system, - pedicellariae, - dermal branchiae, - basic pentaradial symmetry in the adults ## General Characters: * Body unsegmented with radial, body rounded, cylindrical, star shape, or pentamerous symmetry * No head or brain; few specialization sensory organ * Nervous system with circumoral ring and radial nerve; usually two or three systems of network located at different levels in the body * Endoskeleton of dermal calcareous ossicles with spines or of calcareous spicules in dermis * Water-vascular system of coelmic origin that extends from the body surface as a series of tentacle projections (podia or tube feet) * Locomotion by tube feet which project from ambulacral areas (grooves) * Digestive system usually complete, anus absent in ophiuroids * Coelomic extensive, forming the perivisceral cavity and the cavity of the water vascular system, coelomic of enterocoelous type, coelomic fluid with amebocytes * Blood vascular system (heamal system) much reduced and surrounded by extension of coelomic (periheamal sinuses) * Respiration by dermal branchiae, tube feet, respiratory tree (Holothuroida), and bursae (Ophiuroidea) * Excretory organs are absent * Sexes separate, fertilization usually external * Development indirect through free swimming * Autonomy and regeneration of lost parts conspicuous ## Phylum Echinodermata Summary: - **Subphylum:** Pelmatozoa - Mouth and anus on oral surface - Body in form of cup or calyx - Open ambulacral grooves - Madreporite absent - **Class Crinoidea** - 5 arms branching at the base and bearing pinnules - Ciliated ambulacral groove on oral surface with tentacle-like tube feet for food gathering - Feather star have long, many-branched arms, and adults are free-moving - Many crinoid are deep-water forms but feather star mostly inhabit in shallow water. - **Crinoidea Structure** - The body disc (calyx) covered with a leathery skin (tegmen) containing calcareous plate - 5 branching arms branch to form many more arms each with many lateral pinnules - Calyx and arms together are called the crown. - Sea feather have a long, jointed stalk attached to the aboral side of the body. - Stalk is composed of plates and bear cirri. - **Subphylum:** Eleutherozoa - **Class Asteroidea** - Star-shaped, with arms not sharply marked off from central disc; ambulacral grooves open, with tube feet on oral side; tube feet often with suckers; anus and madreporite aboral; pedicellariae present. - Examples: Astropecten relitaris. - **Form And Function** - **External Features** - Anus - Arm - Central disc - Madreporite - Mouth - Spines - Tube feet - Ambulacra grooves - Sensory tentacles - **Endoskeleton** - Beneath the epidermis of sea stars is mesodermal endoskeleton of small calcareous plates, or ossicles, bound together with connective tissue. - Catch collagen can be changed from a "liquid" to a "solid" form very quickly when stimulated by the nervous system. - Muscles in the body wall move the rays and can partially close the ambulacral grooves by drawing their margins together. - **Coelom, Excretion, and Respiration** - Body coelom filled with fluid amebocytes (coelomocytes), bathes internal organs, and projects into papulae. - The ciliated peritoneal lining of the coelom circulates the fluid around the body cavity and into the papulae. - Exchange of respiratory gases and excretion of nitrogenous waste, principally ammonia, occur by diffusion through the thin walls of papulae and tube feet. - **Water-Vascular System** - It is a set of canals and specialized tube feet that, together with the dermal ossicles, forms a hydraulic system. - In sea stars the primary functions of the water-vascular system are locomotion and food gathering, in addition to respiration and excretion. - The water-vascular system operates hydraulically and is an effective locomotor mechanism. - The basic design applies muscular pressure to coelomic fluid in tube feet to stiffen them for walking. - The ampulla at the top of the tube foot serves as a fluid reservoir. - Each tube foot has in its walls connective tissue that maintains the cylinder at a relatively constant diameter.. - Contraction of muscles in the ampulla forces fluid into the podium, extending it. - Valves in the lateral canals prevent backflow of fluid into the radial canals. - Conversely, contraction of the longitudinal muscles in the tube foot retracts the podium, forcing fluid back into the ampulla. - Contraction of muscles in one side of the podium bends the organ toward that side. - Small muscles at the end of the tube foot can raise the middle of the disclike end, creating suction when the end is applied to a firm substrate - Tube feet are innervated by the central nervous system. - Nervous coordination enables tube feet to move in a single direction, although not in unison - **Feeding and Digestive System** - Sea urchins generally feed by scraping algae off of rocks. - Accomplished via a complex chewing apparatus called Aristotle's latern - Madreporite - Anus - Intestinal cecum - Gonad - Ambulacral Ridge - Ampulla - Cardiac stomach - Pyloric stomach - Pyloric duct - Pyloric cecum - Eye Spot - **Blood-Vascular System: Hemal System** - the hemal system appears to play a role in distributing digested nutrients - Dorsal sac - Stone canal - Axial complex - Axial sinus - Madreporite - Anus - Ring canal - Cardiac stomach - Aboral hemal ring - Pyloric hemal canal - Gastric hemal ring - Perithemal ring - Mouth - Oral hemal ring - Radial hemal canal - **Nervous System** - The nervous system consists of three units lying within the disc and arms. - oral (ectoneural) system composed of a nerve ring around the mouth and a main radial nerve into each arm. It appears to coordinate the tube feet. - A deep (hyponeural) system lies aboral to the oral system, and an aboral system consists of a ring around the anus and radial nerves along the roof of each ray. - An epidermal nerve plexus or nerve net freely connects these systems with the body wall and related structures. - **Sense Organs** - Sense organs are not well-developed, but echinoderms do respond to changes in temperature, chemical composition of their surroundings, and light intensity. - Tactile organs and other sensory cells are scattered over the surface, and an ocellus is at the tip of each arm. Sea stars are usually more active at night. - **Reproductive System, Regeneration, and Autotomy** - Most sea stars have separate sexes. - Fertilization is external. - Echinoderms can regenerate lost parts. Sea-star arms can regenerate readily, even if all are lost. - Sea stars also have the power of autotomy and can cast off an injured arm near its base. Regeneration of a new arm may take several months. - **Development** - Some species produce benthic egg masses in which juveniles develop. Other species produce eggs that are brooded, either under the oral side of the animal or in specialized aboral structures, and development is direct. - Some species even have viviparous brooding of young in the gonads of the adults. - However, most sea stars produce free-swimming planktonic larvae. - **Class Ophiuroidea** - Brittle star are found in benthic marine habitat - Ambulacral grooves closed, covered by ossicles - Tube feet without a sucker and not used for locomotion - Pedicellarie are absent - Anus absent. - The arms of brittle star are movable. - The madreporite located on the oral surface. - Each jointed arm consists of a column of articulate ossicles (vertebrae). - Locomotion by arm movement. - Five movable plates that serve as jaws surrounding the mouth. - Stomach is saclike and there are no intestine. - Five pairs of invaginations called bursae open to ward the oral surface by genital slits at the bases of the arms and water circulate in and out of these sacs for gas exchange - Sex usually separate. - Larva called ophiopluteus - **Defining Characteristics:** - Well-developed ossicles in the arms form a linear series of articulating “vertebrae,” joined together by connective tissue and muscles. - The oral surface bears five pairs of invaginations (bursal slits), which may serve for gas exchange and as brood. - **Biology of Brittle Star** - Brittle star active at night. - Feeding on variety of small particles. - Podia are important to transferee the food to the mouth. - Some brittle stars extend arms into the water and catch suspended particles by mucous strands between arm and spines. - **Class Holothuroidea** - Compared with other echinoderms, holothurians are greatly elongated in the oralaboral axis, and ossicles are much reduced in most; consequently, these animals are soft bodied. - **Form And Function** - Body wall is usually leathery, with tiny ossicles embedded in it, a few species have large ossicles forming a dermal armor. - The body wall contains circular and longitudinal muscles along the ambulacra. - Locomotor tube feet are restricted to the five ambulacral areas or occur all over the body, but most sea cucumbers have well-developed tube feet only in the ambulacra normally applied to the substratum. - The side applied to the substratum has three ambulacra and is called a sole. - Tube feet in the dorsal ambulacral areas, if present, are usually without suckers and may be modified as sensory papillae. - All tube feet, except oral tentacles, may be absent in burrowing forms. Oral tentacles are 10 to 30 retractile, modified tube feet around the mouth. - **Hemal System** - The hemal system is better developed in holothurians than in other echinoderms. - Their water-vascular system is peculiar in that the madreporite lies free in the coelom. - Sexes are usually separate, but some holothurians are hermaphroditic. - Among echinoderms, only sea cucumbers have a single gonad. The gonad is usually in the form of one or two clusters of tubules that join at the gonoduct. - Fertilization is external, and the free-swimming larva is called an auricularia. - Some species brood their young either inside their body or somewhere on the body surface. - Sea cucumbers are sluggish, moving partly by means of their ventral tube feet and partly by waves of contraction in the muscular body wall. - Most sedentary species trap suspended food particles in mucus of their outstretched oral tentacles or pick up particles from the surrounding surface. They then stuff their tentacles into the pharynx, one by one, ingesting captured food. - Others crawl along the substrate grazing the seafloor with their tentacles. - **Class Echinoidea** - **Defining Characteristics:** - Ossicles are joined to form a rigid test. - Podia pores pass through the ambulacral plates. - Adults generally possess a complex system of ossicles and muscles (Aristotle's lantern) that can be partially protruded from the mouth for grazing and chewing. - **Sea Urchins** - Rounded echinoderms, Spherical body, (hemispherical shape) enclosed endoskeleton - Radial symmetry - Lack arm - Body is enclosed in a shell or test - Body surface is usually covered with moveable spines - Echinoid test is a compact skeleton of double plates with movable spines - The ambulacral rows are homologous to five arm in sea star - Ambulacral plates bearing tube feet that radiate out toward the aboral surface - Use podia and spines during locomotion. - The spines are moveable and articulate with the calcareous ossicles. - Inside the test are the coiled digestive system and a complex chewing mechanism (in regular urchins and sand dollar), called Aristotle's latern. - A ciliated siphon connects the esophagus to the intestine and enables water to pass the stomach to the concentrate food for digestion in intestine. - Sea urchin eat algae and other organic materials (graze by their teeth). - sex are separate eggs and sperm shed into the sea for extenal fertilization. - In Pencil seaurchin brood their young in depressions between the spines.