PHYLUM ECHINODERMATA BY DR O A IYIOLA Introduction

PHYLUM ECHINODERMATA BY. DR. O. A. IYIOLA

Introduction to Phylum Echinodermata • The term Echinoderm means “spiny skin. • They are strictly marine and some echinoderms can regenerate limbs or other body parts. • They are of interest because of all the invertebrates, are considered to be most closely related to vertebrates.

Introduction: Phylum Echinodermata • Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. • Contains about 7, 000 living species, making it the second-largest grouping of Deuterostomes. • Deuterostomes are the echinoderms and chordates • Flatworms, Molluscs, Annelids, Arthropods & roundworms are the Protostomes • Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.

• • General Characteristic features of Phylum Echinodermata Unique water vascular system of coelomic origin The water vascular system extends from body surface as tentacle-like tube feet called podia Water vascular system opens to the exterior as Madreporite or Hydropore. Endoskeleton made of dermal calcerous ossicles with spines.

Characteristic features of Phylum Echinodermata • Adult’s body is radially symmetrical with penta-radiate basis usually in multiples of 5. • But larva is bilaterally symmetrical with a more centralized nervous system than adult. • Adult are more primitive. • Nervous system and sense organs not welldeveloped in adult.

• • • Characteristic features of Phylum Echinodermata A large coelom is present with simple alimentary canal. A peculiar water vascular system. Body has an internal calcerous skeleton made of mesodermal origin which bears spine There is no trace of metameric segmentation. Lack a definite head & brain but a mouth is present which is ventral in position.

General Characteristic features of Phylum Echinodermata • Sexes are separate but few are hermaphroditic & fertilization is external. • Larvae are free swimming, their form & development indicate some relationship with Phylum Chordata. • The chordate-like features of the Echinoderms are Deuterostomes: • In this group the blastopore becomes the adult anus & not the mouth as in annelids, molluscs, & arthropods

General Characteristic features of Phylum Echinodermata • Excretory organ absent • Respiration is by papulae, tube-feet, respiratory tree (Holothuroids) & bursae (Ophiuroids) • Blood vascular system (hema system) is much reduced playing little if any role in circulation. • Blood vascular system is surrounded by extension of coelom. • Nervous system with circumoral ring • Digestive system complete (axial or coiled) but anus absent in Ophiuroids

THE FIVE CLASSES ECHINODERMATA OF PHYLUM • CLASS ASTEROIDEA eg Asterias rubens (Star fish) • CLASS OPHIUROIDEA eg Ophiothrix (Brittle star) • CLASS ECHINOIDEA eg Echinus esculenta (Sea urchins), Sand dollars • CLASS HOLOTHUROIDEA eg Sea cucumber (Cucumaria sp) • CLASS CRINOIDEA eg Sea lilies, feather stars, Antedon sp

REPRESENTATIVE MEMBERS OF EACH CLASSES OF ECHINODERMS

Water vascular system(w. v. s) • W. v. s is very unique to Echinoderms. • It is a network of fluid-filled canals & specialized tube feet, that together with dermal ossicles, forms a hydraulic system • W. v. s derived from the coelomic compartment (body cavity) • Functions in gas exchange, feeding, sensory reception and is an effective locomotor mechanism. • W. v. s varies between classes of echinoderm but typically opens to the exterior through a sieve-like madreporite which may be on the aboral or oral surface of Echinoderms

The water vascular system: • Assists with the distribution of nutrients throughout the animal's body • Most obviously expressed in the tube feet which can be extended or contracted by the redistribution of fluid between the foot and the internal sac. • In Holothuroids, the podia may be reduced or absent and the madreporite opens into the body cavity so that the circulating liquid is coelomic fluid rather than sea water.

Characteristic Asteroidea features of Class • Are star-shaped or pentagonal with 5 or more arms or rays projecting from the central disc • Members move freely in water, unattached • Calcerous spines on upper surface which may be modified into minute pedicellariae • These pedicellariae keep the upper surface free from dirts. • Mouth located at the centre of oral or upper surface leads sac-like stomach & 5 pairs of hepatic caeca

Characteristic features of Class Asteroidea • Has median ambulacral groove • Tube feet are used as locomotor organs & prey capture (Carnivores). • Aboral side has inconspicuous anus & conspicuous circular Madreporite. • Madreporite is the opening of water vascular system located exteriorly at the ventral region. • Nervous system is made of nerve ring around the mouth & nerve cord in the arms. • Fertilization is external: Bipinnaria larva metamorphose to Brachiolaria larva later changes to young adult starfish.

STARFISH- CLASS Asterias rubens ASTEROIDEA-

STARFISH- CLASS ASTEROIDEAAsterias rubens

Characteristic features of Class Ophiuroidea • Brittle star are largest of the major group of Echinoderms • Arms sharply marked off from central disc • They crawl across the ocean floor using their flexible armfor locomotion • They have no pedicellariae or papulae

Characteristic features of Class Ophiuroidea • No ambulacral groove • Have tube feet without suckers & ampullae, merely used as tactile organ • The tube feet aid in feeding • In contrast to the Class Asteroida, the Madreporite of the Class Ophiuroidea are found on the oral and not in aboral surface.

Oral View of spiny Brittle star (Ophiothrix sp)

Ophiuroid with aboral disc cut away to show principal structures like Gonads, Bursae (fluid-filled sac )where water constantly circulates for respiration.

Pictorial View of spiny Brittle star (Ophiothrix sp)

Characteristic features of Class Echinoidea • Body is covered by endoskeletal test or shell • The test reflects a typical pentamerous plan of echinoderms in their 5 ambulacral areas • Ambulacral plates have pored plates through which the tube feet emerge • Mouth with five hard teeth arranged in a circlet (known as Aristotle's lantern) • Move with tube feet (podia) or ”walk” on their spines

Characteristic features of Class Echinoidea • Madreporite located on the aboral region • Fertilization is external with Echinopluteus larva formed with later develops into adult. • Traditionally divided into 2 groups: regular (Regularia) and irregular echinoids(Irregularia)

Characteristic features of Class Echinoidea • Sea urchins use their feet to prevent the larvae of encrusting organisms from settling on their surfaces; potential settlers are moved to the urchin's mouth and eaten. • Some burrowing sea stars extend their elongated dorsal tube feet to the surface of the sand or mud above and use them to absorb oxygen from the water column.

Differences between Regular and Irregular Echinoidea Regular Echinoidea • • Has hemispherical shape Radial symmetry Medium to long spines Move by means of tube feet with the aid of spines • Prefer rock surfaces • Example is sea urchins Irregular Echinoidea • • Has irregular shape become secondarily bilateral Short spines Move chiefly by means of spines • Prefer to burrow in sand • Examples are heart urchins & sand dollars

Characteristic features of Class Holothuroidea • Bear a remarkable resemblance to vegetable called cucumber • They are different from other Echinoderms in that they are greatly elongated in the oral-aboral axis. • Ossicles are much reduced in most members • Coelomic cavity is spacious & fluid-filled • Digestive system empties posteriorly into a muscular cloaca • Fertilization is external & the free-living larva is called articularia

Internal Structure of Holothuroidea

Characteristic features of Class Holothuroidea • Have respiratory tree which consist of two long manybranched tubes which also empties into the cloaca • Gas exchange occurs through the skin and the tube feet • Among all Echinoderms, only Sea cucumber has a single gonad • Sexes are separate but some Holothuroideas are hermaphrodite • Sea cucumber has a peculiar power of self-mutilation whereby when irritated or under unfavourable condition cast out its visceral content through the anus as a means of defense mechanism.

Characteristic Crinoidea features of Class • They differ from other Echinoderms by being attached during a substantial part of their lives. • Sea lilies have a flower-shaped body at the tip of an attached stalk • Feather stars have long, many branched arms • Adult are free-living although they may remain in the same spot for a long period. • Water vascular system follows the basic echinoderm plan • Eg Sea lilies, Feather stars

Characteristic Crinoidea features of Class • There is no madreporite to allow exchange of fluid with the surrounding environment. • The aboral system is more highly developed in Crinoids than in other Echinoderms • Sexes are separate • Gonads are simple • The larva of Crinodea is called Doliolaria

Oral view of Sea lily (Crinoidea) showing ambulacral groove

Summary of Diversities in the 5 classes of Echinoderms Features Holothuroides e. g Sea cucumber Shape, Body surface Arms Cucumbershaped , with Soft, leathery skin, No spines No arm Larva Auricularia Madreporit Opens into the e coelom, rather than outside Mouth Located Anteriorly Crinoidea e. g Sea lily Echinoidea eg Echinus esculenta (Sea urchin) Feather-shaped, Heart or globular No spines -shaped, With numerous fine spines Arm with No protruding heavily calcified arms plate Vitellaria/Dolio Echinopluteus laria Asteroidean eg Star fish Ophiuroidea eg Brittle star Star-shaped, with ciliated, pigmented epidermis Protruding arm Star-shaped with Leathery skin Bipinnaria & Branchiolaria Ophiopluteus No madreporite On Aboral surface Circular & on On oral Aboral surface Directed upward At the center of Central, on lower oral surface At the center of lower oral surface Protruding arm

Diversity in larvae forms of Echinoderms • BIPINANARIA LARVA – ASTEROIDEA • BRANCHIOLARIA - ASTEROIDEA • OPHIOPLUTEUS –OPHIUROIDEA • ECHINOPLUTEUS- ECHINOIDEA • AURICULARIA –HOLOTHUROIDEA • DOLIOLARIA- CRINOIDEA

Diversity in larvae forms of Echinoderms

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