Phylum Echinodermata

Introduction

• Comes from the greek words echinos meaning sea urchin, hedgehog + derma meaning skin + ata meaning characterized by.

• Belongs to the Deuterostamia branch of the animal kingdom,

• They are marine forms and include the sea stars or starfish, brittle stars, sea urchins, sea cucumbers, and sea lilies.

• 7000 species.

Body Plan

• Body segmented• Endoskeleton is calcareous and spiny, some

are pedicillariae.• Unique water vascular system• Regeneration• Coelomic fluid with amebocytes.

Pedicellariae

Fertilization and Sex

• Sexes separate(except a few hermaphroditic) with large gonads, single in holuthoroids but multiple in most; simple ducts, with no elaborate copulatory apparatus or secondary sexual structures; fertilization usually external; eggs brooded in some.

Locomotion

• Locomotion by tube feet, which project from the ambulacral areas, by movement of spines or by movement of arms, which project from central disc or body.

Ambulacral areas

Nervous System

• No head or brain; few specialized sensory organs; sensory system of tactile and chemoreceptors, podia, terminal tentacles, photoreceptors, and statocysts.

• • Nervous system with circymoral ring and radial

nerves; usually two or three systems of networks located at different levels in the body, varying in degree in degree of development according to group.

Digestive System

• Is usually complete; axial or coiled; anus absent in ophiuroids.

Digestive System

Circulatory System

• Blood-vascular system(hemal system) much reduced, playing little if any role in circulation, and surrounded by extensions of coelom(perihemal sinuses); main circulation of body fluids(coelomic fluids) by peritoneal cilia.

Respiration

• Respiration by dermal branchiae, tube feet, respiratory tree(holuthoroids) and bursae(ophiuroids)

Dermal branchiae

Respiratory Tree

Class Asteroidea

• Sea stars or Starfish• Most Famous echinoderms• Habitat is along the shore lines, muddy and

sandy bottoms and among coral reefs• Often brightly colored• 1800 species

Asteroidea's Water Vascular System

The central disk contains the madreporite.

FeedingAsteroids feed on other, usually sessile organisms such as barnacles and mussels.

Reproduction

• Asteroids may reproduce sexually or asexually. There are male and female sea stars, but they are indistinguishable from one another. These animals reproduce sexually by releasing sperm or eggs into the water, which, once fertilized, become free-swimming larvae that later settle to the ocean bottom.

Sexual Reproduction

Asexual Reproduction

• Asteroids reproduce asexually by regeneration. It is possible for a sea star to not only regenerate an arm, but also nearly its entire body if at least a portion of the sea star's central disc remains.

Asexual Reproduction

Chocolate Chip Starfish - Protoreastor nodosus

Class Ophiuroidea

• Brittle stars, serpent, basket.• Largest of major groups of echinoderms in

number of species, 4000 species• Very fragile looking, worm-like arms and

basket stars have a series of branching arms resembling a basket.

Ophiura sarsi

Ophiuroids

• These marine invertebrates are not 'true' sea stars, but have a similar body plan, with 5 or more arms arranged around a central disc. The central disk of brittle stars and basket stars is usually relatively small, under one inch, and the whole organism itself may be under an inch in size

Feeding

• Depending on the species, basket stars and brittle stars may be predators, actively feeding on small organisms, or may filter-feed by filtering organisms from the ocean water. They may feed on detritus and small oceanic organisms such as plankton and small mollusks.

Reproduction

• an arm if it is being threatened by a predator - as long as a portion of the brittle star's central disc remains, it can regenerate a new arm fairly quickly. Brittle stars and basket stars reproduce sexually, by releasing eggs and sperm into the water, or asexually, through division and regeneration. A brittle star may purposely release

Class Echinoidea

• Sea urchins, Sand dollars and heart urchins• Have a compact body enclosed in an

endoskeletal shell• Lack arms• Five ambulacral areas• Hemispherical shape, radial symmetry

Class Echinoidea

• Colorful• Spines are usually very short• Move by the help of tube feet and spines

Sea Urchins

Sand Dollars

Characteristics• 10 double rows of plates that bear movable stiff

spines.• -5 pairs of ambulacral rows are homologous to the

five arms of the sea star and have pores • -5 converging teeth• -Aristotle Lantern – it is where teeth are attached• -Ciliated siphon connects the esophagus to the

intestine to enable the water to bypass the stomach to concentrate the food for digestion in the intestine.

• -Hermal and Nervous systems are the same with the asteroids

• -Sexes are separate

Aristotle Lantern

Class Holothuroidea

• Sea cucumbers• Resembles a vegetable• Elongated• Ossicles are much reduced in most• Soft –bodied

Characteristics

• Usually leathery with tiny ossicles• Locomotor tube feet are equally distributed to

five ambulacral areas• Oral tentacles are 10 to 30 retractile, modified

tube feet around the mouth• Hydrostatic skeleton• Cloaca

Tube Feet

Cloaca

Characteristics• Respiratory tree• Gas exchange through skin and tube feet• Hermal system is more developed than other echinoderms• Some are hermaphroditic• Single gonad• External fertilization• Move by means of ventral tube feet and waves of

contraction of body walls.• Trap suspended food particles in their oral tentacles and

pick them up and swallow them• They defend themselves by casting out a part of their

viscera

Overview of Viscera

• When in danger, these animals will expel their viscera together with the Cuvierian organ. In the water it becomes larger and splits into long white sticky threads that adhere to the enemy’s body. The venom of the sea cucumbers quickly weakens the muscles of the enemy and if the Cuvierian tubules come into contact with the eyes, the result may be permanent blindness.

The Power of Viscera

Stichopus

Class Crinoidea

• Sea Lilies and Feather Stars• Primitive characters• Once far numerous than they are now• Have a flower shape bodies – sea lilies• Have long many branched arms and remain at

same spot in long period of times – feather stars

Sea Lilies

Feather Stars

Class Concentricycloidea

• Sea daisies• Little, 1 cm in diameter• Disc shaped animals• Pentaradial in symmetry but have no arms• Only 2 species are discovered

Astropecten irregularis

Phylogeny

• Their ancestors are bilateral• Their coelom is trimetric• First echinoderms were sessile and later became radial• The adaptive radiation of the echinoderms has been

determined by the limitations and potentials of their most important characteristics: radial symmetry, the water-vascular system, and their dermal endoskeleton. If their ancestors had a brain and specialized sense organs, these were lost in adoption of radial symmetry.

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