Echinoderms

Name Echino = spiny Dermis = skin Animals with bumpy and irregular texture

General Characteristics Echinoderms have spiny skins. Internal skeleton They have radial symmetry (usually 5 parts) They lack body segmentation. Water vascular system Tube feet = Suction cup like structures There are more than 7000 species of Echinoderms.

The larvae is bilaterally symmetric They are deuterostomes If they are radially symmetric, why are they considered a “higher” evolutionary phyla? Echinoderms are the “highest” invertebrates  the most closely related to humans! The larvae is bilaterally symmetric They are deuterostomes

Nervous System Decentralized nervous system Radial nerves run under the ambulacra (legs) Central nerve ring surrounds the gut Eyespots that can detect light No specialized sensory organs and no definitive brain The arrangement of the central nervous system of echinoderms is quite different from that in other deuterostomes. Radial nerves run under each of the ambulacra, and contain the cell bodies of almost all motor neurons and interneurons. A central nerve ring surrounds the gut, and is composed primarily of fiber tracks connecting the radial nerves. No known echinoderm contains anything that could be called a brain, although ganglia are present along the radial nerves in some echinoderms. Unlike most bilaterian phyla, echinoderms lack any trace of cephalization, and have no specialized sense organs. Sensory neurons are located primarily within the ectoderm of podia, and send axons to the radial nerves.

Circulatory Structures -A Echinoderm has water pumped through its body as part of its very simple circulation system -no specific structures for the circulatory system Hemal system of water pumps through the coelom.

Digestive/Excretory System Tubes grab onto food -> invert their stomach -> secrete/squirt juices (enzymes) that digest -> reabsorb digested food through mouth under the center -> wastes out the aboral anus

Locomotion Vascular system consist of a network of hydraulic canals branching into extensions called papullae (tube feet), which provides: slow movement feeding and gas exchange Tube feet uses hydraulics to create negative pressure which acts as a suction force.

SENSORY STRUCTURES -rudimentary senses including: -light sensitive eyespots sensory tentacles (modified tube feet) at the tips of the arms small patches of cells sensitive to chemicals or touch.

Reproductive System Most are dioecious, with separate male and female individuals, but some are hermaphrodites. Each arm contains two gonads, which release gametes through openings called gonoducts, located on the central body between the arms. dioecious

Types of Echinoderms

Class: Crinoidea Class: Holothuroidea Class: Echinoidea Echinoderm Classes Class: Crinoidea Class: Holothuroidea Class: Echinoidea Class: Ophiuroidea Class: Asteroidea

Class Crinoidea Sea lilies and feather stars fossils Arms branched attached by a stalk or free-moving. The mouth and anus on oral surface. No spines. Filter feeders. Most primitive. Sedentary life, attached to substrate. fossils

Class Holothuroidea Sea cucumbers Elongated body with no arms or spines. Skeleton only of microscopic plates mouth ringed by retractile tentacles(modified tube feet). Detritus feeders. Move in herds.

aboral surface oral surface Class Echinoidea Sea urchins and sand dollars Skeleton rigid (plates fused), mouth parts present, mouth with 3-jaws. Spines movable. Detritivores and grazers. Sea urchin Sand dollar Mouth parts Sea biscuit aboral surface oral surface aboral Aristotle’s lantern endoskeleton oral

Class Ophiuroidea Basket star Aboral surface Oral surface Brittle stars and basket stars Arms distinct from central disc. Tube fee without suckers (not used in locomotion). Can move very fast to escape predators and can leave an arm if caught (detached arm keeps moving to distract predators) Basket star Aboral surface Oral surface

Class Asteroidea Sea stars and starfish Aboral surface Oral surface Arms are not sharply distinct from central disc. Tube feet with suckers (used for locomotion). Carnivores (extreme predators). Can regenerate from parts. Aboral surface Oral surface Aboral surface Oral surface

Life Series Time Lapse Echinoderms