“Spiny skin”

Introduction to Phylum EchinodermataPhylum Echinodermata is a group of

invertebrates that includes sea stars, sea urchins, sea cucumbers, and sand dollars.

Sea star Sea urchin Sea cucumber

Sand dollar

Introduction to Phylum EchinodermataThe members of this phylum are called

echinodermsThey inhabit marine environments ranging from

shallow coastal waters to deep ocean trenches.They vary in diameter from 1cm to 1m and are

often brilliantly colored

Crown of thorns Starfish

Patrick Patiria miniata (Bat Star)

Introduction to Phylum EchinodermataThey start off life as bilaterally symmetrical

larvae and develop into radially symmetrical adults. This feature of development indicates that echinoderms almost certainly evolved from bilaterally symmetrical ancestors.Step 1: Fertilization occursStep 2: Each fertilized egg divides into bipinnariaStep 3: Free swimming and eats small planktonStep 4: It has arms and a suction. Star attaches to bottom of ocean and metamorphosis begins developing into pentaradially symmetrical adult

Introduction to Phylum EchinodermataThe fossil record of echinoderms dates back

to the cambrian period, more than 500 million years ago. Early echinoderms from this period appear to have been sessile, and biologists believe these animals evolved radial symmetry as an adaptation to a sessile existence. Echinoderms later evolved the ability to move from place to place. Today the vast majority of the 7,000 or so species can move by crawling slowly along the ocean bottom.

Introduction to Phylum EchinodermataEchinoderms are deuterostomes (radial cleavage; anus

first). This means that they are animals in which embryonic development is controlled by genes and the 2nd opening in the gastrula (embryo) becomes the mouth.

In protostomes (spiral cleavage; first mouth; mollusks, annelids, arthropods), the 2nd opening becomes the anus.

Introduction to Phylum EchinodermataBecause both echinoderms and chordates are

deuterostomes, it is likely that they have a common ancestor.

Most echinoderms have a type of radial symmetry called pentaradial symmetry, in which the body parts extend from the center along five spokes.

Introduction to Phylum EchinodermataIn addition to their pentaradial symmetry,

echinoderms have three other major characteristics that are not shared by any other phylum:1. They have endoskeleton composed of calcium

carbonate plates know as ossicles. The ossicles may be attached to spines or spicules that protrude through th skin. In fact, the name echinoderm actually means “spiny skin”.

2. They have a water vascular system, which is a network of water-filled canals inside their body

Introduction to Phylum Echinodermata3. They have many small, movable extensions

of the water-vascular system called tube feet, which aid in movement, feeding, respiration and excretion.

Phylum Echinodermata

Taxonomists divide the 7,000 species of echinoderms into six classes, five of which we

will discuss

Class CrinoideaCalled crinoids, include the sea lilies and

feather stars.The name crinoid means “lily-like.”About 600 living species.Sea lilies most closely resemble the fossils of

ancestral echinoderms from the Cambrian period. They are sessile as adults, remaining attached to rocks or the sea bottom.

Sessile Free-moving

Class CrinoideaFeather stars, in contrast, can swim or crawl

as adults, although they may stay in one place for long periods.

In both types of crinoids, five arms extend from the body and branch to form many more arms – up to 200 in some feather star species.

Fossil specimen of stalked sea lily

Class CrinoideaSticky tube feet located at the end of each arm

filter small organisms from the water. The tube feet also serve as a respiration surface across which crinoids exchange oxygen and carbon dioxide with the water.

Cilia on the arms transport trapped food to the crinoid’s mouth at the base of the arms. The mouth faces up in crinoids, while in most other echinoderms the mouth faces toward the sea bottom.

Class OphiuroideaConsists of basket stars and brittle stars.Distinguished by their long narrow arms, which allow

them to move more quickly than other echinoderms.About 2,000 species – the largest echinoderm class.

Basket stars Brittle star

Class OphiuroideaBrittle stars, so named because the coiled

branches of their flexible arms break off easily, can regenerate missing parts

Most basket stars and brittle stars are active at night and are usually found beneath stones or seaweed or buried under the sand.

Class EchinoideaConsists of about 900 species of sea urchins and

sand dollars.Echinoidea means “spinelike”Sea urchins are well adapted to live on hard sea

bottoms. They use their tube feet for locomotion and feed by scraping algae from hard surfaces with the five teeth that surround their mouth.

Underside of urchin showing teeth

Class EchinoideaIn some sea urchins, the spines are flexible,

while in others, they are hollow and contain a venom that is dangerous to predators as well as swimmers.

Pencil Sea Urchin (flexible spines)

Purple Urchin

Class EchinoideaSand dollars live along seacoasts. They are usually

found in coastal areas and have the flat, round shape of a silver dollar. Their shape is an adaptation for shallow burrowing. The short spines on a sand dollar are used in locomotion and burrowing, and they help clean the surface of the body. They use their tube feet to capture food that settles on or passes over their body.

Class EchinoideaSand dollars live along seacoasts. They are usually

found in coastal areas and have the flat, round shape of a silver dollar. Their shape is an adaptation for shallow burrowing. The short spines on a sand dollar are used in locomotion and burrowing, and they help clean the surface of the body. They use their tube feet to capture food that settles on or passes over their body.

Class HolothuroideaSea cucumbers belong to the class

HolothuroideaArmless. Live on the sea bottom, where they

crawl or burrow into soft sedimentAbout 1,500 speciesThe ossicles that make up their endoskeleton

are very small and are not connected to each other, so their bodies are soft.

Class HolothuroideaSea cucumbers belong to the class

HolothuroideaArmless. Live on the sea bottom, where they

crawl or burrow into soft sedimentAbout 1,500 speciesThe ossicles that make up their endoskeleton

are very small and are not connected to each other, so their bodies are soft.

Class HolothuroideaModified tube feet form a fringe of tentacles

around the mouth. When these tentacles are extended, they resemble the polyp form of some cnidarians. That explains the name of this class, which means “water polyp.”

A sea cucumber uses it tentacles to sweep up sediment and water. It then stuffs its tentacles into its mouth and scrapes the food off them.

Unique defensive behavior: Can forcefully eject part of their internal organs when threatened.

Class AsteroideaThe sea stars belong to the class Asteroidea,

which means “starlike”About 1,500 speciesThey live in coastal waters all over the worldThey exist in a variety of colors and shapes

and can have dozens of armsThey are economically important because

they prey on oysters.