“Spiny skin”

Introduction to Phylum Echinodermata Phylum Echinodermata is a group of invertebrates that includes sea stars, sea urchins, sea cucumbers, and sand dollars. Sea starSea urchinSea cucumber Sand dollar

Introduction to Phylum Echinodermata The members of this phylum are called echinoderms They 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)

Why is this phylum placed above the bilateral derived characteristic when they are obviously radially symmetrical?

Introduction to Phylum Echinodermata They 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 occurs Step 2: Each fertilized egg divides into bipinnaria Step 3: Free swimming and eats small plankton Step 4: It has arms and a suction. Star attaches to bottom of ocean and metamorphosis begins developing into pentaradially symmetrical adult

Introduction to Phylum Echinodermata The 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 Echinodermata Echinoderms are deuterostomes (radial cleavage; anus first). This means that they are animals in which embryonic development is controlled by genes and the 2 nd opening in the gastrula (embryo) becomes the mouth. In protostomes (spiral cleavage; first mouth; mollusks, annelids, arthropods), the 2 nd opening becomes the anus.

Why do Echinoderms and Chordates share a common ancester?

Introduction to Phylum Echinodermata Because 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 Echinodermata In 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 Echinodermata 3. 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 Crinoidea Called 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. SessileFree- moving

Class Crinoidea Feather 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 Crinoidea Sticky 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 Ophiuroidea Consists 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 Ophiuroidea Brittle 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 Echinoidea Consists 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 Echinoidea In 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 Echinoidea Sand 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 Echinoidea Sand 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 Holothuroidea Sea cucumbers belong to the class Holothuroidea Armless. Live on the sea bottom, where they crawl or burrow into soft sediment About 1,500 species The ossicles that make up their endoskeleton are very small and are not connected to each other, so their bodies are soft.

Class Holothuroidea Sea cucumbers belong to the class Holothuroidea Armless. Live on the sea bottom, where they crawl or burrow into soft sediment About 1,500 species The ossicles that make up their endoskeleton are very small and are not connected to each other, so their bodies are soft.

Class Holothuroidea Modified 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 Asteroidea The sea stars belong to the class Asteroidea, which means “starlike” About 1,500 species They live in coastal waters all over the world They exist in a variety of colors and shapes and can have dozens of arms They are economically important because they prey on oysters.