Echinoderms and Invertebrate Chordates

Phylum Echinodermata Name means spiny skin Include organisms such as  Asteroidea sea stars  sea urchins, sand dollars  sea lilies  brittle stars  sea cucumbers. All inhabit marine environments

Characteristics Five-part radial symmetry as adults, bilateral symmetry as larvae  Radial symmetry helps slow or fixed animals sense food or predators from all directions Endoskeleton  For support and protection Water-vascular system  Movement, exchange of gases, capture food, and excrete wastes

Endoskeleton calcium carbonate (calcite) plates, ossicles, and spines that are covered with a thin layer of skin Some spines on sea stars are modified to into pincer like appendages- protect and clean the surface of a sea star Can contract muscles to tighten their skin to make the calcite plates rigid, or relax the muscles to enable flexibility

Varied methods of nutrition Sea stars are carnivorous, prey on clams Sea urchins are herbivores, graze on algae Brittle stars, sea lilies, sea cucumbers feed on dead and decaying matter

Invertebrate Chordate Phylum Chordata Chordate criteria  Notochord  Dorsal hollow nerve cord  Gill slits  Post anal tail  Muscle blocks

Notochord Rodlike structure located between digestive system and dorsal hollow nerve cord.  Retained until adulthood in invertebrate chordates  Replaced by backbone in vertebrates  Develops from mesoderm  Provides support so that side to side movement can propel the animal forward

Dorsal hollow nerve cord Develops from ectoderm that forms a tube composed of cells surrounding a fluid filled canal that lies above the notochord. These cells develop into the spinal cord. Cells in anterior portion of cord develop into brain Nerves connect the nerve cord to each block of muscles.

Gill Slits Paired openings located in the pharynx behind mouth. Many chordates only have gill slits during embryonic development Those that have gill slits as adults, strain food from water – the fishes have internal gills that exchange gases during respiration

Lancelets Subphylum Cephalochordata. Small, fish-like, no scales, repeating segments, live in sand with heads sticking out Retain all chordate features throughout life Filter feeders Separate sexes