31.1 Echinoderms Chordates are most closely related to echinoderms Both groups are deuterostomes Characteristics of Echinoderms Marine animals Endoskeleton made of calcium-rich plates Spines stick out of their skin Adults exhibit radial symmetry Larva are bilateral

Echinoderms include: Sea lilies Sea cucumbers Brittle stars Sea urchins sand dollars Sea stars

Echinoderm Diversity

31.1 Echinoderms Sea Stars Found along shorelines on rocky surfaces Five-rayed body with mouth on underside (oral) and anus on upper side (aboral) On oral surface, each arm has a groove surrounded by tube feet Structures project through skin Spines for protection Pedicelleriae: around base of each spine, keep body surface free of debris Skin gills: extensions of skin for gas exchange

31.1 Echinoderms Sea Stars Feeding Nervous system Opens bivalve with its tube feet Everts cardiac stomach through open shell and releases enzymes Digested food taken in and digestion completed in pyloric stomach Intestine is very short and terminates at anus on aboral (upper) surface Nervous system No central brain Central nerve ring gives off branches to each arm Eyespot at tip of each arm

31.1 Echinoderms Sea Stars Locomotion depends on a water vascular system Water enters through madreporite on aboral side Madreporite leads into stone canals, and these lead into radial canals in each arm Water is pumped into tube feet Suction is created by each small foot No respiratory, excretory, or circulatory systems Reproduction is both sexual and asexual A body fragment, if large enough, can regenerate an entire animal Bilateral symmetry in larva

Sea Star Anatomy and Behavior Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. arm aboral side bivalve mollusc a. © Randy Morse, GoldenStateImages.com

Sea Star Anatomy and Behavior arm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. central disc arm pedicellaria endoskeletal plates skin gill digestive gland eyespot ampula radial canal coelomic cavity tube feet b. Aboral side showing ray cross-section

Sea Star Anatomy and Behavior Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. rectum rectal cecum madreporite anus stone canal pyloric stomach cardiac stomach gonads esophagus ring canal mouth gonopore lateral canal central nerve ring c. Aboral side showing internal cross-section

Sunflower star

Tube feet

Crown of Thorns Starfish

Table. 31.1

31.2 Chordates Phylum Chordata characteristics Notochord Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Chordata characteristics Notochord Dorsal tubular nerve cord Pharyngeal pouches Postanal tail postanal tail notochord dorsal tubular nerve cord pharyngeal pouches

31.2 Chordates Evolutionary trends among the chordates Invertebrate chordates: tunicates and lancelets Vertebrate chordates: fishes, amphibians, reptiles, birds, mammals Cartilaginous fish: first to develop jaws Some early bony fish had lungs Not all bony fish have lungs Amphibians: first to have jointed appendages and invade land Reptiles, birds, mammals: terrestrial adaptations for reproduction

Phylogenetic Tree of Chordates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. mammary gland common ancestor amniotic egg Mammals Amniotes limbs Reptiles* Tetrapods Lungs lungs Amphibians bony skeleton Gnathostomes Lobe-finned Fishes Vertebrates jaws Ray-finned Fishes Chordates vertebrae Cartilaginous Fishes Jawless Fishes ancestral chordate Tunicates Lancelets *includes birds

31.2 Chordates Nonvertebrate Chordates Tunicates (subphylum Urochordata) Sea squirts squirt water when their siphons are disturbed Live in ocean and are filter-feeders Larva is bilaterally symmetrical and has four chordate characteristics Adults are sessile, thick-walled, sac-like organisms The only chordate characteristics in the adults are pharynx and gill slits

Tunicate Life History Larva undergoes metamorphosis to adult form oral opening atrial opening pharynx with gill slits Larva undergoes metamorphosis to adult form Tunicate adult pharynx nerve cord notochord gut Tunicate larva Figure 26.3 Page 446

Tunicates

Tunicate (Sea Squirt)

Sea Squirt, Halocynthia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. excurrent siphon incurrent siphon gill slit tunic © Rick Harbo

31.2 Chordates Nonvertebrate Chordates Lancelets (Subphylum Cephalochordata) Knife-shaped bodies a few centimeters long Live in shallow coastal waters Retain all four chordate characteristics as an adult Segmentation is present Muscles are segmentally arranged Nerve cord has branches

Lancelet, Branchiostoma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. rostrum pharynx notochord oral hood with tentacles dorsal tubular nerve cord dorsal fin gill bars and slits caudal fin atrium atriopore ventral fin anus

Lancelet, Branchiostoma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Heather Angel/Natural Visions

Lancelet, Branchiostoma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. rostrum pharynx notochord oral hood with tentacles dorsal tubular nerve cord dorsal fin gill bars and slits caudal fin atrium atriopore ventral fin anus © Heather Angel/Natural Visions