MARB 435 1st Edition Lecture 20 Current Lecture Phylum Echinodermata Approximately 6 000 living species Good fossil record 13 000 described fossil species Morphology endoskeleton of calcareous ossicles pentamerous radial symmetry in the adults body can be divided into five similar parts arranged around a central axis but bilateral symmetry in larvae Tricoelomate Catch connective tissue Coelomicwater vascular system forms hydraulic tube feet for locomotion feeding and gas exchange Catch connective tissue A k a mutable connective tissue Variable and reversible rigidity of connective tissue Nerves control the stiffness of extracellular matrix Increase in Ca2 stiffens the ECM probably by forming bridges between proteins Allows automy voluntary casting off of arms in a sea star or viscera in a sea cucumber as escape mechanisms Development Typical deuterostome development These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute radial cleavage Blastopore becomes anus mouth forms secondarily Coelomic cavities develop by enterocoely Mesoderm is derived from archenteron Larva is always bilaterally symmetrical Class Stelleroidea Subclass Asteroidea Approximately 1500 species Star shaped body Occur worldwide mostly in coastal waters Benthic Can be colorful Usually 5 arms but sometimes up to 40 Asteroidea morphology Mouth lies in the middle of the oral surface ambulacra grooves extend into the arms Each ambulacrum contains 2 4 rows of tube feet for locomotion Movable spines on each side can cover the ambulacrum A small eyespot lies at the end of each ambulacrum Endoskeleton Consists of ossicles small calcareous plates secreted by sclerocytes Can form spines rods plates or crosses pedicellariae claw shaped ossicles Defense against parasites or small settling organisms Sometimes also used for prey capture Nervous system Central nervous system Circumoral nerves Radial nerves Peripheral nervous system ectoneural system lies in the epidermis and is mainly sensory hyponeural system lies in the coelomic lining and is mainly motoric Sense organs Eyes at tip of arms Sensory tube feet Digestive system and feeding Many asteroids can evert their cardiac stomach for extra oral digestion Stomach releases digestive enzymes and engulfs the prey Most asteroids are scavengers and carnivores Asexual Reproduction Some species can automize and regenerate arms Some can reproduce by fission by softening themutable connective tissue Sexual Reproduction Gonochoric 10 gonads 2 in each arm Each gonad has its own gonopore between the bases of the arms Most sea stars are free spawners a single female can release up to 2 500 000 eggs Most have planktonic larvae but some brood their offspring Sea Star Wasting Syndrome First discovered in the ochre star Pisasterochraceus in June 2013 in Olympic National Park Affects at least 20 species Has been observed on the north American west coast from Alaska to northern Mexico in intertidal and subtidal habitats Subclass Ophiuroidea About 2000 species Mostly cryptic lifestyles Five jointed arms that are clearly set off from the central disc Arms lack ambulacral groove Tube feet have no suckers Reproduction and development Asexual reproduction common by autotomy of arms Sexual Reproduction Have small pockets at the bases of the arms called bursae Gonads open into the bursae Larvae are often brooded in the bursae Planktonic larvae ophiopluteus