Phylum Echinodermata

Characteristics n Echinodermata are all marine, triploblastic unsegmented coelomates n Phylum has 3 unique features: u pentagonal symmetry (bilateral in larvae) u calcite spicules embedded in the skin, often partly fused u Tube feet (podia)

Characteristics n There is no cephalization F Which explains why Patrick isn’t the smartest creature in bikini bottom! n There is a meaningful gradient in all echinoderm bodies: u one surface has the mouth and tube feet (oral or ambulacra), u while one does not (aboral) n The anus is often, but not always, aboral.

An unhurried phylum.. n No echinoderm moves fast, apart from a very few deep sea holothurids which swim actively n Crinoids are sessile, the others crawl at a rate of mm / minute n During one Antarctic marine survey a starfish was tagged. A year later the same animal was in the same exact spot, having apparently done nothing at all!

Originally… n The ancestral echinoderm was a sessile filter-feeder, extending its oral surface upwards to capture food n This sedentary design has evolved into motile forms where the feeding surface faces downwards

Characteristics n The only connected phylum is our own, the chordates - based on embryological evidence. F Look at Evolutionary Tree in textbook n Deuterosome u Radial cleavage u Anus forms first n First species to evolve with this type of development

Characteristics n The aboral surface is rough and spiny n Around the base of the spines are pedicillaria: tiny jaws used to keep the body surface free of debris, protection and aide in food capture

Water Vascular System n Primary function is locomotion and food gathering, in addition to respiration and excretion n From the aboral surface is a madreporite (allows pressure equalization and top up water supply) which is the only asymmetrical tube in the system n It connects to an inner Ring Canal in which branches into 5’s lateral canals (one down each of the star fishes arms)

Water Vascular System n From the Lateral canals is many ampulla (muscular sacs) which connected to the suckers on the outer surface of the starfish F Some lack suckers n By filling the ampulla and coelom with liquids and applying pressure, allows arms to stiffen creating a hydraulic system.

Tube feet n Podia (tube feet) are not scattered over the body surface n They lie in 10 rows (5 pairs), the ambulacral grooves n Each tube foot + its ampulla is isolated from the water vascular system by a valve n Tube feet vary - starfish have muscular suction cups, other forms have sticky tips. n Crinoids are different - primitive

Reproduction n Gonads lie as 10 (2N) paired structures at the base of ambulacral grooves. n External reproduction n Sexes are separate, and discharge gametes into the sea water

Development n Larval Stage- free-swimming, bilateral (some with direct development) n Metamorphosis u Metamorphosis involves a dramatic reorganization of a bilateral larva into a radial juvenile u Larval mouth and anus disappear and a new mouth and anus will form. u What was the left side becomes the oral surface u What was the right side becomes the aboral surface

Phylum Echinodermata EVOLUTION

Sadly... n Of the 13 classes of echinoderms known, 8 are extinct. n Echinoderms were dominant forms in Carboniferous seas, but have suffered a long-term decline in phyletic richness

Classes n Class Crinoidea n Class Asteroidea n Class Ophiuroidea n Class Echinoidea n Class Holothuroidea

Class Crinoidea n Feather stars & Sea lilies n Abyssal filter feeders n 5000 fossil spp, 620 living n Body made of ossicles n 10 arms have podia (no ampullae) feeding particles to the mouth. n Arms can move n Mouth and anus are both on oral side

Class Asteroidea n “Starfish” n Active predators u feed on bivalves u use suction cups to pull open the shells with forces of up to 5kg n The stomach is eversible, and can be partially inserted inside prey’s shell (enzymes but no toxins)

Class Ophiuroidea n Brittle Stars n Have arms sharply demarcated from the body disc. n The internal structure of the arms involves interlocking internal ossicles (also called vertebrae) n Are primarily filter feeders, raising their arms in a current to capture particulate s

Class Echinoidea n Recipe: take a starfish and roll its 5 arms together into a ball, then fuse and calcify with an external armor n The armor is called the test n Very small aboral surface

Class Echinoidea n Sea Urchins n Herbivores, preferring macro- algae n They can be highly effective grazers, creating “urchin barrens” devoid of algae n The mouthparts are unique, known as Aristotle’s Lantern. u 5 continually growing chisel teeth u Each tooth with 8 supporting skeletal pieces

Class Holothuridae n Sea Cucumber n They have no calcitic skeleton, except for spicules embedded in a leathery skin n Most are immobile, and lie on the sea bed rolling back and forth with the swell. Some have limited mobility using their tube feet. n Despite retaining 5-radiate anatomy, they have re-evolved bilateral symmetry along their long axis (the oral-aboral)

Class Holothuridae n They mainly feed on detritus n Oxygen exchange is performed using gills inside their anus n They have 2 odd defensive strategies: u Squirting a sticky goo u Voiding their entire intestines