Phylum Echinodermata and Transitional Invertebrates Phylum Echinodermata Cambrian to recent
Phylum Echinodermata Cambrian to recent
All marine, bottom dwellers, (~6000 species). Many fossil forms.
Name means “spiny skin”
Exhibit Pentamerous radial symmetry (5-part)
bilaterally symmetric plankton
Only major invertebrate phylum that is a Deuterostome:
All higher animal forms(including chordates) are deuterostomes. Echinoderms considered to be more highly developed; (also protein structure is more similar to chordates)
Unique water vascular system provides a hydraulic system of tube feet: a series of suction disks used for locomotion; and finding and capturing prey.
Endoskeleton of calcareous spines or plates; covered by the epidermis.
Protects and supports internal tissues
Provides place for muscle attachment
Simple nervous system; un-centralized (no head)
Dioecious with external fertilization
There are 5 classes:
Class Asteroidea “Sea Stars”
Sizes ranges 1cm to 1 yard in diameter; many colors!
Most abundant in tropical areas
Anus is located on the Aboral (upper) surface; Madreporite- circular disk filter for water coming into water vascular system
Mouth located in center of oral surface; with ambulacral grooves that radiate out onto arms.
Brittle Star, Basket star
long thin arms; clear demarcation from central disk. Break off easily
move by wipe like lashes or arms; are very mobile
Sea urchins, sand dollars, sea biscuits
No arms; body enclosed in fused plates
Many movable spines
In sea urchins, the tube feet extend out through holes in the ambulacral plate. The spines are located on the interambulacral plate.
Class Holothuroidea- “Sea Cucumber”
Elongated body; spines small; soft body
These are detritus feeders
Can eviscerate (disembowel) themselves if threatened.
These are the stalked Echinoderms
Most primitive Echinoderms
Filter feeders with feathery arms
Also called Protochordates
Groups of animals that show some similar features to vertebrates
All deuterostomes (in larva the blastopore becomes the anus).
Phylum Chaetognatha “arrow worms”
Holoplankton (permanent plankton); have long narrow transparent body; hard to see (1-3cm); looks like glass
Name means “bristle-jaw”- stiff hairs around mouth; voracious plankton feeders
Very common in plankton samples.
Have a notocord (a strong, flexible, rod-like structure) sometime during life cycle
Have a hollow dorsal nerve cord (above notocord)
Have gill slits (paired openings in wall of pharynx) sometime during their development
Called “tunicates” or “sea squirts”
Adult forms are simple, vase-like, usually transparent; sessile, benthic filter feeders (all marine)
Water is strained through gill chamber by ciliary action; also used in respiration
Begin development as a free swimming larva—tunicate larva
Chordate characteristics apparent only in the larva
Neoteny- condition in nature where the adult form is lost and the immature form becomes reproductive
Retention of juvenile characteristics in the adult form
Ex: 1) Tadpole---frog (adult form)
2) Salamander- immature becomes reproductive; adult form is lost
Means “chordate with head” (cephalization); feelers for sensory
Retains chordate characteristics throughout life (neotony); apparently arose from sessile ancestors
Called “lancelets” due to shape; have definite gill slits that function in filter feeding and respiration
Have strong striated muscles (for swimming) and small fins
Believed to “reflect” possible ancestor type of vertebrates
Earliest chordates date back to Cambrian Period called (graptolites)