Phylum Echinodermata “spiny skin” Over 6000 marine species

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

Things they share Symmetry –Adults with pentaradial symmetry Round body with body parts radiating from center

Water vascular system Locomotion Attachment Feeding

Water vascular system Complex system of water filled canals Extensions of tubed feet Modification of the coelom Ciliated internally

Figure 16.4 Ring canals associated with each arm Lateral canals end at each tube feet Madreporite serve to replace water lost from the WVS and equalize pressure

Water Vascular system con’t Ring canal that surrounds the mouth Ring canal opens to the outside or body cavity through a stone canal and an opening called a Madreporite

Tube feet Usually emerge through openings in skeletal ossicles Extensions of the canal system

Figure 16.5 Suction cups

Figure 16.6 Oral opening- or mouth normally faced downward with moveable oral spines around it

Tube feet Also permit exchange of respiratory gases and nitrogenous waste Sensory functions

Nervous system Echinoderms have a diffuse nervous system with no “brain” Nerve ring that encircles the mouth Radial nerves that extend to each arm Coordinate the functions of tube feet Nerve net that coordinates the function of the body wall

Hydraulics These are far more complex than the nervous system! Main hydraulic systems are derived from the coelom, although separate sections of the coelom also surround viscera The podia are operated by a hydraulic system called the water-vascular system

Class Asteroidea Sea stars Some live in sandy or muddy substrates

Sea Star Various colors Usually five arms that radiate from a central disk 1,500 species Live on hard substrates

Exception to the rule Some sea stars that have 6 or 7 arms OR MORE!

Figure 16.7 Development of a sea star

Regeneration Arm An entire sea star?

Madreporite Is stated to allow pressure equalization and top up water supply to the WVS There is something of a mystery here - the madreporite shows a continual water influx, but animals in which it is experimentally blocked appear to function and move normally Is absent in crinoids

Gonads Sexes are separate, and discharge gametes into the sea water in response to chemo-stimulus of other gametes. There are gonopores, ie 2 per arm in asteroidea at the base of ambulacral grooves. Gonads can be large - echinoid gonads almost fill the test, and can be eaten as a delicacy.

Figure 16.8 Sea daises

Class Crinoidea Crinoids or feather stars - almost certainly close to the ancestral form of the phylum These are mainly abyssal filter feeders, though in previous geological periods were dominant in shallow waters Some Carboniferous fossil beds are made of crinoid ossicles

Crinoidea Body is mainly made of ossicles 10 arms have podia (no ampullae) lining ciliated grooves feeding particles to the mouth. Podia seem to catch large particles Arms can move, thanks to muscles between arm ossicles Mouth and anus are both on oral side (!)

Figure Class Crinoidea Sea lily

Figure Class Crinoidea Feather Star

Comatulids Free living crinoids - “feather stars” Have >10 arms, often migrating vertically to filter feed in shallow waters at night, usually by crawling Antedon: A. bifida is found in UK waters. This can swim actively.

Figure The mouthparts are unique, 5-radiate (of course!), known as Aristotle’s Lantern. This involves 5 continually growing chisel teeth, each with 8 supporting skeletal pieces. This gives the teeth remarkable versatility in their action.

Class Echinoidea- Sea Urchin Are all herbivores, preferring macro-algae so are mainly found in sunlit waters. They can be highly effective grazers, creating “urchin barrens” devoid of algae

Figure (a)

Sea Urchin test

Figure (b)

Sand dollar and Sand biscuit

Ophiuridae - brittle stars These resemble bony starfish in general appearance, but have arms sharply demarcated from the body disc. The internal structure of the arms involves interlocking internal ossicles, confusingly called vertebrae.

.. Are primarily detrital or filter feeders, raising their arms in a current to capture particulates

Figure 16.9 (a)

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

Holothuridae They have 2 odd defensive strategies: –Squirting a stick goo from cuverian glands. –Voiding their entire intestines. …yummy

They mainly feed on detritus, collected by oral tentacles which are derived from tube feet. Oxygen exchange is performed using gills inside their anus Hmm…

Figure 16.13

holothuroidea Sea cucumber Sea apple