Echinoderms
Deuterostomes - Organisms whose mouth forms opposite to the blastopore
ECHINODERMATA
Echinatus = prickly (Latin)
Derma = skin (Greek)
Ata = characterized by
Characteristics
Bilateral symmetry
Pentaradial symmetry(Pentamerism)
Oral, aboral surfaces
Ambulacral groove
Test
Ossicles
Dermal plates
Water vascular system
Madreporite
Aristotle’s lantern
Dermal branchiae/skin gills
Pedicellaria
Tube feet
Skin gills
LARVAL FORMS
o Bipinnaria of asteriods
o Brachiolaria of asteroids
o Ophioleteus of ophiuroids
o Echinopluteus of echiniods
o Auricularia of holothuroids
o Doliolaria of crinoids
ASTEROIDEA
o Sea stars
o Found along shorelines and may aggregate on rocks
o Some live on muddy or sandy bottoms and along coral reefs
o There are about 1500 extant species
o Variable colors and structural features
o Body is flattened underneath and the epidermis is covered with cilia
o The mouth is at the center
o Oral region is facing down at the substratum
o Coevered by peristomial membrane
o Ambulacral area runs from the anus to the tip of the arms
o Tube feet – also known as Podia
o Protected by spines since it is quite delicate
o Hollow structures that continue into the inner portion as a muscular sac called the ampulla
o Ampulla – acts as a water reservoir
o Central to the ambulacral groove is the radial nerve (5)
o Ossicles are the ones that make up the test
o Test – endoskeleton which is composed of small parts known as ossicles
o Body coelem is filled with fluid and amoebocytes
o Amoebocytes are cells that give protection to the organisms; protective cells
o Papillae – respiratory structures
o Small finger like projections
o Found on the epidermis
o Where removal of excretory products occur (along with the tube feet)
o Water vascular system is made with a series of canals
o Used primarily for food gathering
o Pedicellaria – big spines; pincer like appendages on the surface of the echinoderm
o Modified spines
o Protects the echinoderm from predators
o Cleans the sruface off debris
o Madreporite – connects the water vascular system to the environment
o Sea stars feed on mollusc, other echinoderms, and even small fishes
OPHIUROIDEA
Brittle stars
Largest of the major group with approximately 2000 extant species
They are mainly marine
Brittle stars are slender and is distinctive of their slender central disk
They don’t have pedicellaria or papillae
They have tube feet, but don’t have suckkers
Able to hide within crevices of rocks
Arms can regenerate as long as they are in sea water
ECHINOIDEA
o Sea urchins and sand dollars
o Approximately 950 extant species
o Endoskeletal tests
o Lack arms but their tests show a five-part symmetry with five ambulacral areas that are visible as spiky bands
o Notable modification from ancestral body plan is having tube feet on oral surface
o Regular sea urchins have hemispherical shape with radial symmetry and variable length spines
o Sand dollars and heart urchins are irregular ruchins because they are bilateral with very short spines
o No ambulacral grooves
o They have a number of movable spines
They control their movement with the help of their water vascular system
Aristotle’s lantern – a claw-like mouth found at the oral surface
HOLOTHUROIDEA
Sea cucumbers
They look like cucumbers
There are around 1150 extant species
Greatly elongated in the oral-aboral axis
Ossicles are reduced
Some species crawl on the ocean bottom
Others are found under rocks or burrows
Its ossicles are spearate small structures that are embedded in the leathery body wall
Few species have their ossicles into their dermal armor
Body wall contains muscles
Tube feet may be found all over the body
Oral tentacles – 10-30 modeified tube feet (depending on the species) tha brancehs extensively around the mouth
Digestive system ends in a cloaca at the end
Cuverian tubules – evisceration;