Download Echinoderms

Echinoderms
Kingdom: Animal
Phylum: Echinodermata
Phylum Characteristics:
General Characteristics
6000 species
Invertebrate
Aquatic (mostly marine, some freshwater)
None are parasitic
Mostly free swimming, some attached
Body Structure
Radial symmetry
Triploblastic
Coelome present
Lack head, brain or segmentation
Rays : long tapered arms, covered with tough spiny skin
Endoskeleton
Pedicellariae: “little foot”, specialized spines, jaw-like,
protection or cleaning (sea stars & sea urchins)
Water Vascular System
Enables movement, exchange gases, capture food & excrete
wastes
Hydraulic system using water pressure
Sea star
o Water enters and exits through madreporite (sieve-like
disc on upper surface)
o Tube feet : hollow, thin walled tubes, end in a suction cup
works like a suction cup, each works independently
of the other,
Gas exchange and waste eliminated through
diffusion in tube feet
o Ampulla : round, muscular structure, acts like a bulb on
an eye dropper
o Moves by alternately pushing out and pulling in tube feet
Digestion
All have mouth, stomach, intestines
Method of obtaining food vary
Sea star: carnivorous (bi-valves), Sea urchins: herbivores,
Brittle stars, sea lilies, sea cucumbers: feed on dead and
decaying matter
Lacking excretory organs
Nervous system
Simple nervous system
Central nerve ring, surrounds mouth
o Nerves extend into each arm, provides sensory info
Most do not have sensory organs
o (do have cells to detect light & touch)
Sea Stars have eye spot (collection of light-detecting cells) at
end of ray
Circulatory System
Radiates and reduces to vessels encircling mouth and five
radial vessels
Gas exchange
Gills or in papulae (project from coelome or tube feet)
Reproduction
Sexual; most species have male & female, few are
hermaphrodites
Echinodermata Classes
Class: Asteroida
Sea Stars (star fish)
General Characteristics
Central disc with five tapered arms
Mouth at center of disc on the under side
Many blunt spines project on upper surface
At the end of each arm is an eye spot
Epidermis has tiny epidermal projections (pedicellariae) which
are jaw like structures
Close to anus is the madreporite, sieve like opening of the
water vascular system
Digestive system: mouth opens into a sac-like stomach
Class: Ophiuroidea
Brittle stars and basket stars
General Characteristics
Most are quite small, with the central disc no larger than a
dime
Five arms are long and delicate, more freely movable than a
star fish
Echinoidea
Sea urchins & Sand dollars
General Characteristics
Spherical body with no arms
Flattened plated fused together to form an internal shell
 Body may be covered in sharp spines, can be moved because
they are attached to muscles
Holothuroidea
Sea cucumbers
General Characteristics
Elongated body, with an oral opening at one
end and an anus at the other end
Long bands of muscle enable animal to expand and contract
Crinoidea
Sea lilies & Feather stars
General Characteristics
Often brightly colored
Many fossil examples, more numerous in ancient past
 Only echinoderms with mouth directed upward (both mouth and
anal opening on upper surface)