Download Phylum Echinodermata

Phylum Echinodermata
The “spiny skinned” creatures
-Sea stars and sea urchins-
General Characteristics
– All members of the phylum exhibit 5 part radial
symmetry
• The larvae are all bilaterally symmetrical
• They have arms in multiples of 5 extending from a central
disc
– This is a large group of more than 7000 species who
are all marine
– All members have the ability to regenerate lost parts
as long as the central disc is unharmed
– Most are slow bottom crawlers
General Characteristics
– They have well developed endoskeletons
• Composed of individual plates called ossicles
• Covered by a thin layer of skin
• In some species spines form from the endoskeleton and project out
of the skin
– Water Vascular system is used for movement
• A water filled system of interconnected canals that connect to tube
•
•
feet
Used for moving the arms (rays)
Also aides in feeding and gas exchange – diffusion occurs through
the thin walls of the tube feet
– Coelomic circulation and respiration
• Movement of nutrients and gases move freely through a large fluid
filled cavity to nourish all the cells
Feeding and Digestion
• Many members feed by extending or spitting out
their stomach to envelop their food
– The stomach acids digest the food externally
– The nutrients and the stomach are then sucked back
into the animal
• In sea stars, the intestine is very short or missing,
in sea urchins and sea cucumbers the intestine is
very long and coiled in the animal to allow for the
slower digestion of plant material
• Nutrients are passed through the coelomic fluid to
the individual cells
Nervous System
• They have a very rudimentary (simple)
nervous system
• Nerves coordinate movement
Reproduction
• Male and female organs are found in different
individuals
• The fertilization occurs externally through
spawning (male releases sperm and females
release eggs into the water column and rely on
luck)
• The larvae are planktonic and rarely resemble the
adult
• Asexual reproduction of a sort occurs if the animal
is cut into two pieces – each piece develops into a
new organism (regeneration)
Class Asteroidea
• This includes the sea
stars
• Can have between 5
and 50 arms radiating
from the central disc
• Usually act as predators
to bivalves, snail,
barnacles and other
slow-moving animals
Class Ophiuroidea
• This includes the brittle
stars
• The five arms are
extremely long and
flexible
• Eat mostly detritus
Class Echinoidea
• This class includes the
sea urchins and sand
dollars
• Endoskeleton forms a
hard rigid ball
• Movement is achieved
using the long spines
that radiate out of the
endoskeleton
• Usually herbivores
Class Holothuroidea
• This class includes the sea cucumbers
• Superficially worm like in appearance
– They have the basic body plan of a sea urchin but the body has
been elongated
– Endoskeleton consists of microspicules (like a sea sponge)
which gives it its warty appearance
• most are deposit feeders
• have a novel defense mechanism – when threatened the sea
cucumber will throw up 80 percent of its internal organs
– the sea cucumber has the ability to regenerate the lost organs
– hopefully the predator will eat the organs and allow the animal
to live
Phylum Hemichordata
General Characteristics
– Act almost like the missing link between
chordates and echinoderms
– they have a dorsal nerve cord – allows the
movement of nerve messages to the arms
and legs of the body
– they have a ventral nerve cord that runs
along the proboscis
– small phylum with only 90 species
– usually detritus feeders