Download PHYLUM ECHINODERMATA

Key classes of Phylum Echinodermata
Phylum Echinodermata, Class Asteroidea
Example: Sea stars
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Body plan
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Usually with 5 arms, but some have more (i.e. Pycnopodia helianthoides)
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Body systems (i.e. water vascular system, nerves, branches of digestive system, etc...)
radiate down each arm
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Its calcareous internal skeleton provides it with most of its structure
Feeding
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Many sea stars (including Pisaster ochraceus, the one you studied in lab) feed by everting
their stomachs and using enzymes to digest most of their food outside of their bodies.
They then draw the digested food back into their stomachs via ciliary action.
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Many sea stars are predators, able to hold onto and pry apart prey (such as mussels) with
their tube feet. They can insert their stomach into small spaces.
Gas exchange location (with the seawater)
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Tube feet
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Dermal papulae
Protection
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Hang on tightly to surfaces with tube feet.
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Pedicellariae “pinch” any small larvae (i.e. barnacle larvae) or algae spores, keeping them
from settling onto the sea star’s surface.
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Can regenerate arms if lost (but only if at least part of the central body is present)
Phylum Echinodermata, Class Echinoidea
Example: Sea urchins and sand dollars
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Body plan
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The dermal ossicles (elements of the calcareous internal skeleton) of echinoids fit tightly
together to form the "test" and form its structure
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Body systems (i.e. water vascular system, nerves, branches of digestive system, etc...) are
in five parts, even though you can’t tell from the outside.
Feeding
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Sea urchins feed with a five-toothed structure, Aristotle's lantern. Most use this structure
to chew on algae, although they can also be scavengers and even predators (as you saw
with those little white ones in the video!)
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Living sand dollars are positioned upright and partially buried in the sand. They trap small
planktonic particles in mucous. Cilia and tube feet then direct the food down the rivulets
(notice the rivulets in the oral surface) and toward the mouth.
Gas exchange location (with the seawater)
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Tube feet
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Peristomial gills
Protection
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Hang on tightly to surfaces with tube feet.
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Spines!
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Pedicellariae “pinch” any small larvae (i.e. barnacle larvae) or algae spores, keeping them
from settling onto the sea urchin’s surface (same as for the Asteroidea).
Phylum Echinodermata, Class Holothuroidea
Example: Sea cucumbers
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Body plan
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Dermal ossicles of the calcareous internal skeleton of sea cucumbers are loosely scattered.
A sea cucumber is supported by its fluid-filled coelom, which forms a hydrostatic
skeleton.
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Body systems (i.e. water vascular system, nerves, branches of digestive system), etc... are
in five parts, even though you can’t tell from the outside.
Feeding
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Holothuroids feed with their mucous-covered “buccal” (or “mouth”) tentacles, modified
tube feet that extend from the mouth. They collect the food and then shove each arm into
their mouth, wiping off the food. Some sea cucumbers sift through the substrate and clean
off organic material. These types produce copious amounts of fecal material
Gas exchange location (with the seawater)
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Tube feet
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Buccal (mouth) tentacles
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Water is pushed up through the anus and into the respiratory tree that forms fine branches
off the gut.
Protection
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Toxic sticky tubules are ejected from the anus in some species
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Some can eviscerate from anus or mouth. The guts may be toxic, or, the predator may eat
the guts but spare the animal. Sea cucumbers can regenerate their “guts” and the rest of
their body systems!
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Also, some live in crevices and can quickly retreat to safety
Phylum Echinodermata, Class Ophiuroidea
Example: Brittle stars, basket stars
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Body plan
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Ophiuroids can be recognized by their central disk and long, flexible arms.
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Body systems (i.e. water vascular system, nerves, branches of digestive system), etc... are
in five parts, similar as for Class Asteroidea
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The tube feet of ophiuroids do not have adhesive discs
Feeding
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Ophiuroids are deposit feeders, and trap particles with their mucous-covered arms. The
food is directed towards the mouth with cilia. Some ophiuroids drag their arms through
the water to collect food, while others hold their arms up into the current. Ophiuroids can
also capture prey by wrapping their arms around it.
Gas exchange location (with the seawater)
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Tube feet
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Thin-walled pockets called bursae... (don’t worry about these...)
Protection
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Can quickly retreat to safety under rocks, in crevices or buried in sand
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Can lose arms and regenerate
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Some species will bioluminesce when disturbed. Predators will then go after the flashing
arm that has been severed from the body, allowing the rest of the brittle star to retreat to
safety.