Mollusks
By: Caitlyn Gress, Bri
Baran & Cole Davis
Echinoderms:
 What is an echinoderm?
A marine invertebrate of the phylum Echinodermata, such as a starfish, sea urchin, or sea cucumber. Echinoderm comes from a Greek word meaning “spiny
meaning “spiny skin”.
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Echinoderms have a unique body system, such a radial symmetry. This means that their body is arranged in a way that it comes together around a
around a central axis. An echinoderm has no left or right half, only a top and bottom side.
Have a shell made up mainly of calcium carbonate which is covered by skin.
Starfish: Have several, often 5 arms, arranged around a central disk.
Sea Urchin: Normally have a spine.
 Echinoderms Water Vascular System:
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Instead of blood, echinoderms have a water vascular system which is used for movement and predation.
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They pump sea water into their body through a sieve plate or madreporite, and the water being pumped fills the echinoderms feet.
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The echinoderm moves by filling its feet with water to extend them, and using muscles within their feet to retract them.
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Their tube like feet allow them to hold onto rocks and prey by suction.
 Echinoderm Reproduction:
 Most echinoderms reproduce sexually.
 They reproduce by releasing eggs or sperm into the water. The egg or sperm is already fertilized which then results in free
results in free swimming larvae that will eventually settle to the bottom.
 Echinoderms can also reproduce asexually by regenerating body parts such as one of their arms or legs.
 Feeding for Echinoderms:
 Starfish are carnivores and scavengers.
 The tiny tube feet are involved in passing collected food towards the central mouth. These animals are detritivores
 How Echinoderms digest their food:
 Starfish with short inflexible legs ingest their prey whole before digesting them.
 Echinoderms with longer more flexible legs are able to turn the stomach inside-out through the mouth. This is how
they are able to feed on bivalves such as oysters and muscles.
 Habitat:
 Echinoderms can survive being washed up and dried out on shore.
 Starfish and Sea Cucumbers prefer rocky areas when most other echinoderms prefer sandy areas.
 Some echinoderms use the skin of a fish as their home.
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Niche:
Some starfish are carnivorous and inhabit zones of the ocean.
Maintains balance of species in the community.
If removed from area, there will be a great increase of muscles and they will crowd out other species effecting
the communities’diversity.
Sea Urchin
Arthropods:
Types of Arthropods:
Chelicerates
Mandibulates
Have a pair of oral appendages called
chelicerae which chew food
Have mandibles (Jaws) and can crush
and chew food with them
Decapods, mantis shrimp, krill, copepods,
amphipods, barnacles
Horseshoe crab, four main parts are
cephalothorax, abdomen, telson, and
carapace
Sea spiders, only marine invertebrates
known where male carries the egg,
have sensory structures called palps
Mostly crustaceans, three main parts are head,
thorax, and abdomen
Decapods – Crabs, lobsters, true shrimp
Deca=10 Pods=feet
Many have special defense mechanisms like
camo or hiding in a shell
Reproduce through sexual reproduction
More information on Arthropods:
Types of Arthropods
•Amphipods resemble shrimp, are also burrowers
Feeding
•Krill are filter feeders, and are also bioluminescent
•Barnacles are the only sessile crustaceans, attach onto surface of a host to grow
•Copepods are the largest group of small crustaceans, suspension feeders
•Most crustaceans are food sources for other animals
•Krill is harvested
Reproduction
•Almost all arthropods reproduce through sexual reproduction, most of them lay eggs
•A select number of arthropods can grow body parts back asexually
Niche/Habitat
•Can live in the deep sea, coastal waters, terrestrial habitats, freshwater rivers and streams, forests, deserts,
deserts, scrublands, and grasslands
•Arthropods are food sources for many other types of animals, and in many ways they act as a bridge
bridge between trophic levels
Annelids, Nematodes, Tunicates &
Cephalochordates:
Annelids
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Body is divided internally and externally in segments that make them more mobile by leverage enhancement
Hydrostatic Skeleton- body support gained by fluid, usually water, contained in a body compartment
Body wall contains longitudinal and circular muscles letting them crawl, burrow, and swim
Setae- small bristles on skin used for locomotion, digging, anchorage, and protection
Polychaetes- most common annelids in marine environments but usually go unnoticed. Known as sandworms, clamworms, feather duster worms,
duster worms, and tubeworms
Usually less than 4 inches long, can grow to over 10 feet
Coloring can be red, pink, green, multicolored, or iridescent
Burrow in sand and mud, under rocks and corals, in crevices and other organisms shells and tubes they produce
Errant Polychaetes- free moving, active Polychaetes
Sedentary Polychaetes- immovable forms that live in self-constructed stable burrows or tubes
Burrowers and tube dwellers often live in large numbers on the ocean floor and compose a major part of the soft bottom infauna
Population size is limited by predators like fish and crabs, but they do not have a lack of resources
Some Polychaetes have teeth allowing them to be active predators of small invertebrates, including other Polychaetes
Many sedentary Polychaetes are filter feeders or suspension feeders, collecting detritus and plankton with special feeding structures on their head
Nematodes:
Body is divided internally and externally in segments that make them more mobile by leverage enhancement
Hydrostatic Skeleton- body support gained by fluid, usually water, contained in a body compartment
Body wall contains longitudinal and circular muscles letting them crawl, burrow, and swim
Setae- small bristles on skin used for locomotion, digging, anchorage, and protection
Polychaetes- most common annelids in marine environments but usually go unnoticed. Known as sandworms, clamworms, feather duster worms,
and tubeworms
Usually less than 4 inches long, can grow to over 10 feet
Coloring can be red, pink, green, multicolored, or iridescent
Burrow in sand and mud, under rocks and corals, in crevices and other organisms shells and tubes they produce
Errant Polychaetes- free moving, active Polychaetes
Sedentary Polychaetes- immovable forms that live in self-constructed stable burrows or tubes
Burrowers and tube dwellers often live in large numbers on the ocean floor and compose a major part of the soft bottom infauna
Population size is limited by predators like fish and crabs, but they do not have a lack of resources
Some Polychaetes have teeth allowing them to be active predators of small invertebrates, including other Polychaetes
Many sedentary Polychaetes are filter feeders or suspension feeders, collecting detritus and plankton with special feeding structures on their head
Tunicates:
Tunicates- sessile animals that are widely distributed in all seas
Named for their body covering, the tunic
Tunicates are known as sea squirts because they excrete water when irritated
Many live in shallow, tropical water in old coral heads and the underside of coralline rock
Form clusters on gorgonian corals and mangrove roots or massive rubbery lobes on rocks
and pilings
Sea squirts can be solitary, colonials or compound organisms
Sea squirts are filter feeders, primarily on plankton
They can regenerate damaged body parts
Salps- free-swimming tunicates
As they swim, water pumps through their body and they extract food
Some salps are bioluminescent
Larvaceans- another group of free swimming tunicates
Both larvaceans and salps increase in population when there’s an abundant amount of
food
Cephalochordates:
Cephalochordates- fish like chordates that are collectively known as lancelets
Slender, laterally compressed, and eel-like in appearance and behavior
Usually .4-3.2 inches in size
Burrow in coarse, shelly, current-swept sands in shallow near-shore areas
Ingest large quantities of particles from which they extract organic material and
eliminate water through gills
Lancelets are an important source of food in Asia
Eel-like in appearance
Echinoderms:
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Unique
Characteristics:
Echinoderms have no brain or eyes.
About 7000 species found on sea floor from every marine habitat.
Have a wide variety of colors.
There are about 800 species of echinoderms on the Great Barrier Reef alone.
Arthropods:
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75% of all identified animal species
Hard exterior, jointed appendages, sophisticated sense organs
Exoskeleton- hard protective outer layer composed of protein and chitin
Molting – The process in which an old exoskeleton is shed and a new one is formed
Highly developed nervous systems, adapt quickly to environmental changes resulting in the most successful group
of animals in the animal kingdom
Cleaning shrimp have a symbiotic relationship with some reef fishes, cleaning external parasites off of them and
consuming them as food
Some barnacles are commensal with many species
Glass shrimp can recycle cellulose
Barnacles foul ships (parasite)