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 skin”.

 

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 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:

  Instead of blood, echinoderms have a water vascular system which is used for movement and predation.

  They pump sea water into their body through a sieve plate or madreporite, and the water being pumped fills

the echinoderms feet.  

The echinoderm moves by filling its feet with water to extend them, and using muscles within their feet to retract them.  

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 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 performing similar functions to earthworms on the land in recycling nutrients.

They are attracted to the bodies of dead animals on the ocean floor. Particularly feed on other invertebrates, such as bivalves, snails, crustaceans, marine

worms, other echinoderms and even fish. Sea Urchins are more into the algae on rocks or of larger marine plants. 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. 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:

Chelicerates Mandibulates

Have a pair of oral appendages called chelicerae which chew food

Have mandibles (Jaws) and can crush and chew food with them

Horseshoe crab, four main parts are cephalothorax, abdomen, telson, and carapace

Decapods, mantis shrimp, krill, copepods, amphipods, barnacles

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 shrimpDeca=10 Pods=feet

  Many have special defense mechanisms like camo or hiding in a shell

  Reproduce through sexual reproduction

   

Types of Arthropods:

More information on Arthropods:

Types of Arthropods•Amphipods resemble shrimp, are also burrowersFeeding•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 harvestedReproduction•Almost all arthropods reproduce through sexual reproduction, most of them lay eggs•A select number of arthropods can grow body parts back asexuallyNiche/Habitat•Can live in the deep sea, coastal waters, terrestrial habitats, freshwater rivers and streams, forests, deserts, scrublands, and grasslands •Arthropods are food sources for many other types of animals, and in many ways they act as a bridge between trophic levels

Annelids, Nematodes, Tunicates & Cephalochordates:

Annelids• 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

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 swimSetae- small bristles on skin used for locomotion, digging, anchorage, and protectionPolychaetes- most common annelids in marine environments but usually go unnoticed. Known as

sandworms, clamworms, feather duster worms, and tubewormsUsually less than 4 inches long, can grow to over 10 feetColoring can be red, pink, green, multicolored, or iridescentBurrow in sand and mud, under rocks and corals, in crevices and other organisms shells and tubes they

produceErrant Polychaetes- free moving, active PolychaetesSedentary Polychaetes- immovable forms that live in self-constructed stable burrows or tubesBurrowers and tube dwellers often live in large numbers on the ocean floor and compose a major part of

the soft bottom infaunaPopulation size is limited by predators like fish and crabs, but they do not have a lack of resourcesSome Polychaetes have teeth allowing them to be active predators of small invertebrates, including other

PolychaetesMany sedentary Polychaetes are filter feeders or suspension feeders, collecting detritus and plankton with

special feeding structures on their head

Tunicates- sessile animals that are widely distributed in all seasNamed for their body covering, the tunicTunicates are known as sea squirts because they excrete water when

irritatedMany live in shallow, tropical water in old coral heads and the

underside of coralline rockForm clusters on gorgonian corals and mangrove roots or massive

rubbery lobes on rocks and pilingsSea squirts can be solitary, colonials or compound organismsSea squirts are filter feeders, primarily on planktonThey can regenerate damaged body partsSalps- free-swimming tunicatesAs they swim, water pumps through their body and they extract foodSome salps are bioluminescent Larvaceans- another group of free swimming tunicatesBoth larvaceans and salps increase in population when there’s an

abundant amount of food

Tunicates:

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 sizeBurrow in coarse, shelly, current-swept sands in shallow near-

shore areasIngest large quantities of particles from which they extract

organic material and eliminate water through gillsLancelets are an important source of food in Asia

Eel-like in appearance

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.

Unique Characteristics:

Echinoderms:

Arthropods: 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)