Mollusks & Echinoderms

Learning Target Objectives (I can…)• Compare and contrast each group of mollusks and echinoderms and list examples of each.• Identify: body systems and their components, body structures (anatomy) and functions (physiology).• Differentiate between open and closed circulatory systems.

Vocabulary:

Mollusk * ganglia * cephalization * mantle * visceral mass * gastropoda * hemocoel * radula * bivalvia * adductor muscles * incurrent/excurrent siphon * gills *cephalopod * echinoderm * endoskeleton * external fertilization * water vascular system * regeneration * aboral surface * oral surface * skin gills * parthogenesis

Mollusks & Echinoderms

Mollusks – “soft” bodied organisms

- true coelom (fluid filled cavity within the mesoderm

- many have top-shaped larva called a trocophore. This can swim using cilia. The cilia are also used to draw food into the mouth.

- bodies usually have 3 distinct parts:

1) muscular foot

2) head (except bivalves)

3) visceral mass (contains the organs, or “guts”)

- have the following body systems: circulatory, respiration, digestive, excretory, nervous, reproductive

The muscular foot of a mollusk is used for locomotion (movement).

The head (when present) has a mouth, sense organs, and cerebral ganglia (nerves) (cephalization)

The visceral mass contains:

heart – circulatory system

stomach, intestine, anus – digestive system

kidney – excretory system

a reproductive system

Above the visceral mass is the mantle (forms from epiderm) that usually secrete a shell made of calcium carbonate. Organisms with shells have less surface area for gas exchange. Some have gills located in the space between the mantle and the visceral mass. These are specialized for gas exchange. Gills = respiratory system

Section 27-4

Shell

Mantle cavity

Foot

Gills

Digestive tract

Snail

Earlymollusk

Clam

Squid

Mollusk Body Plan

Classes of Mollusks:

1) Class Gastropoda Gastropoda means “stomach foot”

- most are univalves (have a single shell, or “valve”), some have no shell

- distinct head region

- body twists over so head is near anus in snails

This class includes: snails, slugs

a) Snails

- have gills (aquatic snails) or modified lungs (terrestrial snails) which must be kept moist for gas exchange (respiratory system). In dry times, snails pull into their shell & seal the opening with a mucus plug.

- open circulatory system – blood does not remain in vessels during circulation. It spills into a “blood cavity” called a hemocoel.

- radula – “tongue” covered with chitinous teeth (used to scrape off algae or cut off leaves)

- Land snails are hermaphroditic. Aquatic snails have separate sexes.

- internal fertilization

- create mucus for foot to slide on

- have 2 eyes on retractable tentacles (these can be pulled into the head area when in danger)

- eaten as “escargot”

b) Slugs

- no shells

- live in moist environment (land slugs come out at night)

- cause crop damage

2) Class Bivalvia (or Pelecypoda = “hatchet foot”)

Bivalvia – “2 valves” (2 part shells)

Ex: clams, oysters, scallops

- filter feeders

- most are sessile

- no distinct head but have ganglia at anterior end

- a muscular foot

- 3 shell layers:

a) thin outer layer protects from acidic water conditions

b) thick, middle layer of calcium carbonate for protection

c) smooth, inside layer protects soft body with mother of pearl. Layers of this are laid around any irritant, such as sand, that gets between the mantle & shell.

- All are aquatic

- 2 adductor muscles pull shell tightly closed

- 2 tubes:

a) incurrent siphon – carries water with food particles into the mantle area (cavity area). Food particles are trapped in mucus on gills.

b) excurrent siphon – water is pumped out of the mantle cavity

- gills are used for gas exchange (respiratory system) as well as food gathering (digestive system). Cilia on the gills fan food into the mouth. Gills also hold eggs of female clam (reproductive system).

- open circulatory system

- kidneys (excretory system)

- 3 pairs of ganglia (nervous system)

- seperates sexes (sperm leaves through excurrent siphon & enters female’s incurrent siphon – eggs are located on gills!)

Section 27-4

Mouth

Shell

Stomach CoelomHeart

Nephridium

Adductor muscle

Anus

Excurrentsiphon

Incurrentsiphon

Gills

Mantle cavity

Foot

Intestine

Mantle cavity

Adductormuscle

Anatomy of a Clam

3) Class Cephalopoda

Cephalopod – “head foot”

- well-developed head with an eye structure like ours

- foot divided into tentacles with suckers (squids = 10 tentacles, octopus = 8 nautilus = many, but shorter)

- free-swimming

- radula & a strong beak for eating

- closed circulatory system (blood stays within vessels)

- most have no shell or have an internal shell

- well developed nervous system, large brain

- marine predators

- may release “ink” which dulls a predators sense of smell & distracts them, allowing escape

Exs: squid, octopus, nautilus, cuttlefish

Comparing the Three Major Groups of MollusksComparing the Three Major Groups of Mollusks

MOLLUSK GROUP

Gastropods

Bivalves

Cephalopods

MOLLUSK GROUP

Gastropods

Bivalves

Cephalopods

SHELL

Shell-less orsingle-shelled

Two shells held together by oneor two muscles

Internal shell orno shell

SHELL

Shell-less orsingle-shelled

Two shells held together by oneor two muscles

Internal shell orno shell

FOOT

Muscular foot located on ventral side and used for movement

Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot.

Head is attached to a single foot. The foot is divided into tentacles or arms.

FOOT

Muscular foot located on ventral side and used for movement

Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot.

Head is attached to a single foot. The foot is divided into tentacles or arms.

EXAMPLES

Snail, slug, sea hare, nudibranch

Clam, oyster, mussel, scallop

Octopus, squid, cuttlefish, nautilus

EXAMPLES

Snail, slug, sea hare, nudibranch

Clam, oyster, mussel, scallop

Octopus, squid, cuttlefish, nautilus

Section 27-4Compare/Contrast Table

Echinoderms

Echinoderm – “spiny skin”

- larva are bilaterally symmetrical

- adults are radially symmetrical

- have endoskeleton – internal skeleton with spines poking outward

- tube feet help movement, respiration, feeding, & excretion

- No true circulatory, respiratory, or excretory systems

- Do have a nervous system but no brain

- separate sexes

- external fertilization (each arm has 2 gonads which release egg or sperm)

- sexual and asexual reproduction is possible

- water vascular system (found ONLY in echinoderms) – used in movement & food getting. It includes:

a) sieve plate – opening on dorsal surface of starfish, etc. where water enters

b) canals – which form a ring around the mouth area & then run down each arm

c) tube feet – these are connected to the canals. Water pressure changes allow these to grab & release objects

- regeneration – as long as the cut off piece includes part of the central disk (where the mouth & stomach are found)

- ALL are marine

- aboral surface – top of body

- oral surface – underside of body

Section 28-4

Eyespot

Endoskeletal plates

Anus

Stomach

Madreporite

Reproductive glands

Tube footSucker

Ring canalRadial canal

Digestive glands

Anatomy of a Starfish

- skin gills (hollow tubes) along with the thin surface of the tube feet are used for gas exchange

- sea stars (starfish) have an eyespot (on each arm) that responds to light

- sea stars eat clams, etc. by turning their stomachs inside out through their mouths & into a clam’s shell. This way it digests the clam right in the clam’s shell.

- sea cucumbers may defend themselves by evisceration, ejecting their internal organ lining. This regenerates later.

- parthogenesis – ability of eggs to develop without fertilization. This is common in sea urchins.

Exs: sea stars, sea urchins, sand dollars, sea cucumbers

Comparing Groups and Major Characteristics of EchinodermsComparing Groups and Major Characteristics of Echinoderms

Feeding

Shape

Movement

Feeding

Shape

Movement

Sea urchins and sand dollars

Detritivores

Disc- or globe-shaped, no arms

Burrow in sandy ocean bottom or wedge in rock crevices using moveable spines attached to endoskeleton

Sea urchins and sand dollars

Detritivores

Disc- or globe-shaped, no arms

Burrow in sandy ocean bottom or wedge in rock crevices using moveable spines attached to endoskeleton

Section 28-4Compare/Contrast Table

Characteristic Brittlestars

Sea cucumbers

Seastars

Sea lilies andfeather stars

Detritivores

Star-shaped, arms

Move rapidly along ocean floor using arms

Detritivores

Cucumber-shaped, no arms

Move slowly along ocean floor using muscular body wall to crawl

Most carnivores

Star-shaped, arms

Creep slowly along ocean floor using arms

Herbivores

Stalk with feathery arms

Cannot move; attached to ocean bottom

Venn Diagram

Mollusks Echinoderms

Venn Diagram

Compare Any 2 Mollusks:

Venn Diagram

Compare Any 2 Echinoderms: