Phyla Molluska & Echinodermata

Invertebrate Zoology

Mollusks are ______ and protected by _____

soft bodied; calcareous shell

3 body regions of mollusks

Head

Visceral hump (mantle)

Muscular foot

What secretes the shell?

the mantle

All organs are found in the ______.

visceral hump (mantle)

Mollusks have radula which are

a ribbon of small teeth used for feeding

Reproduction in mollusks

Mono/Dioecious

Many mollusks have larval stages like _____ and ______

trochophore and veliger

What kind of development do mollusks have?

protostomic development (mouth forms first in embryo)

What are the four main classes of mollusks?

Polyplacophora, Gastropoda, Bivalvia, Cephalopoda

What are the key shell and body features of chitons (Class Polyplacophora)?

8 dorsal plates, strong foot, reduced head

Class Polyplacophora

All marine.

Radula used for scraping algae.

Lives mostly in the intertidal zone.

What is the defining shell feature of chitons (Class Polyplacophora)?

8 dorsal plates

Where do chitons live and what do they eat?

marine intertidal zone and graze on algae

Class Gastropoda

Marine, freshwater, land.

Mostly benthic.

Undergo torsion.

Close shell with operculum.

From Class Gastropoda - Cone snail (Conus) has a _________.

radula with deadly toxins which can kill by respiratory paralysis

What major developmental feature defines gastropods?

Torsion - twisting of the visceral mass, shell, and mantle

What is the function of the operculum in many snails?

Acts as a trap door that closes the shell for protection.

For gastropods, what larval type is specific to marine species?

veliger

Bivalves = ______

filter feeders

Cephalopods = _______

predators/carnivores

Odontophore

cartilage structure that supports the radula

Osphradium

sensory organ that checks water for silt + food particles

What are nudibranchs (sea slugs)?

Shell-less, brightly colored gastropods

What are pteropods (“sea butterflies”)?

Pelagic gastropods that swim using wing-like extensions of their foot.

What type of mollusk are sea slugs (nudibranchs)?

shell-less; brightly colored gastropods

What adaptations do nudibranchs have for defense?

Chemical defenses or store stinging cells

Tegula (Black Turban Snail)

Conical, rounded shell.

Dark charcoal to black; top (apex) eroded to gold/white.

Nucella (Whelks)

Heavy, coiled spiral shell.

Color varies.

Eats barnacles.

Littorina (Periwinkles)

Broad/conical shells.

Live in intertidal zones.
Algal grazers.

Haliotis (Abalone)

Low, open spiral shell.

Row of respiratory pores along the shell edge.

 

Cone snail

Black Turban Snail

Sea slug (nudibranch)

Red Abalone (has row of respiratory pores)

Three layers of bivalve shell:

Periostracum (outer)

Prismatic (middle)

Nacreous (inner)

What major anatomical structures do bivalves lack?

Head and radula. They filter feed with gills.

How do clams, scallops, oysters, and mussels differ in locomotion/attachment?

Clams - dig with hatchet foot

Scallops - swim by clapping valves

Oysters - permanently attached by one valve

Mussels - attach with byssal threads

How do bivalves feed and breathe?

Large gills (filtration/gas exchange) and siphons (water flow)

Marine Bivalve Life Cycle

egg hatches into trochophore, grows into veliger, attaches to substrate on sea floor, becomes adult

How do freshwater bivalve larvae (glochidia) develop?

develops inside female, attach to fish gills/fins as parasites, let go and fall down, become juveniles then adults

How are pearls formed?

When an irritant gets trapped between shell and mantle, causing layers of nacre to be deposited

What major anatomical modification defines cephalopods?

The foot is modified into 8-10 arms and tentacles surrounding the mouth.

What are the two major cephalopod groups and examples of each?

Nautiloids: Nautilus (shell)

Coleoids: Octopus, squid, cuttlefish (no shell)

What structure do male cephalopods use for reproduction?

hectocotylus

What unique shell feature does the Nautilus have, and what is it used for?

A coiled, chambered shell filled with gas to control buoyancy

What is the daily behavior pattern of the Nautilus?

Surface at night, stay benthic during the day in cooler water

For Nautilus: Suckers absent but __________​

tentacles are coated with sticky matter to which crabs, shrimps, etc. get stuck

Loligo (Market Squid)

10 appendages.

Seasonally abundant near shore; lay large communal egg masses on sand

Octopus

8 arms.

Body is red-brown, but can change color.

Nocturnal (active at night and hides during the day).

What type of symmetry do echinoderms (starfish) have, and what major structures do they lack?

Radial symmetry; lack head and brain

What is the water vascular system (WVS) used for in echinoderms?

Locomotion, feeding, respiration, and attachment

What type of skeleton do echinoderms have?

Endoskeleton of CaCO3 ossicles

Water Vascular System (WVS) ​

made of tubes and canals through which seawater circulates ​

Flow of water in WVS

Madreporite

Stone canal

Ring canal

Radial canal

Tube feet​

Seas stars have a ______ at the center of the body and are surrounded by ______.

central disc; 5 arms

What contributes to the spiny skin of sea stars?

CaCO3 plates

What is Sea Star feeding like?

Carnivores; normally consume shellfish and coral​

What are the larval stages of sea stars?

Bipinnaria (1st stage)

Brachiolaria (2nd stage)

What feeding strategy do some brittle stars use?

Filter feeding by raising arms and using mucus strands to catch particles.

Do brittle stars use tube feet for movement?

No, their tube feet lack suckers so they instead use them for feeding

Why are brittle stars called “brittle”?

They intentionally break off arms to distract predators and escape; arms regenerate

What unique defensive feature do some brittle stars have?

Bioluminescence

What are the two main groups within Class Echinoidea?

Regular echinoids (sea urchins) and irregular echinoids (sand dollars, heart urchins)

What is the “test” of a sea urchin?

A hard skeleton made of fused ossicles, covered with movable spines.

What structure is used by sea urchins for chewing, and how many teeth does it have?

Aristotle’s lantern, with five teeth

Which echinoid species is dangerous due to long spines that can puncture human skin?

Diadema

Two forms in Class Crinoidea

Sea lilies (attached)

Feather stars (mobile)

How do crinoids obtain food?

They are suspension feeders, using many branched arms to trap particles

What features do sea cucumbers not have that other echinoderms do?

No arms, no spine, and the madreporite is internal

What is evisceration?

A defense where sea cucumbers remove internal organs or sticky tubules to deter predators

What is the body symmetry of sea cucumbers?

Bilateral symmetry

What are the oral tentacles of sea cucumbers derived from?

They are modified tube feet

How do pearlfish interact with sea cucumbers?

They live inside their respiratory trees, entering through the anus (commensal)

Why is there little fossil evidence of early protochordates?

They were soft-bodied, so they did not fossilize well.

Why are early developmental stages (cleavage, blastula, gastrula) important for studying chordate evolution?

These stages are highly conserved, revealing ancestry

What major group do chordates share a common origin with?

Deuterostomes

5 major vertebrate groups of Phylum Chordata

fish, amphibians, reptiles, birds and mammals​

4 special features of Phylum Chordata​

Notochord

Dorsal tubular nerve cord

Pharyngeal gill slits

Post-anal tail

Invert chordates have 3 classes:

Ascidicia (sea squirt), Thaliacea(salps), and Larvacea​

Where are sea squirts commonly grown?

on boats, docks, reefs, or other hard substrate ​

Feeding system of sea squirts

Water enters through incurrent siphon, goes to pharynx, exits through excurrent siphon

Pharynx of sea squirts has many ________ for __________.

pharyngeal slits; filtering plankton

Which chordate features are present in the larval tunicate (sea squirt)?

Notochord, dorsal nerve cord, post anal tail

Reproduction of sea squirts

Monoecious, cross fertilize, zygote hatches as tadpole larva

What material is a tunicate’s outer covering made of?

A tunic made of cellulose

Class Thaliacea (salps)

Free-living/planktonic. ​

Tunic is transparent and thin. ​

In/excurrent siphons pre­sent. ​

Pharyngeal gill slits present.

Class Larvacea

Tiny/planktonic​

Paedomorphic. ​

Adult lives in transparent filter house. ​

Paedomorphic

when sexually mature individuals retain the larval body form