Survey of the phyla: Mollusca through Echinodermata


The Animal Kingdom

Mollusks, Arthropods, and


Nancy G. Morris

Volunteer State Community College

Subgrade Coelomata


Includes chitons, oysters, clams, snails, slugs. octopus, squid

General Characteristics:

 molluscus = soft body coelom greatly reduced main cavity is hemocoel - blood-filled cavity in open circulatory system show no segmentation bilateral symmetry obscure

Subgrade Coelomata


Soft body composed of 3 main parts:

1) foot

– large muscular, usually ventral, locomotion

2) visceral mass

– contains digestive system, kidneys, heart, internal organs

3) mantle

– heavy folds of tissue which cover the visceral mass; secrete shell; form siphons, develop gill & mouth

Subgrade Coelomata


 radula – rasping, tongue-like organ found in all except bivalves trochophore larvum – freeswimming; links mollusks and annelids to a common flatworm ancestor

Anatomy of a


Phylum Mollusca Classes

Class Amphineura chiton

Class Bivvalvia clams, oysters, mussels

Class Cephalopoda – squid, octopus, chambered nautilus

Class Gastropoda – snails, slugs, abalones, whelks, periwinkles, giant conch

Review: Animal


Phylum Mollusca Classes

Class Amphineura -

“both nerves”

 no eyes or tentacles marine

 elliptical, shell of 8 plates chiton

Polyplacophora: chiton

Phylum Mollusca Classes

Class Bivalvia -

 soft body between two halves of a hinged shell highly developed muscular foot bilateral symmetry obscured most marine, some fresh water no tentacles, head, radula

 clams, oysters, scallops, mussels

Phylum Mollusca Classes

Class Bivalvia -

Pearl Production – protective function; foreign substance gets between mantle & shell, mantle secretes pearly layers of nacre around substance

 clams, oysters, scallops, mussels

Phylum Mollusca Classes

Class Cephalopoda

“head foot” shell reduced & internalized in squid no shell in octopus largest invertebrates possess eyes and tentacles most active & intelligent

Phylum Mollusca Classes

Class Cephalopoda

 most highly developed mollusk

 squid & octopus possess ink sacs which produce melanin ; protective function head-foot arrangement forms a siphon through which water can be forcibly expelled producing “jet propulsion”

 squid, octopus, chambered nautilus

Phylum Mollusca Classes

Class Gastropoda –

“stomach foot”

 univalve – single or one-piece shell some have no shell largest – giant conch – 1 foot length

Urosalprix – “oyster drill” bores hole in oyster + digests

 snails, slugs, abalones, whelks, periwinkles, giant conch

Phylum Onychophora

 missing link between annelids and arthropods ???


Figure 33.26 Campbell

 suggests a stage in evolution of arthropods from a segmented, coelomate ancestor common to both the annelids & arthropods

Phylum Onychophora

Annelid characteristics:

– segmentally arranged nephridia

– muscular body wall

– ciliated reproductive tract

– eye structure

Arthropod characteristics:

– tubular heart

– tracheae

– hemocoel

– large ganglion

– mouth parts modified appendages

Subgrade Coelomata

Phylum Arthropoda

General Characteristics:

 most successful and adaptable of all animals

 largest phylum in terms of numbers of species means “jointed foot” all have segmented bodies & exhibit metamerism suggests a common ancestry w/annelids segments fused into specialized regions

Subgrade Coelomata


General Characteristics:

Exoskeleton of chitin – semi-rigid but flexible; permeable to water; waxy cuticle prevents dessication

 coelom & hemocoel exhibit metamorphosis (change in form) exhibit molting (ecdysis)

Trilobite fossil

Phylum Arthropoda Classes

Class Archnida -

 spiders, ticks, scorpions, mites arthropod w/ 8 legs

Arachnids: scorpion & mites

Phylum Arthropoda Classes

Class Crustacea lobsters, crayfish, shrimp, crabs

Class Chilopoda -

“100 leggers” - centipeds; 1 pr legs per segment carnivorous; poisonous

Class Diplopoda -

1000 leggers”- millipedes; 2 pr legs per segment; herbivorous


Diplopoda: Millipede

Anatomy of a Crayfish

Phylum Arthropoda Classes

Class Insecta -

 terrestrial & aquatic insects

Class Merostomata -

 horseshoe crab, king crabs;

“thigh mouth”

Insect metamorphosis

Limulus: A living fossil

A natomy of a G rasshopper

Subgrade Coelomata


(Campbell p. 625)

General Characteristics:

“spiny skin”

 all members marine exhibit secondary radiality

(adults radials, but ancestors & larval forms bilateral) bipinnaria larvum resembles hemichordate larvum nearest in relation to chordates

Subgrade Coelomata


General Characteristics:

 endoskeleton w/ external spines or ossicles unique water vascular system for locomotion body parts in 5’s or multiples of 5 dioecious external fertilization

Subgrade Coelomata


General Characteristics:

 no segmentation or well defined head region autotomy (self-amputation) survival mechanism regeneration no parasitic members deutrostomes (embrylogic development resembles chordates)

Phylum Echinodermata Classes

Class Asteroidea – characterized by “star” starfish, sea stars

Class Echinoidea – characterized by “spines” sea urchins, sand dollars

Class Holothuroidea – characterized by “whole” sea cucumbers


Sea Cucumber

Echinoderm water vascular system

bivium trivium madreporite stone canal ring canal radial canal ampulla ampulacral groove tube feet aboral oral

This is where you draw and label the essential components of a starfish. The list on the left should guide you.