Activity 21_ppt Phylum Mollusca

Activity 21: Phylum Mollusca

CHARACTERISTICS  Second

largest phylum in the animal kingdom – – –

Microscopic to macroscopic Slow to active organisms Terrestrial, freshwater, or marine environments

 Microscopic

to macroscopic  Have different modes of nutrition  Occur in a wide variety of environments

GENERAL BODY PLAN        

Head Ventrally located muscular foot Dorsally located visceral mass Mantle / pallium – for shell/spicule secretion Radula (except for bivalves) Complete digestive tract Gonads in visceral mass Monoecious or dioecious

CLASSIFICATION 

Subphylum Conchifera – with 1 shell; (-) spicules – – – – –



Class Gastropoda Class Bivalvia Class Cephalopoda Class Scaphopoda Class Monoplacophora

Subphylum Aculifera – with multiple shell plates; (+) spicules – Class Polyplacophora – Class Aplacophora

Class Gastropoda 

 

Members usually sluggish and sedentary Mostly with asymmetrical bodies Most with single, conical and spiral shell – May be reduced or absent (e.g. nudibranch)

   

(+) Cephalic tentacles Simple eyes Radula Jaws

eyespots tentacles jaws

RADULA 





toothed chitinous ribbon in the mouth of most mollusks used for cutting and chewing food before it enters the esophagus It is present in all molluscs except bivalves

Pila (freshwater kuhol) – Subphylum Conchifera; Class Gastropoda

Shell made of CaCO3

Haliotis (abalone) – Subphylum Conchifera; Class Gastropoda

Turbo (turban snail) – Subphylum Conchifera; Class Gastropoda

•Torsion •Whorl •Spire

Cypraea (cowries) – Subphylum Conchifera; Class Gastropoda Shell uncoiled

Nudibranch soft-bodied snails gills rhinophores

Spanish shawl

Sea slug

Class Bivalvia / Pelecypoda  Shells

have 2 lateral valves  Elastic ligament  Body is enclosed by a 2-lobed mantle (elevation)

Class Bivalvia / Pelecypoda  hatchet

shaped foot in burrowers  Head lacks eyes, radula and tentacles

Tridacna (giant clam) Subphylum Conchifera; Class Bivalvia

Spondylus (scallop) Subphylum Conchifera; Class Bivalvia S. princeps

S. versicolor

Chlamys (scallop) – Subphylum Conchifera; Class Bivalvia C. swifti

C. islandicus

Perna (mussel) – Subphylum Conchifera; Class Bivalvia

P. veridis

Crassostrea (oyster) – Subphylum Conchifera; Class Bivalvia

Pacific oysters

Atlantic oyster

Anodonta (freshwater clam) – Subphylum Conchifera; Class Bivalvia

A. suborbiculata

A. anatina

Class Cephalopoda  Free-swimming  Fast

moving  Active carnivores  Elongated body  Skeleton may be external, internal or absent Octopus arm  Foot developed into prehensile arms or tentacles

Class Cephalopoda  Well-defined

head  Complex eyes  Brain in cartilaginous cranium  (+) radula  Beak-like jaws  Tentacles

Loligo (squid) – Subphylum Conchifera; Class Cephalopoda mantle

siphon

8 arms and 2 tentacles ctenidia

Sepia (cuttlefish) – Subphylum Conchifera; Class Cephalopoda

Octopus (octopus) – Subphylum Conchifera; Class Cephalopoda

Nautilus (nautiloid) – Subphylum Conchifera; Class Cephalopoda

Class Scaphopoda  Burrowing

and sedentary  Shell in one piece  Shell opens on both sides  With modified conical foot  Head is reduced or absent  No eyes  With radula, jaws and thin tentacles

Dentalium (Elephant’s tusk shell)

Subphylum Conchifera; Class Scaphopoda posterior

anterior shell

Class Monoplacophora  Bilaterally

symmetrical  Have a dorsal, single, dome- or capshaped shell  Has a broad, flattened foot  Includes many fossil species

Neopilina –

Subphylum Conchifera; Class Monoplacophora

N. galatheae

Class Polyplacophora  Include

marine chitons  Bodies elongated and dorsoventrally flattened  Shell divided into: – 7 or 8 overlapping plates – Flat, creeping foot  Head

reduced  No eyes  Well defined mouth with radula

Chiton –

Subphylum Aculifera; Class Polyplacophora C. glaucus

girdle

Mu

8 calcareous plates

scu

lar

foo

t

Acanthozostera –

Subphylum Aculifera; Class Polyplacophora A. gemmata

Class Aplacophora  Worm-like

molluscs called SOLENOGASTERS  With oblong, cylindrical to vermiform bodies  No shell  Lack a well-defined head  Radula and jaws sometimes present

Neomenia –

Subphylum Aculifera; Class Aplacophora

N. yamamotoi

Chaetoderma –

Subphylum Aculifera; Class Aplacophora C. japonicum

View the following slides:  Helix/

Pila/ Haliotsis/ Cypraea/ Turbo  Perna/ Anodonta  Loligo/ Sepia  Dentalium/ Chiton

Fin. Merci.