12. Phylum Mollusca Notes

MollusksKingdom Animalia

Phylum MolluscaClass GastropodaClass BivalviaClass Cephlapoda

Mollusks50,000 species10 classesIncludes:

◦ Squid◦ Octopus◦ Clams◦ Conches◦ Snails◦ Sea slugs◦ Oysters

Basic Anatomical Structures:a) Mantle – muscular bag that

surrounds the gills and most organs and is used to circulate water

1. some use it to circulate water or jet propulsion

2. secretes calcium carbonate shell

Basic Anatomical Structures:b) Foot – muscular structure used for

movement

1. In snails & slugs it’s used to crawl

2. In bivalves it’s used to dig

3. In squids, it takes the form of tentacles

Basic Anatomical Structures:

c) Radula – a tongue like structure with scraping teeth

Class Gastropoda

Includes snails, slugs, whelks, & abalone

Defining Characteristics:

- Radula- Some have a shell- Sensitive Tentacles- Shell-less members

can produce toxins or store eaten nematocysts

Snails Sea Slugs

Whelks Abalone

Class Bivalvia:

Includes clams, oysters, mussels, scallops

Defining characteristics:

- Two hinged shells- No head, but

sensory organs on shells edge

- Two siphons extend out of the shell

- Mantle pumps water

Clam Oyster

Mussel Scallop

Clam Oyster

Mussel Scallop

Pearl Making Abilities

When ever sand or an irritant gets inside a shell of an oyster, it coats it in a substance called nacre, creating a pearl

Pearl farmers put seeds inside oysters to create pearls

Class Cephalopoda

Includes squid, octopus, nautilus, cuttlefish

Defining Characteristics:

- Little to no shell, ranging from gastropod like shell (nautilus) to internal leaf like shell (cuttlefish) to thin internal bar called a pen (squid) to nothing (octopus)

Class Cephalopoda

Defining Characteristics:- Specialized foot called a siphon for jet

propulsion- Ink sac- Chromatophores – cells that can change

color- Complex nervous systems consisting of

large eyes and critical thinking abilities

Octopus8 armsBeak like jawsNo shellBottom dwellers

SquidBetter adapted for

swimming due to elongated body and two fins formed by the mantle

Ten arms, two of which are longer are called tentacles

A reduced shell called the pen can be found embedded in the upper surface

CuttlefishResemble squidsEight arms and

two tentaclesFlattened with a

fin along the sides

Internal Shell

NautilusSmooth exterior

shellContains several

gas filled chambers that aid in buoyancy

Has 60-90 arms to catch prey