seashells (mollusks) & beachcombing

Seashells (mollusks) & beachcombing

Maia McGuire, PhDFlorida Sea Grant Extension Agent

Mollusks• Includes Gastropods (snails), Bivalves (e.g.

clams) and Cephalopods (e.g. octopus)• Second largest invertebrate phylum (after

arthropods)• Generally have a muscular

foot, a calcareous shell and a feeding organ called a radula

• Have gills, blood vascular system, stomach, heart, sensory organs (e.g. eyes)

Molluscan reproduction• Sexual reproduction• Most are single sex (gonochoric)• Fertilization is external• Larvae are often planktonic (most common

type is called a veliger)

Gastropods

• Snails and sea slugs• “Head foot”• Carnivores and herbivores• There are gastropods in salt water, fresh water

and on land, but all are restricted to that particular habitat. Land snails have lungs.

• Many have an operculum (“trap door”) to seal the entrance to their shell.

Gastropod adaptations

• Operculum (‘trap door”)– Used to help protect snail from predators– Used to help prevent snails from drying out

(especially for intertidal snails)– Different types of snails have different types of

opercula (range from thin and flimsy, to made of calcium carbonate)

Some snails are predators

• Remember that radula?• It becomes a drill or rasp that some snails use

to drill through the shells of other snails or bivalves (e.g. clams)

www.seaslugforum.net

Common gastropods

• Slipper shell• Moon snail/shark’s eye• Olive• Auger• Wentletrap• Baby’s ear• Whelks• Tulips

Gastropod egg cases

• Sand collar (moon snail)

• Whelk and tulip egg cases

www.jaxshells.org

Baby snails

• Often planktonic (carried by ocean currents)• Have a tiny shell, which becomes the tip of the

shell after the animal settles and grows.

Snail growth

• Snails add to their shell (at the opening/lip, and in thickness) as they grow.

• The mantle used calcium and bicarbonate ions from the water to create calcium carbonate.

• We cannot age a shell based on growth lines (unlike trees and corals)

Sea slugs• No external shell• Variety of defense mechanisms• Some are herbivores, others are carnivores

Bivalves• Have two, hinged shells• Examples include oysters, clams, mussels,

scallops• Many can live 20-30 years; some more than

100 years!• Most are filter-feeders• Many attach to hard surfaces; some have threads or cement

Bivalve shells

• Some bivalves have a periostracum (thin, often brown covering over the shell)—provides camouflage.

Common bivalves

• Ark clams

• Pen shells

• Coquina clams

• Jingles

• Cockles

• Scallops

Cephalopods

• Octopus, squid, nautilus, cuttlefish• Swim by producing a jet of water through a

funnel• Most have 2 tentacles with suction cup ends;

8 arms with suction cups• Horny, parrot-like beak; radula functions as a

tongue• Have pigment cells in skin

Cephalopod biology

• Many can squirt ink as a defense• Eyes and nervous system are well-developed• Carnivores• Poisonous saliva• Have gills, heart, brain• Gonochoric• Squid die after mating• Female octopus die after

brooding their eggs

• Paper nautilus

• Ram’s horn shell

www.manandmollusc.net

Cephalopods

www.seabean.comwww.seabean.com

Activities

• “I Have a Shell” (Monterey Bay Aquarium)• “CSI: Clamshell Investigation” (NJ Sea Grant)

Weird and Wonderful things…

• Mermaid’s purse

• Sand dollar

• Sea stars

Jellyfish• Portuguese man-o-war– Don’t touch!– Associated companions—”By-the-wind

sailor”, “blue buttons”, purple sea snail, man-o-war slug, man-o-war fish

www.enature.com

www.amonline.net.au

Cannonball jellyfish

www.jaxshells.org

Moon jellyfish

www.jaxshells.org

Sharks’ teeth

Sea beans

• www.seabean.com• Any of a number of seeds

that are adapted to germinate even after spending a period of time floating in water

• Mostly from tropical plants, many from vines

Activity

• Beach Treasures