Seashells (mollusks) & beachcombing Maia McGuire, PhD Florida 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)

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

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 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 Cephalopods

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

Cannonball jellyfish

Moon jellyfish

Sharks’ teeth

Sea beans 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