Exam 2 Flashcards
Mollusc Features
Bilateral symmetra
Triploblastic
Eucoelomate
Unsegmented
Coelom reduced
Complete gut with specialization (often with ceca)
–Possess mouth and anus
Dorsal visceral mass
Secretory mantle produces shell (shell lost in many clades)
Mantle cavity
Muscular foot
Radula (NOT bivalves)
Open circulatory system with heart
Trocophore and veliger larvae
Phylum Mollusca: 2 Clades
Aculifera: Polyplacophora and 1 other class
Conchifera: Cephalopods, gastropods, bivalves, and 2 other classes
Class Bivalvia
2 lateral shells/valves
Radula LOST
Suspension/filter feeders
–Use gills + labial palps to filter feed
Sedentary (NOT larvae, they are mobile)
Little cephalization
Most are marine
Tiny to gigantic in size
DERIVED mollusc group
Little cephalization
Rotary crystalline style
Used to pull in string of food
Rotates to draw in food string
Most endangered North American group:
Bivalves
35 species extinct, 70 endangered/threatened, 180 critically imperiled
______________ makes bivalves especially susceptible to water pollution and changes in physical habitat
Filter-feeding
_____ are sensitive indicators of health of aquatic ecosystems
Bivalves
Phylum Mollusca: 4 Classes
Polyplacophora (chitons)
Cephalopoda (octopuses, squids, nautiluses)
Gastropoda (snails, slugs, nudibranchs)
Bivalvia (clams, mussels, scallops)
Useful taxonomic features used to distinguish MOLLUSCAN species:
Radula
Size and arrangement are species specific
Oldest part of bivalve shell
Umbo
Typhlosole
Fold in the intestine
Increase surface area for digestion, nutrient absorption
Class Gastropoda
Largest molluscan class
Diverse lifestyles (carnivores, herbivores, scavengers)
Diverse habitats
Univalve, coiled shells
Radula
Most closely related to bivalves
Trocophore and veliger larval stages
Typical freshwater mussel life cycle
Females lay eggs and brood them in specialized chambers in their gills
Males release sperm in water
Females draw in sperm
Larvae hatch and begin to develop inside female
Must infect host fish to finish development
Female attracts fish with a fleshy lure
Mussel releases the larvae (glochidia) into fish’s gills
Fish swims away to disperse young
Freshwater mussel’s most endangered animal in US
Glochidia
Mussel larvae
Parasitic (develop on fish host)
Bivalve Shell features
3 layers:
1) Nacreous layer: Innermost, “pearly,” closest to mantle
2) Prismatic Layer: Middle layer
3) Periostracum: Top/exterior layer
ALL made of calcium carbonate or calcium salts/proteins
Nacreous layer can produce pearls
Function of pearls
Defense mechanism
Gastropod Shell
Coiled
- Small apex/tip: oldest part of shell
- -Same idea as umbo in bivalves
- Coils/whorls get larger as you get further down the structure
- Body whorl:
- -Largest whorl
- -Contains most of animal
- Inside columella:
- -Supports entire length of shell
- -Columellar muscle wraps around the columella
- Shell aperture:
- -External opening
- -The “Achiles’ heel” of the animal
- -Operculum:
- –Thick plate seals up the shell aperture to prevent dessication
- –Forms on posterior portion of the foot of the snail
Bivalves: Ctenidia/Gills
Used for respiration, filter feeding, and reproduction
Gastropod Foot
Most of the visceral mass is held within the main body whorl
Ctenidium = gill
-Sits in mantle cavity
Able to do twisting movements, flip self over, hunt and capture prey, all using ONE foot
Gastropod Larval stages
Trocophore
Veliger
Gastropod: Trocophore
Band of cilia around “equator”
Digestive tract:
- Mouth
- Anus
Looks like a diamond
Very short-lived
Plaktonic (free-swimming)
Veliger
Possess a SHELL
- Even sea slugs, nudibranchs have shell in this larval stage
- -They LOSE shell when they reach adulthood
- -Why lose the shell?
- –More mobile
- –Produce toxins as chemical defense, no need for physical defense
Foot
Velum:
- -Cilia on fringe edges
- -Used for FEEDING and LOCOMOTION
- –ONLY present in veliger stage
TORSION occurs in this larval stage