Midterm II (Mollusca) Flashcards
Phylum Mollusca
- From Latin Molluscus = “soft”
- Extremely diverse (around 90k living species) and disparate (8 classes)
- Simple to some of the most complex invertebrates!
- E.g., snails, clams, chitons, octopuses, nudibranchs - Cosmopolitan distribution: marine, FW, terrestrial
- Carnivores, herbivores, filter feeders, parasites…
- Most are small (<10 cm), but also some of the biggest invertebrates (giant squid > 18 m)!
- Human importance!
Molluscs and Us
- Food
- Calamari, escargot, mussels, scallops, clams…
- Threatened by climate change, CO2, ocean acidification, weak shells - Pearls and shells
- Cowries = currency! - Bioindicators
- Environmental indicators.. and filters! - Pests
- Bites, stings, crops, parasites/intermediate hosts, biofouling - Biotechnological/medical importance
- Shell strength, nerve cells and axons, venom, nacre (strong substance, bullet proof vests)
The Archimollusc
- Hypothetical Ancestral Mollusc (HAM)
What makes a Mollusc a Mollusc?
- Head-Foot
- Visceral Mass
Head-Foot (The Head)
The Head
- Feeding
- Sense organs
- Brain, eyespots-to-eyes, tentacles
Head-Foot (Radula)
The Radula
- Chitinous ribbon of teeth
- NOT in any Bivalve
- Odontophore cartilage holds teeth
- Separate muscles to move odontophore (in/out) and radula
Head-Foot (The Foot)
- Locomotion, attachment
- Ventral
Visceral Mass (organs)
Internal organs
- Digestive, excretory, reproductive and respiratory
Visceral Mass (Mantle and mantle cavity)
Mantle = the “skin”
- Can have muscles, or chemoreceptors, etc
- makes the shell
Mantle Cavity = Open to “world”
- excretion (metabolic and digestive), respiration, reproduction, even jet propulsion!
Visceral Mass (Mantle and shell)
Mantle and shell
- Made by the outer layer of mantle
- Three layers:
1. Periostracum
- Outer organic layer
(resistant protein conchiolin)
2. Prismatic layer
- Calcium carbonate stacks
3. Nacre
- Continuously thickens
- Calcium carbonate + protein sheets
- AKA “mother of pearl”
Pearls
- Mantle secretes a layer of nacre
- Pearl = defense strategy, any bits of dirt between shell and mantle, the mantle will secrete layers of nacre on top of obstruction, accumulates and makes a pearl
Basic Internal Characteristics
- Bilaterally symmetric coelomates
- (Reduced coelems)
- Mantle/cavity for respiration
- Gills, lungs, diffusion
- Most have open circulatory system (except cephalopods: squids, octopuses)
- Complex digestive system (filter feed, carnivorous, diverse)
- Varied nervous system (small, non-existent to complex brains and CNS)
Reproductive System
- ALMOST never asexual
- Dioecious (separate males and females) or monoecious (hermaphroditic)
- Trochophore larvae in most
- Veliger larvae common
- aquatic bivalves and gastropods
- Some have direct development (no larvae, mini adult (like humans))
The Aplacophorans
Clade including classes Caudofoveata and solenogastres
- AKA spicule worms
- Wormlike and shell-less
- Calcareous scales/spicules
- Reduced head, no foot
- Marine detrital/microorganisms consumers - burrowers!
- Solenogastre like to eat ctenophores, crawl on bottom
Class Polyplacophora: The Chitons
- “Many plates”
- 8 moveable plates
- Mantle girdle around outside
- Some serial repetition seen
- Multiple ctenidia (gills) on lateral grooves of mantle cavity
- Marine intertidal grazers on hard bottom
Class Monoplacophora
- “one plate”
- Thought to be extinct until 1952!
- Single cap-like round shell
- Large foot
- Serial repetition of soft parts
- gills, nerves, gonads, nephridia
- Deep-sea grazers on hard bottom
Class Gastropoda
- “Stomach + foot”
- Most taxonomic rich (diverse) mollusc class: around 70,000 spp.
- snails, periwinkles, limpets, sea slugs, slugs
- Coiled shell, domes shell, no shell
- some with protective operculum
- Widest range of habitats;
- Marine (benthic and pelagic), freshwater, terrestrial
Main (functional) Groups of Gastropods
- “Prosobranchia”
- “gills in front of heart”
- Most marine snails (periwinkles, limpets, conchs…) - “Opstobranchia”
- “gills behind heart”
- (mostly) marine shell-less forms (nudibranchs, sea slugs..)
- Cerata - “Pulmonata”
- “breathe air”
- Most land and freshwater snails and slugs
- Mantle cavity modified into lung (no gills)
Torsion and Coiling (difference important!)
- Both happen at about the same time in embryonic development (veliger)..
- … but coiling is earlier evolutionarily
- Torsion: 180 rotation of the mantle/mantle cavity
- Coiling: whorling of the shell (appeared evolutionarily first) (leaning shell, lose gills on one side)
- can use foot to cover opening of shell (Operculum)
Feeding and Ecology of Gastropods
- Even though extremely varied, they all feed with some adaptation of the radula
- Scraping. drilling, piercing..
- Herbivores, scavengers, carnivores..
- Some even incorporate photosynthetic endosymbionts!
Love Darts and Slug Orgies
- Simultaneous hermaphrodites
- Love darts (not a penis).. a pre-mating sperm booster
- Eversible gonopores (penises + vaginas) and simultaneous sperm transfer
Class Bivalvia
- “two valve” shells
- clams, mussels, oysters, scallops, cockles, etc.
- No head, no radula
- Laterally compressed body
- Hinged dorsally; gap open ventrally
- Abductor mussels (keep the shell closed)
Basic Internal Features (bivalvia)
1 pair of Ctenidia (gills):
- Particle/filter feeding AND respiration
Bivalve Locomotion
- Foot to burrow (clams)
- Adductor muscles to swim (scallops)
- Some sessile
- Byssal (byssus) threads (mussels)
- Cemented (oysters)
