Midterm II (Mollusca)

Question 1

Phylum Mollusca

Answer 1

• 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!

Question 2

Molluscs and Us

Answer 2

1. Food
   - Calamari, escargot, mussels, scallops, clams…
   - Threatened by climate change, CO2, ocean acidification, weak shells
2. Pearls and shells
   - Cowries = currency!
3. Bioindicators
   - Environmental indicators.. and filters!
4. Pests
   - Bites, stings, crops, parasites/intermediate hosts, biofouling
5. Biotechnological/medical importance
   - Shell strength, nerve cells and axons, venom, nacre (strong substance, bullet proof vests)

Question 3

The Archimollusc

Answer 3

• Hypothetical Ancestral Mollusc (HAM)

Question 4

What makes a Mollusc a Mollusc?

Answer 4

1. Head-Foot
2. Visceral Mass

Question 5

Head-Foot (The Head)

Answer 5

The Head
- Feeding
- Sense organs
- Brain, eyespots-to-eyes, tentacles

Question 6

Head-Foot (Radula)

Answer 6

The Radula
- Chitinous ribbon of teeth
- NOT in any Bivalve
- Odontophore cartilage holds teeth
- Separate muscles to move odontophore (in/out) and radula

Question 7

Head-Foot (The Foot)

Answer 7

• Locomotion, attachment
• Ventral

Question 8

Visceral Mass (organs)

Answer 8

Internal organs
- Digestive, excretory, reproductive and respiratory

Question 9

Visceral Mass (Mantle and mantle cavity)

Answer 9

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!

Question 10

Visceral Mass (Mantle and shell)

Answer 10

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”

Question 11

Pearls

Answer 11

• 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

Question 12

Basic Internal Characteristics

Answer 12

• 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)

Question 13

Reproductive System

Answer 13

• 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))

Question 14

The Aplacophorans

Answer 14

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

Question 15

Class Polyplacophora: The Chitons

Answer 15

• “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

Question 16

Class Monoplacophora

Answer 16

• “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

Question 17

Class Gastropoda

Answer 17

• “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

Question 18

Main (functional) Groups of Gastropods

Answer 18

1. “Prosobranchia”
   - “gills in front of heart”
   - Most marine snails (periwinkles, limpets, conchs…)
2. “Opstobranchia”
   - “gills behind heart”
   - (mostly) marine shell-less forms (nudibranchs, sea slugs..)
   - Cerata
3. “Pulmonata”
   - “breathe air”
   - Most land and freshwater snails and slugs
   - Mantle cavity modified into lung (no gills)

Question 19

Torsion and Coiling (difference important!)

Answer 19

• 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)

Question 20

Feeding and Ecology of Gastropods

Answer 20

• Even though extremely varied, they all feed with some adaptation of the radula
• Scraping. drilling, piercing..
• Herbivores, scavengers, carnivores..
• Some even incorporate photosynthetic endosymbionts!

Question 21

Love Darts and Slug Orgies

Answer 21

• Simultaneous hermaphrodites
• Love darts (not a penis).. a pre-mating sperm booster
• Eversible gonopores (penises + vaginas) and simultaneous sperm transfer

Question 22

Class Bivalvia

Answer 22

• “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)

Question 23

Basic Internal Features (bivalvia)

Answer 23

1 pair of Ctenidia (gills):
- Particle/filter feeding AND respiration

Question 24

Bivalve Locomotion

Answer 24

• Foot to burrow (clams)
• Adductor muscles to swim (scallops)
• Some sessile
  
  • Byssal (byssus) threads (mussels)
• Cemented (oysters)

Question 25

Class Scaphopoda

Answer 25

• Tusk shells/tooth shells
• Tubular shell: open at both ends
• A lot of diffusion in mantle cavity
  
  • No heart, no gills..
• Tentacular foot (captacula) for burrowing and food capture (foraminifera (microscopic animals))
• Sedentary, marine benthic/burrowers

Question 26

Cephalopoda

Answer 26

• “head-foot” (as opposed to stomach-foot
• Small to large
• Predators (beak-like jaws)
• Arms, tentacles, siphons
• Exclusively marine
  Cuttlefish, Nautilus, Octopus, Squid

Question 27

Basic Body (Cephalopods)

Answer 27

8 arms
- Squids and cuttlefish also have 2 tentacles
Most have 1 pair of gills
Closed circulatory system
Incredible nervous system
- Huge vision centre in the brain
- Large, lensed (camera) eyes
- Innervation of arms
- Intelligent and likely sentient

Question 28

Shell? (cephalopods)

Answer 28

• Nautiloids - large shell
• Cuttlefish - internal shell: cuttlebone
• Squid - proteinaceous pen
• Octopus - no shell at all

Question 29

Locomotion (cephalopods)

Answer 29

• Fins, arms, and jet propulsion

Question 30

Camouflage and Ink

Answer 30

• Masters of illusion and disguise
  
  • 4 cell types
    
    • Chromatophores
• Ink sac - melanin (some also contain mucus)
• Out the rectum!

Question 31

Reproduction

Answer 31

• Diecious (separate males and females)
• With some amazing mating rituals!
• Copulation (one arm specialized as sperm packet, inserts through her siphon)
• Direct development (no larvae)
• All but a couple species die after giving birth (semelparous)