Phylum Mollusca Flashcards by Cassie Bosma

Blastula development

Protostome

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What is the Super-Phylum for Mollusca?

Lophotrochozoa

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What are 4 main phylogenetic characteristics of Mollusca?

Coelomates
Bilateral symmetry
Trochophore larva
Well developed organ systems

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What animals are included in phylum Mollusca?

Clams, mussels, geoducks, scallops, chitons, squid, octopus, snails, slugs, abalone, limets, whelks, nudibranchs

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What 4 main parts are found in the generalized mollusc head region?

Mouth and sensory organs
Simple to complex eyes
Tentacles
Radula in mouth

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What is the Radula made of?

Chitin

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What is the Radula?

Rasping, protrusible, tongue-like organ
(not found in bivalves and some nudibranchs)
Lined with teeth and supported by cartilage structure (Odontophore)

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What is an Odontophore?

A cartilage structure that supports radula and teeth

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What controls the Radula?

Muscles

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Where does radula transport food?

To the esophagus

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How do the radula work?

Radular teeth scrape, pierce, tear or cut food particles

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What is the Foot used for?

Locomotion or attachment

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What assists the foot in movement?

Mucus

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Where is the foot located?

Ventral position

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What animals have the foot?

Snails, mussels, squid

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What does the mantle do?

Secretes shell
Covers viscera
Creates mantle cavity

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What does the mantle cavity do?

Houses respiratory organs and accepts visceral mass products/wastes

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What organs/systems empty products, and where do the wastes go?

Digestive, excretory, and reproductive products

- Into mantle cavity

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How is the shell created?

Secreted by mantle

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What are the three layers of the shell?

Periostracum
Prismatic layer
Nacreous layer

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What is the Periostracum?

Outer horny layer made of conchiolin

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What is conchiolin?

Protein resistant to erosion and boring

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What is the prismatic layer?

Densely packed prisms of calcium carbonate and protein

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What is the nacreous layer?

Composed of calcium carbonate sheets laid down over a thin protein matrix

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Class Polyplacophora

Chitons

Class Scaphopoda

Tusk shells

Class Gastropoda

Snails, slugs, limpets

Class Bivalvia

Clams, mussels, and scallops

Class Cephalopoda

Squid, Octopus

What is the larval stage of an aquatic mollusc?

Trochophore, then Veliger

What are the habitats of Molluscs?

- Tropic to polar seas - Marine, some freshwater and terrestrial - Hard and soft substrates - Benthic and pelagic - Protected and exposed coasts Pretty much everywhere

Monoicious or Dioecious

Most Dioecious, some gastropods are hermaphrodites (Monoecious)

What does the trochophore larva look like?

Microscopic, 'top'-shaped, circlet of cilia around midsection

5 Characteristics of Class Polyplacophora

- Primitive class - Eight articulating plates or valves - Trochophore larva only - Dioecious - May have shell eyes and osphradia (chemosensory)

What are the purposes of the mantle and mantle cavity in Chitons?

- Mantle forms girdle around edge of plates | - Mantle cavity houses gills on two sides

Chiton habitat

Rock surfaces, intertidal, return to same location at low tide to graze on algae

Size range of Class Polyplacophora

most small (2-5cm), some reach 30cm

Chiton reproduction

Eggs fertilized in mantle cavity and released

6 Major parts of a Chiton

- 8 plates - Girdle (houses gills) - Mantle cavity - Radula - Nerve Ring - Gills (along circumference of foot)

Describe Tusk shells and general size range

- Slender body covered with mantle and tubular shell | - Most 2.5-5cm long (range 4mm-25cm)

What is the foot used for in Tusk shells?

Burrowing in sand or mud, shell protrudes from sediment

What do tusk shells feed on and how do they get food?

- Protozoa and Detritus | - Tentacles

How do tusk shells breathe?

Gas exchange by diffusion across mantle surface | - no gills

What are tusk shells?

Sedentary marine mollusc with a slender body and tubular shell - local west coast and used as indigenous currency

Gastropod habitat?

Marine, freshwater, and terrestrial

What is the operculum in gastropods?

A plate to cover shell aperture

Describe gastropod shell

Single shell or no shell | - Visceral mass found in shell

Gastropod feeding habits

Herbivorous, carnivorous, detritivore (scavengers)

What is different about moon snails?

Extensible proboscis Equipped with radula Used to bore into bivalve shells

Gas exchange in gastropods

Marine - use gills | Terrestrial and Freshwater - use lung

Symmetry of Gastropods

Secondarily asymmetrical due to torsion

What is torsion in gastropods?

Rotation of visceral mass, mantle, and shell 180 degrees in development - Brings mantle cavity and anus to anterior position above the head

Gastropod reproduction

- Dioecious, some hermaphrodites - Copulation is common - Eggs laid in gelatinous masses or singularly

Gastropod larva

Trochophore, then Veliger in marine species

What is a rare occurrence in regards to snail shells?

- Few species may have shell covered by mantle

What is the Pneumostome (odd 'hole' found on the anterior side of a slug viewed in lab)?

- Breathing pore or respiratory opening

Describe Class Bivalvia

- Shell with 2 valves - Range from 1mm-2m - Limited cephalization with no head or radula - Shell opens and closes using hinge and muscles

What is the lifestyle of a Bivalve?

- Sedentary suspension feeders

How do Bivalves feed?

- Incurrent and excurrent siphons - Feeding currents produced by cilia on gills - Gills filter food from water

What is the foot used for in Bivalves?

Burrowing in sediments

How do non-burrowing bivalves attach to substrates?

Anchor to rock using byssal threads (mussels) or cement (oysters)

Bivalve habitat

Aquatic, mostly marine, some freshwater | - attached to substrate or burrowed in substrate

Bivalve reproduction

- Dioecious | - Trochophore and veliger larva

What are the common names of animals found in Class Cephalopoda?

Squid, octopuses, nautilus, cuttlefish

Cephalopoda habitat

Marine, pelagic

What is the function of the foot in Cephalopods?

forms funnel to expel water from mantle cavity

Size range of Cephalopods

Large range | - 2-3 cm all the way to giant squid

Cephalopod locomotion

Jet propulsion

How many arms to octopus, cuttlefish and squid have each?

Octopus - 8 | Squid and Cuttlefish- 10

What are 3 evolutionary developments found in Cephalopods?

- Chromatophores for colour change - Ink sacs for defense - Well developed eyes

What happened to the shell in Cephalopods?

Mostly internal or lost

Feeding mode of Cephalopods

All predatory

Cephalopod reproduction

- Dioecious - Copulate - Tentacles transfer sperm sac - Eggs attached to substrate (brooded in octopus)