Lecture 9+10 (BIO-2040)

Molluscs

• all derived from worm-snail primitive form

• include 7 families and at least 50,000 living species and a large amount of fossils

Basic Body Plan of Molluscs

• shell

• mantle

• mantle cavity

• foot

Molluscs feeding

open and complex digestive systems

Radula

toungue like organ with teeth for scraping, present in Molluscs

Molluscs circulation

• open

• heart inside the coelom

Molluscs excretion

• by meta-nephridia

• blood collects waste

• diffuse into the coelom

Meta-nephridia

takes and places waste in mantle cavity

Molluscs respiration

• depends on class

• by gills or lungs located in mantle cavity

Molluscs Classes

• bivalva

• gastropoda

• cephalopoda

• polyplacophora

• monoplacophora

• Aplacophora

• Scaphopoda

Bivalva

• Only mollusc class with no radula

• 30,000 species

• marine or freshwater

• burrower or sedatary

• live in soft or hard bottom

Bivalva Evolution

• shell grew to cover the body

• compressed laterally 

• became hinged

• head shrink/organs rearrange

• foot becomes a “blade”

Deposit feeders Bivalva

• mouth faces up

• mantle cavity faces up

• some adapt siphons + feeding tentacles

• eat sediments

• They process the seafloor

Suspension feeders Bivalva

• Gills filter water and retain food

• extensive use of siphons

• They increase water clarity

• Some are ecosystem engineers

Bivalva Nervous System

not well developed compared to other mollusc classes

Bivalva reproduction

• most species are dioecious

• most with external fertilization

Gastropoda

• about 60,000 species

• many are grazers

• marine, freshwater, terrestrial

• herbivores, carnivorous, scavengers

Gastropoda evolution

• bigger head, better bigger shell

• shell is coiled for stability

• body had to twist

• some systems become modified

Gastropoda diversity

typically a single shell to deal with desiccation or predators

Operculum

a round plate that seals the shell to deal with desiccation or predators

Gastropoda reproduction

• most have internal fertilization

• many protect their eggs in cases or capsules

Chromatophores

skin adpats to mimic the background

Cephalopoda

650-700 species

Cephalopoda evolution

• dorsal-ventral axis lengthened; the anterior foot became tentacles, the posterior part is a funnel

• The shell became divided by septa

• shell become coiled (nautilus)

• shell got lost

Cephalopoda feeding

• catch prey with tentacles

• have jaw and predominant radula

• have ink sac or “smoke screen” to escape predators

Cephalopoda Locomotion

jet-propulsion by stretching mantle muscles

Cephalopoda nervous systems

• highly developed

• giant axons

• eyes comparable to vertebrate

Cephalopoda Reproduction

• seperate sexes

• external or internal fertilization

Cephalopoda classification

• Nautilids

• Octopus

• Squid and cuttle fish

Arthopods

• segmented

• marine, freshwater, and terrestrial

• >75% of known animal diversity

New appandages

joint legs for the first time

Prominant exoskeleton

• thick cuticle

• some cuticles become carapaes

• hardened plates and flexible joints

Reduced Coelom

exoskeleton means no need for hydrostatic skeleton

growth by molting

1) old cuticle seperates from epidermis

2) new cuticle secreted

3) old cuticle splits and sheds

4) new cuticle hardens

Arthopods digestion

a full set of modified mouth parts for different feeding modes

Arthopods nervous systems

well developed

• large brain to coordinate movement

• many different chemo-sensory organs

Arthopods respiration

hard cuticle reduces permeability

There is a need for gills, trachea, etc. specific organs or structures depend on groups

Insect excretory

Malpighian tubules

Spider excretion

coxal glands

Crustaceans excretion

green glands

Trilobita

3-region body

• head

• trunk

• pygidium

many pairs of appendages

• pair 1 → absent

• pair 2 → antennae

• pair 3 → similar and biramous

found in western canada

Chelicerata

body in 2 regions

• cephalothorax (head and thorax)

• abdomen

6 pairs of appandages

• pair 1 → chelicerae

• pair 2 → pedipalps

• others → walking legs

Class Chelicerata

• primitive class

• all marine

• large carapace

• abdomen with a telson

Class Pycnogondia

• all marine

• elongated cephalothorax

• reduced abdomen (looks like one region)

Class Anachnida

• mostly terrestrial species

• prominant wax on cuticle

• important to people

Spiders

• body with narrow waist

• spinnerets to produce silk, and nets

• nets are for feeding, dispersion, holding eggs, etc.

• They are hunters and ambush predators

Scorpions

• with terminal stinger

• tropical, carnivorous species

• some can be lethal

Mites and Ticks

• most diverse, ecto parasite

• no waist

• scavengers

Crustacea

3 regions (tegmata)

• cephalon

• thorax

• abdomen

appandage pairs

• pair 1+2 → antannae

• pair 3-5 → mandibles + maxillae

• others → walking, respiration, etc.

Class Malacostraca

• most diverse (75% of all crustaceans)

• includes the decapods (crabs and shrimp)

  • 5 pairs of legs (chelipeds, with claws and chelae)

  • 6 pairs of abdominal (pleads + uropods)

Crustacea Reproduction

• most are dioicous

• eggs brooded (in most)

• different larvae: nauplius, zoea, and megalopae