Triploblastic - bodies derived from 3 primary germ layers
Coelomates - possess a true coelom, a fluid-filled body cavity lined by mesoderm
Mollusc body plan
Head-foot portion (ventral) - contains head, sensory organs, foot for movement
Visceral mass (dorsal) - contains internal organs
Mantle
Protective layer that can secrete the shell
Shell
Hard, protective outer structure
Visceral Mass
Area containing the internal organs
Anatomical features common to molluscs
Mantle and mantle cavity
Muscular foot
Visceral mass containing internal organs
Radula
Tongue-like organ with chitinous teeth used for feeding, to scrape or cut food before ingestion
Many molluscs have a trochophore larval stage in their development, a free-swimming larva common among marine invertebrates
Circulatory system of molluscs
Open circulatory system - blood flows freely through cavities and bathes organs directly
Cephalopods have a closed circulatory system - blood contained within vessels for more efficient transport
Parts of the mollusc body
Mantle
Shell
Visceral Mass
Heart
Intestine
Anus
Mantle Cavity
Gill
Coelom
Digestive Gland
Stomach
Mouth
Radula
Eye
Head-Foot
Foot Retractor Muscles
Parts of the radula
Esophagus
Radula (ribbon-like structure with rows of teeth)
Radula sac
Muscles
Odontophore cartilage
Layers of the mollusc shell
Periostracum
Prismatic layer
Nacreous layer
Mantle epithelium
Tissue of the mantle that secretes the shell's materials
Mantle
Layer of tissue that drapes over the visceral mass and secretes the shell components
Shell gland
Specialized region of the mantle responsible for initiating shell secretion
Gastropods are among the most numerous and diverse groups of molluscs, inhabiting marine, freshwater, and land environments
Torsion
Unique developmental process characteristic of gastropods, resulting in the rotation of the visceral mass, mantle, and shell 180 degrees with respect to the head and foot
Stages of torsion in gastropods
Pre-torsion stage
Post-torsion stage
Torsion allows the gastropod to retract into its shell with the head entering last, which can be an effective escape response
Torsion introduces complications like the potential for fouling, as waste material from the anus is now in close proximity to the head and feeding structures
Reproductive strategies in gastropods
Egg-laying
Dioecious (distinct male and female)
Monoecious (hermaphroditic)
Protandry (start as male, later change to female)
Livebearing
The typical larval stage in marine gastropods is the trochophore, which then develops into a veliger larva
Bivalves
Possess a shell consisting of two hinged parts (valves)
Many lead a mostly sedentary lifestyle, attaching to substrates
Some can move by clapping their shells together to "swim"
Inhabit almost every aquatic habitat
Filter feeders, drawing in water through their gills to filter out plankton and organic particles
Anatomical features of bivalve shells
Adductor muscle scars
Line of mantle attachment
Teeth
Grooves for teeth
Umbo
Anterior
Posterior
Dorsal
Ventral
Bivalve body parts
Mantle
Shell
Adductor muscle
Incurrent aperture
Excurrent aperture
Paired gills
Foot
Suprabranchial chamber
Nephridium
Heart and blood vessels
Digestive tract
Bivalve digestive system
Mouth
Labial palps
Esophagus
Stomach
Style sac
Digestive gland
Intestine
Anus
Gonad
Heart
Pericardial cavity
Nephridium
Gill
Mantle
Cerebral ganglion
Pedal ganglion
Foot
Bivalve circulatory system
Heart
Pericardial cavity
Anterior aorta
Posterior aorta
Visceral mass
Vein from foot
Artery to mantle
Blood sinus of foot
Bivalvia - Circulation
Heart: Two auricles and one ventricle, pumps blood into arteries
Pericardial Cavity: Space surrounding heart where blood is collected from gills and pumped back into body
Anterior Aorta: Carries oxygenated blood from heart to anterior body
Posterior Aorta: Carries oxygenated blood from heart to posterior body
Visceral Mass: Area where internal organs are located, blood flows around to supply nutrients and oxygen
Vein from Foot: Blood vessels that return deoxygenated blood from foot to gills
Artery to Mantle: Carries oxygenated blood to mantle for gas exchange and shell formation
Blood Sinus of Foot: Cavity in foot filled with blood for nutrient/waste exchange
Artery to Foot: Delivers oxygenated blood to muscular foot for movement and burrowing
Red arrows represent flow of oxygenated blood, blue indicates return of deoxygenated blood to heart and gills
Bivalves do not have a separate set of capillaries, arterial blood is released directly into visceral mass sinuses
Bivalvia - Reproduction: Reproductive Modes
Dioecious: Separate male and female individuals
Monoecious (Hermaphroditic): Produce both eggs and sperm
Protandrous: Function as male then female at different life stages
External Fertilization
Gametes released into water column, fertilization occurs externally
Developmental Stages
Trochophore: Free-swimming larval stage with cilia for swimming and feeding on plankton
Veliger: Larval stage with shell development and velum for feeding/propulsion
Unionid Bivalves and Brooding
Unionids brood larvae in mantle cavity
Glochidium Release: Larvae released to parasitize fish
Parasitic Stage: Larvae develop on fish host
Class Cephalopoda: General Characteristics
Modified Foot: Arms/tentacles surround head, foot evolved into funnel/siphon
Head and Visceral Mass Alignment: Head above body, head-first swimming
Muscular Mantle: Covers body, role in locomotion via jet propulsion
Cephalopoda: Circulation and Sensory Adaptations
Closed Circulatory System: Blood contained in vessels for efficient oxygen transport
Advanced Sensory and Nervous Systems: Complex brains, highly developed eyes