Phylum Mollusca > 100,000 extant species At least 45,000 extinct species Nice fossil history based...
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Transcript of Phylum Mollusca > 100,000 extant species At least 45,000 extinct species Nice fossil history based...
Phylum Mollusca
• > 100,000 extant species
• At least 45,000 extinct species
• Nice fossil history based on shells– Fossils from Pre-Cambrian
• Importance?– Shells - collectors, jewelry– food
Mollusca characteristics:
• 1. Foot
• 2. Mantle
• 3. Secretes shell
• 4. External surfaces - ciliated epidermis w/ mucous glands– Food capture, feeding, locomotion,
cleaning body surfaces
Cilia move mucous and create water flow
• Gas exchange + bring food in
• Sorting surfaces separate food particles by size
6. Open circulatory system
• Blood sinuses (no capillaries)
• Heart = one or two auricles – collecting chambers
• one ventricle – pumping chamber
More circ. system
• Hemocyanin pigment in blood (copper)– Blood w/ O2 = blue
– Blood w/o O2 = colorless
• Pulmonate gastropods have hemoglobin
• Cephalopods have closed circulatory system
7. Digestive system
• Sclerotized buccal cavity
• Tubular esophagus
• Cone-shaped stomach
• Long, coiled intestine
Stomach • Contains style sac, rotates contents
– Pulls strands of mucous from esophagus– Mucous viscosity decreases w/ low pH– Stomach wall is chitinized
• Crystalline rod = hyaline mucoprotein
• Style has hydrolase digestive enzymes
Stomach, cont.
• Sort food particles by size
• Intracellular digestion in digestive gland walls
• Some extracellular dig. in stomach
• Carnivores have no style
8. Nitrogenous waste
• Pair of coelomoducts– Open to pericardial cavity
• Discharge into mantle cavity via nephridiopores– Probably not homologous to annelid
metanephridia (annelid origin = mesoderm; mollusk origin = ectoderm)
9. Nervous system - varied• Polyplacophora (chitons) - decentralized, no
ganglia
• Cephalopods - as developed as in vert’s
• Primitive gastropods:– Nerve ring around esophagus, 2 pair of major nerve
cords
Reproduction and development
– Pair of gonads in coelom– Eggs + sperm into pericardial cavity,
outside via coelomoducts– Fert external in sea water– Molluscs mostly dioecious, some
gastropods hermaphroditic
Most gastropods, all cephalopods:
• Sperm transferred to female’s mantle cavity
• Internal fertilization
• Hermaphroditic gastropods do reciprocal cross-fertilization
Development
• Trochophore larvae = free-swimming
stomach
prototrochciliated band
mouth
protonephridiumanus
intestine
eye
Trochophore larvae
• Archaeogastropoda
• Polyplacophora
• Aplacophora
• Most marine bivalves
• Develops into veliger larvae– Foot, shell, other structures appear
Phylogenetic significance of trochophore larvae
• Hatschik (1878)
• Present in molluscs, annelids, other phyla
• Promotes ctenophora - trochophore theory of bilateral animals from radial ancestors– body shape, apical sense organs,
statocysts, nervous systems
7 mollusca classes
• Polyplacophora
• Aplacophora
• Monoplacophora
• Gastropoda
• Scaphopoda
• Bivalvia
• Cephalopoda
Class Polyplacophora
• Chitons and oval-flattened beasts - mostly in rocky intertidal zones
• All marine, ~ 800 spp.
• Mostly 2 - 12 cm
• Largest (30 cm)is Cryptochiton stelleri from N. Pacific coast of N. America
= Pacific gumshoe chiton
Chiton characteristics:
• Most feed on algae and micro-organisms on rock surfaces
• Few are predators on small inverts
• 1. Rudimentary head– No tentacles or eyes
Characters
• 2. Mantle covers dorsal surface– Secretes 8-piece shell
• 3. Broad, ventral foot
• 4. Many paired gills in mantle cavity
• 5. Anterior mouth with radula
Repro:
• 6. Dioecious– trochophore larvae, no veliger– external fert. in sea water
mouthGills in mantle cavity
mantle
foot
Classification of Polyplacophora - 2 orders
• Order Lepidopleurida: few genera, Hanleya NE coast
• Order Chitonida - most chitons– Chaetopleura (New England - Fl)– Chiton (gulf coast)– Katherina (N. Pacific coast)– Cryptochiton (N. Pacific coast)– Mopalia– Ishnochiton
Class Aplacophora
• Solenogasters are worm-like molluscs 0.5 - 30 cm long– Largest is Epimenia verrucova; 30 cm
• All marine• Mostly deep waters, 20 - 9000 m• Some crawl and feed on hydroids and
corals • Poorly known, seldom seen, ~ 250 spp.
Characteristics:
• 1. Worm-like body shape
• 2. No shell, mantle, or foot
• 3. Cuticle w/layers of imbedded calcareous spicules
• 4. Ventral surface has longitudinal pedal groove
• 5. Hermaphroditic
• 6. Radula well-developed
Class Monoplacophora
• Originally known only from fossils
• Living Neopalina from 3600 m in Pacific Ocean coast of Costa Rica (1952)
• Two genera – Neopalina (7 spp.) and Vema
Characteristics:
• 1. Dorsal surface covered by flat conical shell.
• 2. Ventral surface with mantle, paired gills and foot.
• 3. Multiple paired gills, coelomoducts, heart chambers, gonads, and retractor muscles.