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

Shell: 3 layers

Periostracum: horny protein, conchiolin in some

Prismatic layer: calcite crystals w/membranes between

Nacreous layer: CaCo3

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

Cilia over gill surface Water movement opposite of blood flow

5. Coelom is reduced Only pericardial cavity

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

Radula Chitin-toothed Rasping organ for scraping algae

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

Sorting in stomach

Intestine Fecal compaction Anus opens into mantle cavity

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)

Waste product? Ammonia in aquatic molluscs Uric acid in terrestrial molluscs

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 eye stomach prototroch ciliated band mouth intestine protonephridium anus

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

Problem with ctenophora-trochophore connection Flatworms don’t fit Degenerate annelids?

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 3. Broad, ventral foot 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 mouth Gills 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

Pedal groove cloaca

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.

Neopalina: Dorsal Ventral

Dissection: bivalve umbo anterior

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