Class Bivalvia (Pelecypoda) 2nd largest mollusc class ~ 20,000 living; 20,000 fossil spp. Appear in Cambrian Height of diversity ~ 350 mya

Class Bivalvia (Pelecypoda) Sizes: 2 mm to > 1.35 m (Tridachna gigas, giant clam can weigh 440 lbs.) 1. Bivalve shell 2. Bilateral symmetry, body compressed laterally 3. Rudimentary head, no eyes, no tentacles, no radula

Characters, cont. 4. Large blade-like foot 5. Pair of large, complex, ciliated gills –Filter feed on plankton, sediments 6. Some sessile species have byssal threads for attachment to substrate –Mussels and oysters –Secreted by gland at based of foot

Bivalves 7. Most are dioecious External fertilization, or in mantle chamber (some marine and most freshwater spp.) 8. Marine species: trochophore + veliger larvae present –Freshwater Unionacea veliger = glochidia Parasitic on fish gills

Fishes are host to glochidia

Subclass Protobranchia Primitive, small, marine bivalves Nut clams Nucula yoldia Cryptodont Solemya 0.45 cm 1.5 cm

Subclass Lamellibranchia 98% of bivalves A. arks, Arca –Hinge straight w/ numerous fine, regular teeth –Bitter sweet clams, Glycemeris

Subclass Lamellibranchia B. Mussels, winged or tree oysters, pen shells –Byssal threads for attachment –Mytilus, Modiolus are edible mussels –Pearl oysters Pinctada are winged oysters

Subclass Lamellibranchia C. Scallops Pectin, jingle shells, file shells –Scallops swim by clapping their valves –Numerous blue eyes on mantle margin

Subclass Lamellibranchia D. Oysters Osstrea, Crassostrea (Asian) –Form large attached colonies –Oyster farming began over 100 years ago in U.S.

Subclass Lamellibranchia E. Unionacea, freshwater clams Small commercial fishery in Indiana and elsewhere in U.S. produced “mother of pearl” Currently for Japanese pearl industry

You are required to know: Megalonaias nervosa = washboard Amblema plicata = three ridge Quadrula metanevra = monkeyface Elliptio crassidens = elephant ear Obovaria subrotunda = hickorynut Corbicula fluminea = Asian clam

Megalonaias nervosa = washboard

Amblema = three-ridge

Quadrula metanevra = monkeyface

Elliptio crassidens = elephant ear

Obovaria subrotunda = hickorynut

Corbicula fluminea = Asian clam

Subclass Lamellibranchia F. Lucines, jewel boxes, and cockles Cockles are edible and popular in Europe, Cardium

Subclass Lamellibranchia G. Giant clams, Tridachna are tropical sessile species Rely on commensal algae for much of nutrition Most species are endangered in many areas by shell collectors

Subclass Lamellibranchia H. Sphaeridae: freshwater fingernail clams Corbicula, Asian clams Common, most < 1/4 inch

Subclass Lamellibranchia I. Razor clams - elongate valves J. venus clams –Mercenaria is the tasty cherrystone or hard-shelled clam

Subclass Lamellibranchia K. Soft-shell clams (in comparison with Mercenaria) –Mya is commercial clam in U.S. –Geoducks –Panopea

Corbicula fluminea, Asian clam Corbiculidae Hermaphroditic Introduced to North America early 1900’s Widespread E., S., and far W. United States

Corbicula Life history adapted for unstable, unpredictable habitats Highly invasive, replaces native Sphaeriid populations –Highest filtration and assimilation rates of any freshwater bivalve –Highest growth and production rate –3-6 mos. to maturity –Single adult can produce 68,678 juv/year

Dreissena spp., zebra mussel and quagga mussel Widespread colonial, sessile bivalve from Europe –Caspian Sea Spread through European drainages in 1700’s

Zebra and quagga mussels Lake St. Claire by ship water ballast entire Great Lakes and St. Lawrence Continues to spread through rivers

Zebra and quagga mussels Tend to foul pipes - industry, boats, etc. Dioecious, trochophore and veliger larvae Adults attach by byssal threads Very small eggs, –30, ,000 per female –Kill natives by overcolonization

Boring clams (Pholas) and shipworms (Teredo) Shipworms cause economic damage by boring in pilings and submerged wooden structures

Subclass Septibranchia Watering pot shells Elongate tube-shaped with tiny shells Live in mud or bore in rock, coral, or clamshells

Class Cephalopoda - octopus and squids Extremely complex, advanced molluscs Nervous and sensory system development surpasses all other invert’s ~ 1000 extant spp. ~ 10,500 fossil spp. Appear in Cambrian –Peaks in abundance Paleozoic + Mesozoic

Cambrian = 500 mya 65 mya present 250 mya 65 mya 550 mya 250 mya

Largest invertebrate animal is giant squid of North Atlantic (Architeuthes) –to 16 m with long arms All marine + carnivores Class Cephalopoda - octopus and squids

Characteristics: 1. Primitively - straight or coiled shell divided into compartments by septa –Shell used for buoyancy –Many cephalopod shells are reduced or absent –Compartments connected by siphuncle Secretes or absorbs nitrogen-rich gas into chambers –New chambers secreted w/growth

Characters 2. Bilateral symmetry 3. Well-developed head w/prominent, well- developed eyes Eyes resemble vertebrate eyes 4. Prehensile tentacles - derived from anterior of foot - suckers (except Nautilus)

Characters 5. Dorsal-ventral axis of body has become functional posterior-anterior axis, by elongation 6. Mantle encloses body –Thick and muscular –Opening to cavity is funnel-shaped siphon –Pump water out for backwards “jet- propulsion”

Characters 7. Mouth equipped with pair of chitinous jaws - resemble hawk’s beak –Radula present 8. Respiration- pair of gills in mantle cavity. –No cilia 9. Ability to change skin color by melanophores in most spp.

Characters 10. Brain large + complex. –Behavior and learning highly developed 11. Dioecious: copulation by transfer of spermatophore by one of tentacles 12. Egg development direct - no larva

Classification 1. Subclass Nautiloidea –Nautiloids, shelled –Living Nautilus with 3? spp. Indo-Pacific –Many fossil species –Don’t confuse with “paper nautilus” - an octopus

2. Subclass Ammonidea Ammonoids Shell w/ complex sutures Silurian - Cretaceous

3. Subclass Coleoidea - shell internal or absent A. Belemnites - extinct, w/chambered internal shell. Probably ancestral to other coleoids B. Spirula - coiled chambered internal shell. –Deep-water denizen of tropics

Subclass Coleoidea C. Cuttlefish –straight, chambered, internal shell –Sepia –Rossia (bob-tailed squid)

D. Squids Shell chitinous, no chambers, serves as body skeleton Many pelagic and deep-sea spp.; few in shallow waters Loligo Lolliguncula Architeuthes

E. Vampire squid Octopus-like forms with webbed arms Vampyroteuthis infernalis Black skin

F. Octopods Eight arms, no fins Octopus Argonauta (produces shell-like egg- case, has dwarf males)

It appears that: Molluscs have evolved from ancestors of flatworms by acquisition of: –1. Complete gut –2. A shell –3. “body cavity” (elements of circulatory system spaces) –See online Mollusca Phylogeny paper