class bivalvia (pelecypoda) 2nd largest mollusc class ~ 20,000 living; 20,000 fossil spp. appear in...
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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
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
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
• 1985 - Lake St. Claire by ship water ballast
• 1990 - 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 - 40,000 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
• 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
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
F. Octopods
• Eight arms, no fins
• Octopus
• Argonauta (produces shell-like egg-case, has dwarf males)