Mollusca

andIntroduction to Spiralia

Phylogeny of Protostomes

Protostomia

Bilateria

Spiralia

Deuterostomia

Ecdysozoa

Ancestry of Mollusca

Protostomia

Spiralia Ecdysozoa

Lophotrochozoa

Platyhelminthes,Rotifera LophophorataEutrochozoa

AnnelidaMollusca

Trochophore Larvacompare Hickman Fig. 16-6

• basis of the term Eutrochozoa• present in many marine mollusks and annelids

Marine Mollusk Larvaecompare Hickman Fig.’s 16-6 and 16-7

Veliger

Phylum Mollusca• Name means “soft-shelled nut”• 2nd largest phylum in number of species • Most are free-living and marine

– but many clams and snails are freshwater or terrestrial

• Feeding habits:– Scrapers and suspension feeders (rarely,

carnivores)

Eucoelomate Body Design

Coelom: fluid-filled cavity between gut and body wall that is lined with mesodermal cells (peritoneum).

acoelomate

pseudocoelomate

eucoelomateendodermmesodermectoderm

(muscles, not peritoneum)

peritoneum

Important Mollusk Features• coelom - just the pericardium, a sac around the

heart• muscular foot - posterior, ventral, locomotory• mantle - dorsal epidermis that makes the shell

– also encloses the body in a mantle cavity– ciliated mantle cavity helps with respiration and

sometimes feeding• radula - tongue-like scraper used for feeding

Molluscan Anatomy(chiton; Hickman Fig. 16-9)

Mollusk Body DesignsHickman Fig.’s 16-9, 16-18, 16-31, 16-38

• not present in Bivalvia

Radula Hickman Fig. 16-2

motion while feeding

Mollusca Classesrequired in ZO 110

• Bivalvia - clams, mussels, oysters, etc.• Polyplacophora - chitons• Gastropoda - snails and slugs• Cephalopoda - squid, octopus, nautilus

Bivalviaclams and mussels

• shell of two "valves”• lateral, ciliated gills for respiration and

filter-feeding• narrow foot for burrowing• head just mouth and labial palps - no radula

Clam Filter-Feeding FlowHickman Fig. 16-30, 16-31

Pos.

Ant.Dor.

Ven.

Valuable Bivalvia

• many are edible– oysters, scallops, blue mussels, clams

• river mussels – harvested for making seed pearls– symbol of freshwater biodiversity

• popular with collectors

Bivalve PestHickman Pg 343

Dreissena, the zebra mussel

Polyplacophorachitons

• eight dorsal shell plates• slow-moving - foot has strong suction• grazer-scrapers with radula

– eat algae from rocks between or below the tides

Gastropodasnails and slugs

also conchs, limpets, abalones, and sea hares• terrestrial, freshwater, or marine• single shell, or none• scrape up food or attack prey with radula • most diverse mollusk class

– > 40,000 named species

Gastropod Body DesignCampbell Fig. 16.18

Snail AnatomyHickman Fig. 16-18

Shell-less GastropodsHickman Fig. 16-22, 16-23

Conus Eats a FishHickman Fig. 16-16

Class Cephalopodanautilus, squid, octopus

• modification of foot, addition of a beak for carnivory

• reduced shell or flotation for swimming• improved respiration, circulation, and

neural/behavioral complexity support high activity levels

NautilusHickman Fig. 16-36

• many tentacles, without suckers• large shell, floated by chambers of gas

Squid FeaturesCompare Hickman Fig. 16-38

• streamlined shape• undulating lateral fins• funnel• arms & tentacles with

suckers, sometimes poison

Usual direction of movement - dorsal

Giant Squid!

Artituthus can be 30 ft+

Complex Squid BehaviorHickman Fig. 16-39

• shell reduced to pen • mood and camouflage colors• ink for concealment

OctopusHickman 16-40

• 8 arms with suckers• shell lost, body soft• ink sac

Pop Quiz 4

1. Term for the hard structure used by cephalopods in feeding: _______

2. Term for the molluscan coelom that is restricted to the area around the heart: __________

3. Class name for the chitons: ______