Phylum Mollusca: Classes

Gastropods (Snails, slugs, and limpets)

Bivalves (Mussels, clams, scallops, oysters)

Cephalopods (Octopus, squid, cuttlefish, nautilus)

Polyplacophora (Chitons)

Scaphopoda (Tusk shells)

Monoplacophora (cap shells, body uncoiled)

Aplacophora (wormlike)

Characteristics of Molluscs

•Soft body with a shell *•Mantle•Bilateral symmetry•Muscular foot for movement•Head with eyes *•Radula * (feeding structure)•Gills >200,000 spp in ocean, arthropods are the only larger phylum.•usually

Figure 7.19

Radula (feeding structure)

Cooper’s nutmeg snail (blood-sucking snail)

Predator onelectric rays

Phylum MolluscaClass Cephalopoda (“head foot”)

octopussquidcuttlefishnautilusextinct forms (ammonoids)

Characteristics of Cephalopods

•Voracious predators•Exclusively marine•Foot is modified into arms and tentacles•8-10 arms/tentacles (octopus squid)•Hard chitinous beak for tearing flesh•Suckers on arms/tentacles, some with teeth•thick, muscular mantle•Ink•Fast movement•Siphon (funnel)

Reproduction in cephalopods

Internal fertilization (male deposits sperm packet in female using a modified armEggs laid in capsules

octopus guard eggs; squid do notHatch as miniature adultsSquid live for one year

Cephalopods squirt ink to create a smoke screen.

Giant Squid (Architeuthis)

•Largest invertebrates on earth - up to 20 m long•Over 100 found washed up on beaches or in fishing nets•Eaten by sperm whales (20 cm sucker scars = 75 m squid)•3 m long arms, tentacles 10-12 meters•Suckers armed with teeth•Eat fish and other squid

http://news.bbc.co.uk/1/hi/sci/tech/2910849.stm

Mesonychoteuthis hamiltoni Discovered, Antarctica, 2003

Squid: conservation status

Caught with trawls along bottom and lights and hooks(Jigging)

Food fishery - mostly to Asia

MBARI Seafood Watch says “Proceed with Caution” on squid fishery:

bycatch (incidental catch) of sea lionssquid important food for tuna, marlin, dolphins, etc

California set limits in 2001 on squid catchNZ sets limits on allowable number of sea lions killed

http://www.amcs.org.au/campaigns/sustainable_seafood_guide/ss_fishing_gear_in_focus.html

Squid jigging Bottom Trawl

Squid facts

Eat fish, crustaceans, other squidAre eaten by tuna, marlin, whales, dolphins, sharksDaily migrationsOne of most abundant animals in sea after fishLive for one year (annual species)Grow fast

Humboldt squid videohttp://www.oceanfootage.com/stockfootage/Squid///%3FDVfSESSCKIE=b3846d9577e8310fb0778120c1b93d4501a5a0f1

Cephbase videoshttp://www.cephbase.utmb.edu/viddb/viddb.cfm

Sharks

Shark factshttp://www.flmnh.ufl.edu/fish/education/questions/Basics.html

Sharks, rays and skates:

-skeleton of cartilage, not bone-gill slits, rather than a gill cover (usually 5 gill slits)-heterocercal tail-urea to aid in buoyancy (no swim bladder)- internal fertilization; males have claspers

The Evolution of Sharks The first sharks appeared 400 mya. (200 million

years before dinosaurs, reptiles, or birds) Fossil evidence of early sharks is from fossilized

teeth and a few skin impressions

Megalodon (“Giant Tooth”)

Extinct giant shark: went extinct 1.6 million years ago

huge, streamlined version of the great white shark could have swallowed a Great White Shark whole fossilized Megalodon teeth up to 6.5 inches long

How big was megalodon?

1) Based on a complete set of fossil jaws (Harmatuk 1992)40 feet long (12 meters)Jaws 6 feet acrossFossil teeth are black (in life probably white)Estimated height of enamel on teeth to sharkLength in living sharks

2) Gottfried said tooth enamel height does not nec. Increase with Great White Shark length…

Estimate 52 feet long (15.9m) and 48 tonsLargest GWS is 23.5 feet (7.1 m) and 2.3 tons

http://www.elasmo-research.org/education/evolution/reconstruct_megalodon.htm

Sharks

360 species of shark (20,000 spp of fish)

Many habitats (deep sea, coastal, worldwide)

Big size range (8-inches to 59 feet)

Mostly top predators (whale shark is a filter feeder)

Shark Reproduction: three traits

1. internal fertilization with copulation

2. Maternal nourishment of embryos

3. Birth of large young that are well-developed “mini-adults” (up to 3 feet long and 40 lbs at birth)

• No parental care• Few young per pregnancy:

- sand tiger shark has 2 young- blue shark has 135 young

• Long gestation (9-12 months typically, but spiny dogfish is 24 months)

• Many give birth in shallow water (estuaries, bays) • Reproduce every other year• Late maturity and long life-span

– 6-18 years for requiem sharks– Dogfish can live for 70 years!

Two main modes of reproduction in sharks:

1) Oviparity = lay eggs

2) Viviparity = give live birth

a) ovoviviparity = embryos develop inside mother using yolk sac for nutrients

b) placental viviparity = placental connection

Most sharks are ovoviparous.

Ovoviviparity - embryo develops in an egg, inside mother

Most common reproductive strategy in sharks: e.g., dogfish sharks, cow sharks, frill sharks, angel sharks, tiger sharks, and some nurse sharks are ovoviviparous.

• no placenta• produces large young • embryos are nourished by yolk sac• shelter from predation and environmental hazards• Few, large young produced

-- sometimes embyro feeds off yolk in its egg sac only-- or the first embryo hatches and eats other eggs inside mother (mako shark)

oophagy

sand tiger shark is EMBRYOPHAGOUS

the first shark to hatch inside mother eats all of its siblings and then settles down to eating eggs (an extreme type of oophagy)

Why??

PLACENTAL VlVIPARITY

• placental connection• empty yolk sac grows a connection to

mother’s blood supply• requiem and hammerhead sharks

placental viviparity

Umbilical cord and placenta of the smooth dogfish.

http://na.nefsc.noaa.gov/sharks/repro/reprointro.html

Appendicula of the bonnethead shark:• leaf like structures on umbilical cord for greater gas/nutrient exchange• "Uterine milk” secreted by special uterine cells

http://na.nefsc.noaa.gov/sharks/repro/reprointro.html

shark courtship and mating

• internal fertilization with claspers of male• female weighs 1000s of pounds, tricky

maneuvering required by both to mate• terminal spurs and sharpened ridges on

claspers transfer sperm into female during copulation using water jets

shark courtship and mating:which is female and which is male?

shark courtship and mating:female skin 3x thicker than male skin, must be

thicker than his teeth

shark courtship and mating

• male bites female until she is receptive

scars on skin of female

Chances for mating are rare in sharks (migratory, usually solitary animals)-

Chances for mating are rare in sharks (migratory, usually solitary animals):

•males transfers large quantifies of sperm

•female can store sperm for years

•spines and ridges on claspers of males suggest “sperm competition”

Sharks are easily overfished:

--long-lived, mature late--few, large young with long gestation--internal fertilization, complex social behavior--top predators-Special habitat requirements:

lots of space! migratory bays and estuaries to give birth

Shark fishing

Shark steaksShark fin soup