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 on electric rays

Phylum Mollusca

Class Cephalopoda (“head foot”)

octopus squid cuttlefish nautilus extinct 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 arm Eggs laid in capsules octopus guard eggs; squid do not Hatch as miniature adults Squid 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 lions squid important food for tuna, marlin, dolphins, etc California set limits in 2001 on squid catch NZ sets limits on allowable number of sea lions killed

Squid jigging Bottom Trawl http://www.amcs.org.au/campaigns/sustainable_seafood_guide/ss_fishing_gear_in_focus.html

Squid facts

Eat fish, crustaceans, other squid Are eaten by tuna, marlin, whales, dolphins, sharks Daily migrations One of most abundant animals in sea after fish Live for one year (annual species) Grow fast

Humboldt squid video http://www.oceanfootage.com/stockfootage/Squid///%3FDVfSESSCKIE=b3 846d9577e8310fb0778120c1b93d4501a5a0f1 Cephbase videos http://www.cephbase.utmb.edu/viddb/viddb.cfm

Sharks

Shark facts http://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 across Fossil teeth are black (in life probably white) Estimated height of enamel on teeth to shark Length 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 tons Largest 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

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

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 steaks Shark fin soup