Chapter 12 Marine Fishes

Protochordates and Jawless Fishes Section 12.1 Protochordates and Jawless Fishes

Objectives List the distinguishing features of the protochordates and the jawless fishes Explain the importance of studying protochordates Discuss the differences between the protochordates and jawless fish.

Classification Phylum Chordata (Chordates) Hollow dorsal nerve cord Notochord (flexible, rodlike, supports spinal cord) Pharyngeal gill slits Protochordates “first chordates” Subphylum Vertebrata (Vertebrates) Skeleton Backbone Skull Brain

protochordates Agnatha vertebrates

An evolutionary Connection Vertebrates include fish, amphibians, reptiles, birds, and mammals. Vertebrates differ from protochordates: Both have a notochord, but in vertebrate embryos it develops into a backbone The ancestors of protochordates are the link between invertebrate animals and vertebrates!

Protochordates Sea squirts (tunicates) Covered by a clear tough membrane Incurrent/excurrent siphon Hermaphrodite with no self fertilization External fertilization Larva is fishlike, with dorsal nerve cord, a notochord, and gill slits Adult lives attached to substrate and these structures dissappear

Tunicate Larva

Protochordates Lancelets (Amphioxus) Tiny, transparent, fishlike Lives buried in sand, filter feeds plankton Adult retains dorsal nerve cord, notochord, and gill slits Separate sexes External fertilization and development

Lancelet

Jawless Fishes Superclass Agnatha “without jaws” The most primitive of the vertebrates Lack jaws and a true backbone Adults retain the larval notochord Two extant groups Hagfish Lamprey Lamprey Hagfish

Jawless Fish Sea Lamprey (Petromyzon marinus) parasitic Lives in estuaries from Maine to Florida Uses sucking disk on its mouth to attach to living trout and other host fish Uses teeth and rasping tongue to make a hole, then sucks out blood and tissue

Sea Lamprey Damage

Jawless Fish Pacific and Atlantic Hagfish Use sharp teeth in their rounded mouth to burrow into bodies of dead or dying fish devour prey from the inside Secrete mucus (slime) when captured to evade predators

Jawless Fish

Cartilaginous Fishes 12.2

Cartilage Cartilage is a flexible connective tissue composed of cells and proteins Your ears, nose, and joints contain cartilage!

Cartilaginous Fishes Class Chondrichthyes “cartilage fishes” Contains Sharks, Skates, and Rays

Characteristics First Jawed fish Have placoid scales –tiny teeth embedded in the skin (feels like sandpaper) ventral gill slits (breathing) with no flap Spiracles – breathing holes behind each eye

Characteristics Ventral mouth Rigid fins Pectoral fins provide lift to prevent sinking and to glide

Rays and Skates Highly developed pectoral fins for swimming Many are bottom dwellers Ventral mouth for bottom feeding

Rays Stingray (Dasyatis) Lives in the sand in the Gulf of Mexico and from Carolinas to Brazil Sharp spine on tail for defense

Skates Skate (Raja) No spine on tail Found in temperate waters along the Atlantic and pacific coasts Eat crustaceans and mollusks in subtidal zone

Sawfish Unusual Cartilaginous fish Virginia to Brazil, and the Gulf Long bladelike snout full of teeth Uses snout as weapon to stun and kill prey fish

Sharks! About 350 known species

Structure and Behavior Sharks are called “living fossils” because they resemble some early ancestral forms Sharks have very sensitive sensory receptors

Lateral line Organ A faint line along each side of a sharks body Picks up sound vibrations over long distances

Sense of Smell Can detect small amounts of blood over half a kilometer away 2/3 of the sharks brain is dedicated to smelling!

Ampullae of Lorenzini Tiny pores in the shark’s snout (rostrum) Sense the electric fields generated by the muscles of fish and other prey How might this be beneficial at night?

Body shape and Movement Sharks are streamlined for quickly moving through water Accelleration accomplished by powerful muscle contractions along the sides of body Move the caudal fin and generate thrust

Teeth Predatory sharks have several rows of teeth Lost teeth are replaced by new teeth from behind Hunneds of teeth!

Reproduction Internal fertilization Male sharks have claspers between pelvic fins Transfer sperm into females reproductive tract Claspers

Gestation and Birth Vivipary Ovovivipary Ovipary Live young develop inside mother Ovovivipary Eggs hatch within mother Oophagy Hatched young eat unhatched eggs Ovipary Eggs are laid and hatch externally

Mermaid’s Purse Egg casing produced by some sharks and skates Black and leathery 1 or more embryos develop within (>1 year)