Characteristics

• Have 3 basic traits of Phylum Chordata

1. Single, dorsal nerve chord
2. Gill slits
3. Notochord

• Backbone

General Points

• Most abundant vertebrates
• 22,000 species
• 58% are marine

Class Chondrichthyes

• Cartilage instead of bones
• Movable jaws, teeth, generally a ventral mouth
• Paired lateral fins
• Tiny teeth-like scales on skin

Sharks

• Well developed caudal fin, larger dorsally
• 2 dorsal fins, first largest
• Pectoral fins large and pointed
• 5-7 gill slits
• Most sharks must swim continuously.
• Rows of numerous teeth imbedded in a tough, fibrous membrane
• Sizes of sharks range from 25 cm to 18 m
• Most are predatory, some are filter feeders (plankton)
• Found throughout ocean at all depths
• ~250 species

Class Osteichthyes

• Terminal mouth
• Fins of thin membranes supported by bony spines (fin rays)
• More flexible jaws, teeth fused to jawbone
• Flexible, overlapping scales derived from bone
• Operculum protects gills
• Upper & lower lobes of caudal fin generally =
• Swim bladder for controlling buoyancy
• ~21,500 species, a little more than half marine

Coloration

• Chromatophores containing pigment give color
• Chromatophores can be contracted or expanded
• Iridophores containing crystals give structural colors
• Functions & types of color patterns

• Denote reproductive status
• Warning
• Cryptic
• Disruptive
• Countershading

Locomotion

• Often by rhythmic contractions of myomeres
• Buoyancy in sharks

• Pectoral fins give lift
• Oil rich liver gives bouncy
• Upper lobe of caudal fin causes tail to ride a little lower than head

• Dorsal & anal fins used as rudders
• Pelvic fins used for balance and breaking
• Flexibility of fins in Osteichthyes allows some to use fins only for locomotion
• Some fish have suckers composed of modified fins (clingfishes, remoras)

Sharks

• Many feed by taking bites from larger animals
• Nurse sharks feed on bottom invertebrates
• Cookie-cutter sharks
• 3 species are filter feeders, using gill rakers to gather plankton
• Mantas are also filter feeders

Osteichthyes

• Most are carnivores
• Some prefer unusual foods like sponges or coral
• Some are grazers (seaweed eaters)
• The most abundant fishes are plankton feeders

Digestion

• Food passes to stomach through the pharynx & esophagus then to intestine
• Pyloric caecae present at anterior end of many Osteichthyes to secrete enzymes
• Pancreas & liver (produces bile for fat metabolism) also present
• A few fishes lack a stomach
• Length of intestine determined by foods eaten

Circulatory System

• Two-chambered heart
• Arteries go away from heart to capillaries
• Veins go from capillaries back to heart

Respiratory System

• Each gill in a separate gill chamber with separate gill slit
• First pair of gill slits rounded and called spiracles
• Spiracles dorsal on rays & skates
• Spiracles allow for water flow to gills even when mouth is blocked

• Gills on each side share a common gill chamber
• Gills protected by operculum
• Mouth opens, opercula close, water sucked in
• Mouth closes, water forced out through gills
• Some fast swimmer simply keep mouth & opercula open

Structure of the Gills

• Gill arches support gills
• Gill filaments extend out from arches
• Gill rakers on arches keep particles from entering gills
• Rows of plates or discs on filaments are called lamellae & increase surface area
• Gas exchange is made efficient by a countercurrent system of flow