Phylum: Chordata
Superclass:Gnathostomata
Class: Chondrichthyes (Sharks)

Chondrichthyes

• 850 species – Sharks, rays, and skates
• Some of the largest vertebrates
• Whale Shark: plankton feeder: 1million liters food/hour
• Cartilaginous skeleton
• Most Marine (few freshwater)

External Characteristics

• Stream-lined
• Fusiform (spindle shaped)
• Cannot maneuver easily –heterocercal tail
• Lidless eye
• Covered in placoid scales
• Dentine
• Enamel/blood supply

Nervous System

• Electroreceptors – Ampullae of Lorenzini (mostly on head of shark)
• Track bioelectric fields
• Vision – good up close, no color (most)
• Large olfactory system – detect prey 1ppb or 1 km away
• Vibrations detected – Lateral line system lined with neuromasts

Circulatory System

2 chambered heart

Respiration

• RAM ventilation – Must keep swimming to push extra oxygen over gills
• Force water over gills via mouth and nostril
• Nurse shark can rest

Digestion

• Mouth – pharynx – esophagus – stomach – intestine (w/secretions from pancreas & liver) – intestine (short & straight w/ spiral valve) – rectum – cloaca
• Squalene from liver keeps afloat

Excretion

• Opisthonephric kidney  -- urea waste product, some retained in blood.
• Rectal gland works with kidney and secretes NaCl solution & regulates ions
• All urine secreted out cloaca

Reproduction

• Internal fertilization via claspers into cloaca. One clasper at a time & some have hooks and spurs that dig into oviduct & anchor.
• Spermatophores via grove in clasper fertilizes egg. Shell gland secretes around egg.
• Egg size & gestation varies

Reproduction

• Sexes congregate to mate – mating circles
• Females have thicker skin…. Ovary on the right more developed
• Claspers – rolls of cartilage stiffened w/calcium. Testis on right more developed.

Oviparous

Lay yolky eggs in thick capsule & usually attach to substrate (algae, coral, pushed in sediment)

Viviparous

embryos nourished via placenta or uterine secretions. 2-20 pups. Parental care ends after birth

Ovoviviparous

Most common. Eggs develop & hatch in uterus. Retain developing young in uterus. Less pups. Yolk sac – no direct nourishment from mom. Young may eat other eggs – oophagy/oviphagy or each other – intrauterine cannibalism