ZOL 353 Lecture Notes - Lecture 25: Sawshark, Aquatic Feeding Mechanisms, Stethacanthus
Document Summary
Hagfish and lampreys are chordates, and arguably true vertebrates. Hagfish, class myxini, agnatha/cyclostomata: about 20 species, all marine, cold fairly deep temperate waters, locally abundant, few predators, (cid:862)brai(cid:374)(cid:272)ase(cid:863) just a fi(cid:271)rous sheath, keratinous toothplate, no lens, poor vision, no vertebral column, no stomach. Gnathostomata: jawed (all remaining) vertebrates: jaws allowed diversification of feeding styles and foods, allowed evolution of fast-moving, large, complex vertebrates. Smooth tailward, rough headward: heterocercal tail, upper lobe longer than lower, no swim bladder but tail shape provides some lift. Internal fertilization: two grooved pelvic claspers in males, viviparous, ovoviviparous, or oviparous, may have placenta, oophagy common. Elasmobranchii: sharks, rays, sawfish, skates: several paired gill clefts that open directly to water, rigid dorsal fin, series of teeth that are regularly shed. Swellsharks: cat sharks that use water or air intake to increase girth by 2-3x as an antipredator defense. For hunting in low light: can rotate eyes upward, diel vertical migrant.
