3Phylum Chordata4 major characteristics seen at some point during developmentNotochord – stiff rod along back of the embryo during development (vertebral column in humans)Dorsal nerve cord (hollow) – nerves attached (spinal cord in humans)Pharyngeal slits – openings along wall of pharynx (gills)Post-anal tail – extends beyond anus
4Sub phylum Vertebrates Chordates with a backbone which gives support and protection of spinal cordAllows for larger growth in organism (compare to size of invertebrates)Also share: segmentation, bilateral symmetry, 2 pair of appendages, cephalization, complex brain and sense organs, true coelom, closed circulatory system, chambered heart, higher level of cellular organization
5Evolution of fish/sharks 1st chordates – 550 myaSharks – 400 myaSpecial adaptations of sharks for survivalStreamlined – faster in waterPaired fins supported by spines – finer controlDevelopment of jaws for grasping prey
6Class: Chondrichthyes sharks, rays and skates Sharks – cartilaginous fish – skeleton made of cartilage strengthened by calcium carbonate, light but strongSuperior design for swimmingTeeth are modified scales, 6 – 10 rowsRespiration through gills with gill slits
7ReproductionOviparous – internal fertilization following release of eggsOvoviviparous – internal fertilization and development without nutrition from mother, eggs retain in body until hatched SHARKSViviparous – internal fertilization and development with nourishment (mammals)
8Sharks detect prey 3 well developed senses Ability to sense electric currents in waterLateral line system – sense pressure caused by a fish or other animal swimming nearbyKeen sense of smell, detect 1 drop of blood in 25 gallons of water.
9External Dogfish 3 main body regions – cranial, trunk, caudal Placoid scales – cone shaped, rough textureCountershading – dark gray above, light underLateral line – carries impulses to CNSAmpullae of Lorenzini – openings around eyes, snout and nostrils to sense temp change, water pressure, electrical fields and salinity.Fusiform – body shape of shark, streamlined for least resistance
10External Head Rostrum – snout Nostrils – nares – openings of external nostrils, underside of rostrum, anterior to jawsIncurrent – sense of smellStrong jawsEyes – transparent cornea protects eyeUpper and lower lids – protectionConjunctiva – inner membrane inside lower lid
11External Spiracles – posterior and dorsal to eyes Reduced 1st gill, respiration while sharks mouth is closed or eatingGill slits – most have 5 externalWater taken in passes over internal gills, oxygen removed, carbon dioxide excreted, water leaves via gill slitsEndolymphatic pores – top of head, between spiracles, serve as primary equilibrium organ.
12ExternalFins –2 dorsal – anterior (larger) and posterior, spines lie anterior to each dorsal fin, defense, contains toxinsCaudal fin – asymmetric, 2 lobesPectoral fins – deflect water to maintain shark moving in horizontal directionPelvic fins – on either side of cloacal openingCloaca – ventral surface, between pelvic fins, receives products of intestine, urinary and genital ductsClaspers – male organs used for reproduction, fertilization is internal, inserted in oviduct of female