1. Dogfish Dissection
Squalus acanthias

2. Classification Kingdom – Animalia Phylum – Chordata
SubPhylum - Vertebrata
Class – Chondrichthyes (cartilaginous fish)
Subclass – Elasmobranchii (sharks and rays)
Order – Squaliformes (dogfish sharks)
Family - Squalidae
Genus - Squalus
Species- acanthias

3. Phylum Chordata
4 major characteristics seen at some point during development
Notochord – 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

4. Sub phylum Vertebrates
Chordates with a backbone which gives support and protection of spinal cord
Allows 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

5. Evolution of fish/sharks
1st chordates – 550 mya
Sharks – 400 mya
Special adaptations of sharks for survival
Streamlined – faster in water
Paired fins supported by spines – finer control
Development of jaws for grasping prey

6. Class: Chondrichthyes sharks, rays and skates
Sharks – cartilaginous fish – skeleton made of cartilage strengthened by calcium carbonate, light but strong
Superior design for swimming
Teeth are modified scales, 6 – 10 rows
Respiration through gills with gill slits

7. Reproduction
Oviparous – internal fertilization following release of eggs
Ovoviviparous – internal fertilization and development without nutrition from mother, eggs retain in body until hatched SHARKS
Viviparous – internal fertilization and development with nourishment (mammals)

8. Sharks detect prey 3 well developed senses
Ability to sense electric currents in water
Lateral line system – sense pressure caused by a fish or other animal swimming nearby
Keen sense of smell, detect 1 drop of blood in 25 gallons of water.

9. External Dogfish 3 main body regions – cranial, trunk, caudal
Placoid scales – cone shaped, rough texture
Countershading – dark gray above, light under
Lateral line – carries impulses to CNS
Ampullae 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

10. External Head Rostrum – snout
Nostrils – nares – openings of external nostrils, underside of rostrum, anterior to jaws
Incurrent – sense of smell
Strong jaws
Eyes – transparent cornea protects eye
Upper and lower lids – protection
Conjunctiva – inner membrane inside lower lid

11. External Spiracles – posterior and dorsal to eyes
Reduced 1st gill, respiration while sharks mouth is closed or eating
Gill slits – most have 5 external
Water taken in passes over internal gills, oxygen removed, carbon dioxide excreted, water leaves via gill slits
Endolymphatic pores – top of head, between spiracles, serve as primary equilibrium organ.

12. External
Fins –
2 dorsal – anterior (larger) and posterior, spines lie anterior to each dorsal fin, defense, contains toxins
Caudal fin – asymmetric, 2 lobes
Pectoral fins – deflect water to maintain shark moving in horizontal direction
Pelvic fins – on either side of cloacal opening
Cloaca – ventral surface, between pelvic fins, receives products of intestine, urinary and genital ducts
Claspers – male organs used for reproduction, fertilization is internal, inserted in oviduct of female