Dogfish Dissection

Dogfish Dissection
Squalus acanthias
Kingdom – Animalia
Phylum – Chordata
 SubPhylum
Class – Chondrichthyes (cartilaginous fish)
 Subclass
- Vertebrata
– Elasmobranchii (sharks and rays)
Order – Squaliformes (dogfish sharks)
Family - Squalidae
Genus - Squalus
Species- acanthias
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
Post-anal tail – extends beyond anus
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
Evolution of fish/sharks
1st chordates – 550 mya
 Sharks – 400 mya
 Special adaptations of sharks for survival
– faster in water
 Paired fins supported by spines – finer control
 Development of jaws for grasping prey
 Streamlined
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
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)
Sharks detect prey
3 well developed senses
Ability to sense electric currents in water
2. Lateral line system – sense pressure
caused by a fish or other animal swimming
3. Keen sense of smell, detect 1 drop of blood
in 25 gallons of water.
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
of Lorenzini – openings around eyes, snout
and nostrils to sense temp change, water pressure,
electrical fields and salinity.
 Ampullae
Fusiform – body shape of shark, streamlined for
least resistance
– snout
 Nostrils – nares – openings of external nostrils,
underside of rostrum, anterior to jaws
 Rostrum
Incurrent – sense of smell
 Strong
 Eyes – transparent cornea protects eye
Upper and lower lids – protection
Conjunctiva – inner membrane inside lower lid
Spiracles – posterior and dorsal to eyes
1st gill, respiration while sharks mouth is
closed or eating
 Reduced
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.
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