Cartilaginous Fish Test Study Guide
The chordate phylum is the animal phylum with which everyone is most familiar since it includes humans and other vertebrates. However, not all chordates are vertebrates.
All chordates have the following features at some point in their life.
In the case of humans and many other vertebrates, these features may only be present in the embryo.
Major Characteristics of All Chordates (including humans)
Notochord - long, thin solid rod of cartilage
Dorsal nerve cord (spinal cord)
Gills
Tails
A. Invertebrate Chordates - Where the notochord does not develop into vertebral column
Sea squirts
Larvaceans
Lancelet (amphioxus)
B. Subphylum Vertebrata: about 38,000 species
7 classes:
Jawless fish (Agnatha)
Cartilaginous fish (Chondrichthyes)
Bony fish (Osteichtyes)
Amphibians (Amphibia)
Reptiles (Reptilia)
Birds (Aves)
Mammals (Mammalia)
Jawless Fish - lampreys and hagfish
Only two jawless vertebrates to survive today
Most primitive of vertebrates
Are the least changed from the first vertebrates
Characteristics of Jawless Fish
No jaw
No paired pectoral (shoulder) or pelvic (hip) fins
Their notochord persists for life, never being completely replaced by a backbone
They have no scales
Circular mouth with teeth for holding on to a host or for scavenging their prey
Lamprey is parasitic at one stage in its life
Found in Great Lakes and some fresh water streams, sucking fluid out of a host fish
Hagfish is bottom dwelling scavenger
Found in the ocean, scavengers of dead and dying fish - eat internal organs.
No eyes, but great sense of smell
Produces lots of mucus
Chondrichthyes (Cartilaginous Fish)
Sharks, skates, and rays
Total close to 1000 species
No bone - skeleton made of cartilage
Biting jaws with true teeth
Paired lateral fins (pectoral and pelvic)
No swim bladder
5-7 pairs of gill slits with no covering (no operculum) (unless it’s a chimaera)
Sharks
Sharks renew their teeth throughout their lives; as one tooth breaks off or wears out, another one rotates forward from the inside of the jaw to replace it
Sharks have a special valve inside the intestines that looks like a spiral staircase on its side. Spiral valves increase surface area for absorption of food. This increases absorption efficiency through their short, compact intestines
Large, oily livers give sharks some buoyancy. Also fin position provides lift when sharks swim (just like airplane wings)
Shark skin looks and feels as though it’s covered with tiny teeth. In fact, their small, rough placoid scales (also called dermal denticles).
Denticles have the same structure as sharks’ teeth! Shark skin was sometimes used as sandpaper in colonial America
Most sharks have asymmetrical tails; the upper half is longer than the lower half. (Symmetrical tails are found on fast moving sharks)
Sharks are internal fertilizers
Eggs are fertilized in female’s bodies
When sharks mate, the male inserts one of his claspers which are appendages on the male’s underside (extensions of the pelvic fins) into the female’s cloaca (the genital opening)
Egg Development:
Oviparous: Some sharks lay egg-filled cases on the bottom of the ocean, called devil’s wheelbarrows or mermaid’s purses. Yolk provides nourishment.
Approximately 40% of all shark species and all known skates are oviparous. No rays are known to be oviparous.
Viviparous: Some sharks have a placenta to nourish the young and give births to live young. Examples: hammerhead sharks, lemon sharks
Ovoviviparous: Most sharks give birth to live young; they keep their eggs within their bodies while the young sharks develop, nourished by a yolk. Ovoviviparous sharks include mako sharks, sand tiger sharks, nurse sharks, great white
Gestation
Gestation period in sharks varies with each species
Ranges from nine months to as long as 22 (spiny dogfish)
Depending on species, sharks can produce 2 to 135 young at one time
Shark Sense
One important sense the shark uses in detecting its prey is sound. Their acute hearing can detect a struggling fish 2 km away. Sharks do not have external ears. Instead, a tiny duct carries sound waves to the inner ear.
Sharks can also detect sound (vibrations) with their lateral line system. This system is made up of hundreds of pores along the side of the shark’s body. It is also highly sensitive to wave movements, pressure changes and vibrations in the water.
Sharks have an incredible sense of smell; some shark species can smell one drop of blood diluted in one million drops of sea water.
Sharks have good eyesight, especially when prey is closer than 15m. Sharks have a sophisticated and complex retina that is poorly understoof at this time.
Sharks can sense electrical impulses produced by animals. This sense helps them detect animals hidden beneath the sane. (ampullae of Lorenzini)
Sharks with barbels (whisker-like feelers) use them to taste and feel their way to food (nurse shark)
Invertebrate Chordates have 2 subphyla:
Urochordata
Members of the subphylum Urochordata are tunicates (also called sea squirts)
Cephalochordata
Members of the subphylum Cephalochordata are lancelets.
Both tunicates and lancelets are small and primitive. They are probably similar to the earliest chordates that evolved more than 500 million years ago.
Urochordates:
3000 species of tunicates
Found in shallow marine waters (intertidal zone and offshore)
Larvae are free swimming
Adult is sessile and no longer have notochord and “post-anal” tail
Hermaphrodites (sexual) and can undergo budding (asexual)
Barrel shaped with two siphons
Filter feeders
Cephalochordates:
25 living species
Live on ocean shore (shallow water)
Larvae are free swimming
Adults can swim but spend most of their time buried in the sand
Filter feeders
Separate sexes so they reproduce sexually
Unlike tunicates, the lancelet retains all 4 defining Chordate characteristics
Chordates include vertebrates and invertebrates that have a notochord.
Invertebrate chordates do not have a backbone (vertebral column)
Both of the invertebrate chordates are primitive marine organisms.