CARTILAGINOUS FISHES

Download an ADOBE version of the lecture outline

return to vertebrate zoology syllabus

Chapter  5 - Chondrichthyes

  GNATHOSTOMATA

Learn  more about gnathostomes from the Tree of Life

• Characteristics
1. internal jaws (palatoquadrate, Meckel's cartilage) are present.
2. paired appendages (paired pectoral and pelvic fins) supported by an internal skeleton provide more efficient locomotion
3. three semicircular canals
4. teeth - modified dermal scales
5. more proficient predators than the jawless fish
• Taxa
  • the jawed vertebrates include the extinct ,armored Placoderms, the cartilaginous fish, and the bony fish (including the tetrapods).
  • Phylogenetic relationships of the jawed fishes (Fig. 3-13)

• Learn  more about cartilaginous fish from the UCMP.
• Learn about the anatomy of sharks and bony fishes from the Florida Museum of Natural History
  1. Body Features and Measurements of Sharks 
  2. Fin Features and Measurements of Sharks
  3. Head Features and Measurements of Sharks

Characteristics

1. internal skeleton is composed of cartilage, which may be prismaticly calcified
2. placoid scales ( a bone-like tissue is present at base of placoid scales)
3. second gill arch (hyoid) involved in jaw suspension
4. swim bladder or lung absent; have oil filled liver to provide neutral buoyancy [sharks are slightly negatively buoyant-will sink]
5. claspers (modified pelvic fins) present in males [internal fertilization]
6. persistent notochord
7. intestine with spiral valve
8. ventral mouth
9. replacement teeth rows [Fig. 5-2]

Taxa

• living chondrichthyans include sharks, skates, rays, and the ratfish. [Table 5.1]
• approximately 815 species.

Characteristics

1. advanced forms with hyostylic jaw support (hyomandibular is a mobile connection between braincase and palatoquadrate; postorbital connection lost). Mouth frequently opens ventrally.
2. placoid scales are modified to form teeth
3. 5-7 pairs of gill slits with separate external openings and a spiracle
4. vertebral centra strongly calcified; notochord constricted except intervertebrally
5. enlarged nasal capsules: chemoreception. sensitive to one part in 10 billion; widely spaced nostrils in hammerheads may increase sensitivity for locating prey
6. neuromast organs: mechanoreceptors
7. Ampullae of Lorenzini [Fig. 4-7] electroreception for detection of prey, possibly for navigation
8. heterocercal tail (may or may not provide lift--see p. 63)

General information on elasmobranch classification from ReefQuest by R. Aidan Martin.  This web site is a an important source of information about many aspects of elasmobranch biology.

ORDER SQUALOMORPHA

• Squalus, the spiny dogfish, is characteristic
• also includes cookie-cutter sharks
• fin spines present
• anal fin absent
• spiracle large
• body rounded

DIET in NEOSELACHIANS

predators

• Carcharodon carcharias--white shark: up to 7 m long .  some great white statistics from the Florida Museum of Natural History
• the extinct megatooth shark Carcharocles megalodon was up to 15 m long
• Isistius: cookie-cutter shark: a small species; deep water dweller; slow swimmer, strong sucking mouth, sharp lower teeth. takes bite out of squid, sharks, fish or whales (and submarines).

The largest chondrichthyans are filter-feeders

• Whale shark Rhincodon up to 18 meters long, 41 metric tons; feeds on small fish
• Basking shark Cetorhinus: up to 10m in length; filter-feeders on plankton
• Megamouth Megachasma: 5 m in length; very large mouth, lives at 200 m (deep scattering layer) by day, ascends at night to near surface.
• Manta ray or Devil fish Manta: Up to 9 m wide

SUBCLASS HOLOCEPHALI

Characteristics

1. gills close behind braincase (primitive)
2. jaw support autostylic (holostylic)
3. dentition a small number of large, continuously growing tooth plates
4. fin structures similar to sharks

 CHIMAERIFORMES

• ratfish, rabbitfish, spookfish, and ghostfish; 25 species
• information from ReefQuest by R. Aidan Martin

Characteristics

1. Fleshy operculum covers four gill slits
2. Skin naked; placoid denticles present primitively, absent in Recent forms
3. No spiracle
4. flattened, grinding teeth; eat seaweed, mollusks, echinoderms, crustaceans, and other small fish; rabbit fish has nipping teeth
5. tail a narrow whip in recent genera
6. claspers on pelvic fins and forehead
7. recent forms marine

Return to: