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WEEK 4, BIOLOGY 03051, VERTEBRATE ZOOLOGY: CARTILAGINOUS FISHES 2/10/00

Dr. W Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)

Text (7th ed.): Ch. 27, pp. 587-591

HVCC library A/V resource: VT 3382,"Eyewitness: Shark" (to be seen in recitation)

possible web site: http://www.oceanstar.com/shark/ (Fiona's Shark Mania--lots of fun)

With more than 850 species today, cartilaginous fish (Class Chondrichthyes"cartilage fish") are first seen in the Devonian Period, with many ancient features still visible today.

What make cartilaginous fish stand out? External features:

  1. Placoid scales (denticles), looking like teeth (and in fact the teeth are derived from placoid scales), help to reduce drag while swimming.
  2. Gill slits are exposed, not covered by an operculum or gill flap (except in a ratfish).
  3. Paired fins, pectoral and pelvic, do not allow fancy maneuvering with their broad attachments, compared to the bony fish. The anterior pectoral fins help to control direction in swimming, and the posterior pelvic fins are stabilizers that in males are modified into claspers for copulation.
  4. Unpaired dorsal fins (of Jaws fame) are also stabilizers and the caudal fins of the heterocercal tail assist in propulsion.
  5. Mouth and pair of nasal sacs (well-developed olfactory skills, especially for blood!) are on the underside of the head. Organs of Lorenzini sense biological electric fields. A lateral line is present on either side of a shark, consisting of a row of small, mucus-filled pores that can sense the presence of other animals via pressure changes.

What make cartilaginous fish stand out? Internal features:

Cartilage, not bone, is the supportive structure. There is no lung or swim bladder is present. Instead, buoyancy is assisted by oil in the large liver.

  1. digestive system: a spiral valve in the intestine slows digestion and allows for more surface area. A cloaca is a common opening for the digestive, urinary, and reproductive tracts.
  2. circulatory system: Blood circulates in a pattern basic to most fish, with a two-chambered heart and a one-pass circulation.
  3. respiratory system: Between the external and internal gill slits are the gill chambers. Gill arches are cartilage supports underlying the gills. Along each gill are gill filaments (primary lamellae) that supports tiny folds or secondary lamellae, where the gas exchange occurs. Blood in the capillaries flows countercurrent to the outflow of water. Gill rakers on the internal side of the gill help to direct food away from the gills and into the esophagus and the digestive tract.
  4. urogenital system: testes vs. ovaries. Many sharks bear live young (ovovivipary). During copulation, a clasper is inserted in the the female cloaca and sperm runs along a groove on the clasper to fertilize. In general, sharks reproduce slowly: the current craze for shark cartilage for"cancer-fighting" properties decimates shark numbers.1,3

Rays: sawfishes, rays, stingrays, manta rays. Differences between sharks and rays include2:

  1. Sharks are tapered at each end; rays are dorsoventrally flattened.
  2. Sharks have 5-7 lateral gill slits on either side, with a rounded spiracle, or modified first gill slit close behind the eye. In rays, the gill slits are ventral and the spiracle is correspondingly larger.
  3. Shark pectoral fins are smaller than those of rays, which are broadly attached to make up the"wings."
  4. Shark tails are large compared to the reduced ray tail.

The ratfish (chimaera) remains relatively unchanged as a living fossil in deep water, using flat teeth to crush small prey. Features unlike other cartilaginous fish are an upper jaw fused to the skull, a tapered tail, an operculum, and no adult placoid scales.2,4

  1. CP Hickman Jr et al., Biology of Animals, 7th ed., (WCB McGraw-Hill, Boston, 1998) p. 590.
  2. NM Jessop, Schaum's Outline of Theory and Problems of Zoology, (McGraw-Hill, New York, 1988), pp. 280-293.
  3. MD Lemonick,"Under Attack," Time 150 (6):58-64 (August 11, 1997).
  4. FH Pough et al., Vertebrate Life, 4th ed. (Prentice Hall, Upper Saddle River, NJ, 1996), pp. 197-199.

 


|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|


Please send comments and questions to: cronewil@hvcc.edu

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This web page last updated on February 15, 2000