Ichthyology
Spring 1999
T. Turner
Lecture 10 - Living Chondrichthyes I: Sharks
Lecture 8
lecture10
Class Chondrichthyes:
Key Morphological Features:
- Cartilaginous skeleton with calcified (not ossified) vertebral
centra
- Male intromittent organ (pelvic claspers)
- Sutureless chondrocranium
- Ceratotrichial fins
- Placoid scales-- reduction of drag, defensive armor, modification into
spines; teeth are modified placoid scales
- Heterocercal tail (chimaeras and sharks)/ modified pectoral fins
(skates and rays)
Key Physiological features
- Lack lungs/swim bladder; use lipid filled liver and urea for
buoyancy regulation; also urea and TMAO are less dense than water and
implicated for buoyancy reg. http://www.biologists.com/JEB/188/01/jeb9154.html
- Possess spiracles (rudimentary arches) and/or gill slits for
respiration; two-stage pump to ram ventillation
- Very keen olfactory sense, electroreception
Key Life history features
- Slow growth, maturity, produce very few young
- Internal fertilization
- Large eggs, direct development
- Oviparity, Ovoviviparity, Viviparity
- Nearly all carnivorous, many are top predators
Subclass Elasmobranchii (ca. 820 spp.):
- sharks, saw sharks, angel sharks, guitarfishes, sawfishes, rays,
skates
Key Features
- Chondrocranium with hyostylic suspension
- Large bodied, slow growth
- 5 pairs of gill slits (usually); six- and seven-gill sharks
(Hexanchidae)
- carcinogenic tumors are unknown in elasmobranchs; hypothesized to
possess factors that are tumoricydal, or prevent neurovascularization of
tumors http://www.shef.ac.uk/uni/academic/A-C/csi/1997/JARR4.HTML
Subclass Holocephali (ca. 31 spp.)
- Includes Chimaeras, ratfishes, plownose chimaeras
Key features
- Pelvic claspers and clasper located on head (unknown function in
reproductions
- autostylic suspension
- operculum-like flap covering gill slits
Subclass Elasmobranchii (ca. 820 spp.):
Super Order Galeomorphi
Order Heterodontiformes
- Family Heterodontidae
- 8 species, all marine; all oviparous
- Horn sharks
- Anterior teeth for grasping, posterior teeth for crushing
Order Lamniformes- 7 families; 16 spp., All marine
- Cetorhinidae - basking shark; plankton feeder
- Ondontaspididae - sand tigers
- Megachasmidae - discovered in 1976; 160 m depth; sub/tropical Pacific
- Alopiidae -- thresher sharks -- large upper lobe of caudal fin
- Lamnidae -- mackeral sharks; great white shark
- Pelagic, fast swimmers, highly predatory
- Nearly homocercal tail
- Megatooth shark may have exceeded 13 m (45 ft.)
Order Orectolobiformes- 7 families; 31 spp., All marine
- Rhincodontidae -- whale shark (up to 18 m)
- Ginglymostomatidae -- two-pump respiration-- mollusk eater
Order Carcharhiniformes - 8 families; 210 spp. mostly
marine
- Scyliorhinidae -- cat sharks; usually small; tropical and
temperate
- Carcharhinidae -- highly predatory
- Bull shark (Carcharhinus leucas) occasionally found in f.w.
- Sphyrnidae -- hammerhead sharks
Superorder Squalimorphi
Order Hexanchiformes - 2 families; 5 spp.; all marine
- Chlamydoselachidae-- frill sharks
- Hexanchidae -- cow sharks, six and seven gill sharks
Order Squaliformes - 3 families; 74 spp.; all marine
- Widely distributed -- Atlantic, Pacific, Indian Oceans, tropical
to subarctic latitudes
- Squalidae -- dogfish sharks; usually small, inshore and deep water
scavengers (great nuisance to fisherman)
Order Pristiophoriformes- 1 family; 5 spp.; all marine
- Pristiophoridae - saw sharks
Superorder Squatinomorphi
Order Squatiniformes- 1 family; 12 spp.; marine
- Squatinidae - angel sharks
Superorder Batoidea (4 orders;13 families; 456 spp. marine and
freshwater)
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Updated 26 February 1999, T. Turner