Marine Fishes
BIOL265
Dave Werner
Kingdom Animalia – Phylum Chordata
Major Characteristics found in all chordates:
1. Notochord – a stiff but flexible rod along the length of the body
2. Dorsal hollow nerve chord – neural structure that develops into the
brain and and central nervous system
3. Pharyngeal gill slits – openings or grooves found on the cavity behind the mouth
(found in all chordates at least at some stage of their life cycle)
4. Post-anal tail
Kingdom Animalia – Phylum Chordata
Subphylum Urochordata : Tunicates - ~1400 entirely marine species, including
sea squirts.
Sessile, filter feeders…
Body may look like that of a sponge
but they have a leathery outer protective
layer called the tunic that feels very
different from sponges… internally, they
are quite complex…
Kingdom Animalia – Phylum Chordata
subphylum urochordata
Although urochordates are sessile, they typically have motile larvae that truly exhibit
all the chordate characteristics…
In a few cases however (i.e. salps); the
urochordates retain the larval form even
as adults, remaining motile…
Tunicates
Also, tunicates may be solitary…
… or colonial
What would be the advantages or disadvantages of
each of these lifestyles?
Kingdom Animalia – Phylum Chordata
Subphylum Cephalochordata : Lancelets - ~ 29 species of small “fish-like” organisms
with all the typical “fish” characteristics, other than
a backbone…
They live on soft bottoms, and use gill slits to filter feed…
Kingdom Animalia – Phylum Chordata
Subphylum Vertebrata :
The vertebrates represent a
diverse group of animals…
Simply put however, they are
chordates with a backbone.
Their backbone (or vertebral
column, or spine) is made up of
a dorsal row of hollow skeletal
elements that protect the nerve
cord (or spinal cord).
Marine Fishes
Class Agnatha – Jawless fishes … feed by suction and help from their round muscular
mouth with rows of teeth…
Include hagfish (or slime eels) that feed on dead or dying organisms…
sometimes from the inside out!!! … include about 20 species.
Other agnathans include lampreys which either feed on invertebrates, or
attach to other fish and such their blood… include about 30 species.
Jawless Fish
Phylum: Chordata
Sub-Phylum: Vertebrata
Class: Agnatha
• There are two primary marine types of the class
Agnatha. They are Hagfish and Lampreys.
• Most Primitive living fishes
• Hagfish are of the order, Myxiniform. They are
related to the slimefish. They have the peculiar habit
of tying themselves into knots in order to shed their
slime coat and make a new one.
Hagfishes
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•
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•
20 known species
Deep, cold waters
2.6 ft.
Skin is used for leather goods
Hagfish
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feed on polychaete worms, shrimp, and dead or dying fish
attach to fish, form a knot in the tail and pass it forward to rip off
flesh. Image © BIODIDAC.
usually enter coelomic cavity and feed on soft parts
• many mucous glands present for antipredator defense
Lampreys
http://itech.pjc.edu/jwooters/zoology/virtual_review/lamprey.htm
• Lampreys are of the
order,
Petromyzontiform. They
are suckers and attach
themselves to fish in
order to parasitize off
them.
• Found in Freshwater
• 30 species
Sea Lamprey Life Cycle
•
A. Sea lampreys go through an extended larval phase before metamorphosing into the bloodsucking
parasitic phase. Each summer and fall there is one group of parasitic sea lampreys actively feeding in the
Great Lakes.
B. The next spring, that group leaves the lake and migrates into tributary streams where they must build
nests in clean gravel with flowing water.
C. Each female spawns an average of 60 to 70 thousand eggs.
D. After hatch, the larvae drift downstream to areas with slower currents and sand/silt bottoms. There,
they establish permanent burrows and enter a larval stage varying in duration from 3 to 10-ormore years.
E. Larvae lack eyes and the oral disc. Living concealed in their burrows, they are harmless and filter
microscopic material from the water for food. When they reach lengths of 120 mm or more, some
individuals begin metamorphosis in mid summer.
F. During metamorphosis they develop eyes, the oral disc, and changes in their kidneys that (in their native
range) would allow them to enter the salt water of the Atlantic Ocean. That fall or the following spring,
they instead enter the Great Lakes to feed parasitically on fish that summer and fall, and mature and
spawn the next spring—completing their life cycle. Sea lampreys only spawn once and then die after
spawning.