Download Chordates

Chordates
Chordates
• A chordate (Phylum Chordata) is an
animal that has, for at least some stage of
its life, a dorsal, hollow nerve cord; a
notochord; pharyngeal pouches; and a tail
that extends beyond the anus
• Some chordates possess all these
characteristics as adults; others, only as
embryos
• Most chordates are vertebrates
Chordates
(continued)
• Notochord – long flexible supporting rod at some stage
of development – usually during the embryonic
stage/supports the nerve cord
• Hollow dorsal nerve cord – runs dorsally above the
notochord
• Pharyngeal slits/pouches – paired structures located in
throat region, disappear in higher vertebrates as they
develop
Notochord
Muscle segments
Tail
Hollow
nerve cord
Anus
Mouth
Pharyngeal pouches
Nonvertebrate Chordates
• Lancelets – small, fishlike creatures
– Contain all four
characteristics but lack a
backbone
– No jaws or appendages
– Primitive heart, closed
circulatory system
– Long pharyngeal region,
many gill slits, filter
feeders
Nonvertebrate Chordates (continued)
• Tunicates – Sea
Squirts – Mogula sp.
– The larvae contain all
four characteristics;
adults lack the tail and
notochord and are
sessile filter feeders
– Marine chordates
– Body covering called
“tunic”
Fishes
• Aquatic vertebrates that are characterized
by paired scales, fins, and pharyngeal gills
• Jawless fishes – primitive
• Cartilaginous fishes
• Bony fishes – most advanced – 97% of
species
Anatomy of a Fish
Kidney
Pyloric
cecum
Stomach
Vertebra
Muscle
Esophagus
Swim
bladder
Brain
Spinal Gills
cord
Mouth
Operculum
Urinary
bladder
Heart
Anus
Reproductive
organ
Pancreas
Intestine
Gallbladder
Liver
Feeding in Fish
• All types – generalists (carp) to specialists
(piranha)
• Swallow food, don’t chew
Respiration in Fish
• Gills for gas exchange – most fish
• Modified swim bladder for use in oxygen
poor water and gills (lungfish)
Circulation in Fish
• Two chambered heart with an atrium and a
ventricle. The ventricle forces oxygen poor
blood to the gills. Have a single loop circulatory
system
Gills
Brain and
head
circulation
Body
muscle
circulation
Digestive
system
circulation
Heart
Sinus Venosus
Oxygen-poor blood
from the veins collects
in the sinus
venosus.
Ventricle
The ventricle pumps
blood into the bulbus
arteriosus.
Blood enters the
atrium and flows
to the ventricle.
Bulbus Arteriosus
The bulbus arteriosus
moves blood into the
ventral aorta and
toward the gills.
Excretion in Fish
• Nitrogenous wastes through gills or
kidneys or both
• Kidneys counter osmosis (salmon)
Response in Fish
• Fairly well-developed nervous system
• Well developed brain containing: olfactory
bulb – smell, optic lobes – sight,
cerebellum – coordination of movement,
medulla – organ function
• Lateral line system, taste, sight
Movement in Fish
• Use swim bladder for bouyancy and paired
fins to control movement
Reproduction in Fish
• Most have external fertilization,
but sharks have internal
fertilization
• Separate males and females –
some species change males to
females or females to males, few
are both
• Oviparous – lay eggs
• Ovoviviparous – young developed
from eggs inside female
• Viviparous – live bearing, young
nourished by mother
Groups of Fishes
• Three major Classes of Fish:
– Class Agnatha
– Class Chondrichthes
– Class Osteichthes
Class Agnatha – Jawless Fishes
• Veracious feeders, not vertebrates
• Some are parasitic
• Lampreys – larvae are filter feeders and
adults are parasitic – attach to fishes, rasp
with tongue and suck fluids
• Hagfish – use toothed tongue to scrape
hole in dead fish and crawl in – most
primitive, six hearts and open circulatory
system
Examples of Class Agnatha
Class Chondrichthes – Cartilaginous fishes
– Sharks and Skates
• Skeletons are made of cartilage, tooth-like
scales on skin
• 3,000 teeth, 6-20 rows, 20,000 teeth in a lifetime
• Sharks are dominant predators (bony jaws)
• Most eat fish, some filter feed, some scavenge,
few man eaters
• Rays and skates, flattened sharks, most
harmless, flat and glide
Examples of Class Chondrichthes
Class Osteichthes – Bony fishes
• Flexible backbones vary among species. The
more rigid a backbone, the faster a fish swims
using its strong tail
• 40% of all vertebrates, most advanced
• Three subclasses:
– Lungfish – have lungs and gills
– Lobe-finned – 1 specie – Coelacanth – genus
Latimeria – thought to be extinct 70 million years ago,
but was discovered off Africa in 1938, 1.5 meters
long, closest thing to ancestor to all land vertebrates
– Ray-finned – fins are fan shaped
• Most are ray-finned
Examples of Class Osteichthes
Origin of Fish
• Fossils indicate jawless fish lived in the Ordovician period (500
million years ago)
• After 100 – 150 million years, jawed fish first appeared
• Armored (scaled fish), are common ancestors