CHAPTER 35 Flashcards
Phylum Chordata
Chordates are deuterostome coelomates
Nearest relatives are echinoderms (the only other deuterostomes)
Fishes, amphibians, reptiles, birds, and mammals
4 Features
Dorsal, hollow nerve cord Notochord May be replaced by vertebral column Pharyngeal slits Pharyngeal pouches present in all vertebrate embryos Postanal tail
All chordates have all four of these characteristics at some time in their lives
Other characteristics also distinguish chordates
Chordate muscles are arranged in segmented blocks called somites
Most chordates have an internal skeleton against which the muscles work
Phylum Chordata can be divided into three subphyla
- Urochordata
- Cephalochordata
- Vertebrata
Subphylum Urochordata
Tunicates and salps are marine animals
Larvae are tadpolelike and have notochord and nerve cord
Are free-swimming but do not feed
Adults typically lose the tail and notochord
Are immobile filter-feeders
Many secrete a tunic (cellulose sac) that surrounds the animal
Subphylum Cephalochordata
Lancelets are scaleless chordates
Notochord persists throughout animal’s life
Spend most of their time partly buried
Have no distinguishable head
Feed on plankton using cilia-generated currents
Closest relatives to vertebrates
Subphylum Vertebrata
Vertebrates are chordates with a VERTEBRAL column
Distinguished from nonvertebrates by
Vertebral column—bony or cartilagenous – Encloses and protects the dorsal nerve cord
Head – Distinct and well-differentiated possessing sensory organs
Vertebrates also have
Neural crest – unique group of embryonic cells that forms many vertebrate structures
Internal organs – liver, kidneys, endocrine glands, heart, and closed circulatory system
Endoskeleton – made of cartilage or bone—living tissue that is strong but not brittle
Makes possible great size and extraordinary movement
The first vertebrates appeared in the oceans about 545 MYA
Mouth at one end, fin at the other
Jawed fishes soon became dominant
Amphibians invaded the land
Reptiles replaced them as the dominant land vertebrates
Birds and mammals became dominant after Cretaceous mass extinction
Fishes
Most diverse vertebrate group
Over half of all vertebrates
Provided the evolutionary base for invasion of land by amphibians
Fishes have the following characteristics
Vertebral column
Hagfish exception and lamprey rudamentary vertebrae of cartilage
Jaws and paired appendages
Hagfish and lamprey exceptions
Internal gills
Single-loop blood circulation
Nutritional deficiencies
Inability has been inherited by all their vertebrate descendants—cannot synthesize certain amino acids—must get them in their food.
HR
History of the Fishes
The first fishes had mouths with no jaws
Agnatha extant as hagfish (class Myxini) and lampreys (class Cephalaspidomorphi)
Ostracoderms (jawless) are now extinct—first vertebrates
The development of jaws occurred in the late Silurian period
Jaws evolved from the anterior gill arches that were made of cartilage
Armored fishes (placoderms) and some spiny fishes (Acanthodians) both had jaws
Spiny fish were common during early Devonian – replacing ostracoderms
Cartilage skeleton but skin had small plates of bone
Extinct at close of Permian
Placoderms became common in late Devonian
Jaw more improved than spiny fishes’
Upper jaw fused to the skull and the skull hinged on the shoulder
Extinct by end of period
At the end of the Devonian period, essentially all of these pioneer vertebrates disappeared, replaced by sharks and bony fishes in one of several mass extinctions
Sharks and bony fishes first evolved in the early Devonian, 400 MYA
Jaw was improved even further allowing the mouth to open much wider than was previously possible
Class Chondrichthyes
Sharks, skates, rays
Became the dominant sea predators in the Carboniferous period (360–280 MYA)
Cartilage skeleton “calcified” with granules of calcium carbonate
Light, strong skeleton
No swim bladder
Sharks were among the first vertebrates to develop teeth
Evolved from rough scales on mouth’s skin
Not set into the jaw so easily lost but continuously replaced
Sharks (and bony fishes) have a fully developed lateral line system
Series of sensory organs under the skin that detects changes in pressure waves
Reproduction in sharks differs from that of other fishes
Eggs are fertilized internally
Most pups are born alive
A few species do lay fertilized eggs
Sharks have long gestation periods and relatively few offspring
Therefore, are not able to recover quickly from population declines
Bony fishes
Evolved at the same time as sharks about 400 MYA
However, they adopted a heavy internal skeleton made completely of bone
Bony fishes are the most species-rich group of all vertebrates (> 30,000 living species)
Significant adaptations include swim bladder and gill cover
Swim bladder
Gas-filled sac that allows bony fishes to regulate their buoyant density
In most modern fish, filled and drained with gases internally
Gill cover
Hard plate, the operculum, covers gills
Flexing plate permits water pumping over gills
Efficient bellows system when stationary
Gases are taken from the blood, and the gas gland secretes the gases into the swim bladder; gas is released from the bladder by a muscular valve, the oval body
Two Major Groups of Bony Fishes
Ray-finned fishes (class Actinopterygii)
Parallel bony rays support and stiffen each fin
There are no muscles within the fins
Lobe-finned fishes (class Sarcopterygii)
Have paired fins that consist of a long fleshy muscular lobe
Supported by central core of bones with fully articulated joints—muscles can move fin rays
Almost certainly the amphibian ancesto
