9.4.5 Gnathostomata
This superclass is divided into six classes, (Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia). The grathostomata have true jaws and paired appendages. Class Chondricthyes (Cartilaginous fishes)
These have spindle-shaped bodies The mouth is ventral and semi-circular and nasal sacs do not open to the oral cavity Tough skin is covered with sandpaper-like placoid scales. though 5-7 pairs of gills, without
The endoskeleton is completely cartilaginous. The swim bladder is absent. They have a cloaca Stomach is a J-shaped Venous or branchial or single circuit heart; consists of a single auricle and single ventricle. 5-7 pairs of aortic arches. Sexes are separate and possess paired gonads. Fertilization is internal, oviparous or ovoviviparous
The largest of all fishes are included in this group (30-50 feet long). Examples: skate, rays, stingrays, electric rays, dogfish (sharks), etc.
9.4.5 Class Osteichthyes (Bony fishes).
Their body is also spindle-shaped mouth is terminal and variable in shape the dermal scales are nonacid, either provided by ganoid, cycloid, or ctenoid scales. Respire through, four pairs of pills which are supported by bony arches and covered with lid called an operculum.
Mostly possess a bony endoskeleton Swim bladder usually helps in buoyancy they have a Stomach that is variable in shape The venous heart consists of two chambers (an auricle and a ventricle)
They have 4 pairs of aortic arches.
- Sexes are separate and paired gonads.
- Mostly external fertilization, few exhibit internal.
- Mostly oviparous however some are ovoviviparous
- Beain has ten pairs of cranial nerves. Examples:- trout, cod, carp, catfish, etc.
Economic Importance of Chondrichthyes:
Beneficial(1) Source of food (especially sharks and rays). Many commercial products are prepared by them (such as the oil of shark liver is the source of vitamins A and D. The skin leather of sharks is being used for making bags and shoes. Great medicinal value of the pituitary gland of sharks.
Harmful effect:
Sharks feed on most of the seafood which is used by humans like prawns, crabs, lobsters, and palatable fishes.Economic Importance of Osteichthyes:
Beneficial effects:
- Both fresh water and marine bony fishes are important sources of our food cod, herein,g, and salmon are examples of marine, and trout, carp, catfish and mallet are freshwater fishes.
- Commercial products such as fish oil, fish meat, and liquid glue are made from bony fish.
- Cod liver oil is the source of vitamins A and D.
Adaptation of Aquatic Life in Fishes (Pisces):
Their body becomes streamlined, which offers little resistance to water during swimming.
The presence of swim bladder in bony fishes helps in buoyancy Fine paired and unpaired fins help them in swimming.
4. Gills for respiration
Developed central nervous system and sensory organs Adaptation of Animals for Terrestrial (Land) Mode of Life The Following adaptations are made by animals for a terrestrial mode of life, The skin is developed for protection against conditions Shelled eggs prevent the embryo from dry
A large quantity of yolk as stored food Development of lungs for terrestrial respiration. Modification of jointed appendages for running, walking, climbing, and flying Well-developed senses and specialized central nervous system.
9.4.6 Class Amphibia (Gk.Amphi;both, bios; life)
First land vertebrates (ie, transition from aquatic to land habitat).
Origin:
probably originated from Dipnoi which are lobe fin lung fishes Skin smooth, moist, scale and with many mucus glands, (also poisonous glands in some amphibians, chromatophores are also present) Body is divided into head, trunk, tail, or without tail.
Appendages:
usually two pairs of legs but some are leg less (caecilians)
Respiration:
In larvae, it occurs through gills while in adults it occurs through langs and skin or a few with gillseg. in Siren
Blood vascular system:-
Five-chambered hearts (right and left auricle, a single ventricle, sinus venous, and truncus arteriosus) Seses are separate with paired sex organs. Fertilization is usually external (in some internal).
Mostly oviparous and exhibit Indirect development through metamorphosis They are Anamniotes (The embryo lacks a protective membrane), and Poikilothermic (cold-blooded) which is why they hibernate in winter. Examples frogs and toads tailless, and salamanders are tailed amphibians.
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