1. Lecture 18: 8- Phylum: Chordata
The phylum of Chordata includes four subphyla:
1- Subphylum: Vertebrataالفقاريات
2- Subphylum: Urochordataالذيل حبليات
3- Subphylum: Cephalochordataالرأس حبليات
4- Subphylum: Hemichordata النصف حبليات
All vertebrates have backbones العمود الفقري
Humans, mammals, birds, lizards, snakes, turtles, amphibians, fishes are vertebrates.
They share several unique features including a backbone.

2. All animals are grouped as either an invertebrate or a vertebrate.
95% of all animals are invertebrate organisms.
The animals do not have a backbone or vertebral column.
5% of all animals are vertebrates.
These animals do have a backbone.
The subphylum of vertebrata includes seven classes:
1- Class: Cyclostomataدائرية الفم (اللافكيات)
2- Class: Chondrichthyesالأسماك الغضروفية
3- Class: Osteichthyesالأسماك العظمية
4- Class: Amphibia البرمائيات
5- Class: Reptilia الزواحف
6- Class: Aves الطيور
7- Class: Mammalia الثدييات

3. Diversity of Chordates:
Section 33-1

5. Why are fishes so successful?
Adapt to environment.
Extract oxygen from small amounts of oxygen per unit volume.
Efficient locomotor structures.
High sensory system.
Efficient reproduction (produces overwhelming number of offspring).

6. Nutrition and Digestion:
Most are predators (always searching for food):
Swallow prey whole.
Capture prey: suction-closing the opercula and rapidly opening mouth.
Some filter feeders- Gill rakers: trap plankton while the fish is swimming with mouth open.
Some herbivores and omnivores.

7. Reproduction and Development:
Oviparous: Lay undeveloped eggs, External fertilization (90% of bony fish), Internal fertilization (some sharks and rays)
Fish lay huge numbers of eggs; a female cod may release 4-6 million eggs.
Ovoviviparous: Internal development- without direct maternal nourishment-Advanced at birth (most sharks + rays).
Viviparous: Internal development- direct nourishment from mother-Fully advanced at birth (some sharks)
In fishes, oviparity is most common; the eggs are inexpensive to produce, and as eggs are in the water, they do not dry out (oxygen, nutrients are not scarce). The adult can produce many offspring, which they broadcast into the plankton column. When the offspring settle out of the plankton, they may be in totally new environments, allowing for a great area in which the young may survive. This mode also comes with its disadvantages; when born, the fish must first go through a larval stage for growth before they transform into the adult stage. In this larval stage, they must fend for themselves in obtaining food and avoiding predation. They may not find a suitable environment when they settle out of the plankton column. The survival of individual eggs is very low, so millions of eggs must be produced in order for the parent to successfully produce offspring. The other modes have their advantages, the eggs are much less prone to predation when carried within the mother, and the young are born fully advanced and ready to deal with the environment as miniature adults. These advantages come with a price-tag also; the adult must supply nutrients to its offspring and can only produce a few eggs at a time. The young are limited to the environment that their parents were in, and if this environment is deteriorating, they are stuck with it.

8. Phylum: Chordataالحبليات Subphylum : Vertebrataالفقاريات Class: Amphibiaالبرمائيات Frog (amphibian)الضفدعة
Amphibian means “two lives,” a reference to the metamorphosis of many frogs from an aquatic stage, the tadpole, to the terrestrial adult.
Tadpoles are usually aquatic herbivores with gillsخياشيم , a lateral line system, and swim by tail.
During metamorphosisالتحول , the tadpole develops legs, and gills are replaced by lungs.
Adult frogs are carnivorous hunters.
Most amphibians retain close ties with water and are most abundant in damp habitats.

9. External Structures:
Mucous-covered skin: protection from microorganisms, UV, desiccation, and mechanical injury.
Allows for: Gas exchange, temperature regulation, and absorption/storage of water.
Amphibians’ skin keeps them moist, aids in mating, can produce toxins, even change color.
All this without scales, feather or hair.
Skin has lots of glands.

10. Nutrition and digestion:
Adults:
Mostly carnivores feeding on invertebrates.
Hunt by sight, wait for prey to pass by Salamanders and caecilians use olfactory senses to help catch prey.
Larvae:
Mostly herbivores

11. Vocalization: Usually used for mating. Calls are species specific.
Attract females.
Mark territory.
Calls are species specific.
Can give a distress call.
Hopefully enough to scare a
predator.
Helps ensure a mate of the
proper species is found.

12. Metamorphosis:
Series of abrupt structural, physiological, and behavioral changes.
Anurans have the most dramatic metamorphism:
Limbs and lungs develop
Gill are lost
Tail is reabsorbed
Skin thickens
Head and digestive
tract change to allow them
to digest prey.