Question

The main features of chordates. How can they be described according to examples of representative species, basic morphology, type of symmetry, germ layers and coelom, digestive system, respiratory system, circulatory system, excretory system, nervous system and types of reproduction?

Answer 1

The main features of chordates

Representative species - Reptiles, Birds, Mammals, Fish, etc.

Basic Morphology - Chordates posses notochord,a semi-flexible rod running along the length of the animal. All chordates have a notochord at some stage in their lives, but in some (such as tunicates) the notochord is lost in the adult, whereas in others (such as the vertebrates) the notochord is present in the embryo, but in later stages is mostly replaced and surrounded by the vertebrae, or backbones. Another chordate feature is the dorsal nerve cord that runs beneath the notochord. The chordate nerve cord is hollow, with pairs of nerves branching from it at intervals and running to the muscles. The anterior (forward) end of the nerve cord is often enlarged into a brain. Another morphological feature is Pharyngeal slits, the openings between the pharynx, or throat, and the outside. The post-anal tail is also a common feature among chordates which is an extension of the notochord and nerve cord past the anus.

Type of symmetry - Chordates has bilateral symmetry

Germ layers and coelom - Three germ layers in chordates are endoderm, mesoderm and ectoderm. Chordates has true coelom,to be more precise they have enterocoelom (Coelom arises from endoderm).

Digestive system - Chordates have an opening (mouth) for food intake followed by a pharynx or esophagous in some species. The food particles then moves through stomach and nutrients are absorbed using intestine. Most ofthe chordates contains specilised glands in their digestive system.

Respiratory system - Primitive chordates use gills for respiration where as in advanced chordtes they are evolved in to lungs.

Circulatory system - They have a closed circulatory system and most of the chordates contains a pump (Heart) for pumping their blood through the blood vessels.

Excretory system - Most of the chordates use an urinary system for excretion and they contains a specilised organs like kidney which fecilitates excretion. But there are fishes which uses their gills also for excretion.

Nervous system - Chordates have a nervous system based upon a single, hollow nerve cord located under the dorsal surface. The anterior (forward) end of the nerve cord is often enlarged into a brain.

Types of Reproduction - Reproduction in chordates begins with the union of sperm and egg. In primitive chordates, fertilization occurs externally, in the water. Chordates mainly shows asexual reproduction. Asexual reproduction also takes place in a few chordates. Hermaphroditism (possessing both male and female reproductive organs) is found in tunicates and some fishes. Larvae (very young forms that differ considerably from the juveniles and adults), when they do occur, differ in structure from the larvae of nonchordates. Internal fertilization, viviparity (giving birth to young that have undergone embryological development), and parental care are common in tunicates and vertebrates.