Echinoderms are characterized by spiny skin, five part
radial symmetry, an internal skeletion, a water vascular system, and
suction-cuplike structures called feet.
The water vascular
system carries out many essential body functions in echinoderms, including
respiration, circulation, and movement.
Classes of echinoderms include sea lilies and feather stars,
seas stars, brittlestars, sea urchins, and sand dollars, and sea cucumbers.
- A unique feature of echinoderms is a system of internal tubes called a water vascular system, which is filled with fluid, carries out many essential body functions in echinoderms, including respiration, circulation, and movement. It opens to the outside though a sievelike structure called a madreporite. In sea stars, the madreporite connects to a ring canal that forms a circle around extend along body segments.
- Attached to each radial canal are hundreds of tube feet, these are structures that operate much like a suction cup. Each tube foot has a sucker on the end. Muscles pull the center of the sucker upwards, forming a cup shape. This action creates suction on the surface to which the foot is attached, so the tube foot pulls on the surface. Hundreds of tube feet acting together create enormous force, allowing echinoderms to walk and even to pull open shelled prey as clams.
Reproduction in echinoderms
Echinoderms reproduce by external fertilization. In most sea
star species, the sexes are separate. Sperm are produced in testes, and eggs
are produced in ovaries. Both types of gametes are shed into open water, where
fertilization takes place. The larvae, which have bilateral symmetry, swim
around for some time and the swim to the ocean bottom, where they develop into
adults that have radial symmetry.
Respiration in echinoderms
Other than the water vascular system, echinoderms have few
adaptations to carry out respiration or circulation. In most species, the
thin-walled tissue of the tube feet provides the main surface for respiration.
In some species, small outgrowths called skin gills also function in gas
exchange.
Phylum Chordata
- A dorsal, hollow nerve cord: Which runs along the back part of the body. nerves branch from this cord and connect to organs.
- A Notochord: It is a long supporting rod that runs through the body below the nerve cord.Most chordates only have them when they are embryos.
- Pharyngeal pouches: Paired structures in the throat region.
- A tail that extends beyond the anus.
The most known subphylum of chordates is the vertebrata, which is divided into classes:
- class Osteichthyes
- class Amphibia
- class Reptilia
- class Aves
- class Mammalia
There are two subphyla of chordates that don't have backbones:
Tunicates
Lancelets
Tunicates and lancelets are both soft bodied marine organisms. Even though they have a nerve cord, a notochord, pharyngeal pouches and a tail at some stage of their life, they are non vertebrates.
Classification of the Phylum Chordata
