phylum Annelida
The annelids include earthworms, polychaete worms, and leeches.
ECOLOGICAL ROLE
Annelids are found all over the world in many marine, freshwater and terrestrial environments. They are passive filter feeders to voracious and active predators. They help keep soils healthy. They are extremely important in soil creation and without them, agriculture and life as we know it may never have evolved. In marine environments the numerous species play an important role in the maintenance of food chains and the whole ecological balance of the seas. Support terrestrial food chains and are important in aeration and enriching the soil.
Annelids are found all over the world in many marine, freshwater and terrestrial environments. They are passive filter feeders to voracious and active predators. They help keep soils healthy. They are extremely important in soil creation and without them, agriculture and life as we know it may never have evolved. In marine environments the numerous species play an important role in the maintenance of food chains and the whole ecological balance of the seas. Support terrestrial food chains and are important in aeration and enriching the soil.
MOVEMENT STRUCTURES/ TYPE
Being segmented helps with body movements. The body wall of annelids is made up of both circular and longitudinal muscle fibers surrounded by a moist cuticle. They have parapodia for locomotion. The septa enables them to change the shapes of certain segments which helps with movement by sending ripples that pass along the body, or by undulations that improve the effectiveness of the parapodia. They have two layers of muscles that coordinate muscular contractions and most species have setae for movement. The circular muscles make a segment longer and slimmer when they contract, while under them are longitudinal muscles, usually four distinct strips, whose contractions make the segment shorter and fatter.
Being segmented helps with body movements. The body wall of annelids is made up of both circular and longitudinal muscle fibers surrounded by a moist cuticle. They have parapodia for locomotion. The septa enables them to change the shapes of certain segments which helps with movement by sending ripples that pass along the body, or by undulations that improve the effectiveness of the parapodia. They have two layers of muscles that coordinate muscular contractions and most species have setae for movement. The circular muscles make a segment longer and slimmer when they contract, while under them are longitudinal muscles, usually four distinct strips, whose contractions make the segment shorter and fatter.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
The annelids are bilaterally symmetrical, triploblastic, coelomate invertebrate organisms. The annelid body plan consists of a head followed by a long thin body of numerous similar segments ending in a small pygidium (tail-like). Their bodies have three cell layers each of which develop into various tissues or organs. All the organisms in this group are segmented with each segment containing body systems such as circulatory, nervous, and excretory tracts systems. Annelids have a large, true coelom (one that is lined with a mesoderm). All annelids except leeches have chitinous hair like structures called setae, projecting from their cuticle. Annelids' cuticles are made of collagen fibers, usually in layers that spiral in alternating directions so that the fibers cross each other. These are secreted by the one-cell deep epidermis (outermost skin layer). A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus-secreting glands in the epidermis protect their skins. Under the epidermis is the dermis, which is made of connective tissue, in other words a combination of cells and non-cellular materials such as collagen. Below this are two layers of muscles, which develop from the lining of the coelom (body cavity).
The annelids are bilaterally symmetrical, triploblastic, coelomate invertebrate organisms. The annelid body plan consists of a head followed by a long thin body of numerous similar segments ending in a small pygidium (tail-like). Their bodies have three cell layers each of which develop into various tissues or organs. All the organisms in this group are segmented with each segment containing body systems such as circulatory, nervous, and excretory tracts systems. Annelids have a large, true coelom (one that is lined with a mesoderm). All annelids except leeches have chitinous hair like structures called setae, projecting from their cuticle. Annelids' cuticles are made of collagen fibers, usually in layers that spiral in alternating directions so that the fibers cross each other. These are secreted by the one-cell deep epidermis (outermost skin layer). A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus-secreting glands in the epidermis protect their skins. Under the epidermis is the dermis, which is made of connective tissue, in other words a combination of cells and non-cellular materials such as collagen. Below this are two layers of muscles, which develop from the lining of the coelom (body cavity).
SUPPORT
Annelids do not have any skeletel structures. Hydrostatic pressure and muscles are spread across segments and help maintain body rigidity, allowing muscle contractions to bend the body without collapsing.
Annelids do not have any skeletel structures. Hydrostatic pressure and muscles are spread across segments and help maintain body rigidity, allowing muscle contractions to bend the body without collapsing.
OBTAINING NUTRIENTS
They have a complee digestive system with a mouth and anus, as well as specialized digestive organs such as crop, gizzard and an esophagus.
They have a complee digestive system with a mouth and anus, as well as specialized digestive organs such as crop, gizzard and an esophagus.
RESPIRATION
Annelids do not have respiratory organs, resulting in the gases to be exchanged through the skin or sometimes through specialized gills or modified parapodia.
Annelids do not have respiratory organs, resulting in the gases to be exchanged through the skin or sometimes through specialized gills or modified parapodia.
CIRCULATION
They have a closed, segmentally arranged circulatory system. Most species have septa that circulated the blood throughout the blood vessels and the vessels in segments near the front ends of these species, are often built up with muscles that acts as hearts. They have dorsal and ventral blood vessels as well as five aortic arches which are heavily muscled to help regulate blood pressure.
They have a closed, segmentally arranged circulatory system. Most species have septa that circulated the blood throughout the blood vessels and the vessels in segments near the front ends of these species, are often built up with muscles that acts as hearts. They have dorsal and ventral blood vessels as well as five aortic arches which are heavily muscled to help regulate blood pressure.
EXCRETION
They filter and excrete waste through its anus.
They filter and excrete waste through its anus.
RESPONSE
They have a nervous system with an anterior nerve ring, ganglia and a ventral nerve cord. The nervous system includes a pair of cephalic ganglia attached to double nerve cords that run the length of the annelid along the ventral body wall, with ganglia and branches in each segment. Annelids have some tactile organs, chemoreceptors, balance receptors, and photoreceptors. They are sensitive to light, touch and chemicals. Some annelids have well-developed eyes including lenses. The brain generally forms a ring round the pharynx, consisting of a pair of ganglia (local control centers) above and in front of the pharynx, linked by nerve cords either side of the pharynx to another pair of ganglia just below and behind it.
They have a nervous system with an anterior nerve ring, ganglia and a ventral nerve cord. The nervous system includes a pair of cephalic ganglia attached to double nerve cords that run the length of the annelid along the ventral body wall, with ganglia and branches in each segment. Annelids have some tactile organs, chemoreceptors, balance receptors, and photoreceptors. They are sensitive to light, touch and chemicals. Some annelids have well-developed eyes including lenses. The brain generally forms a ring round the pharynx, consisting of a pair of ganglia (local control centers) above and in front of the pharynx, linked by nerve cords either side of the pharynx to another pair of ganglia just below and behind it.
REPRODUCTION
They can reproduce asexually, but sexually reproduction normally takes place in annelid species. Annelids can have seperate sexes or be hermaphrodites, depening on the species. Some species reproduce asexually by dividing into two or more pieces or by budding off a new individual. Annelids release sperm and eggs and the fertilized eggs develop into trochophore larvae. They later sink to the sea floor and metamorphose into adults.
They can reproduce asexually, but sexually reproduction normally takes place in annelid species. Annelids can have seperate sexes or be hermaphrodites, depening on the species. Some species reproduce asexually by dividing into two or more pieces or by budding off a new individual. Annelids release sperm and eggs and the fertilized eggs develop into trochophore larvae. They later sink to the sea floor and metamorphose into adults.
Classes of annelida
Oligochaeta: species include earth-worms, segmented, lack parapodia, have setae (hair like bristles) arranged in four bundles on each segment, defined head and tail region, complete digestive system, terrestrial & freshwater, eats dead and decaying plant and animal matter, no eyes, light detecing photorecptor cells in some areas, hermaphroditic.
Polychaeta: body segments bear a pair of parapodia (flat lobe like outgrowths) with setae, undulations of the body allow movement, seperate sexes, marine organisms, have eyes, some have gills other use diffusion, seperate sexes, some live permanetly in tubes or burrows,
Hirudinea: species include leeches, flattened, predacious or parasistic, suckers, primarily freshwater dwellers, 34 body segments, each segment has a subdivision of annuli, clitellum instead of parapodia, most can swim, coelom is filled with tissues, photoreceptors all over body, 2-10 eyes, swallow prey whole or suck blood, some have jaws for biting, hermaphroditic.
Polychaeta: body segments bear a pair of parapodia (flat lobe like outgrowths) with setae, undulations of the body allow movement, seperate sexes, marine organisms, have eyes, some have gills other use diffusion, seperate sexes, some live permanetly in tubes or burrows,
Hirudinea: species include leeches, flattened, predacious or parasistic, suckers, primarily freshwater dwellers, 34 body segments, each segment has a subdivision of annuli, clitellum instead of parapodia, most can swim, coelom is filled with tissues, photoreceptors all over body, 2-10 eyes, swallow prey whole or suck blood, some have jaws for biting, hermaphroditic.