phylum platyhelminthes
Common platyhelminthes include flatworms and tapeworms.
ECOLOGICAL ROLE
The flatworm species accounts for a large number of parasitic forms, some of which that have devastating effects on humans and animals.
The flatworm species accounts for a large number of parasitic forms, some of which that have devastating effects on humans and animals.
MOVEMENT STRUCTURES/TYPE & SUPPORT
Movement in some flatworms is controlled by layers of muscle, while other move through the beating of epidermal cilia, leaving a trail of slime behind. The space between the skin and gut is filled with mesenchyme, a connective tissue made of cells and reinforced by collagen fibers that act as a type of skeleton, providing attachment points for muscles. Flatworms use hydrosatic pressure and tegument for support.
Movement in some flatworms is controlled by layers of muscle, while other move through the beating of epidermal cilia, leaving a trail of slime behind. The space between the skin and gut is filled with mesenchyme, a connective tissue made of cells and reinforced by collagen fibers that act as a type of skeleton, providing attachment points for muscles. Flatworms use hydrosatic pressure and tegument for support.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
Flatworms are triploblastic, have bilateral symmetry, are unsegmented, soft-bodied and are dorsal-ventrally flattened. There are free-living worms and parasitic species. They have three main cell layers (endoderm, mesoderm, ectoderm). The epidermis is generally ciliated in the turbellarians, while trematodes and cestodes are covered with a cuticle. Beneath the outer covering are two layers of muscle, an outer circular layer, and an inner longitudinal layer. Flatworms do not have a body cavity other than a gut, but some smaller species may not even have that. Not having a body cavity contributes to the reason why they are flat.
Flatworms are triploblastic, have bilateral symmetry, are unsegmented, soft-bodied and are dorsal-ventrally flattened. There are free-living worms and parasitic species. They have three main cell layers (endoderm, mesoderm, ectoderm). The epidermis is generally ciliated in the turbellarians, while trematodes and cestodes are covered with a cuticle. Beneath the outer covering are two layers of muscle, an outer circular layer, and an inner longitudinal layer. Flatworms do not have a body cavity other than a gut, but some smaller species may not even have that. Not having a body cavity contributes to the reason why they are flat.
OBTAINING NUTRIENTS
Flatworms can obtain food by absorption through surface cells and by consuming food with their mouths. Free-living species are carnivorous or scavengers, and the parasites feed on blood tissue fluids, or pieces of cells from within its host. Their gut is lined with a single layer of endodermal cells that absorb and digest food. Extracellular and intracellular digestion take place in the intestine. Some species break up and soften food first by secreting enzymes in the gut or pharynx.
Flatworms can obtain food by absorption through surface cells and by consuming food with their mouths. Free-living species are carnivorous or scavengers, and the parasites feed on blood tissue fluids, or pieces of cells from within its host. Their gut is lined with a single layer of endodermal cells that absorb and digest food. Extracellular and intracellular digestion take place in the intestine. Some species break up and soften food first by secreting enzymes in the gut or pharynx.
RESPIRATION & CIRCULATION
They are not equipped with any respiratory or circulatory organs but oxygen and nutrients pass through their bodies through the process of diffusion (absorption through the body wall). They circulate substances and gases through direct diffusion to the cells. Respiration through the whole surface of the body makes them vulnerable to fluid loss, and restricts them to environments where dehydration is unlikely: sea and freshwater, moist terrestrial environments such as leaf litter or between grains of soil, and as parasites within other animals.
They are not equipped with any respiratory or circulatory organs but oxygen and nutrients pass through their bodies through the process of diffusion (absorption through the body wall). They circulate substances and gases through direct diffusion to the cells. Respiration through the whole surface of the body makes them vulnerable to fluid loss, and restricts them to environments where dehydration is unlikely: sea and freshwater, moist terrestrial environments such as leaf litter or between grains of soil, and as parasites within other animals.
EXCRETION
Their digestive cavity only has one opening that serves as both a mouth and an anus. They excrete waste by using specialized flame cells. Some long species, however do have a separate mouth and anus since it is difficult to excrete waste through their mouth. All except the simplest flatworms have nephridial tubules, called protonephridia, usually distributed throughout the entire body. Such structures consist of an external opening and a tubule that branches internally, terminating in a number of blind, bulb-shaped structures called flame bulbs, which bear tufts of cilia.
Their digestive cavity only has one opening that serves as both a mouth and an anus. They excrete waste by using specialized flame cells. Some long species, however do have a separate mouth and anus since it is difficult to excrete waste through their mouth. All except the simplest flatworms have nephridial tubules, called protonephridia, usually distributed throughout the entire body. Such structures consist of an external opening and a tubule that branches internally, terminating in a number of blind, bulb-shaped structures called flame bulbs, which bear tufts of cilia.
RESPONSE
In all platyhelminths, the nervous system is concentrated at the head end. Flatworms have several nerve cords extending from a (ganglia) brain along the length of the body. Their cephalized nervous system consists of head ganglion, usually attached to longitudinal nerve cords that are interconnected across the body by transverse branches. Their eyespot is a simple eye that can detect light. In some flatworms, the process of cephalization has included the development in the head region of light-sensitive organs called ocelli. Other sense organs include chemoreceptors, balance receptors and receptors that sense water movement.
In all platyhelminths, the nervous system is concentrated at the head end. Flatworms have several nerve cords extending from a (ganglia) brain along the length of the body. Their cephalized nervous system consists of head ganglion, usually attached to longitudinal nerve cords that are interconnected across the body by transverse branches. Their eyespot is a simple eye that can detect light. In some flatworms, the process of cephalization has included the development in the head region of light-sensitive organs called ocelli. Other sense organs include chemoreceptors, balance receptors and receptors that sense water movement.
REPRODUCTION
Most flatworms can reproduce asexually or sexually. Asexual reproduction occurs through divison/fragmentation and regeneration. Flatworms are hermaphroditic (each individual produces both eggs and sperm), These are released from the flatworm where they become cross-fertilized by other flatworms. Trematodes and cestodes flatworms lay eggs constantly, whereas the turbellarian class has a seasonal cycle where they can reproduce asexually by dividing. Their eggs either hatch into tiny worms or develop in larval form.
Classes of Platyhelminthes
Cestoda (tapeworms): all species are parasitic, long, flat ribbon like organisms, segmented with reproductive organs on each, head has one or more hooked suckers for attachment to host, food is absorbed through body wall; no digestivetract, typically live in digestive tracts of adult vertebrates, humans can be subjected to infection if food is not cooked properly, their body segments are called proglottis.
Trematoda (flukes): leaf shaped flatworms, endoparasistic(attach to internal organs), oral suckers sometimes with hooks that attach to vertebrate host, solid body filled with spongey connective tissue, hermaphroditic.
Turbellaria: dorsoventrally flattened, unsegmented, no body cavity, are solid, diffusion, digestive cavity, osmoregulatory system which is made up of a network of little tubes, and specialized flame cells, more complex sensory organs, move around through use of cilia or undulating their body,
Trematoda (flukes): leaf shaped flatworms, endoparasistic(attach to internal organs), oral suckers sometimes with hooks that attach to vertebrate host, solid body filled with spongey connective tissue, hermaphroditic.
Turbellaria: dorsoventrally flattened, unsegmented, no body cavity, are solid, diffusion, digestive cavity, osmoregulatory system which is made up of a network of little tubes, and specialized flame cells, more complex sensory organs, move around through use of cilia or undulating their body,