Class Turbellaria
Basics: Turbellarians are free living organisms that live in an aquatic setting, both freshwater and marine. Turbellarians are named after the turbulence cause from the beating of their cilia on water. These organisms are either predators or scavengers. Known as flat-worms.
Body Wall: Turbellarians have an epidermis that is exposed to the outside world. The epidermis may have cilia or microvilli. Between the epidermis and the mesodermally derived tissues is a basement membrane. Under the basement membrane lies an outer layer of circular muscle and an inner layer of longitudinal muscle. Between their dorsal and ventral surfaces these organisms have muscles that lie dorsoventrally and obliquely. There are also parenchymal cells that are located between the longitudinal muscles and the gastrodermis.
The endodermally derived gastrodermis is the inner most tissue layer, it is composed of single layer of cells. The gastrodermis functions in secreting enzymes that help in digestion, and the gastrodermis also absorbs the products of digestion.
There are several types of glandular cells on the ventral surface of these organism. One type would be rhabdites, which are rodlike cells that protect the body by creating a mucus sheath. Adhesive glands open up to produce a chemical, which then helps the organism stick to its substrate. Releaser glands secrete a chemical that help dissolve the attachment of the organism.
The endodermally derived gastrodermis is the inner most tissue layer, it is composed of single layer of cells. The gastrodermis functions in secreting enzymes that help in digestion, and the gastrodermis also absorbs the products of digestion.
There are several types of glandular cells on the ventral surface of these organism. One type would be rhabdites, which are rodlike cells that protect the body by creating a mucus sheath. Adhesive glands open up to produce a chemical, which then helps the organism stick to its substrate. Releaser glands secrete a chemical that help dissolve the attachment of the organism.
Locomotion: Turbellarians moving through using cilia and muscular undulations. Under the epithellium are layers of muscle cells, The outer layer runs in a circular direction and the inner layer runs in a longitudinal one. The muscles of tuberarians run obliquely which helps them twist and turn with ease. Dorsal muscles are neccassary for maintaining a flat worms flatten shape . Muscus is produced as the turbellarians move to help with adhesion and traction of the cilia. The cilated ventral surface and flattened bodies helps the turbellarians locomotion
Digestion and nutrition: Digestive cavities differ from each turbellarians , They can be unbranched chambers, highly branched or lobed. The pharynx of turbellarians function as a ingestive organ that varies in structure , From a simple ciliated tube to a complex organ formed from the folding of muscle layers. most turbellarians are carnivores (some are herbivores) The chemoreceptors on their heads help them track food. The pharyngeal glands In turbellarians secret enzymes that help break down food so the pharynx can take it in. Phagocytic cell engulf small units of food and digestion is finalized by intracellular vesicles.
Exchanges with the Enviroment: The turbellarians do not have respiratory organs, so they exchange carbon dioxide and oxygen through body wall diffusion. The Protonephridia are networks of tubules that run the length of tubellarians, many branches of the tubules that originate in the prenchyma as flame cells line the sides of the tubellarians. The nephridiopore is an opening in which the tubules can merge and open to the outside of the body.
Nervous System and Sense Organs: the nervous system found in flatworms are nerve plexus. The neurons are organized into sensory, motor , and association types. Turbellarians respond to environmental stimuli in different ways do to their tactile and sensory cells.
Reproduction and Development: Most turbellarians reproduce asexually through transverse fission. Zooids are the animals that result from reproduction, after the organisms separate they are able to regenerate any missing body parts. In other occasions zooids remained attached until they are fully developed, they later separate into independent individuals.
Turbellarians are monoecious, and their reproductive systems lie in the mesodermal tissues. Testesm, which produce sperm, lie in multiple pairs along side of the organism. From the testes leads a sperm duct, also called the vas deferens. The duct leads into a seminal vessical, then into the protrusible penis. The penis projects into the genital chamber. The female system also has multiple ovaries. From the ovaries leads a oviduct, the duct leads to the genital chamber. The genital chamber is exposed to the outside through the genital pore.
Turbellarians tend to cross fertilize between each other to produce a greater genetic variation. When cross fertilization occurs one partner is inserted into the copulatory sac of the other partner. The sperm makes its way into the genital chamber, through the oviducts, until it reaches the ovaries where fertilization occurs. The eggs may result with or without a gel-like mass. A cocoon, hard capsule, may enclose the eggs. These cocoons use a stalk to attach to a substrate, within the cocoon are multiple embryos. There are two different kinds of cocoons that are laid, summer and autumn capsules. Summer capsules create an immature organisms and tend to hatch in 2-3 weeks. Autumn capsules a=have thick coverings that can resist harsh conditions, and they hatch after overwintering. When turbellarians develop some go through a stage called Muller's larva. this larva has ciliated extensions that aid in feeding and movement. The larva later attaches to a substrate and manages to mature.