- Rotifers are microscopic aquatic animals that can be found living in many freshwater environments. They are bilaterally symmetrical.
- They are multicellular animals with well-developed tissues and organs that have body cavities lined by a mesoderm. They have many specalised organs, which includes a complete one-way digestive tract containing a mouth and an ****.
- Rotifers are very unique as some species are ALL female, meaning they have to reproduce by asexual reproduction as sexual reproduction is not available.
- Rotifers are sometimes calles "wheel animals" because of the crown of cilia that surrounds the mouth. These cilia can be used for both locomotion and feeding. The cilia can move in a synchronised rhythm to gather food and even sort food - this is known as filter feeding.
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Phylum Annelida - Class Oligocheta
- Class Oligocheta is more commonly known as Earthworms.
- Earthworms can be found practically anywhere - they are aquatic, marine and terrestrial.
- Earthworms are segmented worms as their bodies are segmented both internally and externally into well defined segments. Internally, they are segmented by membranous partitions.
- Earthworms do not have a respiration system, so gaseous exchnage occurs through the worms moist skin.
- Earthworms have a coelom. A coelom is a fluid filled cavity between the intestines and the body wall that provides support and structure as it does not have an internal skeleton.
- Earthworms have a complete digestive system with a linear gut, oesophagus, crop, gizzard and intestines. They also have an ****, where waste material is excreted.
- Earthworms also have a well developed closed circulatory system.
- They are hermaphrodties; each individual being both male and female.
- Earthworms are quite complex because they have a nervous system that consists of a cerebral ganglia ( brain).
- They are made up of both circular muscles and longitudinal muscles.
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Phylum Annelida - Class Polychaeta
- Polychaeta are most commonly marine worms that swim freely in the sea.
- They are segmented worms, much like oligocheta, but each segment typicaly has a pair of paddle shaped appendages called Parapodia, which are used for locomotion and gas exchange; increase the surface area to allow more gas exchage through the skin.
- The heads of Polychaeta are highly modified, as they bear eyes and antennae. They may even have palps or tentacles which are used as sensory organs to help see as their eyes are very simple.
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Phylum Annelida - Class Hirudinea
- More commonly known as leeches, which are the most highly specalised type of annelids.
- They are mainly freshwater animals, however have been found in marine and terrestrial environments.
- They are mainly blood sucking parasites, that attach to skin using suckers which are located at the anterior and posterior of the animal. They have teeth made of chitin for biting.
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Phylum Mollusca - Class Bivalvia
- This class includes species such as clams, oysters and mussels.
- Charaterised by two shells which are hinged at the dorsal line.
- They have a hatchet shaped foot that extends out between the two shells to be used for locomotion.
- They have powerful adductor muscles which can close the shells together.
- They have great economic value - some are seen as aphrodisiacs and many contain pearls which are used for jewellery.
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Phylum Mollusca - Class Polyplacophora
- This class includes chitons.
- Around 800 different species of chitons, all of which are marine. They are a very conservative class due to their calcareous shell, with fossils dating back to thelate cambrian approx 500mya.
- They have primitive marine shells, segmented into 8 distinctive plate segments.
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Phylum Mollusca - Class Gastropoda
- Includes snails, slugs and nudibranchs.
- They are the largest and most diverse group of molluscs, with over 80% of molluscs being gastropoda.
- They can be found living in all environments; marine, freshwater, terrestrial and be either be predators or grazers.
- They have a distinct prominent head, with well developed eyes and with one or two pairs of tentacles.
- Torsion occurs in embronic development whih rotates the body and they have a centrally placed shell.
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Phylum Mollusca - Class Cephalopoda
- This class includes squids and octopods.
- They have a prominent head, surrounded by 8 to 10 tentacles which often bear suckers.
- They move by jet propulsion.
- Shell can be either external or internal.
- Marine predators.
- Highly developed sensory and nervous system, with well developed eyes.
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