The acanthocephalans number about 1150 species. They are worm-like creatures without a gut and all of them parasitic. They have elongate, dorso-ventrally flattened forms, ranging from 2mm to approximately 1 metre in length. The most characteristic feature of this phylum is a spiny proboscis which can be everted to act as an attachment organ.
The term acoelomates means "without coeloms", the coelom being a body space surrounded by an extra layer of cells, the mesoderm.
The most important acoelomates are the flat worms contained in the phylum Platyhelminthes, including the free-living Turbellaria, the Trematoda or liver flukes and the Cestoda or parasitic tapeworms. Other phyla included are Nemertina, the ribbon worms, Orthonectida, Rhombozoa and Gnathostomulida, members of which are typically worm-like creatures sometimes classed together as polychaetes, or bristly worms.
Classification in this area of the animal kingdom is unclear.
The phylum Annelida are the segmented worms. The three main groups are the Polychaeta, such as the lugworms, some of which are free living but others living in tubes, the Oligochaeta such as the earthworm and the Hirudinea, which are the leeches. All have bodies supported by internal pressure, a hydrostatic skeleton, and are divided into segments.
This category is for sites devoted to the largest of all animal phyla, Phylum Arthropoda. This phylum includes the insects, spiders, mites and ticks, crustaceans, centipedes, millipedes, isopods, and trilobites.
The arthropods typically share a common body plan. They have an outer tough cuticle and they are divided into segments, each of which may carry jointed appendages. Often there is a head, thorax or trunk and an abdomen. They are an amazingly successful group of creatures and have been around since the Precambrian, 600 million years ago.
The phylum Brachiopoda, or Lamp Shells, contains about 300 living species and about 12,000 extinct species found in the fossil record. Superficially they resemble bivalve molluscs like the cockle, but their internal basic structure is very different. Brachiopods are suspension feeding, marine, benthic lophophorates in two higher taxa, Inarticulata and Articulata.
Bryoza means "moss animals" and there are two distinct phyla, the Entoprocta consisting of about 150 species and the Ectoprocta with about 4000. Some are solitary and some colonial and the individual animals superficially resemble corals, though their body structure is quite different. Some colonies are branched and resemble seaweed but others are encrusting, forming mats on the surface of seaweeds or stones.
Phylum of small, somewhat fish-like, marine invertebrates with one or two pairs of lateral fins and a large horizontal tailfin. They poison their prey with a toxin produced by bacteria carried in their head. There are about 200 known species but there may be many more in the deep ocean.
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The Phylum Chordata, the chordates, is the part of the Animal Kingdom containing organisms that possess a structure called a notochord, at least during some part of their development. The best known chordates are the vertebrates (fishes, amphibians, reptiles, birds, mammals). The vertebrates and hagfishes together comprise the taxon Craniata. Also included in the phylum are the tunicates (Urochordata) and lancelets (Cephalochordata). Some extinct groups are also assigned to this phylum.
The phylum Echinodermata consists of about 7000 living species but there are a further 13,000 extinct species dating back to the Cambrian. They are basically pentaradially symmetric which means that they are five-sided, and all live in the sea. They include the sea lilies, the starfish, the sea daisies, the brittle stars, the sea urchins and the sea cucumbers.
Echiurans are marine worms whose bodies are not segmented. They have an extensible proboscis and a set of small hooks at the posterior end. There are about 150 species, mostly inhabiting warm shallow seas and burrowing in the soft sediment.
Phylum Gastrotricha includes about 430 species worldwide. Members are small to microscopic, free-living, acoelomate, aquatic worms.
Members of this phylum are marine worms less than 1mm long. They have no body cavity but do have a pair of jaws which gives them their name (gnathos is Greek for jaws) and a blind gut with a mouth but no anus. They are very common in marine sediments where they eat bacteria, fungi and protists, and there are about 80 known species.
The hemichordates form a small phylum of a few hundred species. They are worm-like creatures with their bodies divided into 3 parts, a pre-oral lobe, a collar and a trunk. Their name means “half chordate” and they have certain primitive features that resemble those of true chordates. The three main groups are the Enteropneusta, or acorn worms, the Pterobranchia and the Graptolithina.
The Kinorhynchians ("moveable-snouts") are a group of small, marine invertebrates typically less than 1 mm in length and are commonly known as mud dragons. There are about 150 recorded species, found on the sea bottom in habitats ranging from the intertidal zone to the deep ocean.
The lophophorates are a group of marine creatures united by possessing a "lophophore" which is a characteristic feeding organ which roughly resembles a sugar scoop fringed with cilia. There are three major groups of lophophorates, the Brachiopoda, Bryozoa and Phoronida, each of which is considered to be a separate phylum.
This category provides general information about minor protostome phyla, including Tardigrada, Onychophora, Echiura and Sipuncula, and links to categories specific to each phylum.
The Molluscs are a large phylum of about 100,000 species. They are characterised by the shell and the mantle that secretes it, the radula which is a peculiar file-like feeding structure, and the moluscan gills. The phylum includes, as well as certain primitive groups, the Bivalves which include the cockle and mussel, the Cephalopods which include the cuttlefish, squid and octopus, and the Gastropods which include the limpet, whelk, snails and slugs.
Nematodes are the second most diverse animal phylum (after the arthropods), with about 20,000 species. Free-living nematodes are abundant in soils and sediments, where they feed on bacteria and detritus. Some nematodes are plant parasites, including organisms that cause disease in economically important crops. Others parasitize animals (including humans). Well-known parasitic nematodes include hookworms, pinworms, Guinea worm (genus Dracunculus), and intestinal roundworms (genus Ascaris).
Most nematodes are long, slender, almost featureless externally, tapered at both ends, and round in cross section.
The phylum Nematomorpha comprises the Hair Worms, so called because they are remarkably thin though they can be up to a metre in length. They adults are free-living but the larvae are parasites, mainly of arthropods.
The phylum Nemertea, also known as Nemertini or Rhinchocoela, consists of about 900 species. They are known as Ribbon Worms and are mostly cylindrical though some are flat. They are mostly marine, living on the sea bed, but some live in fresh water and a few in moist places on land. They have a proboscis that they can shoot out, propelled by hydrostatic pressure.
The phylum Onychophora comprises about 80 species in two families, one living in the tropics and one in the Southern Hemisphere. They are commonly known as Velvet Worms and look rather like slugs with 14 to 43 pairs of legs, or long caterpillars. They live in damp places and are often brightly colored with an iridescent surface and can be up to 15 centimetres long.
Phoronida is a small phylum consisting of about 12 species. These "horseshoe worms" are U-shaped and live in shallow marine sediments. They filter-feed by means of a ciliated organ called a lophophore, as do the Brachiopods and Bryozoans.
Phylum in the animal kingdom containing a single known species, Trichoplax adhaerens, which creeps over the surface of seaweeds in tropical seas. Placozoans are simple creatures without a clearly defined shape and sometimes behave as if they were colonies of individual organisms.
The phylum Platyhelminthes comprises about 20,000 species. They are commonly known as flatworms and include free-living aquatic flatworms (class Turbellaria), as well as the mostly parasitic flukes and tapeworms (classes Monogenea, Trematoda, and Cestoda). Collectively, they are primitive organisms that are flat, soft-bodied, and symmetrical.
Recent molecular studies suggest that the Platyhelminthes as a whole may have arisen as two independent groups from different ancestral groups. If this is correct, most of the flatworms may belong to the Lophotrochozoa, a large group within the animal kingdom that includes molluscs and earthworms, while the rest are much more primitive.
The Phylum Porifera includes the animals commonly known as sponges. This is a diverse group, with about 5000 known species. Most are marine, but around 150 species live in fresh water.
Considered the simplest of the animals, the cells of sponges are organized into tissues, but the tissues are not organized into organs. Their bodies are a sort of loose aggregation of different kinds of cells. Sponges are characterized by a unique feeding system involving a system of pores and canals through which water passes.
The four Classes of sponges are Calcarea (Calcispongiae), Hexactinellida (Hyalospongiae), Demospongiae, and Sclerospongiae (considered by many to be a subclass of Demospongiae).
Information about the pseudocoelomate group (also known as Aschelminthes or Nemathelminthes) of invertebrates, a group of about 10 separate phyla that are often clustered together. Most members of the group are soft-bodied worms, and many of them are microscopic. The most important phylum in the group is Phylum Nematoda, the roundworms. Other phyla in this group include Kinorhyncha, Rotifera, Acanthocephala and Nematomorpha.
This category is for sites devoted to Phylum Cnidaria (Coelenterates) and Phylum Ctenophora.
The phylum Rotifera comprises about 1800 species. Al the members are aquatic and are less than 1 millimetre in length. They are strange-looking organisms with lobes, bulges and cilia.
The phylum Sipuncula includes about 320 species of marine creature, some resembling sea cucumbers and others sprouting potatoes, with their tentacled mouths at the end of the sprouts. They are thought to be related to the molluscs, annelids and arthropods.
This category contains sites about the phylum Tardigrada.
Submit sites that concern members of the animal kingdom, but not strictly to Tardigrades, to the parent category Animalia or the most suitable subcategory of Animalia.
Tardigrades, also called water bears, are a phylum of microscopic, aquatic animals with segmented bodies. These creatures are related to arthropods and onychophorans. They are known for their adaptation to extreme environments using a low metabolic state called cryptobiosis.