Their body surface is distinctly marked out into segments or metameres [metamerically segmented] and, hence, the phylum name Annelida Latin, annulus: little ring. They exhibit organ-system level of body organization. They are coelomate [true body cavity]. This allows true organs to be packaged in the body structure. They are bilateral symmetric and triploblastic.
They possess longitudinal and circular muscles which help in locomotion. Aquatic annelids like Nereis possess lateral appendages, parapodia , which help in swimming. A closed circulatory system is present. Nephridia sing. Neural system consists of paired ganglia sing. Nereis , an aquatic form, is dioecious [Sexes are separate], but earthworms and leeches are monoecious [having both the male and female reproductive organs in the same individual].
Reproduction is sexual. Phylum — Arthropoda Insects , arachnids and crustaceans are members of the largest category of creatures on the planet: arthropods. Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs and some They exhibit organ-system level of organisation.
They are bilaterally symmetrical, triploblastic, segmented and coelomate The coelomic cavity is blood-filled. The body of arthropods is covered by chitinous The body consists of head, thorax and abdomen.
There is an open circulatory system , and so the blood does not flow in well defined blood vessels. Respiratory organs are gills, book gills, book lungs or tracheal system. Sensory organs like antennae, eyes compound and simple , statocysts or balance organs are present. Excretion takes place through malpighian tubules. They are mostly dioecious.
Fertilisation is usually internal. They are mostly oviparous. Development may be direct or indirect. Arachnids Spiders, harvestmen, mites, ticks and other arachnids are members of the class Arachnida. Crustaceans Crustaceans make up a large group of arthropods that includes animals such as crabs, lobsters, crayfish and shrimp.
They breathe with gills and have two pairs of antennae. Insects In general, insects have three-part bodies, six jointed legs, compound eyes and two antennae. Bees, wasps, beetles, mosquitoes, flies, grasshoppers, ants, butterflies and moths, and dragonflies and damselflies are common types of insects. Phylum — Mollusca Mollusca are the second largest animal phylum.
They are terrestrial or aquatic. They exhibit organ-system level of organization. They are bilaterally symmetrical, triploblastic, coelomate animals. There is little segmentation. They have an open circulatory system and kidney-like organs for excretion. The anterior head region has sensory tentacles.
The mouth contains a file-like rasping organ for feeding, called radula. They are usually dioecious and oviparous with indirect development. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump.
A soft and spongy layer of skin forms a mantle over the visceral hump. Examples are octopus , snails and mussels. Phylum — Echinodermata These animals have an endoskeleton of calcareous ossicles [calcium carbonate structures] and, hence, the name Echinodermata spiny skinned organisms. They are exclusively free-living marine animals with organ-system level of organisation. They are triploblastic with a coelomic cavity [coelomate animals]. The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.
Water-driven tube system [water vascular system] are used for locomotion, capture and transport of food and respiration. They are triploblastic and coelomate animals. Digestive system is complete. An excretory system is absent. Sexes are separate. Fertilisation is usually external. Development is indirect with free-swimming larva. Phylum — Hemichordata Hemichordata was earlier considered as a sub-phylum under phylum Chordata. But now it is placed as a separate phylum under non-chordata.
This phylum consists of a small group of worm-like marine animals with organ-system level of organisation. They are cylindrical [bilaterally symmetrical], triploblastic, coelomate animals. The body is Circulatory system is of open type. Respiration takes place through gills. Excretory organ is present. Fertilisation is external. Development is indirect. Examples: Balanoglossus and Saccoglossus.
Phylum — Chordata Animals belonging to phylum Chordata are fundamentally characterised by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits. They are bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation.
They possess a post anal tail and a closed circulatory system. Contained Within. Subphyla or Classes Contained. Estimated Number of Described Species. Animal Phyla. Not all fossil forms are contained, such as those that remain problematic, were recently discovered, and for which there still exists controversy, for example, see: Cambrian Explosion Lobopodia Extant Animal Phyla. Classes: Archiacanthocephala, Eoacanthocephala, Palaeacanthocephala.
Kingdom Animalia Subkingdom Eumetazoa. Classes: Acoela, Nemertodermatida. Cambrian mya to Present. Classes: Polychaeta, Clitellata, Myzostomida, Archiannelida. Trilobitomorpha , Chelicerata , Myriapoda , Hexapoda , Crustacea. Lower Cambrian to Present. Domain Eukaryota Kingdom Animalia. Complex: Two main groups are Inarticulata and Articulata. Some extant; prodigious fossil species. Ordovician to Present. Classes: Stenolaemata, Gymnolaemata, Phylactolaemata.
Cambrian to Prsent. Classes: Archisagittoidea, Sagittoidea. Some extant. Lower Cambrian mya to Present. Subphyla:Tunicata, Cephalochordata, Vertebrata. More than 60, Precambrian mya to Present. Subphyla: Anthozoa, Medusozoa. Some 11, Domain Eukaryota Subkingdom Eumetazoa. Classes:Tentaculata, Nuda. Some In other words, the coelom white is completely enclosed within the mesoderm layer blue. Coelomates have more complex internal organs and a muscular gut intestines derived from the mesoderm.
Gastrulation in protostome and deuterostome embryos. In protostomes, the initial site of ingrowth or invagination blastopore becomes the mouth. In deuterostomes, the initial site of ingrowth or invagination blastopore becomes the anus. Site Of Embryo Development. Domestic Fowl. Four methods of sex determination in animals. Two examples of marine sponges. The surface contains numerous pores connected to canals and chambers lined by flagellated cells called choanocytes.
Sponges are filter-feeders, taking in microscopic plankton by miniature currents created by the choanocytes. A marine stony coral showing the numerous calcareous chambers that were once occupied by tentacle-bearing polyps. Colonies of stony corals are important reef builders in warm, tropical waters. Reef corals may form 1 fringing reefs extending out to 0.
A wide variety of marine invertebrates, including sponges, jellyfish, sea anemones, corals, gastropods and turbellarians harbor within them golden spherical cells termed zooxanthellae.
The photosynthetic activity of these symbiotic algal cells is vital to the survival of the individual coral animals and to the entire reef ecosystem. The zooxanthellae include several species of unicellular algae in the order Zooxanthellales within the algal division Pyrrophyta also spelled Pyrrhophyta.
The term zoochlorellae refer to several species of symbiotic unicellular green algae of the division Chlorophyta. Along the Pacific coast of North America, zoochlorellae produce the greenish color in sea anemone tentacles.
A pristine tide pool along the Oregon coast of North America. Purple sea urchin, B. Blood Starfish, C. Coralline red algae, D. Six-rayed starfish, and E. Sea anemone. The tentacles of the sea anemone contain zoochlorellae, symbiotic green cells of the algal division Chlorophyta.
A sea anemone and its symbiotic anemone fish. Three comb jellies ctenophores. Comb jellies resemble tiny hot air ballons the size of a walnut or smaller with eight rows of fused cilia comb plates extending down the sides. They propel themselves mouth first by the eight rows of comb plates.
Ctenophores superficially resemble miniature medusae phylum Cnidaria ; however, most medusae arise asexually from a polyp generation and ctenophores have no polyp stage in their life cycle. Tentacles extending from the mouth contain "glue cells" or colloblasts containing spiral threads which snare small fish and crustaceans with a gluelike material.
With the exception of one species, ctenophores do not have the stinging organelles nematocysts of jellyfish and sea anemones. During the day, ctenophores flash prismatically as their ciliary plates refract light; at night they are often bioluminescent, glowing like little lamps. Is this a 1 wet pajama draw string, 2 a long noodle, or 3 a human tapeworm? The answer is 3 , a 20 inch 50 cm human tapeworm. The small head or scolex from which the segments progottids arise is clearly visible in the photograph.
The presence of a scolex is good evidence that the entire worm has been discharged from the host's intestine. Each proglottid contains a complete male and female reproductive system. In fact, one proglottid may contain literally thousands of eggs. Magnified view 30X of the human tapeworm shown in the above photograph showing the anterior end or scolex.
The scolex bears four circular suckers which firmly anchor the tapeworm to the host's intestinal wall. The scolex produces proglottids by budding, which gradually enlarge as more segments are formed. Tardigrades belong to a remarkable phylum of minute multicellular animals. They are adapted to extreme conditions, some of which are more severe than any earth environment. Does their origin defy natural selection? Lateral side view of the exoskeleton of an aquatic tardigrade Hypsibius sp.
There are 4 pairs of stout, stumpy legs, each tipped with several slender claws. The name "water bear" refers to its deliberate "pawing" sort of locomotion. Thomas Huxley, English naturalist and good friend of Charles Darwin, gave tardigrades this name in Photographed with a Sony W digital camera through an Olympus laboratory grade compound microscope x magnification. An aquatic tardigrade of the genus Hypsibius. Its length is approximately micrometers microns , about the same length as the hair follicle mite Demodex brevis.
It is much smaller than a grain of common table salt NaCl. The image was enhanced with Photoshop to bring out detail of the claws. Magnification x. M4V file. Mesozoic rock from Arizona showing numerous brachiopods, evidence of a shallow sea along a continental shelf. An articulate hinged brachiopod. Gastropods shells cowries and cone shells from the south Pacific island of Moorea and Tetiaroa Atoll in French Polynesia.
The lower right shell is from a land snail. The common garden snail Helix aspersa. This snail was introduced into California in the s by European immigrants for use as food. It turned out to be a poor substitute for the edible snail escargot served in French restaurants Helix pomatia. It has since become well-established and a major nuisance in California gardens.
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