Which phylum has bilateral symmetry

The earthworm annelid is a coelomate because it has a true coelom within its mesoderm layer. 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. There are some fish species, such as flounder, that lack symmetry as adults. However, the larval fish are bilaterally symmetrical. Learning Objectives Differentiate among the ways in which animals can be characterized by body symmetry. Key Points Animals with radial symmetry have no right or left sides, only a top or bottom; these species are usually marine organisms like jellyfish and corals.

Only sponges phylum Porifera have asymmetrical body plans. Some animals start life with one type of body symmetry, but develop a different type as adults; for example, sea stars are classified as bilaterally symmetrical even though their adult forms are radially symmetrical. Triploblasts that do not develop a coelom are called acoelomates: their mesoderm region is completely filled with tissue.

Flatworms in the phylum Platyhelminthes are acoelomates. Eucoelomates or coelomates have a true coelom that arises entirely within the mesoderm germ layer and is lined by an epithelial membrane. This coelomic cavity represents a fluid-filled space that lies between the visceral organs and the body wall.

It houses the digestive system, kidneys, reproductive organs, and heart, and it contains the circulatory system. The epithelial membrane also lines the organs within the coelom, connecting and holding them in position while allowing them some free motion.

Annelids, mollusks, arthropods, echinoderms, and chordates are all eucoelomates. The coelom also provides space for the diffusion of gases and nutrients, as well as body flexibility and improved animal motility. The coelom also provides cushioning and shock absorption for the major organ systems, while allowing organs to move freely for optimal development and placement.

The pseudocoelomates have a coelom derived partly from mesoderm and partly from endoderm. Although still functional, these are considered false coeloms. The phylum Nematoda roundworms is an example of a pseudocoelomate.

Bilaterally symmetrical, tribloblastic eucoelomates can be further divided into two groups based on differences in their early embryonic development. These two groups are separated based on which opening of the digestive cavity develops first: mouth protostomes or anus deuterostomes.

Early embryonic development in eucoelomates : Eucoelomates can be divided into two groups based on their early embryonic development. In protostomes, part of the mesoderm separates to form the coelom in a process called schizocoely. In deuterostomes, the mesoderm pinches off to form the coelom in a process called enterocoely. The coelom of most protostomes is formed through a process called schizocoely, when a solid mass of the mesoderm splits apart and forms the hollow opening of the coelom.

Deuterostomes differ in that their coelom forms through a process called enterocoely, when the mesoderm develops as pouches that are pinched off from the endoderm tissue. These pouches eventually fuse to form the mesoderm, which then gives rise to the coelom. Cell Division 2: Molecular Biology 1. Metabolic Molecules 2. Water 3. Protein 5. Enzymes 6. Cell Respiration 9.

Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1.