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. Homeowners spend more money on eradicating this creature than all other invetebrate pests combined. The head has two pairs of retractile tentacles. The longer, upper tentacles each have an eye at the tip.
The shorter, lower tentacles bear chemosensory organs equivalent to taste and smell. The ventral side contains a mouth with a rasping tongue radula for feeding. This snail is hermaphroditic bisexual with both male and female sex organs. Although capable of self fertilization, the normal method is cross fertilization between two mating partners. Polyp Obelia and Portuguese man-of-war also have medusa stage What is the most commonly seen life stage of the Scyphozoa? What is the only life stage shown be members of the Anthozoa?
Phylum Platyhelminthes p. Bilateral symmetry allows complex movements such as crawling, burrowing, flying, or swimming. Cephalization for sensing. What are the functions of the ocellus, intestine, and pharynx? Ocelli eyespots detect light; intestine gastrovascular cavity digests food; pharynx ingests food and is also used for excretion. What is the function of the opisthaptor? Opisthaptor in Monogenea is located at posterior and used to attach to fish host. What is the importance of the cercaria?
Cercaria are the motile larvae of Trematoda that escape from intermediate host to penetrate primary host. Provide the functions of the scolex and proglotids? The scolex of Cestoidea attach to host intestines; proglotids produce eggs. What life stage causes the Hydatid cyst? Late Gut Development: In protostomes, the anus is formed by tunnelling of the gut into the embryo.
But in deuterostomes, the formation of the mouth is by the gut tunnelling into the embryo. Development of Coelom: In protostomes, the body cavity or the coelom is formed by splitting of the mesodermal layer. Thus, they are schizocoelomates since the coelom is created by schizocoely.
On the other hand, the deuterostomes are enterocoelomates where the body cavity or the coelom is formed by the mesoderm pinching off from the gut. Type of Cleavage: In protostomes, the kind of cleavage is determinate, meaning that the blastomere of the early embryonic stage is incapable of developing into independent embryos.
But deuterostomes undergo indeterminate division whereby the early blastomeres can develop into complete embryos. Nervous System: Protostomes have a solid, ventral nerve cord. In deuterostomes, the nerve cord is hollow, with some possessing pharyngeal gill slits.
Body Complexity: Deuterostomes have a more evolved and complex body organisation than the protostomes. This exoskeleton clearly endowed arthropods with great selective advantages: i. Protection - arthropods are armored against a. Strength - for a given quantity of skeletal material, a hollow tubular structure is stronger than a solid rod of material, as is found in our own skeletons.
There is a basic problem with locomotion if the animal is surrounded by a hard shell. This problem was solved by the evolution of jointed appendages.
These muscles are striated, not smooth as in the lophotrochozoa, and are bands associated with the segments - circular muscles wrapping around the body are lost entirely. With the loss of body flexibility, the coelom became useless as a hydrostatic skeleton SO: 3. Coelom reduced to portions of the reproduction and excretory system. Circulatory system open and uses the coelom as a chamber in which internal organs are bathed directly in body fluids. Usually with a pair of compound eyes.
As the name suggests, compound eyes are composed of many similar, closely-packed facets called ommatidia which are the structural and functional units of vision.
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