![]() Phylum Mollusca is a very diverse (85,000 species) group with a dramatic variety of forms, ranging from large predatory squids and octopuses, some of which show a high degree of intelligence, to grazing forms with elaborately sculpted and colored shells. The mantle cavity develops independently of the coelomic cavity. Mollusks are eucoelomate, but the coelomic cavity is restricted to a cavity around the heart in adult animals. The mantle is the dorsal epidermis in mollusks shelled mollusks are specialized to secrete a chitinous and hard calcareous shell. Additionally, a tongue-like organ called a radula, which bears chitinous tooth-like ornamentation, is present in many species and serves to shred or scrape food. Mollusk species that are exclusively aquatic have gills for respiration, whereas some terrestrial species have lungs for respiration. This includes the digestive, nervous, excretory, reproductive, and respiratory systems. The visceral mass is present above the foot, in the visceral hump. The foot is the ventral-most organ, whereas the mantle is the limiting dorsal organ. The foot is a retractable as well as an extendable organ. In shelled mollusks, this foot is usually the same size as the opening of the shell. The muscular foot is used for locomotion and anchorage, and varies in shape and function, depending on the type of mollusk. There are many species and variations of mollusks this illustration shows the anatomy of an aquatic gastropod. For the sake of this course, we will only focus on the groups and material for which you are responsible.įigure 2. Ecdysozoans include the phyla Nematoda (roundworms) and Arthropoda, the largest animal phylum in the world that include the subphyla Hexapoda (insects), Myriapoda (centipedes and millipedes), Crustacea (crustaceans), and Chelicerata (spiders, ticks, scorpions, etc.). ![]() Phyla of this superphylum include Platyhelminthes ( platy = flat, helminth = worm flatworms), Rotifera (rotifers), Nemertea (ribbon worms), Mollusca (mollusks), and Annelida (segmented worms). It also indicates the beginning of cephalization, the evolution of a concentration of nervous tissues and sensory organs in the head of the organism, which is where it first encounters its environment. These phyla are also bilaterally symmetrical, meaning that a longitudinal section will divide them into right and left sides that are symmetrical. The lophotrochozoans are triploblastic and thus possess an embryonic mesoderm sandwiched between the ectoderm and endoderm which is not found in the diploblastic cnidarians. Trochophore larvae are characterized by two bands of cilia around the body. The lophophores are a set of ciliated tentacles surrounding the mouth. As lophotrochozoans, the organisms in this superphylum possess either a lophophore or trochophore larvae.
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