are annelids specialized cells
a) Different from other annelids in well-differentiated head with specialized sense organs, paired parapodia, and no clitellum. b) Many setae, usually arranged in bundles on parapodia. c) No permanent sex organs, hermaphroditic, metamorphosis involving trochophore larva. The phylum Annelida, segmented worms, is characterized by the possession of a coelom (body cavity), setae (moving bristles), and a body divided into segments by transverse rings. The class Polychaeta, meaning many hairs, is a large and extremely diverse group with more than 6,000 living species. 4) Form and Function. a) Different from other annelids in well-differentiated head with specialized sense organs, paired parapodia, and no clitellum. b) Many setae, usually arranged in bundles on parapodia. c) No permanent sex organs, hermaphroditic, metamorphosis involving trochophore larva. Annelids have a true coelom, that is, one that is lined with cells originating from the embryonic mesoderm. The coelom is fluid-filled, which creates hydrostatic (water) pressure and acts as a hydrostatic skeleton. Respiration in annelids occurs primarily through their moist skin, although certain species have evolved specialized gills or use paired projections called parapodia in gas exchange. The annelid excretory system consists of paired nephridia found in each segment which function in excreting nitrogenous waste. They also have a complete, one-way digestive tract with a mouth and anus. The digestive tract is not segmented. Respiration in annelids occurs primarily through their moist skin, although certain species have evolved specialized gills or use paired projections called parapodia in gas exchange. The entire purpose of the circulatory system is to move oxygen and nutrient-rich blood to where it needs to go. Blood is a liquid tissue that is composed of a fluid called plasma and three types of specialized cells: red blood cells, white blood cells, and platelets. The early embryonic development of all annelids is essentially similar. Though eggs can range in size from less than .05 mm in diameter to more than 1 mm, they all show a sequence of spiral cleavage to the 64-cell stage. The tissue layers are formed from a few well-defined cells in the blastula. They secrete and live in their own encasing tube that is made of substances from specialized cells of their epidermis. This tube base may contain calcium carbonate, complex mixtures of proteins and polysaccharides, and/or sticky mucus, to which sediment such as sand and broken shells then adheres (Campbell, 1996). Nephridia are segmentally arranged, paired excretory tubules of many invertebrates, notably the annelids. In a broad sense, any tubule specialized for excretion and/or osmoregulation; with an external opening and with or without an internal opening.
No