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Characteristics of Phylum Annelida


1.- Unique annelid head and paired epidermal setae present (lost in leeches); parapodia present in the ancestral                      condition.


2.- Marine, freshwater, and terrestrial.


3.- Most free-living, some symbiotic, some ectoparasitic.


4.- Body bilaterally symmetrical, metameric, often with distinct head.


5.- Triploblastic body.


6.- Coelom (schizocoel) well developed and divided by septa, except in leeches; coelomic fluid functions as hydrostatic



7.- Epithelium secretes outer transparent moist cuticle.


8.- Digestive system complete and not segmentally arranged.


9.- Body wall with outer circular and inner longitudinal muscle layers.


10.- Nervous system with a double ventral nerve cord and a pair of ganglia with lateral nerves in each segment; brain a          pair of dorsal cerebral ganglia with connectives to ventral nerve cord.


11.- Sensory system of tactile organs, taste buds, statocysts (in some), photoreceptor cells, and eyes with lenses (in some);

      specialization of head region into differentiated organs, such as tentacles, palps, and eyespots of polychaetes.


12.- Asexual reproduction by fission and fragmentation; capable of complete regeneration.


13.- Hermaphroditic or separate sexes; larvae, if present, are trochophore type; asexual reproduction by budding in                  some; spiral cleavage and mosaic development.


14.- Excretory system typically a pair of nephridia for each segment; nephridia remove waste from blood as well as

       from coelom.


15.- Respiratory gas exchange through skin, gills, or parapodia.


16.- Circulatory system closed with muscular blood vessels and aortic arches (“hearts”) for pumping blood, segmentally

       arranged; respiratory pigments (hemoglobin, hemerythrin, or chlorocruorin) often present; amebocytes in blood              plasma.




Integrated principles of zoology / Cleveland P. Hickman, Jr. ... [et al.]. – 14th ed. p. cm.


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