Annelida
a class of animals belong. ing to the sub-kingdom articulata, the annulosa of some naturalists. They are sometimes called red-blooded worms, being the only invertebrated animals possessing this character. They are softbodied animals, mostly living in the water, sometimes in moist earth, but moist earth, ea but never parasitically within the bodies of other animals; the higher ones possessing limbs, though of a rudimentary character, which makes them resemble centipedes; while the lower ones, like the leeches, are wholly destitute of these appendages. The respiration is effected by external branchiæ, by internal vesicles, or by the skin itself. Contractile vessels supply the place of a heart. The nervous system consists of a single or double ventral cord, furnished with ganglia at intervals, and surrounding the œsophagus above.