Search results
Results from the WOW.Com Content Network
Earthworms have a central nervous system consisting of two ganglia above the mouth, one on either side, connected to an axial nerve running along its length to motor neurons and sensory cells in each segment. Large numbers of chemoreceptors concentrate near its mouth. Circumferential and longitudinal muscles edging each segment let the worm move.
Earthworms and their kin, in the subclass Oligochaeta, lack eyes but have photoreceptor cells in the skin, especially in the dorsal portion of the anterior end. They also lack parapodia and appendages on the prostomium, the body and the periproct (terminal segment on which the anus is located).
Nearly all polychaetes have parapodia that function as limbs, while other major annelid groups lack them. Parapodia are unjointed paired extensions of the body wall, and their muscles are derived from the circular muscles of the body. They are often supported internally by one or more large, thick chetae.
Oligochaetes are well-segmented worms and most have a spacious body cavity (coelom) used as a hydroskeleton.They range in length from less than 0.5 mm (0.02 in) up to 2 to 3 metres (6.6 to 9.8 ft) in the 'giant' species such as the giant Gippsland earthworm (Megascolides australis) and the Mekong worm (Amynthas mekongianus).
The embryological origin of the mouth and anus is an important characteristic, and forms the morphological basis for separating bilaterian animals into two natural groupings: the protostomes and deuterostomes. In animals at least as complex as an earthworm, a dent forms in one side of the early, spheroidal embryo.
Gardners beware -- the invasive Amynthas agrestis, also known as the Asian jumping worm, could be wiggling around a garden near you. These worms are known for their insatiable appetite and ability ...
Microscope photograph of a parapodium from a specimen of Arctonoe sp. showing the internal acicula that support the two lobes of the parapodium. This parapodium is from a Museums Victoria specimen. Most species of polychaete annelids have paired, fleshy parapodia which are segmentally arranged along the body axis. Parapodia vary greatly in size ...
The structure and physiology of the calciferous glands of earthworms are described. Many hypotheses had been advanced for their function; Darwin believed them to be primarily for excretion and secondarily a digestion aid. Thin leaves are seized with the mouth, while thick ones are dragged by creating a vacuum.