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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).
Earthworms are environmental indicators of soil health. Earthworms feed on the decaying matter in the soil and analyzing the contents of their digestive tracts gives insight into the overall condition of the soil. The earthworm gut accumulates chemicals, including heavy metals such as cadmium, mercury, zinc, and copper. The population size of ...
Lamellibrachian tube worms have no gut and gain nutrients from chemoautotrophic bacteria living inside them. Feeding structures in the mouth region vary widely, and have little correlation with the animals' diets. Many polychaetes have a muscular pharynx that can be everted (turned inside out to extend it). In these animals the foremost few ...
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).
In polychaetes, these papillae are tiny, fleshy projections on the worm's body or parapodia, often associated with sensory and locomotive functions. [2] Some papillae have sensory receptors to help the worm detect environmental changes , such as touch, water currents , or chemical signals, and support movement by working with parapodia to aid ...
[6] [7] The story is a little more complex, because the blastopore itself does not directly give rise to the mouth of these worms. [1] This suggests that the last common ancestor of bilaterians had a similar gut configuration, and that the anus evolved after the mouth. [1] Exactly how a through gut formed from this blind gut is somewhat harder ...
However, 'earthworm' can be a source of confusion since, in most of the world, other species are more typical. For example, through much of the unirrigated temperate areas of the world, the "common earthworm" is actually Aporrectodea (= Allolobophora ) trapezoides , which in those areas is a similar size and dark colour to L. terrestris .
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 ...