The Phylum Nematomorpha

Etymology:- From the Greek Nema for Thread and Morphe for shape or form.

Characteristics of Nematomorpha:-
1)Bilaterally symmetrical, and vermiform.
2)Body has more than two cell layers, tissues and organs.
3)Body monomeric with a pseudocoelomic cavity.
4)Body possesses a through gut which is normally non-functional.
5)Body possesses in a cuticle and longitudinal muscles.
6)Has a intra-epidermal nervous system with an anterior nerve ring.
7)Has no circulatory system (no blood system)
8)Reproduction normally sexual and gonochoristic.
9)Adults non-feeding, larvae endoparasitic.
10)Aquatic or moist soils, mostly fresh-water.

The nematomorpha are relatively long thin worms (1 to 3 mm diametre and 10cm or 4 in to 1m or 3 ft in length), they are a smallish phylum with about 240 known species. They are called Horsehair Worms, because they used to be found in horse watering troughs and they look like the hairs from a horses tail. Thus before the advent of modern science it was believed they arose spontaneously from hairs from horses tails that fell into the water.


They are closely related to the nematodes, and like them they move by muscularly induced undulating waves passing along the body. The adults do not feed, nor do they live long. Their only function in the life of the species is reproduction. Females are normally sedentary and are searched for by the more active males who curl themselves around the females and deposit a spermatophore near the females cloaca. The sperm then swim into the females seminal receptacle from where they can later fertilise her eggs. The female deposits her eggs in long strings, all stuck together and tangled around aquatic plants.

The eggs take from 15 to 80 days to hatch. The larvae are free swimming and look like the Kinorhyncha with scalid spines around their heads and a set of oral stylets that can be everted or retracted into the body cavity, and not at all like their parents. They are parasites of invertebrates, though not necessarily aquatic ones. The larvae have a better developed digestive system than the adults but it is likely they derive most of their nutrition from nutrients absorbed through their body wall.

Development of the larvae can takes from a few weeks to several months, and there can be several generations per year. It is assumed that the mature larvae somehow manipulate their non-aquatic hosts into seeking out water, though how this is accomplished is unknown. Most species inhabit freshwater, there is one marine genus which parasitises crabs. In some species, individuals that mature in autumn form cysts on grass near to water and wait until spring before continuing their lives.




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