Nematomorpha Etymology: From the Greek Nema for Thread, and Morphe for shape or form.
There are currently 361 species of Nematomorpha known to science (COL), however scientists think there may be many more species as yet unrecognized.
Characteristics of Nematomorpha:
Bilaterally symmetrical, and vermiform.
Body has more than two cell layers, tissues and organs.
Body monomeric with a pseudocoelomic cavity.
Body possesses a through gut which is normally non-functional.
Body possesses in a cuticle and longitudinal muscles.
Has a intra-epidermal nervous system with an anterior nerve ring.
Has no circulatory system (no blood system)
Reproduction normally sexual and gonochoristic.
Adults non-feeding, larvae endoparasitic.
Aquatic or moist soils, mostly fresh-water.
Biology of the Nematomorpha
The nematomorpha (Horsehair Worms) are relatively long, thin worms (1-3 mm diametre and 10-100 cm 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 the hairs from horse 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 female’s 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 arthropods, though not necessarily aquatic ones, particularly beetles, cockroaches, mantids, orthopterans, and crustaceans.. 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 nematomorpha 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 and there is one marine genus which parasitizes crabs. In some species, individuals that mature in autumn form cysts on grass near to water and wait until spring before continuing their lives.
Gordon is an ecologist with two degrees from Exeter University. He's also a teacher, a poet and the owner of 1,152 books. Oh - and he wrote this website.
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What is the living host?
Different species have different hosts, orthoptoroid arthropods are the most common, but they will also use beetles and even crustaceans.