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Octochaetus multiporus

Scientific classification

Kingdom:

Animalia

Phylum:

Annelida

Class:

Clitellata

Subclass:

Oligochaeta

Order:

Haplotaxida

Family:

Megascolecidae

Genus:

Octochaetus

Species:

multiporus

New Zealand has close to 200 native earthworm species, with new species still being identified. In spite of this richness in species, we don’t know much about their population densities, life cycles or their distribution. We do know that, when native forest or tussock grasslands are cleared for agricultural development, native earthworms (especially the topsoil species) disappear. However, one species of native earthworm, Octochaetus multiporus, appears not to be as dependent on native vegetation and in some circumstances can successfully survive in modified habitats. Because of its relative abundance, O. multiporus has received more research attention than many other native species.

O. multiporus are anecic earthworms. They live in the subsoil to a depth of up to 3–5 metres. They are found throughout the southern half of the North Island, in the South Island east of the main divide and in Stewart Island. O. multiporus need moist soil conditions to survive. Their populations are greater in soils that slope away from the Sun and are absent at adjacent sites where the land slopes toward the Sun (soils that are likely to dry out in the summer). Because they live so far down in the soil, they are not as affected by habitat change as earthworms that live closer to the soil surface. O. multiporus make extensive burrow systems. They use mucus (coelomic fluid) to form a cement-like substance to line their burrows. This mucus not only helps to keep the burrow walls from collapsing, but it may also be part of the species’ defence system because it is toxic to soil bacteria.

Physical characteristics

To the average person, most earthworms may look alike, but O. multiporus has a few characteristics that set it apart. First of all, it is a large earthworm species. O. multiporus can grow up to 30 cm in length and have a width of 8–10 mm in diameter. They are pale in colour with a translucent body wall. A purple streak runs along the dorsal (top) midline of their bodies. Mature specimens have a darker pink clitellum (saddle). Overall, O. multiporus have weakly developed muscles, with the exception of the muscles near the head and tail. These muscles are used for burrowing and simply to help such large earthworms move. Their movements are quite sluggish when compared to earthworms that live higher up in the soil profile.

O. multiporus is also unusual because it is bioluminescent. O. multiporus squirts out coelomic fluid from its mouth, anus and dorsal (underside) pores when it is disturbed. The fluid emits a bright orange-yellow light that glows in the dark. It has recently been discovered that the fluid glows in different colours depending on the age of the earthworm. Larger quantities of the luminescent liquid are produced if these earthworms are pierced. For this reason, Māori traditionally used O. multiporus as bait and lures when fishing. ‘Herehere tuna’ refers to a bunch of worms for catching eels.

Nature of science

All scientific knowledge is produced and valued within a wider society and culture. For example, agronomists and others in the scientific community value O. multiporus earthworms for their ability to improve soil structure, aeration and water-holding capacity in pastures. In addition, Māori communities value their usefulness in traditional methods of fishing.

Useful links

Anna Palmer, a Palmerston North Girls’ High School student, won a Royal Society Gold CREST award in 2011 for her study of O. multiporus.
www.royalsociety.org.nz/teaching-learning/crest/gold/recipients/2011/anna-palmer/ external link

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