Phylum Echiura Stephen, 1965
(systematics, ecology and distribution)

by V.Murina

The Echiura popularly called "spoon-worms" are inhabitants of the shore of polar, temperate and tropical seas. They have also been collected from the floor of oceans at great depths.

Morphology. Echiura comprise unsegmented, coelomate, bilaterally symmetrical and soft-bodied invertebrates. They size varies from a few millimetres to 25 centimeters in length. They are sausage-shaped creature, with highly muscular sacs filled with fluid in wich the long alimentary canal and other organ freely move. The name "spoon-worms" is derived from the shape of the contracted proboscis which is muscular, sesory and lies as the anterior end of trunk but cannot be retractor within body. The mouth is anteriorly place usually at the base of the long proboscis used gathering food and the anus at the posterior part of trunk. A pair of setae are usually present on the ventral surface of the body just posterior of the mouth and one or two rings of anal setae encircle the posterior region of two genera. One to numerous nephridia, usually present in pairs, are attached to the ventral surface of the body wall. A pair of anal vesicles serves as excretory organ. Ther sexes are separate, fertilisation is usually external and the larvae is trochophore.

Ecology. Echiurans are marine except for a few species that in brackish water of India. They are soft bodied , almost defenceless creatures, that always live in protected places. Most borrow in sand or mud, where they live in U-shaped burrow. They inhabit also rock crevices, empty shells, sand-dollar tests, pholad holes, roots of marine angiosperms.

Echiurans are detritus feeders. With the aid of their highly muscular and sometimes spoon-or scoop-like probiscis they suck sand, mud, coral fragments and finely divided particles from their surroundings into their mouths and extract organic matter from the ingested material. Some species, however, trap bacteria and very fine particles of food in a slim net which is secreted from the surface of the animal.

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Family BONELLIDAE Lacaze-Duthers, 1858

Family Bonellidae has 28 genera and 70 species. The sexual dimorphism of bonellids distinguishes them from all other families of the phylum. The early larva may develop into a male or female, depending on its proximity to an adult female. It is finds as fastens on the proboscis of the female the developing larva becomes a male. If it does not make contact with a female it eventually becomes a female.

Males are usually small, about 1-6 mm long, planarian-like or nematoform, without a proboscis. Parasitic males usually found in the nephridium of the female.

Distribution. Family Bonellidae occurs widely and thier bathymetric range is extensive. L.A.Zenkevitch (1966) considered that the Bonellidae inhabit mainly the abyssal and ultraabyssal zones of World Ocean. Really 44 species or 63% bonellids are known to occur at depth of over 3000 m. Vitjazema sp. have been draged from depth 10210 m (Philippine Trench) (Beljaev, 1989). All these worms are obligate deposite feeders, sorting detritus from the bottom surface. Most of the species have the Nearcontinental and the lesser part have Oceanic types of distribution (Sokolova, Murina 1997). The distribution of 18 shallow-water species are limited tropical-temperate waters, especially Indo-Westpacific region. The 8 bathyal species are known as having single find with the exception of Eubonellia valida.

Checklist of BONELLIDAE Species

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Family ECHIURIDAE Quatrefages, 1847

Family of Echiuridae has 7 genera and 82 species. The ansence of sexual dimorphism distinguishes the echiurids from the bonellids.

Morphology. Proboscis usually well-developed, sometimes very long but never bifid; often easly detached from the trunk. Trunk sac-like to cylindrical in shape and usually covered with papillae; sometimes green or redish in colour. Longitudinal musculature is some genera is thicked to form longitudinal muscle bands.

Distribution. Echiurids tend to inhabit shallow waters. Only 4 species (Thalassema elapsus, Th.ovatum, Th.steinbecki, Arhynchite arhynchite) are known in abyssal zone at depth more 4000 m (Datta-Gupta, 1981. 1983). The whole of genera of Echiuridae (exception of genus Echiurus) are limited the tropical-temperate waters. Two species of Echiurus (E. e. echiurus and E. antarcticus) are found in the cold-water Arctic and Antarctic.

Checklist of ECHIURIDAE Species

Family Urechidae Fisher and Macginitie, 1928

Family Ikedidae Bock, 1942

total 157 species

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Remarks:

+ these species are preserved in the depository of Institute of Oceanology Russian Academy of Science Moskow.

* species were described by Murina V.V. as n. sp.

Principal publications

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Dr. Murina Galena-Vantsetti has the total information of the bathymetrical and geographical distribution of each from 157 species of the Phylum Echiura. She would be glad to identify of echiurans collection from any region of the World Ocean.

E-mail: murina@ibss.iuf.net
odmi@alpha.mhi.iuf.net

Copyright © 1998. Institute of Biology of the Southern Seas, National Academy of Sciences of Ukraine
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