Loricifera

Abstract

The loriciferans are a group of newly discovered microscopic marine animals with a complex life cycle and worldwide distribution. Despite their small size, they have complex alimentary, reproductive, excretory, nervous and muscle systems. The head of the adult can have more than two hundred appendages, and the larvae always have terminal toes. The loriciferans have their own phylum, which is related to the phyla Kinorhyncha and Priapulida.

Keywords: meiofauna; shell gravel; Higgins larva; neoteny; ultrastructure; paradox of body design

Figure 1.

A female of the type species, Nanaloricus mysticus, from Roscoff, France. The animal is seen from the dorsal view. Abbreviations: an, anus; bu, buccal tube; cv, clavoscalid; du, glandular duct; dv, dorsoventral muscle; fl, flosculum; fu, oral furca; gl, epidermal gland; gu, midgut; lg, lorical spike gland; mo, mouth cone; mt, mouth tube; nu, nucleus; oo, oocyte; os2, secondary oral ridge; pr1–pr2, protonephridia; sr2–sr9, scalid rings, ts1 and ts2, trichoscalids. (Modified from Kristensen 1991a, drawn by Beth Beyerholm.)

Figure 2.

Life cycle of Nanaloricus mysticus, all animals seen from the ventral view. A, female; B, male; C, spermatozoon; D, egg; E, first larval instar; F, last larval instar; G, metamorphosis of Higgins larva to postlarva; H, postlarva. (Modified from Kristensen 1991b, drawn by Beth Beyerholm.)

Figure 3.

A male of Pliciloricus enigmaticus from off the coast of North Carolina, USA; the animal seen from the dorsal view. Abbreviations: an, anus; cm, circular muscle; cv, clavoscalid; fl, flosculum; ri, the double organ from the second‐ring head appendages. sr2, leg‐shaped spinoscalid of second ring; sv, seminal vesicle; te, testis; ts1 and ts2, trichoscalids. (Original drawing by Birgitta Rubaek.)

Figure 4.

Life cycles of Rugiloricus, all animals seen from the ventral view. A, The free‐laid egg; B, embryo inside the egg; C, first instar larva; D, last instar larva with ovary (neoteny); E, old larval exuvium with eggs and embryos in different stages; F, neotenous larva; G, postlarva; H1, female; H2, male. In R. carolinensis the larva can develop direct to adult (D–H). In R. cauliculus the postlarva is always involved in the life cycle. Neoteny can be present in both species. (Original drawings by Stine Elle.)

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Further Reading

Higgins RP and Thiel H (eds) (1988) Introduction to the Study of Meiofauna. Washington DC: Smithsonian Institution Press.

Kristensen RM (1983) Loricifera, a new phylum with Aschelminthes characters from the meiobenthos. Zeitschrift für Zoologische Systematik und Evolutionsforschung 21: 163–180.

Kristensen RM (1991a) Loricifera. In: Harrison FW and Ruppert EE (eds) Microscopic Anatomy of Invertebrates, vol. 4. Aschelminthes, pp. 351–375. New York: Wiley‐Liss.

Kristensen RM (1991b) Loricifera – A general biological and phylogenetic overview. In 6. Zoological systematics Symposium: New higher taxa – presented by their discoverers. Verhandlungen der Deutschen Zoologischen Gesellschaft 84: 231–246.

Neuhaus N, Kristensen RM and Peters W (1997) Ultrastructure of the cuticle of Loricifera and demonstration of chitin using gold‐labelled wheat germ agglutinin. Acta Zoologica (Stockholm) 78: 215–225.

Shirayama Y and Kristensen RM (1988) Taxonomy, ecology and biogeography of Loricifera. Benthos Research 32: 18–20.

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How to Cite close
Kristensen, Reinhardt Møbjerg(Apr 2001) Loricifera. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001591]