KRISTENSEN, R.M.: An Introduction to Loricifera, Cycliophora, and Gnathometazoa

Adult loriciferans are bilaterally symmetrical marine metazoans between 108-485 microns. The body is divided into five regions: mouth cone, head (introvert), neck, thorax and abdomen. The first description of a loriciferan (Nanaloricus mysticus) was in 1983 from specimens collected from shell gravel off the coast of France. The fine structure of the mouth cone, the introvert and the circumenteric brain indicate that the phylum is related to Kinorhyncha and Priapulida. Annulation of the flexible buccal tube, telescoping of the mouth cone and three rows of placoids in the triradiated pharynx bulb are found only in Tardigrada and Loricifera, but may be convergent. The marine Cycliophora is the most recently described animal phylum. Cycliophorans are bilateral acoelomate metazoans with a well-differentiated cuticle. A single microscopic species (Symbion pandora) was described in 1995. Cycliophorans appear to be a new type of epibiont with a very complex life-cycle living mainly on the setae of the mouthparts of several lobster species. Cycliophorans have some similarities to sessile rotifers but are considered related to entoprocts although a molecular study suggests that cycliophorans could be related to Syndermata (Acanthocephala + Rotifera). A new microscopic aschelminth-like animal, Limnognathia maerski with complicated jaws was described in 2000. It was assigned to a new class, Micrognathozoa within Gnathifera, which now includes Gnathostomulida, Micrognathozoa and Syndermata. The ultrastructure of the jaw suggests homology to jaws of gnathostomulids and the rotiferan mastax. Limnognathia maerski has dorsal plates formed by an intercellular matrix as in Rotifera and Acanthocephala, but ventrally the epidermis is “naked” with a thin glycocalyx. The gross anatomy of the body consists of a head, thorax and abdomen. The locomotory organ consists of two rows of cells with cilia.