Gnathostomulida

Gnathostomulida

Microscopic marine worms of uncertain systematic relationship, mainly characterized by cuticular structures in the pharynx and a monociliated skin epithelium. It is the most recently described phylum of the animal kingdom. The total number of species probably exceeds 1000.

Gnathostomulids are worm-shaped, cylindrical or slightly depressed, and semitransparent (or bright red), and sometimes have the external division of head and tail. The skin is a one-layered epithelium that is completely monociliated; that is, each of the polygonal epidermal cells bears only one cilium. The sensory system usually consists of 1–2 pairs of simple and 3–4 pairs of compound bristles (frontally and laterally), and a bundle of stiff cilia (dorsally on the head). The reproductive system consists of a dorsal ovarium and in most cases two caudolateral groups of testes follicles in the same specimen. Fertilization is internal.

The distribution of gnathostomulids is worldwide, the majority of localities being known from European coasts, some from the North American east coast, and some scattered over the western Pacific.

Gnathostomulida

[nə¦thäs·tə′myül·ə·də]
(invertebrate zoology)
Microscopic marine worms of uncertain systematic relationship, mainly characterized by cuticular structures in the pharynx and a monociliated skin epithelium.
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2 and 5 Other Metazoa Phyla Other Eukaryote Phyla Chaetognatha Ciliophora Ctenophora Other Alvelata Entoprocta Amoebozoa Hemichordata Cryptophyta Loricifera Loukozoa Gnathifera Glaucophyta Onochophora Choanozoa Porifera Picozoa Rotifera Foraminifera Xenoturbeiidea Rhodophyta Acanthocephala Myzozoa Chordata Apusozoa Cycliophora Heliozoa Gnathostomulida Percolozoa Kinohycha Euglenozoa Mesozoa Haptophyta Nematomorpha Metamunada Placozoa Cercozoa Priapulida Radiozoa Sipuncula Uncultured unicellular Uncultured Metazoa Eukaryote
Triploblastic relationships with emphasis on the acoelomates and the position of gnathostomulida, cycliophora, plathelminthes, and chaetognatha: a combined approach of 18s rDNA sequences and morphology.
Although adult morphology varies vastly across the group, many core Lophotrochozoa (including the Mollusca, Annelida [including Vestimentifera, Pogonophora, and Echiura, and possibly Myzostoma, and Sipunculida], Gnathostomulida, Nemertea, dicyemid Mesozoa, Entoprocta, and some Platyhelminthes [including polyclad Turbellaria, Catenulida, and Macrostomida]) exhibit spiral cleavage, a highly conserved pattern of early development.
A mitochondrial genomics study was initiated using organisms from invertebrate phyla including Priapulida (Halicryptus spinulosus), Rotifera (Encentrum tectipes), Acanthocephala (Echinorynchus gadi), Gnathostomulida (Gnathostomula peregrini), Cycliophora (Symbion pandora), and Nematoda (Oscheius tipulae and Rhabditoides regina).
Gastrotrichs figure prominently in metazoan phylogeny because they share a suite of complex morphological characteristics with several other members of the Bilateria, including the Gnathostomulida and the Nematoda.