cyclostome

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Related to cyclostomes: agnathans, Ostracoderms

cyclostome

(sī`kləstōm'), jawless fish, member of the vertebrate superclass Cyclostomata (see ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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). This group includes the hagfishhagfish,
primitive, jawless marine fish of the family Myxinidae, of worldwide distribution in cold and temperate waters. Its rudimentary skeleton, of cartilage rather than bone, has a braincase, but no jaw. The circular sucking mouth has rows of horny teeth.
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 and the lampreylamprey,
name for several primitive marine and freshwater jawless fishes of the order Petromyzontiformes. As in the other jawless fish, the hagfish, the adult lamprey retains the notochord, the supporting structure that in higher vertebrates is found only in the embryo.
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.
References in periodicals archive ?
In contrast to the monthly recruitment patterns, clades differed with respect to scale: cheilostomes typically occupying more space than cyclostomes (despite the similarity in recruitment).
Cyclostomes were poor spatial competitors at Lough Hyne, being overgrown by most other encrusting faunal groups.
How do cyclostomes persist alongside superior space competitors?
Since the Mesozoic, cheilostomes have not only dramatically increased at various taxonomic levels (family, genus and species), but also maintained their historical competitive dominance over the cyclostomes (see Taylor, 1993; McKinney, 1995a; Jablonski et al., 1997; McKinney et al., 1998).
The comparative lack of effect on cyclostomes of the K-T boundary event (McKinney et al., 1998) suggests that this clade has been very resilient in the face of major changes with time.
The evolutionary success (species richness) and ecological success (biomass) of the cyclostomes have been decoupled over geological time (McKinney et al., 1998) and, during Recent times, in geographical space, as well.
Recent research on the skeletal ultrastructure of cyclostome bryozoans has revealed an unanticipated diversity of calcitic fabrics (e.g., Boardman et al., 1992; Taylor and Jones, 1993; Taylor et al., 1995).
New investigations of cyclostome bryozoans have shown that calcitic semi-nacre is widespread, particularly in the fixed-walled suborders Tubuliporina and Articulata.
Other investigations of cyclostome skeletons have failed to reveal unequivocal semi-nacre.
Comparison with other cyclostome bryozoan ultrastructures
The semi-nacreous structure is very similar to that described in Hornera (Taylor and Jones, 1993), a free-walled cyclostome belonging to the suborder Cancellata.
The subdivision of the cyclostome bryozoan tablets into alternating soluble and less-soluble sectors has important bearing on the relationship between cyclostome calcitic semi-nacre and molluscan aragonitic nacres.