Trachylina

invertebrate order

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July 14, 2026

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The Trachylina are an order of Hydrozoa, a class of marine invertebrates. A key characteristic of the Trachylina is that they lack a polyp stage in their life cycle. This order includes the suborders Trachomedusae and Narcomedusae. The term "trachylina" is derived from New Latin, possibly combining "trachy-" with the Latin word "linum," meaning flax. The related term "trachyline" can be used as an adjective.1

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2 Britannica Sources

Trachylina
Trachylinae

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cnidarian
Evolution
…ancient of cnidarian classes, and Trachylina is thought to be the most primitive extant order of that group. An alternative view is that anthozoans are the stem of the phylum, which evolved from bilateral flatworms and is secondarily simplified. A corollary to this theory is that the polyp is the…
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…ancient of cnidarian classes, and Trachylina is thought to be the most primitive extant order of that group. An alternative view is that anthozoans are the stem of the phylum, which evolved from bilateral flatworms and is secondarily simplified. A corollary to this theory is that the polyp is the…
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cnidarian
Annotated classification
Order Trachylina Medusa dominant; reduced or no polyp stage. Statocysts and special sensory structures (tentaculocysts). Differ from other hydromedusae by having tentacles inserted above umbrellar margin. Oceanic, mostly warmer waters. Suborder Laingiomedusae Medusae with features of both Narcomedusae and Trachymedusae. Polyp unknown.
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Order Trachylina Medusa dominant; reduced or no polyp stage. Statocysts and special sensory structures (tentaculocysts). Differ from other hydromedusae by having tentacles inserted above umbrellar margin. Oceanic, mostly warmer waters. Suborder Laingiomedusae Medusae with features of both Narcomedusae and Trachymedusae. Polyp unknown.
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