Family Ptilocodiidae Coward, 1909 emend.

Ptilocodiidae Coward, 1909: 729; Bouillon et al., 2006: 151–153; Schuchert, 2009: 470–471; Xu et al., 2014: 264–265.

Diagnosis. Hydroid. Hydrorhiza stolonal, reticular, or encrusting, covered by naked coenosarc; hydranths sessile, naked and polymorphic; gastrozooid tubular, without tentacles; dactylozooids with 4 or more capitate tentacles, sometimes filiform; gonophores on gonozooids or gastro-gonozooids; developing into fixed sporosacs, eumedusoids or free medusae.

Medusa. Mature medusa with more or less bell-shaped umbrella, with or without radial exumbrellar furrows; with marginal nematocyst ring from which usually arise several didermic centripetal nematocyst bands (tracks) or exumbrellar rows of refringent spots; with four marginal tentacles or tentacles absent; four radial canals and circular canal; manubrium with 4 perradial mouth arms ending in nematocyst clusters or 4 simple unbranched perradial oral tentacles arising above mouth rim unarmed terminal nematocyst clusters; gonads four interradial or eight adradial masses on manubrium, or completely perradial gonads; with or without ocelli.

Remarks. According to the original report (Du et al., 2012) and by reexamining its shape, position and attachment of oral tentacles, Tregoubovia perradialis Xu, Huang & Du, 2012 is obvious different from other species of Tregoubovia Picard, 1958 . In T. perradialis, the oral tentacles are arising above mouth rim with ring nematocysts, while the oral arms of Tregoubovia are extending from the perradial corners of mouth margin, and armed with terminal nematocyst clusters. The position of gonads is on perradial position of manubrium in T. perradialis, and interradial in Tregoubovia . According to these, T. perradialis should be removed from the genus Tregoubovia, and a new genus Tregouboviopsis Guo, Xu & Huang, gen. nov. is proposed to accommodate it. The diagnosis was therefore adapted to fit the new scope of the family.

Thus, the family Ptilocodiidae comprises six genera now: Hydrichthella Stechow, 1909, Ptilocodium Coward, 1909, Thecocodium Bouillon, 1967, Hansiella Bouillon, 1980, Tregoubovia Picard, 1958 and Tregouboviopsis Guo, Xu & Huang, gen. nov.

For a recent revision of the family Ptilocodiidae see Bouillon et al. (2006), Schuchert (2009), Du et al. (2012) and Xu et al. (2014).

From the Chinese waters, two genera, Hydrichthella as hydroid and free eumedusoid, and Tregouboviopsis as medusa, are known.

Key to the genera of Ptilocodiidae .

1. Hydroids............................................................................................................................................................................................... 2

Medusae ...............................................................................................................................................................................................4

2. Dactylozooids with two types ................................................................................................................. Hydrichthella Stechow, 1909

Dactylozooids with one type................................................................................................................................................................ 3

3. Hydrorhiza crust-like, not covered by visible perisarc............................................................................... Ptilocodium Coward, 1909

Hydrorhiza a network of perisarc-protected tube-like stolons................................................................. Thecocodium Bouillon, 1967

4. Without marginal tentacles................................................................................................................................................................... 5

With marginal tentacles........................................................................................................................................................................6

5. Four perradial oral arms, ending swollen with nematocyst clusters; gonads interradial.............................. Tregoubovia Picard, 1958

Four perradial simple oral tentacles, arising above mouth rim, without terminal nematocyst clusters; gonads perradial ...................... ................................................................................................................................... Tregouboviopsis Guo, Xu & Huang, gen. nov.

6. Four interradial gonads ........................................................................................................................... Thecocodium Bouillon, 1967

Eight adradial gonads.................................................................................................................................... Hansiella Bouillon, 1980