FAMILY ZYGOPHYLACIDAE QUELCH, 1885 Diagnosis: Solitary hydrothecae arising from hydrorhiza directly, or erect, pinnate or flabellate colonies, with polysiphonic hydrocauli in most species, otherwise monosiphonic. Hydrocladia mostly arranged in one plane, alternate to subopposite. Hydrothecae mostly tubular, seldom campanulate or subuliform, with short to long pedicel, with one or two diaphragms, with or without indentation (intrathecal projections) at distal part of the hydrothecae, and with one to numerous nematothecae on hydrocauli, hydrocladia and/or apophyses of hydrocladia. Gonothecae congregate to form coppiniae on stem or its hydrocladia; coppiniae with or without defensive tubes, the latter occasionally provided with hydrothecae or nematothecae. Individual gonothecae solitary or adnate, generally elongate or ovoid, seldom flask- or carrot-shaped, apices either with a circular aperture or with one to three straight or curved short tubes. Remarks: Molecular data contributed by the present study support the genetic distinction and validity of the family Zygophylacidae (Figs 21, 22). Based on specimens examined in this study and morphological diagnoses proposed by Rees & Vervoort (1987), Vervoort (1987) and Cornelius (1995), both zygophylacids and lafoeids have similar tubular hydrothecae. However, they differ in the fact that nematothecae and hydrothecal diaphragms are commonly present in Zygophylacidae, but are absent in Lafoeidae (Bouillon et al. 2006; this study).

{"references": ["Quelch JJ. 1885. On some deep-sea and shallow-water Hydrozoa. Annals and Magazine of Natural History 16: 1 - 20.", "Rees WJ, Vervoort W. 1987. Hydroids from the John Murray Expedition to the Indian Ocean, with revisory notes on Hydrodendron, Abietinella, Cryptolaria and Zygophylax (Cnidaria: Hydrozoa). Zoologische Verhandelingen, Leiden 237: 1 - 209.", "Vervoort W. 1987. Evaluation of taxonomic characters in the Hydroida, particularly in the Thecata (= Leptomedusae). In: Bouillon J, Boero F, Cicogna F, Cornelius PFS, eds. Modern trends in the systematics, ecology and evolution of hydroids and hydromedusae. Oxford: Clarendon Press, 83 - 103.", "Cornelius PFS. 1995. North-west European thecate hydroids and their medusae. Part I: Introduction, Laodiceidae to Haleciidae. Synopses of the British Fauna 50: 1 - 347.", "Bouillon J, Gravili C, Pages F, Gili JM, Boero F. 2006. An introduction to Hydrozoa. Memoires du Museum National d'Histoire Naturelle 194: 1 - 591."]}

Published as part of Gu, Zhangjie, Ruthensteiner, Bernhard, Moura, Carlos J., Liu, Lihua, Zhang, Rui & Song, Xikun, 2022, Systematic affinities of Zygophylacidae (Cnidaria: Hydrozoa: Macrocolonia) with descriptions of 15 deep-sea species, pp. 52-87 in Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) (Zool. J. Linn. Soc.) 196 on page 60, DOI: 10.1093/zoolinnean/zlac036, http://zenodo.org/record/7035312