Halitrephes maasi is a species of deep sea hydrozoan of the family Halicreatidae. Varitentacula yantaiensis is a species of deep sea hydrozoan of the family Halicreatidae. Aeginura grimaldii is a species of deep sea hydrozoan of the family Aeginidae. Halicreas minimum is a species of deep sea hydrozoan of the family Halicreatidae. "Aglantha digitale" is a small, transparent, hydrozoan with a maximum height of . Aegina citrea is a species of deep sea hydrozoan of the family Aeginidae. Crossota millsae is a species of deep-sea hydrozoan. Having a velum is characteristic of the hydrozoan medusae. Crossota rufobrunnea is a species of hydrozoan. This marine hydrozoan is common in warmer waters. Csiromedusa medeopolis is a species of hydrozoan described in 2010. Turritopsis rubra is a species of hydrozoan of the family Oceaniidae. Turritopsis lata is a species of hydrozoan of the family Oceaniidae. Aequorin is a calcium-activated photoprotein isolated from the hydrozoan "Aequorea victoria". Liriope is a genus of hydrozoan in the family Geryoniidae.