Definitions

1. noun

a class of small, freshwater or marine, colonial animals consisting of a network of stinging tentacles surrounding a gelatinous body

“The hydrozoa found in the lake were fascinating to observe.”

2. plural noun

a group of hydrozoa

“The hydrozoa colony was home to many different species.”

3. plural noun

a class of animals including hydras and Portuguese man-of-war

“Hydrozoa are often found in tropical waters.”