Hydrozoans
(a) Obelia, (b) Physalia physalis, known as the Portuguese Man O‘ War, (c) Velella bae, and (d) Hydra have different body shapes, but all belong to the family Hydrozoa.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Biology. November 17, 2013."
http://cnx.org/content/m44664/latest/?collection=col11448/latest
OpenStax CNX
CC BY 3.0.