Home > Invertebrates > Hydroids

Updated 3/25/2013

Phylum Cnidaria, Class Hydrozoa

Hydroids

Hydroids are colonies of tiny stinging jellies, best described as hundreds of inverted jellyfish  attached to a feather- or seaweed-like base, known as the organism's polyp phase.  Reproduction is achieved by releasing these fertile medusae into the plankton to feed and spawn.  They are abundant on most submerged surfaces including seaweeds but are very small and easily overlooked.  Powerful stinging cells are a primary cause of skin irritation when swimmers contact the reef, seaweed, pilings, floating docks, lines, or debris.  Symptoms may be delayed a day or more, appearing as intensely itchy welts and blisters.  Many species have been unintentionally spread around the world as adults on ship hulls or larvae in ballast water.  Hydroids are eaten by some species of sea slugs, filefishes, puffers, and the Moorish IdolFire Corals are reef-building, photosynthetic hydroids.

 

 HAWAII

Lytocarpia niger

BLACK HYDROID

 

Macrorhynchia philippina

PHILIPPINE HYDROID

 

Pennaria disticha

CHRISTMAS- TREE HYDROID

 

 Solanderia secunda

SEA FAN HYDROID

 

Halecium sp.

 

Halopteris sp.cf. diaphana

Various Hydroids

 

Gymnangium hians

FEATHER HYDROID

 

Velella velella

BY-THE-WIND SAILOR

 

Physalia utriculus

Portuguese Man-O'-War, Waimanalo Beach

PORTUGUESE MAN-O'-WAR

 

Various Siphonophores

 

 

Porpita pacifica

BLUE BUTTON

 


NORTHEAST PACIFIC

Symplectoscyphus turgidus

ZIG-ZAG HYDROID

 

Pinauay crocea

PINK-MOUTHED HYDROID