''Halecium halecinum'', commonly known as the herring-bone hydroid,
is a
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
hydrozoa
Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...
n in the family
Haleciidae. It is native to the eastern Atlantic Ocean, the western Atlantic Ocean and the eastern Pacific Ocean.
Description
This hydroid grows to a maximum height of but a more typical height is . The colony grows in a single plane with stiff erect stems growing from a fibrous base. The growth is
pinnate
Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and ...
, with alternate secondary branches which are parallel to one another and join the main stem at an angle of about 50°, giving a herring-bone appearance. These in turn have stubby tertiary branches which bear the