Physonectae is a suborder of
siphonophore
Siphonophorae (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") is an order within Hydrozoa, a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine ...
s.
Organisms in the suborder Physonectae follow the classic
Siphonophore
Siphonophorae (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") is an order within Hydrozoa, a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine ...
body plan. They are almost all pelagic, and are composed of a colony of specialized
zooid
A zooid or zoöid is an animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals. The zooids can ...
s that originate from the same fertilized egg.
Distribution
The majority of physonect siphonophores are pelagic, with the exception of
Rhodallidae, which are a family of benthic physonects first collected during the
''Challenger'' expedition and described by
Ernst Haekel in his ''Challenger'' monograph.
Physonects, and siphonophores in general, are known to be widely distributed globally, but are understudied. Few individuals have been collected and are often misidentified. As a result, their exact global distributions are unclear.
Morphology
All physonect siphonophores have an
aboral
Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...
, apical pneumatophore filled with gas, which is formed by invagination of the superficial cell layers of the apical side of the larva.
In some species in the suborder Physonectae, the pneumatophore has a pore located either on the apical or basal pole of the organism and plays a role in controlling gas volume and pressure for buoyancy control.
Gas in the pneumatophore is high in carbon monoxide and is secreted by the pneumadenia, or gas gland.
Below the pneumatophore, an organism has a long stem with two distinct regions. The
nectosome is more apical relative to the siphosome and is composed of asexual