San Diego Aglaophenia, Aglaophenia diegensis
San Diego Aglaophenia, Aglaophenia diegensis. Hydrazoan photographed in it’s native environment in coastal waters off Guaymas, Sonora, January 2026. Photograph and identification to the genus level courtesy of Dr. Jake Turin, Albuquerque, New Mexico.
Phylogeny: The San Diego Aglaophenia, Aglaophenia diegensis (Torrey, 1904), is a member of the Aglaopheniidae Family of Hydrozoa. The Aglaophenia genus is one of fourteen genera in the Aglaopehnidae Family, and there are seventy-eight species in the Aglaophenia genus. They are known as the Ostrich-Plume Hydroid and in Mexico as Aglaophenia de San Diego. The family name Aglaopheniidae and the genus name Aglaophenia come from the Greek words meaning something like “shining appearance” or “splendid display”. This refers to the delicate and sometimes iridescent appearance of these hydroids.
Morphology: San Diego Aglaophenia are hydrozoa that have monopodal feather-like stalks, with alternating branchlets. They may be brown, yellowish-brown or greenish-brown in color. They are multicellular eukaryote organisms with very complex systematics. Their bodies consist of mesoglea between two layers of epithelium that are one cell thick. They have a single orifice and body cavity that is used from digestion and respiration. San Diego Aglaophenia may reside in small colonies or as solitary individuals. San Diego Aglaophenia range in height from 10 cm (4.0 inches) to 15 cm (6.0 inches).
Habitat and Distribution: San Diego Aglaophenia are found attached to hard substrates such as rocks and pilings. They live in the intertidal zone and to a depth of 37 m (121 feet). Some sources extend the maximum depth to 243 m (797 feet). The San Diego Aglaophenia is a subtropical to tropical Eastern Pacific species. They found in all Mexican waters of the Pacific Ocean.
Diet: San Diego Aglaophenia are suspension feeders that capture their prey, by tentacles, from the surrounding water. They feed primarily on plankton and suspended organic matter.
Predators: The predation of the San Diego Aglaophenia is poorly documented. Other species in this family are prey for nudibranchs and other gastropods.
Reproduction: San Diego Aglaophenia are gonochoric (male or female for life). They reproduce sexually with sperm and eggs being released from their corbulae, which are prominent brownish rice-grain shaped structures which contain gonophores. The males release sperm into the water which find their way to the female’s gonophores. Upon fertilization, embryos develop into planula larvae within the female’s gonophore. Within a few days the planula settles on a suitable substrate to form a primary polyp. San Diego Aglaophenia also reproduce asexually through budding and fragmentation.
Ecosystem Interactions: The parasitic, commensal, and mutualistic relationships of the San Diego Aglaophenia are poorly documented. Some species within this family host commensal shrimp that seek protection among the hydroid’s stinging cells. Thick colonies of Aglaophenid Hydroids provide protection for amphipods and other small invertebrates.
Human Interactions: San Diego Aglaophenia have a very limited impact on human activities. From a conservation perspective the San Diego Aglaophenia has not been formally evaluated, however they are common and widespread and should be considered to be of Least Concern.
Synonyms: None.