Stinging Bush Hydroid, Macrorhynchia philippina
Stinging Bush Hydroid, Macrorhynchia philippina. Underwater photographs taken in Bahía de Banderas, Puerta Vallarta, Jalisco, July 2026. Photographs and identifications courtesy of Greg Timms, youtube.com/@CoralmasterdivesPuerto-Vallarta/videos.
Phylogeny: The Stinging Bush Hydroid, Macrorhynchia philippina (Kirchenpauer, 1872), is a member of the Aglaopheniidae Family of Hydrozoans. The Aglaophenia Genus is one of fourteen genera in the Aglaopehnidae Family, and there are seventy-eight species in the Aglaophenia Genus. 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. The species name philippina was the type specimen used to discribe the type specimen that was collected in the Philippine archipelago. This species is also known as the Stinging Hydroid and the White Stinger and in Mexico as Hidroide Picador.
Morphology: The Stinging Bush Hydroid is a large, conspicuous, feather-like hydroid that forms erect colonies attached to hard substrates. The colony is attached to the substrate by a network of irregular, root-like rhizoids. The main stems, or hydrocauli, are brownish and are strongly and irregularly branched. The branches bear numerous slender, unbranched, lateral branches called hydrocladia, which are arranged alternately along the stem. This produces the characteristic open, pinnate or feather-like appearance of the colony. The hydrocladia are segmented and bear the feeding structures, or hydrothecae, in a single row. Each hydrotheca is associated with three nematothecae—small protective structures containing nematocysts. The hydranths (feeding polyps) generally possess 8 to 10 tentacles. Underwater, colonies can have a striking white to bluish-white or blue-iridescent appearance. The apparent coloration comes largely from the numerous bright hydranths and the way they reflect available light. Stinging Bush Hydroid colonies are 5.0 cm (2.0 inches) to 40 cm (15.7 inches) in height, although smaller colonies are common.
Habitat and Distribution: Stinging Bush Hydroids are found attached to coral, pilings,Rhodolith beds, rocks, pilings, vessel hulls, artificial structures, and other hard surfaces. They are sometimes associated with seagrass beds. They live at depths between 1 m (3 feet) and 45 m (135 feet), though most are found depths less than than 20 m (66 feet). Stinging Bush Hydroids are a circum-tropical to subtropical species that are native to the tropical and subtropical Indo-Pacific. They have been introduced around the world, and cover a wide span of the Eastern Pacific, Gulf of Mexico, and Caribbean Sea. On Mexico’s east coast they range from Altamira, Tamulipas, around the entire Yucatan Peninsula and south to Belize. They are found along the entire west coast of mainland Mexico, with the exception that they are absent from north of Magdalena Bay, Baja California Sur along the central and northwest coasts of the Baja Peninsula. Stinging Bush Hydroids are one of the more distinctive large hydroids encountered by divers in the Mexican Pacific. In Bahía de Banderas, Jalisco, they are reported to be as one of the more common hydrozoans. Most documentation supports the idea that the Stinging Bush Hydroid was introduced to the Eastern Pacific, possibly from the Indo-West Pacific or Atlantic, with ship-mediated transport considered to be the likely mechanism. The reasoning behind this includes the limited dispersal capability of its medusoids, genetic similarity among geographically distant populations, its ability to colonize on artificial structures and vessel hulls, and the difficulty of explaining its distribution by natural transoceanic dispersal.
Diet: Like other hydroids, Stinging Bush Hydroids are suspension feeders. Individual hydranths use their tentacles and nematocysts to capture small planktonic organisms. Zooplankton are there principal food.
Predation: The primary predator of Stinging Bush Hydroids is the Wormy Nudibranch Lomanotus vermiformis. This nudibranch is adapted to spend its entire life on the hydroid, grazing on the soft tissue. It tolerates the stinging cells and and is well camouflaged among the branches. The Wormy Nudibranch has spread along with the Stinging Bush Hydroid to many parts of the world. Other nudibranchs, sea spiders, and fishes are also known predators.
Reproduction: Stinging Bush Hydroid colonies produces both male and female gonozooids (specialized reproductive individuals within the colony). Reportedly, the coloration differs between the sexes: males are yellowish-brown and females reddish-brown. Reproductive structures develop on specialized modified hydrocladia called phylactocarps. The gonozooids contain sexual medusoids. The medusoids grow asexually through budding. They also reproduce sexually, to increase genetic diversity, by releasing eggs or sperm. The fertilized eggs develop into planula larvae that settle relatively quickly.
Ecosystem Interactions: Insufficient data is available to determine if the Stinging Bush Hydroid is an introduced species or an invasive one. Where introduced colonies grow densely, they compete with native benthic invertebrates and alter local marine habitats. The commensal, mutualistic and parasiticand mutualistic relationships of the Stinging Bush Hydroid are poorly documented.
Human Interactions: The Stinging Bush Hydroid has had a very limited impact on human activities in Mexican waters. From a conservation perspective, they have not been formally evaluated, but based on their rate of spread, they should be considered to be of Least Concern.
Caution: The Stinging Bush Hydroid is a stinging hydroid and has been documented to be venomous to humans. Contact with human skin can produce immediate burning or stinging, redness, pain, swelling, and itching and contact with this hydroid should be avoided. Our experience is that underwater encounters have generated a fairly good burning sensation that lasted several minutes. Others have reported a painful burning sensation that lasted a few hours. The reaction to the venom is most likely dependent on the age of the hy hydroid, the persons sensitivity to the venom in the region the sting occurred and the contact time with the hydroid.
Synonyms: Aglaophenia (Macrorhynchia) perforata, Aglaophenia (Macrorhynchia) philippina, Aglaophenia (Macrorhynchia) urens, Lytocarpus crosslandi, Lytocarpus philippinus, and Lytocarpus phillippinus.