Inconspicuous colonies resembling whitish fuzz of naked hyrdanths 5 mm tall arising from basal mat of stolons; white to pinkish; colonies polymorphic; no free-swimming medusa stage. 

Moderately common, but inconspicuous due to small size; on sides of rocks and in crevices, 

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Conspicuous erect branched colonies to 15 cm tall, bright orange to yellow; main branches composed of several parallel tubes (polysiphonous).  Gonophores attached to main axes; no free-swimming medusae.

Moderately common, but intermittent in wave-exposed sites (Carmel Bay) on sponges, red algae, and corallines.  Also in rocky intertidal.

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Hydrocoral with massive CaCO₃ skeleton; bright purple to pinkish-red. Gastrozooids surrounded by ring of defensive stinging dactylozooids.

Abundant, typically in deeper water at wave-exposed sites (e.g. Carmel Bay).

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Encrusting hydrocoral with CaCO₃ skeleton; purple. Gastrozooids surrounded by ring of stinging defensive dactylozooids. 

Infrequent, in wave-exposed sites, low intertidal to subtidal; on rocky substrate.

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Polyps 5 cm tall, solitary or in well-spaced groups; hydranth pink with 2 concentric rings of tentacles; perisarc of stalk dark. Gonophores located between whorls of tentacles; no free medusae.

Moderately common but inconspicuous, on rocks nestled among colonial invertebrates in exposed and semi-exposed sites.

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Medusa with tall bell to 2-6 cm high; 4 radial canals; numerous tentacles with pigmented ocelli at base; polyp phase unknown. 

Most common in protected areas such as seagrass flats & harbors; spends most of time perched on bottom, swimming upward then drifting back down catching demersal zooplankton & benthic crustaceans.

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Robust feather-like colony to 10 cm tall; brown, orange or tan.  Rice grain-like structures (corbulae) on side branches house reproductive individuals (no free-swimming medusae). 

Abundant, especially in shallow surgy areas where geniculate coralline algae are common; colonies in low intertidal zone often epiphytic on red algae.

Geogr. Range: Alaska to southern California
Synonyms:
Similar species: other feathery hydroid species such as Plumularia are much more delicate that Aglaophenia.

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Planar colony to 8 cm tall, with side branches alternating  from central axis (pinnate); drab tan.  Hydranths (not visible to naked eye) in flask-shaped cups (thecae) that alternate along opposite sides of branches. 

Abundant, colonies often in clusters with plane of colony oriented perpendicular to direction of wave surge.

Geogr. Range: Alaska to southern California
Synonyms:
Similar species: several species of Abietinaria occur in Monterey Bay and are difficult to identify in the field without high magnification. 

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Delicate colonies resembling sparsely branched feathers ~2 cm tall; usually growing in clusters, pale tan.   Gastrozooids widely spaced on side one side of each side branch.

Abundant but inconspicuous, on rocks among other sessile invertebrates and algae.

Geogr. Range: Alaska to Baja
Synonyms:
Similar species: Aglaophenia is much more robust & larger than Plumularia.  Several species of Plumularia occur in Monterey but require a microscope to distinguish.

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Large transparent hydromedusa to 8 cm diameter; numerous radial canals bearing gonads; many  tentacles around margin of bell; bioluminescent.

Intermittently common in waters offshore of kelp forests; preys on other medusae, ctenophores, pelagic tunicates.  Polyp phase rarely encountered in the field but easily cultured in the lab.  Medusa form is source of green-fluourescent protein (GFP) & aequorin (bioluminescent protein) used in research.

Geogr. Range: Alaska to California
Synonyms:
Similar species:

Image:  small ctenophore in foreground (out of focus) is Pleurobrachia.  

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Bushy delicate colony up to 15 cm tall with side branches arising in all planes; pale tan.  Gastrozooids tiny; free-swimming medusae released from reproductive gonozooids.

Abundant on any hard surface; good colonizer of newly open substrate.

Geogr. Range: genus occurs world-wide
Synonyms:
Similar species: several species of Obelia occur in Monterey but require microscopic examination to distinguish.

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Polyps on short unbranched stalks arising from basal stolon overgrowing red algae and other ephemeral substrata, pale tan. 

Can be very abundant; most conspicuous on low-lying red algae such as Rhodymenia pacifica, several species.

Geogr. Range: Alaska to southern California
Synonyms:
Similar species: several species of Orthopyxis occur in Monterey, but require microscopic examination to distinguish.

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Sessile, stalked forms; delicate vase shape with 8 oral arms tipped with clusters of minute tentacles; polyp-like in appearance, but internal anatomy medusa-like; to 3 cm tall; color red, orange, green, olive, or purple; 8 gonads clearly visible though body wall. Pictured specimen is a newly re-described species, H. californiensis.

Inconspicuous; on erect coralines & fleshy red algae at kelp forest depths in temperate waters. Feeds on small crustaceans.  

Geogr. Range: central California to Alaska
Synonyms: 
Similar species: .Manania has herringbone pattern & clear boundary betwn stalk & calyx; occurs farther north.

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Large medusa 70 cm diameter, pale with distinctive dark markings on bell and margin.  Unpleasant sting.    

Can be common but does not form large aggregations; pelagic; specimens encountered just offshore from kelp forests are often damaged.  Late stage larvae & juveniles of the crab Cancer gracilis frequently live on bell & oral arms prior to taking up their more typical benthic existence.

Geogr. Range: central California to southern California
Synonyms: Pelagia colorata
Similar species: C. colorata often misidentified as Chrysaora noctiluca which is a southern, warm water spp.

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Large medusa 30 cm diameter; bell yellow-brown to reddish brown with 24 dark tentacles around margin. Oral arms long & folded, dark with white/clear frills. Unpleasant sting.

Can form large aggregations, especially late summer through winter; pelagic offshore from kelp forests. Late stage larvae & juveniles of the crab Cancer gracilis frequently live on bell & oral arms.

Geogr. Range: Alaska to Baja.
Synonyms: Chrysaora helvola, C. gilberti
Similar species: often misidentified as Chrysaora melanaster.

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Large medusa 60 cm diameter; clear to yellowish bell with central yellow gonads; 16 clusters of tentacles, 16 sensory rhopalia around margin of bell; small individuals often with milky white bell.  Oral arms short & highly folded.  Pale whitish bell with central yellow gonad mass said to resemble a fried egg.  Mild sting.

Does not usually form large aggregations; primarily pelagic, offshore from kelp forests.

Geogr. Range: Kamchatka to Alaska & south  to Chile.
Synonyms:  
Similar species: 

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Shallow bell to 40 cm fringed with many fine tentacles; 4 short oral arms; opaque white, usually with 4 horseshoe-shaped gonads visible.  Very mild sting.

May form dense aggregations (late summer / autumn), pelagic offshore from kelp forests. 

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