Phylum Cnidaria: Subtidal Hydroids & Medusae

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Radially symmetrical predators with relatively simple body structure.  Most are sessile or move only slowly.  Presence of microscopic stinging cells (nematocysts) aids in their effective capture of prey.  10,000 living species.

 Class Hydrozoa
   Subclass Anthoathecata (=Anthomedusae, Athecata)
Garveia annulata Hydractinia Pinauay marina Stylaster californicus Stylantheca porphyra Polyorchis
Garveia
annulata
Hydractinia milleri Pinauay
marina
Stylaster californicus Stylantheca porphyra Polyorchis
spp.
   Subclass Leptothecata (=Leptomedusae, Thecata)
Abietinaria Aglaophenia Obelia Orthopyxis Plumularia Aequorea
Abietinaria Aglaophenia Obelia Orthopyxis Plumularia Aequorea

 Class Scyphozoa
   Order Semaeostomae
 Class Staurozoa
Aurelia labiata Chrysaora colorata Chrysaora fuscescens
Phacellophora camschatica Haliclystus sp
Aurelia
labiata
Chrysaora colorata Chrysaora
fuscescens

Phacellophora camtschatica Haliclystus sp
















Hydractinia milleri
Hydractinia milleri  Torrey, 1902
Phylum Cnidaria, Class Hydrozoa, Subcl. Anthoathecata, Order Filifera, Family Hydractiniidae

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, 

Geogr. Range: British Columbia to Monterey
Synonyms:
Similar species: several species of Hydractinia occur in Monterey, distinguished by size of gastrozooids, number of tentacles and  number & location of gonophores.

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Garveia annulata
Garveia annulata  (Nutting, 1901)
Phylum Cnidaria, Class Hydrozoa, Subcl. Anthoathecata, Order Filifera, Family Bougainvilliidae

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.

Geogr. Range: Alaska to Channel Islands
Synonyms: 
Similar species: bright orange color is distinctive for this species.

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Stylaster californicus
Stylaster californicus  (Verrill, 1866)
Phylum Cnidaria, Class Hydrozoa, Subcl. Anthoathecata, Order Filifera, Family Stylasteridae

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).

Geogr. Range: northern California to Baja
Synonyms: Allopora californica
Similar species: Stylantheca porphyra grows in encrusting sheets rather than branched erect colonies; molecular data suggests these two species may be morphs of the same species.  Several other similar species occur farther north to British Columbia.

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Stylantheca porphyra
Stylantheca porphyra  Fisher, 1931
Phylum Cnidaria, Class Hydrozoa, Subcl. Anthoathecata, Order Filifera, Family Stylasteridae

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.

Geogr. Range: British Columbia to southern California
Synonyms: Allopora porphyra
Similar species: Stylaster californicus grows in erect colonies and is somewhat more variable in color; molecular data suggests these two species may be morphs of the same species. 

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Pinauay (=Tubularia) marina
Pinauay marina  (Torrey, 1902)
Phylum Cnidaria, Class Hydrozoa, Subcl. Anthoathecata, Order Capitata, Family Tubulariidae

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.

Geogr. Range: British Columbia to California
Synonyms: Tubularia marina, Ectopleura marina
Similar species: Pinauay crocea grows in colonies of tangled mats to 15 cm tall, typically in harbors and  protected sites.

Image: Crisia (cntr. bottom), Corynactis (lower left & rt.)

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Polyorchis
Polyorchis spp.  
Phylum Cnidaria, Class Hydrozoa, Subcl. Anthoathecata, Order Capitata, Family Polyorchidae

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.

Geogr. Range:  Aleutians to Gulf of Calif (P. penicellatus)
Synonyms: 
Similar species: Polyorchis penicellatus (Eschscholtz, 1829) is more common & larger with lateral side branches on its 4 radial canals; P. haplus Skogsberg, 1948 is smaller, less common & lacks lateral branches on radial canals. 

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Aglaophenia Aglaophenia spp.
Phylum Cnidaria, Class Hydrozoa, Subcl. Leptothecata, Order Conica, Family Aglaopheniidae

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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Abietinaria
Abietinaria spp.
Phylum Cnidaria, Class Hydrozoa, Subcl. Leptothecata, Order Conica, Family Sertulariidae

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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Plumularia
Plumularia spp.
Phylum Cnidaria, Class Hydrozoa, Subcl. Leptothecata, Order Conica, Family Plumulariidae

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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Aequorea
Aequorea spp.
Phylum Cnidaria, Class Hydrozoa, Subcl. Leptothecata, Order Conica, Family Aequoreidae

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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Obelia
Obelia spp.
Phylum Cnidaria, Class Hydrozoa, Subcl. Leptothecata, Order Proboscoida, Family Campanulariidae

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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Orthopyxis
Orthopyxis spp.
Phylum Cnidaria, Class Hydrozoa, Subcl. Leptothecata, Order Proboscoida, Family Campanulariidae

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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Haliclystus sp.
Haliclystus spp.  Clark, 1863
Phylum Cnidaria, Class Staurozoa, Order Stauromedusae, Soborder Eleutherocarpida,  Family Lucernariidae

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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Chrysaora colorata
Chrysaora colorata  (Russell, 1964)
Phylum Cnidaria, Class Scyphozoa, Order Semaeostomeae, Family Pelagiidae

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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Chrysaora fuscescens Chrysaora fuscescens  Brandt, 1835
Phylum Cnidaria, Class Scyphozoa, Order Semaeostomeae, Family Pelagiidae

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 helvolaC. gilberti
Similar species: often misidentified as Chrysaora melanaster.


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Phacellophora camtschatica Phacellophora camtschatica  Brandt, 1835
Phylum Cnidaria, Class Scyphozoa, Order Semaeostomeae, Family Ulmaridae

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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Aurelia labiata
Aurelia labiata  Chamisso & Eysenhardt, 1821
Phylum Cnidaria, Class Scyphozoa, Order Semaeostomeae, Family Ulmaridae

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. 

Geogr. Range: Oregon to central California
Synonyms:
Similar species: often misidentified as the non-native Aurelia aurita.

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Page created by J.M. Watanabe
All images copyright James Watanabe unless otherwise indicated
Contact:  watanabe_at_stanford_dot_edu                                                                                                                                   Last  update: 30 August 2010