Key to Order Actiniaria:  Anemones

Phylum Cnidaria
 Class Anthozoa
  Subclass Zoantharia (Hexacorallia)

Taken primarily from  Kozloff, 1987, 1996 p. 72 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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1a Body somewhat wormlike, usually with a rounded or bulbous base (in Halcampoides purpurea, choice 6b, the base becomes flattened when the animal contracts), inhabiting mud or muddy sand, not attached to a firm object 2
1b Body not wormlike, with a flattened base that is attached to rock, pebble, shell, wood or some other firm object (note: some species are partly or almost completely buried in gravel, sand, or mud, but their bases are nevertheless attached to a firm object) 7
2a With 10 tentacles Halcampa
2b With 12 or more tentacles, at least in mature individuals 3
3a With 12-18 (usually 16) tentacles; gastrovascular cavity with spherical, ciliated clusters of cells circulating in it; height up to 1.5 cm; mostly in estuarine situations, especially shallow pools in salt marshes Nematostella 
3b Usually with 12 tentacles; gastrovascular cavity without spherical, ciliated clusters of cells circulating in it; height commonly 4 cm or more; often in bays, but not typically in salt marshes or other estuarine situations 4
4a Base bulbous; part of the column covered with a brownish cuticle Edwardsia 
4b Base not bulbous; column without a brownish cuticle 5
5a Column tan to brown; oral disk with distinct folds around the siphonoglyph Peachia
5b Column translucent and colorless to opaque and beige; oral disk without folds around the siphonoglyph 6
6a Lips and pharynx beige, white, or brown; base rounded when the animal is contracted Halcampa
6b Lips and pharynx usually red; base flattened when the animal is contracted Halcampoides
7a With acontia (threadlike structures that can be extruded through the mouth or through pores or breaks in the body wall when the anemone is disturbed or damaged) (photo) 8
7b Without acontia 10
8a Column green to brown, with 7-19 pale orange stripes; height not exceeding 2 cm; usually high intertidal, in cracks or shallow pools in rock (Haliplanella lineata in the original key) Diadumene lineata
8b Column sometimes brown, but not green, and without orange stripes; height commonly more than 2 cm; mostly low intertidal and subtidal, or on floats 9
9a Height not more than 10 cm, and usually not more than 5 cm; column white, gray, brown, or orange, sometimes with dark spots marking the location of the pores through which acontia are extruded; generally with fewer than 100 tentacles; oral disk only slightly lobed; reproducing rapidly by pedal laceration, the pedal fragments developing into complete anemones within about 3 weeks; intertidal and subtidal Metridium
senile subsp. fimbriatum
9b Height often more than 10 cm, and sometimes attaining 1 m; column white, brownish orange, or salmon-orange, without spots marking the location of the pores through which acontia are extruded; generally with more than 200 tentacles in larger specimens; oral disk prominently lobed, except in small individuals; not reproducing by pedal laceration; mostly subtidal Metridium farcimen
10a Column with tubercles (these may, however be small and inconspicuous), often with sand, gravel, or bits of shell adhering to them 11
10b Column without tubercles and usually without adherent material 20
11a Margin of oral disk with white or yellow spherules (these may be hidden by the tentacles) 12
11b Margin of oral disk without spherules 15
12a Tubercles restricted to the upper portion of the column (oral disk often bright pink or orange; tentacles with white bands on a gray, brown, blackish, or green background, or with the colors reversed; without symbiotic algal cells in the tissues; buried in sand or gravel, with the base attached to a rock, pebble, or shell) Anthopleura
12b Tubercles present on all parts of the column 13
13a Prevailing color of column, oral disk, and tentacles green or olive green, due to the presence of zoochlorellae (green algal cells) and/or zooxanthellae (dinoflagellates) in the tissues (specimens growing in caves or other deeply shaded situations may lack the symbionts and therefore be nearly white) 14
13b Prevailing color of column, oral disk, and tentacles white, yellow, or pink (the oral disk has yellow or pink lines radiating from the mouth to the margin, and the tentacles have transverse zigzag lines) (strictly subtidal; broods internally) Cribrinopsis
14a Column green or olive green, often shading to white toward the base; tubercles usually in distinct lengthwise rows; tentacles typically with pink tips and the disk often with dark radial bands; height up to about 5 cm; often in clonal masses formed by asexual multiplication, and frequently covered by sand that accumulates on rocks to which this anemone is attached; mostly mid-intertidal
14b Column almost uniformly green; tubercles usually not in distinct rows; tentacles and oral disk uniformly green; height commonly exceeding 5 cm; solitary, and not covered by sand; low intertidal
15a Column greenish or reddish, with lengthwise rows of tubercles that may be of the same color or lighter; oral disk with conspicuous white stripes radiating from the mouth to the margin (broods internally, releasing young through pores at the tips of the tentacles) Aulactinia incubans
15b Column greenish, olive, brownish, or red (if greenish or olive, it may have red blotches; if red, it may have greenish or olive blotches or white tubercles); oral disk without radiating white stripes 16
16a Column red, its tubercles of the same color (and not arranged in distinct rows); column accumulating sand, gravel, and bits of shell (this species is usually partly buried in coarse sand or gravel); oral disk slightly greenish Urticina coriacea
16b Column red (sometimes with white tubercles), brownish, olive, or greenish (if olive or greenish, often with red blotches); column usually not accumulating sand, gravel, or bits of shells; oral disk usually not greenish 17
17a Column red (rose to maroon), with conspicuous white tubercles 18
17b Column red, brownish, olive, or greenish (if olive or greenish, often with red blotches); with inconspicuous tubercles, these not white 19
18a Tubercles smooth, arranged in lengthwise rows; column rarely more than 10 cm in diameter; intertidal and subtidal Urticina lofotensis
18b Tubercles rough, arranged in circumferential rows; column frequently more than 15 cm in diameter; strictly subtidal Urticina columbiana
19a Tentacles usually with transverse bands; column sometimes of a uniform color (red, brownish, olive, or greenish), sometimes with red blotches on an olive or greenish background; intertidal and subtidal, common on floating docks Urticina crassicornis
19b Tentacles without transverse bands; column uniformly deep red to maroon, appearing velvety; subtidal, and usually situated atop prominences (oral disk often with alternating red and yellow radial markings) Urticina piscivora
20a Column orange or white, or white with orange streaks or blotches (tentacles orange or white, sometimes with orange bands); not brooding young externally; subtidal 21
20b Column brown, orange, red, or green, sometimes with parallel light lines, but never white or with orange streaks or blotches; sometimes brooding young externally on the column; intertidal and subtidal 23
21a Column whitish, with red or orange-red streaks; tentacles with white spots at their bases; column, when extended, not more than 3 cm high, and not appreciably higher than wide; usually attached to shells of Modiolus modiolus (horse mussel) Stomphia coccinea
21b Column cream to pale orange (sometimes with orange or red blotches or streaks) or reddish beige; tentacles without white spots at their bases; column, when extended, often more than 5 cm high, and appreciably higher than wide; not usually attached to shells of Modiolus modiolus 22
22a Color cream to orange, sometimes with orange or red blotches or streaks; with at least 160 tentacles in specimens whose column height is 5 cm or more Stomphia didemon
22b Color uniformly reddish beige; with not more than 130 tentacles in specimens whose column height is 5 cm or more Stomphia sp.
23a Oral disk with radiating white lines (picture); brooding young internally or externally, depending on the species 24
23b Oral disk without radiating white lines; brooding young internally (color drab green, brick-red, dark orange, or deep mustard, sometimes with lighter or darker spots; pedal disk without radiating white lines; mid- to high intertidal, mostly in caves and in surge channels shaded by logs; known only from the San Juan Archipelago) Epiactis fernaldi
24a Column predominantly greenish, reddish, or brownish (sometimes orange in Epiactus lisbethae); radiating white lines on oral disk narrow, originating close to the mouth; pedal disk with radiating white or gray lines; column not accumulating sand grains [except in E. ritteri]; brooding young externally 25
24b Column generally dull red to brown, sometimes with darker spots; radiating white lines on oral disk broad, located mostly close to the tentacle bases; pedal disk with or without radiating white lines; lower part of column with adhesive areas that accumulate sand; brooding young internally (extremely flat when contracted; mostly low intertidal, often under rocks) Epiactis ritteri
25a Diameter of pedal disk not more than 3.5 cm; radiating white lines on pedal disk not continuing up the column for more than part of its height; all mature individuals capable of brooding and do so throughout the year, bearing up to about 30 young of various sizes, mostly in a single circumferential row Epiactis prolifera
25b Diameter of pedal disk up to about 8 cm; radiating white lines on pedal disk of mature individuals continuing up the column for its entire height (the lines are gray, blue-gray, gray-green, or white; some light colored specimens do not have distinct lines); females brooding in spring and early summer, bearing up to several hundred young of nearly uniform size in a circumferential band that is several individuals deep (females that are predominantly red, brown, or green usually have pink young; those that are orange usually have orange young) Epiactis lisbethae

Taxonomic Levels Represented in this Key

  Anthopleura artemisia
  Anthopleura elegantissima
  Anthopleura xanthogrammica
  Cribrinopsis fernaldi
  Diadumene lineata
  Epiactis fernaldi
  Epiactis lisbethae
  Epiactis prolifera
  Epiactis ritteri
  Metridium farcimen
  Metridium senile subsp. fimbriatum
  Stomphia coccinea
  Stomphia didemon
  Urticina columbiana
  Urticina coriacea
  Urticina crassicornis
  Urticina lofotensis
  Urticina piscivora

Page created by Brandon White, 7-2002
Edited by:  Dave Cowles 8-2002, 10-2004, 2005, 2008-
Edited by Hans Helmstetler 12-2002