Key to Class Asteroidea

Taken primarily from  Kozloff, 1987, 1996  p. 448 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	With 5 or 6 rays (except in specimens that have lost a ray, or that have regenerated extra rays after being injured)	2
1b	With 8 to 20 or more rays	24
2a	With 6 rays; diameter rarely greater than 11 cm (Note:  Some individuals may have 4, 5, or 7 rays.  This may be a species complex.  See this note from the 1996 edition for more information.)  Also check here for Leptasterias aequalis.	Leptasterias hexactis
2b	With 5 rays; diameter frequently greater than 11 cm	3
3a	Rays bordered by conspicuous marginal plates that are much larger than any other ossicles visible at the surface (picture) (in Hippasteria spinosa, each plate bears a single stout spine, and in Luidia foliolata each plate bears several spines)	4
3b	Rays not bordered by conspicuous marginal plates (small marginal plates may be present, but these are not likely to be noted without magnification)	11
4a	Marginal plates not visible when the animal is viewed from above, and the plates either without spines or with only 1 or 2 stout spines	Luidia foliolata
4b	Marginal plates visible when the animal is viewed from above, and the plates either without spines or with only 1 or 2 stout spines	5
5a	Each marginal plate with 1 or 2 spines	6
5b	Marginal plates without spines	7
6a	Color of aboral surface orange to vermilion; aboral surface with some conspicuous bivalved, unstalked pedicellariae; most marginal plates with 2 spines (Hippasteria spinosa in key)	Hippasteria phrygiana
6b	Color of aboral surface gray or yellowish; aboral surface without pedicellariae; each marginal plate with a single spine	Ctenodiscus crispatus
7a	Tube feet pointed; diameter up to about 9 cm	Leptychaster pacificus
7b	Tube feet tipped with suckers; diameter generally greater than 9 cm	8
8a	Rays so short that the body appears almost pentagonal (diameter of the disk at least three-fourths the total diameter)	9
8b	Rays not so short that the body appears almost pentagonal	10
9a	Flat-topped plates of aboral surface with 4 to 12 marginal units surrounding 1 to 3 central units	Ceramaster arcticus
9b	Flat-topped plates of aboral surface with 12 to 15 marginal units surrounding 4 to 12 central units	Ceramaster patagonicus
10a	Aboral surface with circular paxillae that consist of numerous granulelike spines, all of which are similar	Gephyreaster swifti
10b	Aboral surface with circular to oval or hexagonal, flat-topped plates, each consisting of about 25 marginal granules and a central mass of slightly different and less markedly flattened granules (picture) (with an odor like that of exploded gunpowder)	Mediaster aequalis
11a	Aboral surface smooth and slippery, with few if any exposed spines	12
11b	Aboral surface rough or gritty due to exposed spines or plates	13
12a	Thickness equal to about one-third the diameter; aboral surface with a conspicuous and slightly elevated central opening (this leads to a spongy cavity that lies between the body wall proper and a superficial membrane); madreporite not visible; color of aboral surface usually pale orange or brownish yellow; without an odor like that of exploded gunpowder, but generally secreting a large amount of nearly gelatinous mucus, especially when first collected; subtidal	Pteraster tesselatus
12b	Thickness less than one-third diameter; aboral surface without a conspicuous and elevated central opening (there is no spongy cavity covered by a membrane distinct from the rest of the body wall); madroporite evident, though sunken; aboral surface usually reddish brown, with some patches of gray or purple; with an odor like that of exploded gunpowder, but not secreting a large amount of nearly gelatinous mucus; intertidal and subtidal	Dermaterias imbricata
13a	Diameter of disk about one-third to one-half the total diameter (found on the west coast of Vancouver Island and in California, but rarely if ever encountered in Washington or Oregon) (Named Asterina miniata in key)	Patiria miniata
13b	Diameter of disk much less than one-third total diameter	14
14a	Pedicellariae absent; aboral surface often with the texture of fine sandpaper when rubbed with a finger, but not noticably spiny when viewed without magnification	15
14b	Pedicellarie present; aboral surface noticeably spiny	20
15	Our representatives of the genus Henricia, couplets 15 to 19, need study.  Although all intertidal and nearly all shallow subtidal specimens will key  to H. leviuscula, this species, as presently understood, is extremely variable.  Several subspecies were proposed by Fisher (1911, 1930) and by Verrill (1914), but they intergrade and no attempt will be made here to separate them.  2010:  The dwarf mottled Henricia pumila is one species of this complex that has just been described.  See its description here.
15a	Plates forming the ridges on the aboral surface with a single row of conical spines (1-4 spines per plate), these largely covered with tissue so that they may not at first be distinct (rare subtidal species; only a few specimens known)	Henricia asthenactis
15b	Plates forming the ridges on the aboral surface bearing minute, scattered spines or clusters of prominent spines, or modified as spiny paxillae, all of these elements exposed and readily apparent with magnification	16
16a	Diameter of meshlike areas on the aboral surface appreciably greater than the width of the ridges that separate them (the ridges bear minute, scattered spines or clusters of spines whose length is commonly 1 to 1.5 mm)	17
16b	Diameter of meshlike areas on the aboral surface no greater than, and generally less than, the diameter of the spiny paxillae that separate them	18
17a	Ridges separating the meshlike areas of the aboral surface with scattered, minute spines (aboral surface yellow to brick red; rare subtidal species)	Henricia aspera
17b	Ridges separating the meshlike areas of the aboral surface with radiating clusters of sharp spines (these commonly 1 to 1.5 mm long, and 2-9 in a cluster) (aboral surface mostly white; rare subtidal species)	Henricia longispina
18a	Marginal plates prominent and arranged in 3 distinct rows; rays not thickened so much at the base that they are separated from one another by a crease that extends into the disk (aboral surface usually orange, brick-red, or brown, but sometimes cream or some other color; color not always uniform, and there may be mottling, gray patches, etc.)	19
18b	Marginal plates not prominent and not forming distinct rows; rays usually noticeably thickened at the base and separated from one another by a crease that extends into the disk (color off-white to orange; subtidal)	Henricia sanguinolenta
19a	Genital pores (located between the rays) slightly aboral with respect to the margin of the disk; diameter frequently exceeding 8 cm; color uniformly orange or orange-red, or with a disk of a different color than the rays (the disk is sometimes mottled, but the rays are not mottled); females not known to brood young (common intertidal and subtidal species) (Note from 1996 key:  Specimens keying to Henricia leviuscula belong to this species and to what may be an undescribed species or hybrid. H. leviuscula reaches a diameter of about 10 cm and its aboral surface is uniformly orange.  Specimens of about the same size, but orange-red or pinkish in color, are perhaps distinct.  Another color morph reaches a diameter of about 15 cm; it is mostly orange or reddish and has gray or lavender patches where the rays join the disk.)	Henricia leviuscula
19b	Genital pores slightly oral with respect to the margin of the disk; diameter rarely greater than 5 cm; disk and rays irregularly mottled; females brooding young under oral surface in winter or early spring (intertidal and subtidal) An apparently undescribed species, believed to be conspecific with the "brooding variety" of H. leviuscula reported by Fisher (1911) (Henricia sp. in original key)	Henricia pumila.
20a	Spines on upper parts of aboral surface generally not higher than 2 mm, typically in irregular clusters or arranged in networklike pattern, though some may be single and some may be in short rows; most pedicellariae in raised, hemispherical cushions that have a central spine	21
20b	Spines on upper parts of aboral surface mostly 3-5 mm, typically well seperated and more inclined to form poorly defined rows than clusters or networks; most pedicellariae concentrated in raised, hemispherical cushions that have a central spine	23
21a	Diameter of disk not more than one-sixth the total diameter; rays typically broadest a short distance way from the disk; jaws of the straight pedicellariae not forked at their tips into a pair of blades; color extremely variable, may be gray, greenish, brown, orange, or red, but not likely to be purple or pink	Evasterias troschelii
21b	Diameter of disk usually greater than one-fifth the total diameter; rays typically broadest where they join the disk; jaws of the straight pedicellariae forked at their tips into a pair of unequal blades; color generally orange, orange-ochre, brown, purple, or some shade of pink	22
22a	Spines on upper parts of aboral surface usually arranged in a networklike pattern; color orange, orange-ochre, brown, or purple; diameter not often exceeding 25 cm; intertidal and subtidal	Pisaster ochraceus
22b	Spines on upper parts of aboral surface usually single or clustered, but sometimes arranged in a networklike pattern; color some shade of pink; diameter commonly exceeding 25 cm, and sometimes exceeding 40 cm; almost strictly subtidal	Pisaster brevispinus
23a	Prevailing coloration of aboral surface some shade of red, often concentrated in blotches or bands that contrast with a light background; teeth on jaws of crossed pedicellariae essentially a series of small serrations, none of them fanglike; intertidal and subtidal	Orthasterias koehleri
23b	Prevailing coloration of aboral surface dark brown, olive, or gray, without any obvious reddish tones; teeth on jaws of crossed pedicellariae long, the pair at the tip of each jaw fanglike; subtidal	Stylasterias forreri
24a	With 8-16 rays (except in very small individuals); without pedicellariae; body not flabby; diameter not exceeding 50 cm	25
24b	With 20-24 rays (except in very small individuals); with pedicellariae; body flabby when separated from the substratum; diameter up to 80 cm	Pycnopodia helianthoides
25a	Paxillae of aboral surface rather widely separated and giving rise to long, slender spines of uneven length (thus the aboral surface appears prickly)	Crossaster papposus
25b	Paxillae of aboral surface crowded, giving rise only to short, blunt projections (thus the aboral surface is rather smooth)	26
26a	Diameter of disk usually about 1/4 the total diameter; aboral surface usually some shade of orange or pink, with a grayish blue streak radiating from the center of the disk to the tip of each ray; intertidal and subtidal	Solaster stimpsoni
26b	Diameter of disk usually about 1/3 the total diameter; aboral surface usually orange, brown, or gray, without conspicuous darker streaks radiating from the center of the disk	27
27a	Rays (of which tere are 8-10) typically narrowing rapidly just after leaving the base, thus becoming slender rather quickly; aboral surface usually orange; subtidal and extremely rare	Solaster paxillatus
27b	Rays typically tapering rather evenly from the base; aboral surface usually orange, brown, or gray; common subtidal species	28
28a	With 7-13 rays (usually 8-11); paxillae of aboral surface almost contiguous; aboral surface usually pale orange, sometimes orange-red	Solaster endeca
28b	With 8-16 rays (usually 11 or 12); paxillae of aboral surface separated from one another for a distance about equal to their diameter; aboral surface usually gray or brown, but sometimes orange, and occasionally showing a mottled pattern in which there are 2 shades of brown	Solaster dawsoni