Key to Gastropoda with Shells

Phylum Mollusca

Taken primarily from  Kozloff, 1987, 1996 p. 192 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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1a  Shell permanently cemented to a hard substratum (usually rock), coiled loosely or irregularly and generally twisted, resembling the calcareous tube of a serpulid polychaete more then a snail shell (picture)  (picture) Family Vermetidae
1b  Shell not permanently cemented to a hard substratum, either tightly coiled or tubular, conical, or cap-shaped 2
2a Shell tubular, conical, or cap-shaped, without obvious coiling  3
2b Shell obviously coiled, although the spire may be short  9
3a Shell tubular, slightly curved, the height more then twice the diameter Family Caecidae
3b Shell conical or cap-shaped, the height rarely exceeding the greatest diameter (photo) 4
4a Shell with a dorsal opening at or near the apex (photo) (photo), or with a slight indentation at the anterior margin (such an indentation is present only in the rare and subtidal Arginula bella; it marks the place where a groove on the interior of the shell, beginning at the apex, reaches the margin)  Family Fissurellidae
4b Shell with neither a dorsal opening at or near the apex nor an indentation on the anterior margin 5
5a Interior of shell with a shelf (photo) (photo) Family Calyptraeidae
5b Interior of shell without a shelf  (photo) 6
6a Apex of the shell usually at or anterior to the middle, sometimes slightly posterior to the middle (if only the shell is available, the open end of the horsehoe-shaped muscle scar faces anteriorly (photo), except in the family Siphonariidae, in which the open end of a nearly C-shaped muscle scar faces the right side [left side, if the shell is observed in ventral view]) 7
6b Apex of the shell decidedly posterior to the middle (at least as far as the beginning of the last quarter) (the foot secretes a calcareous base, and the animal remains attached to this) Family Hipponicidae: 
Hipponix cranioides
7a Outline of the shell, in dorsal view, not symmetrical, the apex slightly to the right of the midline; muscle scar (often indistinct) nearly C-shaped, its open end facing the right side (left side if the shell is observed in ventral view); with a shallow siphonal groove passing through the open end of the muscle scar Subclass
Family Siphonariidae
7b Outline of the shell, in dorsal view, symmetrical (unless deformed by an injury) (photo), the apex on the midline; muscle scar horsehoe-shaped, its open end facing anteriorly (photo); without a siphonal groove 8
8a Interior of shell uniformly whitish, without any color pattern; apex in the anterior third of the shell; exterior with rather conspicuous concentic lamellae (subtidal) Family Lepetidae
8b Interior of shell usually with a color pattern of some sort (a blotch in the apical region, marginal markings, etc.) (photo); apex in the anterior or middle third of the shell (in the middle third in Acmaea mitra, the only species in which the interior is uniformly white); concentric lines not often conspicuous  Order
Families Acmaeidae, 
and Lottiidae
9a Abalones--shell low and earlike, with a low spire near the posterior end, and with a series of holes (some closed) near the left side; length sometimes exceeding 10 cm (picture) Family Haliotidae
9b Shell generally not low and earlike (except in Lamellariidae and Velutinidae), and without a series of holes near the left side; only a few species larger then 10 cm, and nearly all of these have tall spires 10
10a Shell (completely or almost completely internal in Lamellariidae) with a low profile, thus resembling the shell of a abalone (photo) 11
10b Shell not resembling that of an abalone 12
11a Shell thin, translucent white, and completely or almost completely internal  Family Marseniidae
11b Shell rather firmly calcified, covered by an almost velvety periostracum, and to a large extent external (photo) Family Velutinidae
12a Outer lip of the aperture with a deep slit ( the shell, which has a short spire above the proportionately large body whorl, resembles that of a  Margarites or Lirularia [Trochidae], its diameter being about equal to its height; found only at depths greater then 400 m) Family Scissurellidae
12b Outer lip of the aperture without a deep slit (there may, hovever, be a notch or distinct siphonal canal at the anterior end of the aperture, and there may also be a slight notch on the outer lip near the posterior end of the aperture) (includes most intertidal and subtidal prosobranch gastropods, and some opisthobranchs and pulmonates) 13
13a Length of the aperture nearly equal to the height of the shell (if there is a spire, it is not raised) 14
13b Length of the aperture not nearly equal to the height of the shell (there is a raised spire 15
14a Shell thick, similar in shape to that of a cowrie, with a series of teeth on the inside of the outer lip of the aperture; aperture not decidedly wider in its anterior half than elsewhere; height about 3 mm Marginellidae:
Granulina margaritula
14b Shell thin, not resembling that of a cowrie; without teeth on the inside of the outer lip of the aperture; aperture usually widest in its anterior half; height up to nearly 2 cm, but much smaller in some species Subclass Opisthobranchia,
Order Cephalaspidea
15a Much of the periostracum in the form of conspicuous hairs or bristles 16
15b Periostracum not in the form of conspicuous hairs or bristles  17
16a With a prominent siphonal canal that is about 1/3 the total length of the aperture (photo); height up to about 12 cm (or more)  Cymatiidae:
Fusitron oregonensis
16b Without a distinct siphonal canal, but the anterior of the aperture is angled in such a way that it forms a small spout; height generally less than 4 cm Capulidae
(formerly Trichotropidae)
17a Anterior end of the aperture without a distinct siphonal notch, spout, or canal (photo) 18
17b Anterior end of the aperture with a distinct siphonal notch, spout, or canal 34
18a Interior of shell pearly (except in Halistylus pupoideus, family Trochidae); with an operculum (photo) 19
18b Interior of shell not pearly (it may, however, be colored); with or without an operculum 20
19a Operculum thin and horny, with numerous spiral lines (photo) Family Trochidae
19b Operculum calcified and rather thick, with only a few spiral lines Family Turbinidae
20a Diameter of the shell much greater than the height (aperture almost circular, equal to about half the total diameter, which does not exceed 4 mm; without periostracum) Vitrinellidae: 
20b Height of the shell equal to or greater than the diameter 21
21a Columella with 1 or more distinct folds or ridges; height less than 1 cm 22
21b Columella without any folds or ridges; height may exceed 1 cm 24
24a Diameter about equal to the height; shell generally almost globose, consisting mostly of the body whorl (umbilicus either conspicuously open or covered by an obvious callus; height of some species attaining 10 cm) Family Naticidae
24b Height decidedly greater than the diameter; shell not almost globose, the spire usually at least one-sixth of the total height 25
25a Height not more than twice the diameter 26
25b Height considerably more than twice the diameter 30
26a Umbilicus a slit between the columella and the body whorl (generally on eelgrass or on algae, especially kelps, mid- to low intertidal and subtidal) (formerly Family Lacunidae) Subfamily Lacuninae of 
Family Littorinidae
26b Umbilicus absent or indistinct (in some species, there is a narrow space between the body whorl and the edge of the inner lip of the aperture) 27
27a Height commonly exceeding 5 mm, and in some species slightly exceeding 1.5 cm; operculum horny; periostracum not uniformly tan or brown (Almagorda subrotundata is brown, but usually has spiral banding) (mostly at higher tide levels on rocly shores, or on rocks, concrete and wood in bays, sometimes in salt marshes) Family Littorinidae
27b Height not exceeding 4 mm; operculum horny or calcareous; periostracum sometimes uniformly tan or brown (Assiminea californica, Assimineidae, inhabits salt marshes, but members of the other families to which this couplet leads are typically found at lower levels of rocky or gravelly intertidal areas) 28
30a Shell highly polished, in some species slightly bent; suturesbetween whorls so slightly indented that they are barely evident (whorls themselves, moreover, are nearly flat); parasitic on echinoderms, and strictly subtidal Family Eulimidae
30b Shell not usually highly polished, and not bent; sutures between whorls distinct; not parasitic on echinoderms (but the Epitoniidae are parasitic on various cnidarians) 31
31a Spire decidedly tapered and generally with more than three whorls; not typically found at higher tide levels in salt marshes 32
31b Spire scarcely tapered, and generally with only 3 whorls (the older whorls disappear and the uppermost surviving whorl is usually very short and smoothly rounded; typically at highter tide levels in salt marshes Truncatellidae: 
32a Height of the spire shorter than the body whorl; spire usually with 4 or 5 surviving whorls; shell sculpture limited to prominent axial ribs, and when the shell is viewed with the aperture lowermost and facing the observer, the ribs are more nearly parallel to the left side of the shell than to the right side Rissoinidae: 
32b Height of the spire considerably greater than the height of the body whorl; spire usually with at least 6 surviving whorls; shell sculpture sometimes limited to axial ribs, but if so, the ribs are more or less parallel to both sides of the shell  33
33a With both axial ribs and spiral ridges (the intersections of these sometimes form beads), or with spiral ridges only Family Turritellidae
33b Sculpture limited to axial ribs (except for a single spiral ridge near the base of the body whorl) Family Epitoniidae
34a Upper portion of the outer lip of the aperture with an anal notch
If the lip has been fractured, the contours of the growth lines nearest the lip are likely to indicate that an indentation had been present.  In species that do not have a distinct anal notch, the following combination of characters may enable one to recognize them as members of this family; width of the aperture less than one half, and usually less than one third, the height of the aperture; prominent axial ribs; foot milky white.  Presence of an anal notch, however, is the most reliable feature.
In certain species of Antiplanes, the shell is coiled sinestrally rather than dextrally, and this is helpful in assigning them to the Turridae.  Most members of the family are subtidal and they typically inhabit soft sediments.  None in our region is likely to be found in a rocky intertidal habitat.
53 Turridae
34b Upper portion on the outer lip of the aperture without an anal notch or trace of a notch 35
35a Shell highly polished, without any sculpture other then fine growth lines; widest part of the aperture (near its lower end) less then half the diameter of the shell (picture); operculum inconspicuous; typically in sandy substrata Family Olividae
35b Shell not polished, and usually with at least some sculpture; widest part of the aperture (generally near its middle) usually at least half the diameter of the shell; operculum usually conspicuous and large enough to close the aperture tightly (picture picture); not necessarily limited to sandy substrata  36
36a Lowermost portion of the body whorls including the siphonal canal, set off from the rest of it by a conspicuous groove that [may even] interrupt the axial ribs (photo) [though in Nassarius fossatus the axial ribs do not extend this far anteriorly on the body whorl]. Family Nassariidae
36b Lowermost portion of the body whorl not set off from the rest of it by a conspicuous groove that interrups the axial ribs 37
37a Shell with at least 8 distinct whorls, not counting 1 or 2 that may have been worn away at the apex (in specimens that have been abruptly worn down to 4 or 5 whorls, one can estimate, on the basis of the surviving portion of the shell, that about 10 whorls have developed; height not exceeding 4 cm 38
37b Shell with not more than 7 whorls, even if none appears to have been worn away, except in specimens whose hight commonly exceeds 12 cm 41
38a Siphonal canal half the total height of the aperture; axial ribs prominent, not forming beads where they intersect the faint spiral ridges Family Neptuneidae:
Exiliodea rectirostris
38b Siphonal canal less than half the total height of the aperture (photo); axial ribs and spiral ridges sometimes forming beads where they intersect 39
39a Siphonal canal short but obvious; spiral ridges distinctly (and sometimes conspicuously) beaded where intersected by the axial ribs (photo) 40
39b Siphonal canal barely evident; spiral ridges beaded in some species that have axial ribs, but not in the most common species (Bittium eschrichtii); which lacks axial ribs Family Cerithiidae
40a Siphonal canal narrow, directed toward the left at a nearly right angle to the long axis of the shell (as the shell is viewed with aperture lowermost and facing the observer) (photo); with about 12 axial ribs; height up to 3.5 cm; usually in salt marshes Family Batillariidae:
Batillaria attramentaria
40b Siphonal canal broad, directed to the left at about a 45 degree angle from the long axis of the shell; with at least 12 axial ribs (and sometimes more than 30); height not often exceeding 1 cm Cerithiopsidae
41a Shell either with axial ribs as well as spiral ridges, or with only spiral ridges 42
41b Shell with only axial ribs Family Volutidae
42a Shell sculpture limited to spiral ridges 55
42b Shell with axial ribs (these may be low and incospicuous, however) or thin axial lamellae (picture), as well as with spiral ridges 43
43a Axial ribs limited to the spire (the body whorl may have a few irregularly spaced grooves that are perpendicular to the spiral ridges, and young specimans of Searlesia dira, under 2 cm long, have axial ribs on the body whorl) (photo) 44
43b Axial ribs or lamellae extending to the body whorl, even though they may be less distinct on the body whorl than on the spire 45
44a Columella with 2-5 folds; periostracum light brown; spiral ridges faintly evident on the inside of the outer lip of the aperture; subtidal Family Cancellariidae:
Neoadmete modesta
44b Columella without folds; periostracum gray; dark lines in the furrows between spiral ridges of the body whorl visible on the inside of the aperture; intertidal and subtidal Family Buccinidae:
Searlesia dira
45a Axial ribs on the body whorl restricted to the upper half of it (if continued into the lower half of the body whorl, they become much less prominent) (photo) 46
45b Axial ribs distinct on at least much of the lower half of the body whorl, and as prominent as those on the upper half of the body whorl 49
46a With a series of folds on the inside of the outer lip of the aperture as well as on the columella Family Columbellidae 
(in part)
46b Folds sometimes present either on the inside of the outer lip of the aperture or on the columella, but not on both 47
47a With folds on the inside of the outer lip of the aperture (these coincide with spiral ridges on the outside of the body whorl); without folds on the columella Family Fusinidae
47b Without folds on the inside of the outer lip of the aperture; with or without folds on the columella 48
48a Axial ribs rather sharp; with 2-5 (usually 2 or 3) folds on the columella Family Cancellariidae:
Admete gracilior
48b Axial ribs low and broad; without folds on the columella Family Neptuneidae:
Plicifusus  griseus
(now Family Buccinidae,
Colus griseus)
49a Siphonal canal (measured from the angle in the outer lip of the aperture where the canal begins) one-third to one-half the total height of the aperture 50
49b Siponal canal decidedly less than one-third the total height of the aperture (picture) 51
50a Either with axial ribs and spiral ridges equally well developed and prominent, or axial ribs represented by thin lamellae and spiral ridges faint  Family Muricidae
50b Axial ribs poorly developed in comparison with the prominent spiral ridges Family Neptuneidae
51a Axial sculpture consisting of thin, frillylamellae (photo); spiral sculpture, which may be obscured by the lamellae, consisting of 1 or 2 prominent ridges on each whorl (picture)  Nucellidae: 
  Nucella lamellosa
51b Axial sculpture consisting either of fairly broad ribs or of wrinkles (these may be irregular and discontinuous), but not of frilly lamellae; spiral sculpture consisting of closely spaced spiral ridges 52
52a With 2 or 3 folds on the columella Cancellariidae:
52b Either with 1 fold or none on the columella 53
53a Without a fold on the columella; periostracum, if persistent, straw-colored or dark brown Family Neptuneidae
(in part)
53b With 1 fold on the columella; periostracum blackish or whitish 54
54a Periostracum blackish, thick, cracked, but otherwise more or less continuous except where the spire is eroded; inside of aperture purplish brown; axial ribs and spiral ridges about the same size; height up to about 2.5 cm; intertidal, in mudflats Nassariidae:
54b Periostracum whitish or dull brown; inside of aperture white or pinkish; axial ribs much more pronounced than the spiral ridges; height up to 7 cm; subtidal Family Buccinidae:
Buccinum spp
55a Columella with 2 or more folds 56
55b Columella without folds 57
56a Spiral ridges present over the entire shell; columella with about 5 folds; restricted to deep water Family Volutomitridae
56b Spiral ridges present only on the lowest part of the body whorl, near the siphonal canal; columella with 2 or 3 folds; intertidal to shallow subtidal Family Columbellidae
(in part)
57a Sculpture consisting of closely spaced spiral ridges (in Alia, Columbellidae, these are faint and restricted to the lower half of the body whorl, and are sometimes absent) 58
57b Sculpture consisting of only 1 or 2 prominent ridges on each whorl
(the lower part of the body whorl generally has a number of smaller ridges; in occasional specimens of Nucella emarginata, Nucellidae, which typically has spiral ridges over most of the shell, the ridges may be obscure)
Family Nacellidae
(in part)
58a Spiral ridges faint and limited to the lower half of the body whorl (they are most likely to be visible near the columella; use magnification); height up to about 1 cm Family Columbellidae
(in part)
58b Spiral ridges (these may be faint) distributed over all of the larger whorls; height generally greater than 1 cm 59
59a With a sharp tooth on the lower half of the outer lip of the aperture (picture) Nucellidae:
Acanthina spirata
59b Without a sharp tooth on the lower half of the outer lip of the aperture 60
60a Siphonal canal less than one-fourth the total height of the aperture; height generally less than 4 cm; common intertidal species Nucellidae
(in part)
60b Siphonal canal one-fourth to one-third the total height of the aperture (the outer lip of the aperture usually has an angular indentation where the canal begins); height commonly more than 4 cm in most species; strictly subtidal Family Neptuneidae
(in part)

Taxonomic Levels Represented in This Key:

  Order Patellogastropoda
  Family Batillariidae:  Batillaria attramentalis
  Family Buccinidae
  Family Calyptraeidae
  Family Cerithiidae
  Family Columbellidae
  Family Epitoniidae
  Family Fissurellidae
  Family Haliotidae
  Family Hipponicidae: Hipponix cranioides
  Subfamily Lacuninae of Family Littorinidae (formerly Family Lacunidae)
  Family Littorinidae
  Family Muricidae
  Family Naticidae
  Family Neptuneidae:
  Family Nucellidae
  Family Olividae
  Family Trochidae
  Family Velutinidae
  Acanthina spirata
  Colus griseus
  Fusitron oregonensis
  Searlesia dira

Page created by Nathaniel Charbonneau, 7-2002
Edited by: Anna Dyer, Dave Cowles 2005, 2006, 2007, 2008
Hans Helmstetler 12-2002