Molluscs - snails, nudibranchs, bivalves, chitons

Mytilus californianus Conrad, 1837
Phylum Mollusca, Class Bivalvia, Subcl. Pteriomorpha, Order Mytiloida, Family Mytilidae

California mussel; shell bluish-black, heavy; anterior end pointed, posterior rounded; prominent radial ribs (often eroded). Attached with tough, proteinaceous byssal threads. Filter feeder.

Very abundant, exposed outer coast, forms multilayer beds in upper-mid intertidal zone. Dominant space competitor, preyed on by sea stars (Pisaster ochraceus), sea otters, whelks, crabs & birds.

Geogr. Range: Aleutian Islands, Alaska to Baja
Synonyms:
Similar species: bay mussels, Mytilus trosselus & the introduced M. galloprovincialis have thinner smoother shells usually lacking radiating ridges; both occur in more wave-protected locations.
Image: alga is Endocladia muricata

Fissurella volcano Reeve, 1849
Phylum Mollusca, Class Gastropoda, Subcl. Vetigastropoda, Family Fissurellidae

Keyhole limpet; cap-shaped shell 20-35 mm with elongate oval aperture at apex; shell pink with reddish-brown radiating markings; edge of mantle striped with red & white, foot yellowish.

Common on sides of rocks & under overhangs, mid-intertidal zone on protected outer coasts. 

Geogr. Range: northern California to Baja
Synonyms:
Similar species: Diodora aspera is larger, occurs lower on the shore (and subtidally), & has a round rather than oval opening at apex of shell.

Image: tube of Serpulorbis (upper left), Acmaea mitra (rt side, middle)

Haliotis cracherodii Leach, 1814
Phylum Mollusca, Class Gastropoda, Subcl. Vetigastropoda, Family Haliotidae

Black abalone. Oval shell to >20 cm, dark blue to black, smooth with 5-9 holes flush with surface of shell; tentacles & side of foot black.

Rare (listed as endangered in 2009); high intertidal zone to 6 m depth subtidally; bulk of population in crevices in rocky intertidal.  Grazes on diatoms when small, unattached drift algae when larger.

Geogr. Range: central Oregon to Cabo San Lucas (Baja)
Synonyms:
Similar species: this is the only intertidal abalone, but Haliotis rufescens & H. walallensis occur subtidally in kelp forests (see table)

Tegula funebralis (A.Adams, 1855)
Phylum Mollusca, Class Gastropoda, Subcl. Vetigastropoda, Family Trochidae

Black turban snail. Conical rounded shell to 30 mm, charcoal to purplish-black; apex usually eroded to gold & white. Umbilicus closed (arrow); low spiral ridge around center of base ends in a notch & tooth on inner edge of aperture (inset). Foot & head black.

Abundant throughout mid-intertidal zone and lower portion of high zone, protected outer coast; large aggregations shelter in crevices at low tide; herbivorous. 

Geogr. Range: Vancouver Island to Baja
Synonyms: Tegula funebralis
Similar species: Chlorostoma brunnea is similar but has light brown shell (usually covered with dark red non-coralline algal crust) & it occurs lower on the shore down into the subtidal.

Tegula brunnea (Phillippi, 1848)
Phylum Mollusca, Class Gastropoda, Subcl. Vetigastropoda, Family Trochidae

Brown turban snail. Conical rounded shell to 30 mm, light brown but usually encrusted with dark maroon non-coralline red algae. Umbilicus closed (arrow); low spiral ridge around center of base ends in a notch & tooth on inner edge of aperture (inset). Foot black with orange margins.

Common on rocks & algae, lower edge of mid-intertidal zone down into subtidal; protected outer coast; bulk of population lives subtidally in kelp forests; herbivorous.

Geogr. Range: Cape Arago, Oregon to Channel Islands
Synonyms: Tegula brunnea
Similar species: Chlorostoma funebralis is black & occurs higher on the shore. Two other turban snails (Chlorostoma montereyi & Promartynia pulligo) are primarily subtidal but sometimes can be found in the low intertidal zone.

Calliostoma ligatum (Gould, 1849)
Phylum Mollusca, Class Gastropoda, Subcl. Vetigastropoda, Family Trochidae

Conical, rounded shell to 25 mm, dark brown with narrow tan or dark blue spiral lines.  Head & foot black. Coats shell with thin layer of slippery mucus using posterior end of foot.

Common on rocks, red algae, low intertidal zone to subtidal. Omnivorous, but generally browses on sponges, bryozoans, compound ascidians, hydroids & other sessile invertebrates rather than algae.

Geogr. Range: Alaska to San Diego
Synonyms:
Similar species: three other species of Calliostoma live subtidally & are sometimes encountered in the low intertidal zone.

Littorina keenae (Phillippi, 1847) Rosewater, 1978
Phylum Mollusca, Cl. Gastropoda, Subcl. Caenogastropoda, O.Sorbeoconcha, F. Littorinidae

Periwinkle; shell smooth to 23 mm, brown to black with white patches & fine spiral lines (often eroded); aperture longer than half shell length, inside brown with white inward-curving stripe at base (arrow); smooth flattened parietal area adjacent to posterior end of aperture (arrow); tan columella wide & polished.

Abundant on bare rock in high intertidal zone, exposed & protected outer coast; browses on microalgae.

Geogr. Range: Coos Bay, Oregon to central Baja
Synonyms: Littorina planaxis
Similar species: Littorina plena & L. scutulata are smaller; both lack wide columella & smooth patch on parietal area.  Must examine reproductive structures to confirm identification.

Littorina scutulata Gould,1849
Phylum Mollusca, Cl. Gastropoda, Subcl. Caenogastropoda, O.Sorbeoconcha, F. Littorinidae

Periwinkle; shell smooth 13-18 mm, brown, olive, or black overlaid with white checkerboard pattern; aperture less than half length of shell & lacks white stripe on interior; columella narrow & not polished; cephalic tentacles with transverse black bands.

Abundant, high & mid-intertidal zones among algae & barnacles, exposed & protected outer coast; browses on microalgae, lichens, macroalgae, & drift.

Geogr. Range: Sitka Alaska to Baja
Synonyms:
Similar species: Littorina plena has longitudinal black stripe on cephalic tentacles, fine spiral grooves on shell & light stripe on interior of aperture; Littorina keenae is larger, has a white stripe on inside of aperture & has a wider columella w. a flattened parietal area.  Must examine reproductive structures to distinguish species.

Littorina plena Gould, 1849
Phylum Mollusca, Cl. Gastropoda, Subcl. Caenogastropoda, O.Sorbeoconcha, F. Littorinidae

Periwinkle; shell to 19 mm; black or w. fine marbling on background of brown, olive or black, usually w. fine incised spiral grooves; aperture less than half length of shell w. narrow stripe at base of aperture (arrow) but lacks flattened parietal area of L. keenae; columella narrow; cephalic tentacles black or with longitudinal black dark stripe.

Abundant throughout intertidal zone; exposed & protected outer coast, also salt marshes & estuaries.

Geogr. Range: Kodiak Is. Alaska to Baja
Synonyms: included in Littorina scutulata until 1979.
Similar species: Littorina scutulata  has  black bands on tentacles & lacks spiral grooves; L. keenae is larger, has smooth parietal area & a stripe on interior of aperture. Must examine reproductive structures to confirm identification.
Image: L. plena (center & left), probably L. scutulata at right

Thylacodes squamigerus (Carpenter 1857)
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Family Vermetidae

Tube snail; shell attached to rock & uncoils with growth, forming scaly tube with longitudinal ridges; aperture 12 mm; lacks operculum.

Abundant on rocks; solitary or in clusters, mid-intertidal zone to subtidal. Aggregations arise from gregarious larval settlement, not asexual division. Suspension feeds using mucus net.

Geogr. Range: Monterey Bay to Baja
Synonyms: Aletes squamigerus, Serpulorbis squamigerus
Similar species: Petaloconchus montereyensis is much smaller in diameter and lives primarily in subtidal.

Nucella emarginata (Deshayes, 1839)
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Infraorder Neogastropoda, Family Muricidae

Heavy, low-spired spiral shell to 35 mm; sculpturing varies from irregular, nodulous spiral cords & axial ribs to smooth; siphonal canal short & open; indistinct parietal nub present on inner posterior margin of aperture; shell white, yellow, orange, gray, brown or black.

Common, high to mid-intertidal zones, exposed & protected outer coast; drills into prey (mussels, limpets, barnacles) with radula.

Geogr. Range: Halfmoon Bay, central Calif. to northern Baja
Synonyms: Thais emarginata
Similar species: overlaps with northern Nucella ostrina between Halfmoon Bay & Pt. Conception; in zone of overlap, N. ostrina occurs in wave-swept areas; Nucella from Hopkins Marine Station south to Pt. Joe appear to be all N. emarginata with N. ostrina to the south & north.

Nucella ostrina (Gould, 1852)
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Infraorder Neogastropoda, Family Muricidae

Heavy, spiral shell to 30 mm w. slightly higher spire than N. emarginata; sculpturing varies from broad spiral cords & axial ribs to smooth; siphonal canal short; lacks parietal nub on the inner posterior margin of aperture; shell white, gray, brown or black.

Common, high to mid-intertidal zones, exposed & protected outer coast; drills into prey (mussels, limpets, barnacles) with radula.

Geogr. Range: Bering Sea to Pt. Conception, Calif.
Synonyms:
Similar species: overlaps with southern Nucella emarginata between Halfmoon Bay & Pt. Conception; in zone of overlap, N. ostrina occurs in wave-swept areas; Nucella from Hopkins Marine Station south to Pt. Joe appear to be all N. emarginata with N. ostrina to the south & north.

Nucella analoga compressa (Dall, 1915)
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Infraorder Neogastropoda, Family Muricidae

Heavy, ~high-spired shell to 35 mm; distinct broad spiral cords with narrow interspaces in between; short siphonal canal open on ventral side; shell white to dark orange-brown; this is the southern subspecies of N. analoga.

Uncommon, mid-intertidal zone; in mussel beds of wave-exposed outer coast; preys on mussels, limpets, barnacles.

Geogr. Range: central California
Synonyms: previously misidentified as Nucella canaliculata
Similar species: Nucella analoga analoga has narrower spiral cords with narrow interspaces & occurs from SE Alaska to northern California. Nucella canaliculata occurs only from Puget Sound northward; its spiral cords are narrow but with broad deeply-incised interspaces in between.

Acanthinucella punctulata (Sowerby, 1825)
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Infraorder Neogastropoda, Family Muricidae

Spiral shell to 27 mm with low spire; distinct tooth on outer lip of aperture; siphonal canal short & open on ventral side; color pattern of interrupted brown spiral bands against light background (appears speckled); shoulder of shell more rounded than angular.

Locally abundant, high to upper mid-intertidal zones, protected outer coast;  associated with barnacles.

Geogr. Range: Monterey Bay to Baja
Synonyms: Acanthina punctulata
Similar species: Acanthinucella spirata occurs lower on the shore, has a slightly higher spire & has a distinct angular keel at shoulder of shell.

Image: barnacle are mostly Balanus glandula

Acanthinucella spirata (Blaineville, 1832)
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Infraorder Neogastropoda, Family Muricidae

Spiral shell to 28 mm with higher spire than A. punctulata; distinct tooth on outer lip of aperture; siphonal canal short & open on ventral side; color pattern of interrupted brown spiral bands (appears speckled) against gray background; shoulder of shell with distinct angular break (arrow).

Moderately common, mid-intertidal zone (lower than A. punctulata), protected outer coast.

Geogr. Range: Tomales Bay, Calif. to Baja
Synonyms: Acanthina spirata
Similar species: Acanthinucella punctulata occurs higher on shore, has a  lower spire & is more rounded than angular.

Image: snail is surrounded by sand tubes of Phragmatopoma.

Ocinebrina circumtexta Stearns, 1871
Phylum Mollusca, Class Gastropoda, Subcl. Caenogastropoda, Order Sorbeoconcha, Infraorder Neogastropoda, Family Muricidae

Spiral shell to 25 mm; siphonal canal short & open on ventral side; strong spiral grooves with several low broad axial ribs; shell white or gray w. 2 bands of square brown spots per whorl.

Moderately common, mid-intertidal zone, protected outer coast.

Geogr. Range: northern California. to Baja
Synonyms: Ocenebra circumtexta
Similar species: Acanthinucella & Nucella are larger & both lack the incised spiral, somewhat reticulate sculpture of Ocinebrina.

Image: dark crust is Petrocelis phase of (probably) Mastocarpus papillatus.

Cyanoplax hartwegii (Carpenter, 1855)
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Lepidochitonidae

Oval, somewhat flattened chiton to 50 mm long; girdle & shell valves superficially smooth, but with minute closely-spaced granulations; shell valves dull olive-green to olive-brown; girdle usually darker than valves.

Common, especially under fronds of the brown alga Silvetia compressa; mid-intertidal zone, protected outer coast; herbivorous, browses on Silvetia and a variety of red algae.

Geogr. Range: Monterey Bay to Baja
Synonyms: Lepidochitona hartwegii
Similar species:

Image: Lottia scabra (at left); barnacles mostly Chthamalus.

Nuttalina californica (Reeve, 1847)
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Lepidochitonidae

Elongate chiton to 50 mm long; valves often eroded or covered with encrusting algae; girdle wide & covered with short dark spinelets; bottom of foot orange.

Abundant, clinging tightly & wedged into crevices; high to mid-intertidal zones; exposed & protected outer coast with strong wave action; browses erect corallines, Endocladia,  Gelidium, & Cladophora.

Geogr. Range: Puget Sound to San Diego, but uncommon north of central California or south of Pt. Conception
Synonyms:
Similar species: Mopalia muscosa is larger & broader w. larger girdle spines, occurs lower on the shore & in areas less exposed to wave action.

Image: Tetraclita rubescens (barnacles), Lottia limatula (middle top).

Mopalia muscosa (Gould, 1846)
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Mopaliidae

Large oval chiton to 80 mm long; valves coarsely sculptured but often eroded or overgrown; dull brown to blackish purple or gray; girdle covered densely with dark brown simple spines.

Common on & under rocks as well as in tidepools, upper mid- to low intertidal zones, exposed & protected outer coast; browses on red algae, Cladophora, bryozoans, hydroids, & barnacles.

Geogr. Range: British Columbia to northern Baja
Synonyms:
Similar species: Nuttalina californica is narrower & more elongate and occurs in more wave-exposed locations.  Mopalia lignosa is similar in shape & size but is gray-green rather than dark brownish-purple.

Image: tiny white spiral  tubes are polychaete Spirobis.

Mopalia lignosa (Gould, 1846)
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Mopaliidae

Large oval chiton to 70 mm long; valves smooth w. mid-dorsal ridge; gray-green w. brown or white lines; girdle narrower than M. muscosa, cream to brown (orange on underside), with sparser cover of short spines.

Common, mostly on undersides of rocks, mid-intertidal zone to subtidal, protected outer coast.  Feeds on diatoms & a variety of green & red algae.

Geogr. Range: Alaska to Pt. Conception
Synonyms:
Similar species: Mopalia muscosa is similar in shape & size, but  brown-black or purplish with denser spines on a wider girdle.

Katharina tunicata (Wood, 1815)
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Mopaliidae

Large distinctive chiton to 120 mm long; wide shiny black leathery girdle covers most of shell valves.

Common, mid- to low intertidal zones on exposed outer coast where wave action is strong; browses on benthic diatoms & a variety of brown & red algae.

Geogr. Range: Aleutian Is., Alaska to Pt. Conception
Synonyms:
Similar species: no other intertidal chitons are black.

Tonicella lineata  (Wood, 1815)
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Mopaliidae

Pink lined chiton, 5 cm; head valve (arrow) with smoothly arched (not zig-zag) concentric lines of pink or orange, white, dark maroon or black, & sometimes brilliant blue.

Moderately common, low intertidal on crustose corallines & under erect corallines and other algae; also shallow subtidal; grazes on crustose corallines.

Geogr. Range: Aleutian Islands to central California
Synonyms:
Similar species: other Tonicella are mostly subtidal.  Tonicella undocaerulea  has zig-zag concentric lines on head plate, but lacks continuous dark lines.  Tonicella lokii  has zig-zag lines on head plate with continuous dark lines. Tonicella venusta is small (1.5 cm), lines on head valve are hard to see and lines on middle valves often expand into flame-like markings.

Image:  white worm is a nemertean (ribbon worm), probably Amphiporous imparispinosus.

Stenoplax heathiana  Berry, 1946
Phylum Mollusca, Class Polyplacophora, Order Chitonida, Family Ishnochitonidae

Elongate oval 8 cm or more; bottom of foot cream; valves white or tan with brown or green speckles or streaks; very photonegative & moves quickly back toward underside of rock when disturbed.

Common, but cryptic under rocks in sand or shell rubble; lower mid-intertidal zone to shallow subtidal.

Geogr. Range: northern California to Baja
Synonyms: Ishnochiton heathiana
Similar species:  Stenoplax fallax occurs subtidally & has an orange foot and its valves are more purple or reddish.