The Exotics Guide

Littorina saxatilis 4-another view of previous

Another view of the same specimen.

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Littorina saxatilis Key Image

A yellow Littorina saxatilis from San Francisco Bay. Note the obvious shoulders, the brown operculum and the brown interior of the shell.

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Littorina saxatilis Image 2

Littorina saxatilis collected at San Leandro Bay in eastern San Francisco Bay, showing color variations.

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1

Littorina saxatilis crawling on a high intertidal rock in San Francisco Bay. Note the shoulders where one whorl joins the preceding one, and the pattern of spiral ridges. The yellow lower whorl is a common color form in San Francisco Bay.

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Littorina saxatilis (Olivi, 1792)

ROUGH PERIWINKLE

  • Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Gastropoda
  • Order: Neotaenioglossa
  • Family: Littorinidae

Littorina saxatilis is a small Atlantic periwinkle that has been found on the Pacific Coast only in San Francisco Bay. Its shell has 4-5 whorls (a whorl is one full spiral turn of the shell) with a conspicuous shoulder where one whorl attaches to the preceding one, and strong spiral ridges on its surface. It grows to a height of 12 mm in San Francisco Bay, and 18 mm in the Atlantic Ocean. In San Francisco Bay the commonest color is yellow, or yellow on the lowest whorl and gray or brown on the upper ones, sometimes with brown or white spots or spiral brown stripes.

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llyanassa obsoleta Image 9

Ilyanassa obsoleta on the left, with the native hornsnail Cerithidea californica on the right. Shells from San Francisco Bay.

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8

Close up of Ilyanassa egg cases from the previous image.

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7

Ilyanassa obsoleta egg capsules on a log lying on a mudflat in San Francisco Bay. At the left and bottom of the image are the larger, smoother, urn-shaped egg capsules of the snail Urosalpinx cinerea.

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6

Ilyanassa obsoleta shells that had washed up on the shore in San Francisco Bay.

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5

Ilyanassa obsoleta in a tide pool in a discarded tire, grazing among the green seaweeds Ulva lactuca and Enteromorpha intestinalis, in San Francisco Bay.

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