Littorina sitkana Philippi, 1845

Common name(s): Sitka periwinkle, Sitka littorine
Synonyms:  Littorina sitchana
Phylum Mollusca
 Class Gastropoda
  Subclass Prosobranchia
   Order Mesogastropoda
    Suborder Taenioglossa
     Family Littorinidae
Littorina sitkana, from western San Juan Island.  Scale is millimeters.
(Photo by: Dave Cowles, July 2006)
Description:  As with other littorinids, the shell is globose with a short spire and a height approximately equal to or somewhat greater than the diameter.  There is neither a siphonal notch nor an anal notch.  The operculum is horny (photo).  The interior of the shell is not pearly.  The columella has no folds or ridges, and there is no umbilicus.  Littorina sitkana has a diameter almost equal to the height, and sometimes has prominent spiral ridges (photo).  It has only about 4 whorls.  The apex is not acutely pointed.  Its aperture is large and nearly circular (photo), and the interior is purplish or brown.  The columella is whitish.  The outside is light brown to gray or black.  May have yellow or white spiral bands.  The animal is black, with black tentacles.  Height up to about 2 cm.

How to Distinguish from Similar Species:  This is the most globose local littorina.  Others do not have pronounced spiral ridges.

Geographical Range:  Alaska to Puget Sound, Sea of Okhotsk, Japan

Depth Range:  Very high to low intertidal

Habitat:  Mostly in sheltered areas, on rocks or among algae such as rockweed.  Also on pilings and eelgrass.  Areas protected from direct sun may have greater concentrations (photo).  Often found in and around crevices.

Biology/Natural History:  This species can survive long periods out of the water and will eventually suffocate of forced to remain under water.  It ranges very high in the intertidal.  It feeds on diatoms and fine algae, which it rasps off rockweed and off the rocks themselves.  It also eats the black lichen which is found in the high intertidal.  During grazing it also eats tiny settled barnacles.  Predators include snails such as Nucella lamellosa, seastars such as Evasterias troschelii and Leptasterias hexactis, red rock crabs Cancer productus, nemertean worms such as Amphiporus formidabilis, fish such cockscomb pricklebacks (Anoplarchus purpurescens), pile perch (Rhacochilus vacca), clingfish (Gobiesox meandricus), and a variety of ducks, surfbirds, and turnstones.  The empty shells are used by small hairy hermit crabs Pagurus hirsutiusculus.  This species lays its eggs in gelatinous masses on rocks and algae.  The capsules look like tiny reddish flattened lemons.  Eggs are laid in the spring or fall on Vancouver Island, and in summer in Oregon.  One egg mass may contain the eggs of several females, which may help deter dessication.  Unlike L. scutulata, the larvae hatch as juveniles and do not have a pelagic stage.  Adults also do not range far, usually moving less than 1 meter per month.  They are much more active on foggy days.  the foot is divided by a median line and the animal crawls by lifting one half of the foot at a time.  Individuals on more exposed coasts are smaller with thinner shells and a larger foot, but still did not survive winter storms well.  The constant scraping of littorinid (periwinkle) radulas has been estimated to scrape as much as 1 cm off of intertidal rocks per 16 years.


 
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References:

Dichotomous Keys:
  Flora and Fairbanks, 1966
  Griffith, 1967
  Kozloff 1987, 1996

General References:
  Carefoot, 1977
  Harbo, 1997
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris, 1966
  Niesen, 1997
  O'Clair and O'Clair, 1998
  Sept, 1999

Scientific Articles:
Behrens, S., 1971.  The distribution and abundance of the intertidal prosobranchs Littorina scutulata (Gould 1849) and Littorina sitkana (Philippi 1845).  M.S. thesis, University of British Columbia, Vancouver, Canada.

Web sites:
 


General Notes and Observations:  Locations, abundances, unusual behaviors:


In this group the spiral ridges can be seen on those on the left and the horny operculum can be seen on those to the right



This dense aggregation of L. sitkana is in the upper intertidal of San Juan Island.  This aggregation is in a steep-sided cove partly protected from the sun.

Smile

Sometimes the aggregations spontaneously form into pleasing shapes, such as this smile at Slip Point, WA.  Photo by Dave Cowles, July 2012


Authors and Editors of Page:
Dave Cowles (2006):  Created original page