Pagurus hirsutiusculus (Dana, 1851)

Common name(s): Hairy hermit crab

Synonyms: Pagurus (Eupagurus) mertensi, Bernhardus hirsutiusculus, Eupagurus hirsutiusculus, Pagurus (Trigonocheirus) hirsutiusculus, Eupagurus mertensi
Phylum Arthropoda 
 Subphylum Crustacea 
  Class Malacostraca 
   Subclass Eumalacostraca 
    Superorder Eucarida 
     Order Decapoda 
      Suborder Pleocyemata 
       Infraorder Anomura
        Superfamily Paguroidea 
        Family Paguridae
Pagurus hirsutiusculus from the Rosario area
(Photo by: Dave Cowles, August 2005)
Description:  The carapace of  Pagurus hirsutiusculus has setae but no spines, and only the shield is calcified (photo).  The shield is about as wide or wider than it is long.  The carpus of the right cheliped is wider than it is long and is not strongly flattened (photo).  The dactyl of legs 2 and 3 is not twisted.  It does not have longitudinal blue or white stripes, but does have some red stripes (photo).  The dorsal surface of the left chela does not have a prominent ridge or crest, nor a concavity near the midline.  The ventral surface of the merus of the right cheliped has one prominent tubercle, but it is often obscured by the abundant setae (photo).  The chelae do not have stout spines but have closely spaced tubercles, granules, and setae (photo).  The ventral side of the carpus of the right cheliped is not greatly swollen.  The long second antennae are mainly green, with yellow or white bands or spots (photo).  The legs are greenish brown with many setae (photo), and legs 2 and 3 have white or bluish bands at the articulation of the propodus and dactyl (photo), and usually a blue dot at the upper end of the propodus (may also have a blue dot on the dactyl) (photo).  Overall color olive green, brown, or black  Carapace length to 19 mm.

How to Distinguish from Similar Species: Pagurus hemphilli is mostly similar but has orange-red antennae.  Of the very common intertidal species, P. granosimanus has olive-green legs with small blue dots.  P. samuelis has a bright blue dactyl on legs 2 and 3 instead of just a blue band, plus it occurs mainly on the open coast.  P. caurinus is often mistaken for a small P. hirsutiusculus, but P. caurinus has spines on its chelae and its 2nd antennae are reddish brown without spots.

Geographical Range: Pribilof Islands, Alaska to Monterey, CA; Siberia, Japan; smaller and less hairy south of Puget Sound, and even more so south of Monterey Bay.  Common in San Francisco Bay.

Depth Range: Intertidal to 110 m

Habitat: Intertidal tide pools and under rocks and algae, more abundant in protected water.

Biology/Natural History: This species is less resistant to emersion than is P. granosimanus, but it is more tolerant of brackish water.  Many occupy small, light shells which they cannot completely retract into.    They will also abandon their shell more readily than do some other species, such as P. granosimanus (photo), sometimes even when they are berried (carrying eggs (photo).  They seem to have definite shell preferences, but these may be different in different places.  Favorites include Nucella lamellosa, Searlesia dira, Littorina spp, and Olivella biplicata shells.  Diet is mainly detritus, though they will eat live prey opportunistically.  It is known to feed on hatchlings of Nucella emarginata, which lay and attach their eggs in the low intertidal.  Predators include sculpins.  Females become ovigerous in late fall and carry a total of about 5 broods through spring and summer.  Parasites include the parasitic barnacles Peltogaster paguri and Peltogastrella gracilis and the bopyrid isopod Pseudione giardi.

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Dichotomous Keys:
  Coffin, 1952
  Flora and Fairbanks, 1966
  Hart, 1982
  Kozloff 1987, 1996
  Smith and Carlton, 1975
  Wicksten, 2009

General References:
  Brusca and Brusca, 1978
  Harbo, 1999
  Jensen, 1995
  Johnson and Snook, 1955
  Kozloff, 1993
  Morris et al., 1980
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

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

Although Pagurus hirsutiusculus is often the most common intertidal hermit crab in this region, we find few of these on Sares Head.  Perhaps this is because P. hirsutiusculus is most common in the mid-intertidal and Sares Head has few tide pools except in the very low intertidal.  There are plenty of rocks they could hide beneath, though.  They are much more common on the protected side of Fidalgo Island, around rocks in Padilla Bay.

Another individual from Sares Head.

The carapace of P. hirsutiusculus has setae but no spines.  The front part (shield), which is the only part which is calcified, is about as wide as it is long.  In this photo the
shield of the carapace is to the top right, behind the eyestalks.

In this view of the chelae, legs, and second antennae, one can see the setae which cover the chelae and legs, the larger right chela which is characteristic of Pagurus,
and the fact that the carpus of the right chela is slightly longer than wide and it is not flattened.  The antennae are green with white bands.

The dactyls of legs 2 and 3 are not twisted, and there is a white (or blue) band at the junction of the propodus and dactyl.

The ventral surface of the right merus (center of photo) has one prominent tubercle but it is largely obscured by the abundant setae.

This individual jumped out of its shell which was stuck.  That makes it easy to see the abundant body and leg setae.
Photo by Dave Cowles July 2008

This female readily crawled out of her shell even though she is "berried" (carrying eggs under her abdomen).
Photo by Dave Cowles at Kalaloch Beach #4, July 2009

The eyes of Pagurus hirsutiusculus generally seem to have a dark crescent-shaped band in them, as can be seen in this closeup dorsal view of the head.
Photo by Dave Cowles July 2008

Blue bands on chelae

This individual has both white bands and blue spots on the legs.  Photo by Dave Cowles, July 2010 

Shell plus barnacles No shell plus barnacles
Occasionally individuals are encountered with barnacles growing on them.  The individual on the left above is carrying a shell but has a strong encrustation of barnacles on its carapace and on several legs.  The individual on the right was encountered running around without a shell and has a very heavy growth of barnacles on its carapace and several on its legs.  The barnacles appear to be so large that it would be difficult for either of these individuals to find a shell large enough that they could withdraw into, though the left individual can at least tuck its abdomen into its shell.  Both were found in tidepools at Beach #4, Kalaloch, WA.  Photos by Dave Cowles, July 2012.

This juvenile, which apparently hitched a ride on something else into my classroom tank, is small and has few hairy setae on the legs yet but already is developing the white bands on the distal ends of the propodus of the walking legs and the blue spot on the proximal end.  It has selected a Littorina scutulata shell, 8 mm long, for its home.  Photo by Dave Cowles, August 2016.

Authors and Editors of Page:
Dave Cowles (2005):  Created original page