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)

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.

References:

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:

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

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

 

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.
Another individual, found at Kalaloch July 2024. Often, finding a crustacean encrusted with barnacles like this suggests that they have a "terminal molt". Crustaceans molt their exoskeleton as they grow, thus shedding any external growths such as barnacles. However, some species reach a terminal molt, often when they become sexually mature (adult). Thereafter, they cannot molt and so cannot shed the barnacles.

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.