Pagurus stevensae Hart, 1971

Common name(s): Steven's hermit crab

Synonyms:  Pagurus brandtii
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Eucarida
     Order Decapoda
      Suborder Pleocyemata
       Infraorder Anomura
        Family Paguridae
Pagurus stevensae captured at 80 m depth in the San Juan Channel
(Photo by: Dave Cowles July 2001)
Description:  This subtidal hermit crab has a smooth carapace, only part of which (the shield) is calcified (photo).  The rostrum is not pronounced, with a blunt tip (photo).  The carpus of the left cheliped is about 3x as long as wide (photo); while the carpus of the right cheliped is about 2x as long as wide and is not flattened (photo).  The dorsal surface of the left chela does not have a prominent ridge or crest near the midline and the ventral surface of the merus of the right cheliped has no prominent tubercles (photo).  The propodus and dactyl of the left chela meet without a prominent gap in the middle (photo), and the propodus has a double row of divergent spines on the eminence near the midline of its dorsal surface (photo).  The right chela is long and slender, with a granular surface.  There is no white band on the distal part of the merus of the chelipeds (photo).  Color mostly reddish-brown.  No bands on the antennae.

How to Distinguish from Similar Species: P. dalli has only one row of spines on the dorsal surface of its left chela and the carpus of the right cheliped is only about 1.5x as long as wide, plus it has a distinct white band on the distal part of the merus of the chelipeds.

Geographical Range: Akun Island(Bering Sea) to Puget Sound

Depth Range: Subtidal, 5-198 m

Habitat: On shell/gravel bottoms.

Biology/Natural History: This individual is living in the sponge Suberites suberea forma latus.  It may actually be inside the fragments of a badly eroded shell which the sponge covered.  This species usually lives in sponges, though it may live in a shell as well.

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Dichotomous Keys:
  Hart, 1982
  Kozloff 1987, 1996

General References:
  Harbo, 1999
  Jensen, 1995

Scientific Articles:
Hart 1971, J. Fish. Res. Board Can. 28(10):1537. (original description)

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

Another photo of the same individual as above.

The same individual trying to right the sponge.

An underwater photo of Pagurus stevensae by Aaron Baldwin

Guide to keying this species in Kozloff's key:  Photos by Dave Cowles, August 2016, of an animal captured at 100 m depth in the San Juan Channel

The carapace is smooth and only the carapace shield is calcified. The basal portions of the eyescales are not covered by the carapace.  The eyescales do not have a deep median groove and they end with only one point. The rostrum is inconspicuous and not pointed.

Leg 4, shown here in dorsal view on the right side of an animal out of its shell, is reduced in size and subchelate.

Legs 4-5
Here is a ventral view of all 5 legs on the left side of the animal.  Note that both legs 4 and 5 are reduced in size.

The uropods are asymmetrical (one longer than the other)

Right chela carpus
The carpus of the right cheliped is about twice as long as wide.

The dactyls of legs 2 and 3 are not obviously twisted in relation to the propodus, and do not have reddish stripes.  The antenna is not striped.

Right and left chelae
The dorsal surface of the palm (propodus) of the left chela does not have a prominent ridge or crest near the midline.  It does, however, have two rows of spines.
The right chela is larger than the left. (Since this is a ventral view, the right chela is on the left and the left chela is on the right)

Ventral view of right cheliped merus
The ventral side of the merus of the right cheliped (visible to the lower right) has several small spines or tubercles, but does not have two tubercles which are markedly larger than the rest.

Left chela dactyl
The dactyl of the left chela closes firmly against the propodus without a major gap between.  Here, although the propodus is slightly damaged, the crab is tightly gripping my probe.

Dorsal view of left chela carpus
The carpus of the left cheliped is about 3x as long as wide. The left chela is approximately triangular when closed.

Frontal view
This frontal view of the live hermit crab in its Suberites suberea forma latus sponge shows that there is no white band on the merus of either cheliped.
I cut open the Suberites suberea sponge from the above individual to see how large a residual shell remained inside.  I could find no trace of a shell left--all the passages were purely of sponge.  It looked like the passageway involved at least 4-5 loops.  The hermit crab retreated into the sponge and clung to it tightly as I carved it away.  Don't worry--I didn't harm the hermit crab and I gave it a nice, roomy shell to live in when I was finished, which it picked up and packed off.

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