Key To Pacifastacus

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Key To Pacifastacus
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KEY TO THE SPECIES OF THE GENUS PACIFASTACUS

(Applicable to BOTH Sexes)


1.       Rostrum with single pair of marginal tubercles or spines (Fig., 12a-c):.......................................
          .........................................................................................................
Pacifastacus leniusculus........    2
          (The subspecies of P. leniusculus that have been described are not clearly defined, and
           their ranges overlap - at least in part due to introductions -- to such an extent that it is
           questionable that they should be recognized.  Only the most "extreme" representatives
           of the three can be identified here).

  • Rostrum with at least 3 pairs of marginal spines (Figs. 12d, 13)....................................................   4

 
Fig. 12.  Dorsal view of carapacees.  a) Pacifastacus l. leniusculus;  b) P. l. trowbridgii;  c) P. l. klamathensis;  d) P. connectens.

2(1).   Postorbital ridges almost always spiniform cephalically and with pair of spines at posterior
           bases; length of acumen almost always greater than width of rostrum at level of marginal
           spines (Fig. 12a; see also Fig. 14e):.......Pacifastacus leniusculus leniusculus (Dana, 1852).

           (Streams and lakes in British Columbia, California, Idaho, Nevada, Oregon, and
             Washington.  Literature: Faxon, 1885; Riegel).          

  • Postorbital ridges rounded or tuberculiform cephalically and with or without low tuberculiform
    prominences at posterior bases; length of acumen seldom equal to width of rostrum at level
    of marginal spines, never in P. l. trowbridgii (Fig. 12b,c): .............................................................   3

3(2).   Base of postorbital ridges with tubercles (Fig. 12b; see also Fig. 5a):.........................................
           ................................................................Pacifastacus leniusculus trowbridgii (Stimpson, 1857)

         (Streams and lakes in British Columbia, California, Idaho, Nevada, Oregon, and
           Washington.  Literature:  Faxon, 1885; Hagen, 1870; Riegel, 1959).

  • Base of postorbital ridges without tubercles (Fig. 12c): ................................................................
    ................................................................Pacifastacus leniusculus klamathensis (Stimpson, 1857)

          (Streams and lakes in British Columbia, California, Idaho, Oregon, and Washington.
            Literature:  Faxon, 1885; Riegel, 1959).


 
Fig. 13.  Dorsal view of carapaces.  a) Pacifastacus gambelii;  b) P. nigrescens;  c) P. fortis.

4(1).   Dorsal surface of palm of chela with two conspicuous clusters of setae (Fig. 14a,b): .............    5

  •  Dorsal surface of palm of chela without two conspicuous clusters of setae (Fig. 14c,d): ........    6

 


5(4).   Post orbital ridges with 1 or 2 pairs of posterior spines or tubercles;  rostrum lacking
           median carina (Fig. 12d);  dorsal surface of chela with comparatively prominent
           tubercles (Fig. 14a):............................................................Pacifastacus connectens (Faxon, 1914).

         (Streams in Idaho and Oregon.  Literature: Faxon, 1914).

  • Postorbital ridges lacking posterior spines or tubercles;  rostrum often with median
    carina (Fig. 13a); dorsal surface of chela with minute tubercles (Fig. 14b):................................
    ...................................................................................................Pacifastacus gambelii (Girard, 1852).

         (Streams and lakes on the Pacific Slope and in the Missouri River drainage in
            California (?), Idaho, Montana, Nevada, Oregon, Utah, Washington, and Wyoming.
            Literature: Hagen, 1870; Riegel, 1959).


 
Fig. 14.  Dorsal view of chelae.  a) Pacifastacus connectens;  b) P. gambelii;  c) P. fortis;  d) P. nigrescens;  e) P. l. leniusculus.

 

6(4).    Width of palm of chela equal to, or greater than, length of mesial margin (Fig. 14c;
             see also Fig. 13c): ......................................................................Pacifastacus fortis (Faxon, 1914).

           (Streams in Shasta County, California.  Literature: Faxon, 1914, Riegel, 1959).

  • Width of palm of chela less than length of mesial margin (Fig. 14d; see also Fig. 13b):............,
    .........................................................................................Pacifastacus nigrescens (Stimpson, 1857).

          (Streams in the vicinity of San Francisco, California.  Literature:  Faxon, 1914;
             Hagen, 1870; Riegel, 1959).

 


END OF PACIFASTACUS

Last Updated:  08 November 2005
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