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Key To The Crayfishes of Pennsylvania

   

1a    Carapace posterior to cervical groove completely covered with raised tubercles such that the surface feels granular (fig A); male with ischial hooks on 2nd and 3rd walking legs (fig B); gonopod terminating in more than 2 elements (fig C); chelae long and slender (fig D) - Procambarus acutus acutus (Found in eastern and southeastern PA in the Delaware drainage basin.  Possibly in extreme northwestern PA. Mostly near standing water, large river banks, ditches, swamps, etc. Can burrow into mud during drier season.  Can be quite large (> 12cm).)

1b    Carapace posterior to cervical groove smooth, or possibly with a few tubercles, but not extending to dorsal surface; males with ischial hooks on 2nd walking legs only (fig A); gonopod terminating in 2 elements (figs B and C - one type or the other)--> go to couplet 2.

 

 

 

 


2a    Areola linear, obliterated, or nearly obliterated at its narrowest point (ratio of length/width > 24) --> go to couplet 3.

2b    Areola not linear or obliterated at its narrowest point (ratio of length/width < 24) --> go to couplet 5.


3a    Base of immovable finger of chela with conspicuous tuft of setae and base of dactyl with deep notch (fig A); suborbital angle obsolete (not angular) and cervical groove usually interrupted (fig B) - Fallicambarus fodiens (This species is not yet reported in PA.  It might appear in the extreme northwestern and extreme southeastern corners of PA since it is found in Ohio, West Virginia, and Maryland.  Prefers seasonally flooded plains and swampy areas.  Mud chimneys present near opening to tunnel.)

3b    Base of immovable finger of chela without conspicuous tuft of setae and base of dactyl without deep notch (A in fig); suborbital angle acute (angular) and cervical groove usually continuous (B in fig) --> go to couplet 4.


4a    Dorsomesial 1/3 of palm of chela (the area of the chela's propodus below the movable finger (dactyl)) covered with tubercles and gape of chela slight (fig A); eyes are somewhat reduced and postorbital ridges without spine or tubercle (fig B) - Cambarus thomai (Found in southwestern PA.  A burrower, common in roadside ditches and clay banks of larger streams.  Sometimes under stones in streams.)

4b    Dorsomesial 1/3 of palm of chela not covered with tubercles and gape of chela moderate to large (fig A); eyes not reduced and postorbital ridges ending in a spine or tubercle (fig B) - Cambarus diogenes (Common in western PA, and reported in southeastern PA.  A burrower, it is usually near spring-fed swamps around the drier edge, or near steams in logged areas, and is typically found in lower elevations.  Can tolerate turbid water.)


5a    Marginal spines or tubercles on rostrum present (fig A);  terminal elements of gonopod long and slender, straight or curving gently (fig B) --> go to couplet 6.

5b    Marginal spines or tubercles on rostrum absent (fig A);  terminal elements of gonopod strongly curved caudally (towards the tail), claw-shaped, usually to 90o (fig B) --> go to couplet 12.


6a    Ratio of length/width of areola > 9.6; a relatively narrow areola (uncommon; check ahead for rule out) --> go to couplet 7.

6b    Ratio of length/width of areola < 9.6; a relatively wide areola --> go to couplet 8.


7a    Dactyl of large chela with a notch at its base on the inner margin ending with a large tooth (fig A); ventral margin of joint between dactyl and propodus with only 1 tubercle (fig B); terminal process of gonopod strongly curved caudally and subequal (approximately the same) in length (fig C); ratio of length of central process to total gonopod length < 0.30 - Orconectes immunis (Not yet reported in PA.  Expected in extreme northern PA.  Found in ponds and slow-moving water with soft bottoms and thick vegetation. Can be found in streams under rocks with muddy substrate.)

7b    Dactyl of large chela with inner margin nearly straight (fig A); ventral margin of joint between dactyl and propodus with 2 tubercles (fig B); both terminal processes of gonopod weakly curved caudally and the central projection longer than the mesial process (fig C); ratio of length of central process to total gonopod length > 0.30 - Orconectes virilis (Found in extreme north-northwestern and south-central PA.  In ponds, slow moving water with vegetation and debris.  Prefers warm, turbid water and can tolerate high silt.)


8a    Lateral surface of carapace anterior to cervical groove with 2 or more hepatic spines (fig A); gonopods with distinctly divergent terminal elements (fig B) - Orconectes limosus (Common in eastern half of PA. Prefers small quiet streams of low-lands, ponds, ditches.  Also in streams near muddy banks, weeds, and under rocks.)

8b    No hepatic spines; gonopods without distinctly divergent terminal elements --> go to couplet 9.

9a    Cusp of mandible smooth (fig A); sides of rostrum slightly concave (fig B); dactyls of large chelae often with distinct subterminal black bands and mesial margin of largest palm generally with 7 or fewer tubercles in a row (fig C); central process longer than mesial process and ratio of central process to total gonopod length > 0.31 (generally 0.38-0.40) - Orconectes rusticus (Introduced species, found at least in south-central PA.  In moderately sized streams with rocks and vegetation.  Reported to hybridize with O. propinquus and O. limosus.)


9b    Cusp of mandible scalloped (looks like teeth) (fig); sides of rostrum straight; mesial margin of largest palm generally with 8 or more tubercles in a row; terminal elements of gonopod subequal (approximately the same) in length; ratio of central process to total gonopod length < 0.31 --> go to couplet 10.


10a    Rostrum usually with median carina (fig A); ventral anterior margin of carpus without median tubercle or low spine (fig B); gonopod without shoulder (fig C) - Orconectes propinquus (Common in north-northwestern PA. Always under rocks with muddy/sandy bottoms.  Note rubbish pile (clean small pebbles, sand) by edge of stone.  Not in violent streams with stones being moved.)

10b    Rostrum without carina (fig A); ventral anterior margin of carpus with median tubercle or low spine (fig B); --> go to couplet 11.


11a    Gonopod with right-angle shoulder (fig) - Orconectes obscurus (Common in central and western PA. Always under rocks with muddy/sandy bottoms.  Note rubbish pile (clean small pebbles, sand) by edge of stone.  Not in violent streams with stones being moved.)

11b    Gonopod without right-angle shoulder (fig) - Orconectes sanbornii (Not yet reported in PA. Possible only in extreme western-southwestern PA. Found in riffles in small to medium-sized streams with cobble and boulders.  Can be also found in undercut banks and in debris.)


12a    Ratio of length/width of areola > 9.6; a relatively narrow areola (fig) --> go to couplet 13.

     

12b    Ratio of length/width of areola < 9.6; a relatively wide areola (fig) -- go to couplet 14.


13a    Lateral margin of propodus of chela smooth/with round dimples (fig A); mesial margin of carpus with 2-6 sharp spines (fig B); ventrolateral ridge of merus with 3 or less spines (fig C) - Cambarus monongalensis (Common in southwestern PA. Burrows found in foothills near water.  Prefers clear water nearby or underground spring.  Near, but not in, spring swamps.)

13b    Lateral margin of propodus of chela costate (ribbed) (fig A); mesial margin of carpus with 2 sharp spines (fig B); ventrolateral ridge of merus with 3 or more spines (fig C) - Cambarus dubius (Extreme southwestern PA.  Burrower near water, prefers clear water nearby or underground spring in mountains of the Allegheny plateau > 900ft elevation.)


14a    One row of tubercles on mesial palm of chela** (fig) --> go to couplet 15.

14b    Two rows of tubercles on mesial palm of chela (fig) --> go to couplet 16.


15a   Third or fourth tubercle on inner margin of fixed finger enlarged (at least noticeably larger than surrounding tubercles) (fig A); rostrum possibly with thicker margins (fig B); rostrum with or without median carina (fig C); **may have second row of 1-3 tubercles on mesial palm, very reduced - Cambarus bartonii carinirostris (Found in western PA.  In rough, small, cold mountain streams under rocks or abandoned burrows.  This subspecies may just be a morphological variation of the species.)

15b   All tubercles on inner margin of fixed finger about the same size (fig A); rostrum with uniform margins (fig B); rostrum without median carina (fig C);  - Cambarus bartonii bartonii (Very common in most of PA except extreme western PA.  In rough, small, cold mountain streams under rocks or abandoned burrows.)


16a   Rostrum with parallel margins (fig A); second row (more lateral row) of tubercles on palm of chela less developed, numbering 4-5, and adpressed (squashed down) (fig B) - Cambarus bartonii cavatus (Not yet found in PA, but possible in extreme southwestern PA; found in Ohio and West Virginia.  Can be found in burrows in very small streams and headwaters, wet roadside ditches, springs, and under rocks on the banks of larger streams.)

16b   Rostral margins convergent (fig A); two well-developed rows of tubercles of equal size on palm of chela (fig B); lateral margin of propodus with strong, well-developed depression visible from both dorsal and ventral sides - Cambarus robustus (Very common throughout PA, except southwestern corner.  Found in larger cold mountain streams.  Can be quite large.)

 

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Thanks to Dr. Ted Nuttall of Lock Haven University, PA for putting together this key.