Section I
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Horton H. Hobbs Jr.
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Table of Contents -- Section I

 


INTRODUCTION

The keys presented here include all of the species and subspecies described from North America and Middle America prior to January 1, 1972, that I consider to be valid.  In preparing them, I was unable to find characters that would distinguish several previously recognized taxa; consequently, they are omitted and are provisionally relegated to synonymy with previously described species.  Most of the older synonyms have not been cited; however, attention is called to those taxa that are here considered invalid for the first time, or in recent works.  Several species that previously have been relegated to synonymy have been resurrected.  In instances in which it is known that the species cited actually represents a species complex comprising several undescribed species and subspecies, such have been indicated, and, at the appropriate places, attention is called to those sections of the keys in which there is doubt as to the validity of the taxa recognized.

The trend that pervaded the literature dealing with crayfishes for almost three-quarters of a century of applying subspecific designations to superficially similar populations oftentimes led to what appear now to have been erroneous concepts of relationships. Unless there is evidence of intergradation between those populations that have been designated as subspecies, they are here accorded specific rank without presenting arguments for such apparently arbitrary decisions.  The subgeneric designations employed in the genera Cambarus and Procambarus are diagnosed and discussed in Hobbs, 1969b and 1972, respectively.

Appended to the keys is an alphabetical list of the subfamilies, genera, species, and subspecies of the crayfishes occurring in North America and Middle America and the states in which each occurs.  A second list of the states or provinces of the several countries and the crayfishes that are known to occur within their boundaries is also included.

I should be remiss should I fail to warn potential users of these keys that there exist a number of undescribed species, particularly of the genera Cambarus and Orconectes in the southeastern United States.  For obvious reasons, none of them are included in the keys.  Although only 284 species and subspecies are included here, at least an additional 50 taxa are known to exist, and descriptions of a number of them are in press, in manuscript form, or are being prepared by R. W. Bouchard, J. F. Fitzpatrick Jr., H. H. Hobbs, Jr., R.D. Reimer, Alejandro Villalobos, and J. G. Walls.

Many of the following introductory directions of collecting, methods of preservation, and aids in identification are only slightly modified from Hobbs (1968b).


SYSTEMATIC POSITION OF THE FAUNA

The crayfishes of North America and Middle America are members of the holarctic family ASTACIDAE; they differ most conspicuously from their counterparts in the Southern Hemisphere, the PARASTACIDAE, in the modification of the appendages (first pleopods) of the first abdominal segment of the male as organs of sperm transfer.  Three of the four subfamilies of the Astacidae are represented in the fauna:  the ASTACINAE, largely confined to waters west of the continental divide in southwestern Canada and the United States; the CAMBARINAE, except for suspected or known introductions, found only east of the continental divide from New Brunswick southward to Guatemala, Honduras, and Cuba; and the CAMBARELLINAE that range from southern Illinois to the Gulf Coastal region, along the latter from Texas to Florida, and on the Central Plateau and the Pacific slope of Mexico.


INTRODUCTIONS

There is no evidnece that the crayfishes that have been imported from other parts of the world have become established in any part of North or Middle America, but at least three of the American species exist as breeding populations on islands or in other countries: Orconectes limosus in western Europe, Pacifastacus leniusculus in Sweden, and Procambarus clarkii in Hawaii and Japan.  (See Penn, 1954).


HABITS

Members of all of the crayfish genera, except Troglocambarus, have exploited a wide variety of epigean aquatic and semiaquatic habitats.  In addition to frequenting various types of aquatic environments where most individuals secrete themselves during the day under stones, in dense mats of vegetation, or under debris, many dig burrows into the beds or banks of ponds or streams.  Whereas they may seek refuge in such excavations during the daylight hours throughout most of the year, or in dry seasons when the water table sinks below the level of the bed, or when the surface waters freeze, they also may remain in these burrows for weeks or months.  Frequently, during the breeding season, a pair of individuals share, at least for a time, the same burrow, and the female remains there until her eggs are laid and the young have hatched.

Other crayfishes (certain members of the genera Procambarus, Fallicambarus, and Cambarus) seldom, if ever, invade bodied of open water; instead, in areas where the water table is not beyond reach, they tunnel into the soil, often constructing complex, highly branching burrows with several openings to the surface.  Animals with such habits are rarely seen except on warm, humid evenings when they may leave their tunnels and wander about over the surface of the ground.  Such burrows are most often found in seepage or swampy areas or in low-lying flat-woods.  They are especially abundant in the "Black Belt" of Alabama and Mississippi.

Only in North and Middle America and Cuba have crayfishes become so completely adapted to spelean environments that they have assumed a troglobitic existence.  While there are many trogloxenes and a few troglophiles among the astacids, only 21 species and subspecies belonging to the genera Troglocambarus, Procambarus, Orconectes, and Cambarus are known to have become typically albinistic and to exist as troglobites, seldom appearing in epigean waters except following spring floods or heavy rains.


METHODS OF COLLECTING

In streams and other bodies of water that are shallow and not choked with vegetation, no implement provides better results than a -inch mesh seine.  In streams, if the seine is anchored downstream a few feet from the area to be sampled, and stones or debris are vigorously turned or agitated, the animals will "swim" and be carried by the current into the seine.  Dragging the seine across pools or shallow ponds is also often most effective.  In vegetation-choked, or deep bodies of water, wire traps with inverted cones and baited with meat often net fair samples of the crayfish population, particularly if left in the water overnight.  D-ring dipnets are also often useful.  Some of the most successful "crawfishing" accomplished in the United States is conducted in Louisiana where several modifications of a "lift net" are employed.  This net consists essentially of two V-shaped metal rods (about six feet in length) tied together at their apices.  The ends of the rods are affixed to the corners of a two-foot square net, and a lift-cord with a float is attached at the juncture of the rods.  The bait (fish heads, scrap pieces of chicken, etc.) is centered on the net below the juncture of the rods.  Several nets are then "set out" in a shallow slough or bayou, and the fisherman makes his way from one to another, quickly lifting the contraption and removing the crayfish that have been attracted to the bait.

Collecting at night in shallow water is usually most rewarding in that members of a number of species, most of the adults of which remain in their burrows or hidden in mats of vegetation or debris during the day, venture into open water at night.  A headlight for spotting their eyes, which are ruby-red in reflected light, and a small dipnet are indispensable aids for collecting at night.

To collect burrowing crayfishes that seldom, or never, invade open water, several techniques have been found to yield some measure of success:

  1. The chimney should be removed, the burrow opened to the water table, and the opening sufficiently enlarged so that one's hand may be thrust below the water.  If the water is thoroughly roiled and then left undisturbed for 2 to 5 minutes, the occupant often comes to the opening where its antennae may be seen at the surface of the water.  The open hand should be thrust into the opening to "pin" the crayfish against the wall of the burrow.  With careful manipulation, the crayfish can be seized with the fingers and withdrawn from the burrow.  To avoid excessive digging, frequently water may be poured into the burrow to elevate the water level.
  2. In areas in which many burrows indicate the presence of a colony of crayfish, traps may be utilized with some degree of success, especially in relatively warm humid weather.  Jars or cans, baited with meat or peanut butter, with one end removed and buried with the open end flush with the surface of the ground, are adequate, and if left overnight will frequently attract a few individuals.
  3. Collecting at night involves the least labor.  Particularly following rains or when the humidity is high, the burrowing crayfishes come to the mouths of the burrows and often leave them to wander over the surface of the ground.  With the aid of a headlight or some similar light source, they can be obtained in numbers by hand.
  4. For those species that construct a single  vertical passage with only one or two openings to the surface, the use of a "yabbie pump" is often most helpful.  This device consists of a cast iron cylinder some three feet long and about six inches in diameter, open at one end and closed, except for two small hole (1/8 inch in diameter), at the other.  Across the closed end is a foot-long bar (the handle) welded perpendicular to the axis of the cylinder.   In places where the soil is sufficiently wet, the cylinder may be forced (open end down) into the soil around the vertical passage to a depth of one to three feet; the closing the two small holes with the thumbs, it is lifted quickly.  Frequently the crayfish, along with much of its burrow, is removed from the substrate.
  5. To obtain some species, no substitute has been found for a laborious dissection of the complex (branching) burrows with the naked hand and the aid of a trowel or shovel.  Gloves are almost useless, and, if used, the crayfish is often crushed before one realizes that it has been "cornered".

In capturing the troglobitic species, some type of headlight and a small dipnet are indispensable, and in some areas scuba equipment is essential.  If one must resort to diving, a hand net with a sufficiently long trailing bag that might be folded against the rim of the net is highly recommended, for if the bag is too shallow, it is often exceedingly difficult to keep the crayfish in it when the initial swing is completed.

In all National Parks and in some states, collecting of crayfish is prohibited, and they may be taken only after a permit has been obtained from the appropriate agency.  Attention might also be called to the inappropriateness of trespassing on fenced or private property.

A plea is made to be judicious in collecting specimens where populations seem to be of limited size.  Such restraint is particularly advisable in subterranean environments. 


PRESERVATION

Crayfishes are perhaps best killed in 6% neutral formalin, and should remain in the solution, depending on size, for 12 hours to a week.  After being washed in running water for a few hours, they should be transferred to 70% ethyl alcohol or 20 to 30% isopropyl alcohol.  More relaxed specimens may be obtained by immediate preservation in 70 to 80% ethyl alcohol and, after a week or so, transferring them to fresh 70% alcohol.

(Editors Note:  With the advent of molecular genetic techniques, it is suggested that tissue samples be taken and frozen at - 80oC, as extracting DNA from formalin preserved specimens is almost impossible.  Specimens can also be placed directly into 80 to 90% ethyl alcohol, as suggested above by Hobbs, however if DNA is to be extracted from such specimens it should be done within 1-2 months as the DNA tends to degrade in ethanol preserved crayfish specimens over time).


LITERATURE

Despite the number of items cited in the "References" section, this is a selected bibliography.  Several of the citations contain original descriptions of species that have not been treated in subsequent works; however, an attempt has been made to restrict the references to summary studies in which diagnoses, illustrations, ranges, and/or ecological data are included.  In Appendix II, existing regional keys that might be useful in identifying the faunas of the various countries or states are indicated by the references in parentheses.


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Last Updated:  10 September 2004