An Updated Classification of the Recent Crustacea

omura rather than the Brachyura—but does this
hold for all crabs in the former Dromiacea? Thus,
we have in some instances knowingly presented
groupings for which contrary evidence exists for at
least some of the constituent taxa. We have tried to
mention all such areas in the text of the Rationale
section that follows. Several workers noted this
problem and suggested that perhaps no classification
should be attempted until such time that we
have better supported phylogenetic analyses in
hand for all (or at least most) crustacean groups.
There is merit to this argument. But in keeping with
our original goal of updating a classification of the
entire assemblage to benefit students who wish to
view the overall picture of crustacean diversity, we
felt that waiting would not improve the situation.
An additional practical problem faced by the student
wishing to construct a cladistically based classification
is the very real difficulty of representing
complex relationships in a two-dimensional classification.
To accurately depict all of the branching
relationships and show all of the sister groupings
would necessitate a rather large number of additional
taxonomic categories. One proposed solution
is to simply indent the families in the list (without
creating additional names for groupings) to imply
the relationships. But even this is difficult when
dealing with the number of families in, for example,
the gammaridean amphipods or the harpacticoid
copepods. Another proposed solution is to completely
abandon Linnaean hierarchical classifications
in favor of a more phylogenetically based system
(e.g., see Milius, 1999; Cantino et al., 1999).
We feel that, in many cases, a ‘‘standard’’ classification—that
is, a simple list of families—still serves
a purpose for those taxa where the phylogeny remains
uncertain (which is nearly every group of the
Crustacea) in that it at least allows recognition and
placement within well-defined higher groups for beginning
students. Thus, while very much in favor
of the application of cladistic methodology and of
the construction of classifications based on these
methods whenever possible, we have had difficulties
in trying to arrive at a sensible or useful way
of depicting these relationships to the beginning
student of carcinology. Consequently, to many
readers, our current arrangements and ‘‘lists’’ of
families will appear old fashioned and unsatisfactory.
The number of phylogenetic studies on the Crustacea
has risen dramatically since Bowman and
Abele’s (1982) classification. Christoffersen (1994:
135) estimated that 123 cladistic analyses of crustaceans
had appeared in print as of the end of 1992,
and that number has increased dramatically since
then. Reasons for the increase include improved
methods of computation and the availability of cladistic
programs, such as PAUP, McCLADE, and
HENNIG 86, in addition to the growing acceptance
of cladistics as a preferred way of thinking
about and depicting crustacean relationships and
relationships of all other groups as well (see papers
cited in Nielsen, 1995, and Nielsen et al., 1996).
Recent phylogenetic software is reviewed by Eernisse
(1998), and a list of phylogenetic programs
by categories is provided on J. Felsenstein’s ‘‘Phylogenetic
Programs’’ web site at http://evolution.
genetics.washington.edu/phylip/software.html#
methods. The fact that cladistics is almost routinely
employed in studies of crustacean relationships today
can be credited largely to the efforts of F. R.
Schram (e.g., see Schram, 1983a, and papers therein;
Schram, 1986; Schram and Hof, 1998). Although
it is beyond the scope of this project to review
the many cladistic analyses of crustacean
groups that have appeared since 1982, we list below
a few of the more salient papers that treat crustaceans
above the level of family, with the hope that
this might form something of an introduction to the
literature for students of crustacean phylogeny. The
list is not intended to be exhaustive. Instead, we
hope it alerts readers to the fact that very little is
settled with regard to crustacean relationships and
classification and to the fact that cladistic thinking
has profoundly affected our understanding of crustacean
relationships.
In alphabetical order within chronological order,
these works include: Briggs (1983, Cambrian arthropods
and crustaceans [see also Briggs and
Whittington, 1981]), Grygier (1983a, b, maxillopodans),
Sieg (1983a, tanaidaceans), Takeuchi
(1993, caprellidean amphipods), Wheeler et al.
(1993, arthropods including crustaceans), Ho
(1984, nereicoliform copepods), Schram (1984a,
Eumalacostraca; 1984b, Syncarida), Martin and
Abele (1986, anomuran decapods), Schram (1986,
all crustacean groups), Christoffersen (1986, 1987,
caridean shrimp), Grygier (1987a, b, maxillopodans),
Pires (1987, peracarids), Christoffersen
(1988a, b, caridean shrimp), Müller and Walossek
(1988, Maxillopoda), Abele et al. (1989, pentastomids),
Boxshall and Huys (1989a, maxillopodans),
Briggs and Fortey (1989, Cambrian arthropods
including crustaceans), Christoffersen (1989,
caridean shrimp), Schmalfuss (1989, oniscidean
isopods), Brusca and Brusca (1990, all crustacean
groups), Christoffersen (1990, Caridea), Ho (1990,
copepod orders), Kim and Abele (1990, decapods),
Walossek and Müller (1990, ‘‘stem line’’ crustaceans),
Abele (1991, decapods), Brusca and Wilson
(1991, isopods), Abele et al. (1992, maxillopodan
groups), Briggs et al. and Briggs and Fortey (1992,
Cambrian arthropods including crustaceans), Høeg
(1992a, maxillopodans), Spears et al. (1992, brachyuran
crabs), Walossek and Müller (1992, ‘‘orsten’’
fossil crustaceans), Wilson (1992, most major
extant groups), Kim and Kim (1993, gammaridean
amphipod families and amphipod suborders), Walossek
(1993, branchiopods and Crustacea), Poore
(1994, thalassinideans), Spears et al. (1994, thecostracan
maxillopodans), Wagner (1994, peracarids),
Wilson (1994, janiroidean isopods), Glenner et al.
(1995, cirripedes), Scholtz and Richter (1995, decapods),
Bellwood (1996, calappid crabs), Humes
6 � Contributions in Science, Number 39 General Introduction