An Updated Classification of the Recent Crustacea

An Updated Classification of the Recent Crustacea
By JOEL W. MARTIN 1 AND GEORGE E. DAVIS 1
ABSTRACT. An updated classification of the Crustacea down to the level of family is
provided. The classification is based loosely on that given by Bowman and Abele (1982)
and includes all new families and higher level taxa described since that time. In addition,
in several crustacean groupings, new arrangements and assignments have been incorporated,
based usually on phylogenetic information that has accrued or that has become
more widely accepted since 1982. Among the more salient changes, some of which are
more controversial than others, are the recognition of the former phylum Pentastomida
as a group of maxillopod crustaceans based on additional spermatological and molecular
evidence, the inclusion of the parasitic Tantulocarida also among the maxillopods, the
treatment of the Branchiopoda as the most primitive extant group of crustaceans, and
the recognition of Guinot’s (1977, 1978) division of the higher (eubrachyuran) crabs
into two ‘‘grades’’ based primarily on placement of the genital aperture. The revised
classification includes 849 extant families in 42 orders and 6 classes; this is an increase
of nearly 200 families since the Bowman and Abele classification. More than 90 specialists
in the field were consulted and asked to contribute to the update. Some workers
are not in agreement with our final arrangement. In particular, there are questions or
dissenting opinions over our choice of which taxa to recognize, which authorities and
dates to credit for various taxa, and especially over the arrangements among and/or
within the higher taxa. As an aid to future workers in crustacean classification and
phylogeny, comments and dissenting opinions of some of these workers are appended
to highlight areas of uncertainty or controversy. Also appended are a list of the specialists
who were given the opportunity to respond (Appendix II) and a list of printed and
World Wide Web resources that contain information on crustaceans (Appendix III). The
new classification is in part a result of one such site, the Crustacean Biodiversity Survey
(formerly found at URL http://www.nhm.org/cbs/, now temporarily off-line).
GENERAL INTRODUCTION
No group of plants or animals on the planet exhibits
the range of morphological diversity seen among
the extant Crustacea. This morphological diversity,
or disparity in the paleontological jargon, is what
makes the study of crustaceans so exciting. Yet it is
also what makes deciphering the phylogeny of the
group and ordering them into some sort of coherent
classification so difficult. Because of the great age
of the group, extending back at least as far as the
early Cambrian and almost certainly beyond that,
there has been ample time for endless experimentation
with form and function. The result of these
many millions of years of evolution is quite dazzling.
The current estimate of the number of described
species is approximately 52,000 (Land,
1996; Monod and Laubier, 1996). This estimate is
surely on the low side, as a recent estimate of the
1
Natural History Museum of Los Angeles County, Research
and Collections, Department of Invertebrate Zoology,
900 Exposition Boulevard, Los Angeles, California
90007
Email: jmartin@nhm.org and gdavis@nhm.org
number of living species of ostracodes alone is
10,000 to 15,000 (K. Martens, pers. comm., and
discussions on the electronic ostracode listserver
OSTRACON@LISTSERV.UH.EDU) and Kensley
(1998) has estimated more than 54,000 for the reefassociated
peracarids. Among the Metazoa, the estimate
of 52,000 species places crustaceans fourth,
behind insects, molluscs, and chelicerates, in terms
of overall species diversity. But morphological diversity
(disparity) is higher in the Crustacea than in
any other taxon on Earth. There are probably few
other groups of animals (squids come to mind because
of Architeuthis) in which the difference in
maximum size of adults can be a factor of 1,000.
The known size of crabs now ranges from a maximum
leg span of approximately 4minthegiant
Japanese spider crab Macrocheira kaempferi and a
maximum carapace width of 46 cm in the giant
Tasmanian crab Pseudocarcinus gigas (as cited in
Schmitt, 1965) to a minimum of 1.5 mm across the
carapace for a mature ovigerous female pinnotherid,
Nannotheres moorei, the smallest known spe-