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