An Updated Classification of the Recent Crustacea

Bowman and Abele in not recognizing Tasch’s
(1969) family Limnadopsidae.
The superfamilies Cyzicoidea (which contained
only Cyzicidae) and Limnadioidea have been removed,
as there is no longer any need for them in
light of the above reassignments. Indeed, the families
Cyzicidae and Leptestheriidae are probably
more closely related to each other than either is to
the Limnadiidae (Martin, 1992; Sassaman, 1995).
Within the Cladocera, the spelling of the Holopediidae
has been corrected (from Holopedidae in
Bowman and Abele, 1982) in light of the spelling
of the type genus Holopedium (M. Grygier, pers.
comm.). The correct spelling of Macrotrichidae
(rather than Macrothricidae) was also pointed out
to us by M. Grygier (pers. comm), referring us to
Appendix D of the ICZN, third edition, example
24, page 223 (ICZN, 1985a), for examples of family
names formed from genus names ending in -
thrix. However, the fourth edition of the Code
(ICZN, 1999) now allows such misspellings to
stand if they are in ‘‘prevailing use,’’ which the family
name Macrothricidae certainly is. Thus, we retain
the spelling Macrothricidae. (This same logic
(i.e., retention of a misspelling because of prevailing
use) applies also to the family Rhizothricidae in the
harpacticoid copepods.)
Within the Anomopoda, we have removed the
family Moinidae, following the suggestion of G.
Fryer (1995, and pers. comm.). Comparisons of the
trunk limbs of species of Moina and Daphnia indicate
great similarity between these groups; certainly
they are much more similar than are many
macrothricid and chydorid genera to each other. If
a separate family were recognized for Moina and
Moinodaphnia, then we would have to erect a series
of families for various chydorids and macrothricids,
which we see as only adding to the confusion.
Thus, the Moinidae is not recognized here.
For the same reason, we have decided not to recognize
the family Ilyocryptidae as treated by Smirnov
(1992) based on the genus Ilyocryptus (see also
Young, 1998:23). However, it is possible that the
correct course of action would be to acknowledge
anomopodan diversity by recognizing both the
Moinidae and Ilyocryptidae as valid families and
establishing the additional families for other genera
as needed.
The four main cladoceran groupings have been
treated as infraorders. Although we are in full
agreement with Fryer’s (1987a–c, 1995) assessment
of the distinct nature of, and tremendous differences
among, these taxa (Fryer argued for removal of
the terms ‘‘cladocera’’ and ‘‘conchostraca’’ as formal
taxonomic entities), we nevertheless felt that
the four groups are more closely related to one another
than any one of them is to any other crustacean
assemblage, the same conclusion reached by
Richter et al. (2001) and several earlier workers.
This may prove to be a mistake. Certainly, treatment
of the cladocerans as a single order containing
four infraorders and a handful of families has the
unfortunate appearance of minimizing the staggering
morphological and ecological diversity of this
group, and we very much regret that. Schwenk et
al. (1998) provided a preliminary estimate of the
relationships of the Ctenopoda, Haplopoda, Onychopoda,
and Anomopoda based on 16S rDNA sequence
data. See Fryer (1995) for suggested relationships
among the families of the Anomopoda
and Richter et al. (2001) for 12S rDNA-based relationships
among onychopods and between the
‘‘gymnomerans’’ (� onychopods � Leptodora) and
other cladoceran groups.
The taxon ‘‘Eucladocera’’ has been removed, as
we saw no evidence for grouping together all other
cladocerans as the sister taxon to the monotypic
Haplopoda (Leptodora), as proposed by several
workers (most recently by Negrea et al., 1999). Our
classification is more in keeping with the study by
Richter et al. (2001), who supported the monophyly
of the Onychopoda � Haplopoda (the former
Gymnomera) and argued for cladoceran monophyly.
The superfamilies Sidoidea, Daphnioidea, and
Polyphemoidea have also been removed.
CLASS REMIPEDIA
It is a little discouraging that we still know so little
about the phylogenetic relationships of this fascinating
group. The initial establishment of a separate
class (Yager, 1981) met with criticism early on,
and similarities between the limbs of remipedes and
those of certain maxillopods have been pointed out
(Itô, 1989). Felgenhauer et al. (1992) hinted at molecular
data that suggested maxillopodan affinities
as well, although, to our knowledge, these data
have not been published. Spears and Abele (1997)
also suggested possible maxillopodan affinities. In
an early draft of this classification, we had the remipede
families included among the Maxillopoda,
but this was criticized, and rightly so, by several
persons who pointed out that some of the similarities
between Remipedia and Maxillopoda are symplesiomorphies
(although others, such as the loss of
the maxillary endopod, defined precoxa of the
maxillule, and three-segmented endopod of the
trunk limbs, may be synapomorphies) and are insufficient
to warrant the inclusion of the former
among the latter. More detailed morphological
studies (e.g., Schram et al., 1986; Itô and Schram,
1988; Schram and Lewis, 1989; Yager, 1989a, b,
1991; Yager and Schram, 1986; Emerson and
Schram, 1991; Felgenhauer et al., 1992) seem to
confirm the unique nature of the group. Their status
as a distinct class is therefore maintained in this
classification. See also our introductory comments
concerning which class of extant Crustacea appears
most plesiomorphic.
As noted above in the general discussion of the
primitive groups of Crustacea, several workers
(e.g., see Schram, 1986; Brusca and Brusca, 1990;
Briggs et al., 1993a; Schram and Hof, 1998; Wills,
1997; Wills et al., 1998) have suggested that re-
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