An Updated Classification of the Recent Crustacea

ed with additional sequence data and additional
taxon sampling by Abele (1991), whose review of
morphological and molecular data supported a distinct
Dendrobranchiata (the penaeoids) clade and
also three other distinct clades corresponding to (1)
the Caridea (including the procaridoids), (2) the
Stenopodidea, and (3) a ‘‘reptant’’ lineage. (The latter
lineage is responsible for most of the more troublesome
remaining problems in decapod classification.
As Abele (1991) stated, ‘‘there seems to be as
many groupings of these taxa as there are authors
who have studied them.’’) The artificiality of the
‘‘Natantia’’ is also pointed out by Christoffersen
(1988a) and Scholtz and Richter (1995).
Thus, there is no morphological or molecular
support for a natural ‘‘natantian’’ clade that contains
all shrimp-like forms. The features that seem
to unite the natantians appear to be primitive characters
that do not clearly define a monophyletic
group. Consequently, we have recognized the Dendrobranchiata
and Pleocyemata on the basis of
what appear (to us) to be shared, derived features
of both morphological and molecular data.
Within the Dendrobranchiata, classification is
relatively stable, mostly because there are relatively
few taxa in this suborder. Relationships among the
pleocyemate taxa are another story. If Caridea and
Stenopodidea are treated as separate clades, then
an argument could be made for recognition of the
Reptantia (or Macrura Reptantia, following Holthuis,
1993a) as a natural taxon based on the work
of Schram (1984, 1986), Abele (1991), Scholtz and
Richter (1995), and others. Scholtz (pers. comm.)
argues that the evidence for a monophyletic Reptantia
is at least as convincing as the evidence for
recognition of Caridea and other decapod infraorders,
and we tend to agree. Yet the Reptantia of
Abele (1991) and Scholtz and Richter (1995) differ
as to the constituent groups, and we have opted for
treating the ‘‘reptant’’ infraorders (Astacidea, Thalassinidea,
Palinura, Anomura, and Brachyura) separately
rather than combining them in a taxon that
would be the sister group to the stenopodidean and/
or caridean shrimps. Recognition of a natural
‘‘Reptantia’’ would involve using this name at the
level of infraorder and then ‘‘demoting’’ the above
five groups to just below the infraorder level, which
would add considerably to the confusion in an assemblage
that already contains a large number of
taxonomic subdivisions.
Scholtz and Richter (1995) attempted to place
the classification of the reptant decapods on firm
cladistic footing. They argued (as did Christoffersen,
1988a) that the Reptantia was a clearly defined
monophyletic taxon and that its sister group was
possibly the Stenopodidea (which, according to
other authors, are members of the same clade Pleocyemata).
Thus, the branching sequence of the
decapods would be Penaeoidea (Dendrobranchiata),
then Caridea, Stenopodidea, and Reptantia;
this much at least is consistent with other bodies of
data (e.g., Schram, 1984, 1986; Jamieson, 1991a;
Abele, 1991) (although Christoffersen (1988a:342)
suggested that Stenopodidea was the sister group to
a Caridea Reptantia clade). In light of this support,
it is curious, and possibly a mistake, that we
have not included the Reptantia as a monophyletic
clade in our classification, although inclusion or exclusion
of the stenopodideans is unresolved. Scholtz
and Richter (1995) argued convincingly for monophyly
of some of the constituent reptant groups,
such as the Brachyura and Anomura, but other arguments
are (to us) less convincing. The Scholtz
and Richter (1995) classification also included several
new group names, such as the Achelata, Fractosternalia,
Meiura, etc., which we feel are unlikely
to persist (but note that some of these taxon names
already have been employed (although not necessarily
endorsed) in the papers of, e.g., Schmidt and
Harzsch, 1999; Suzuki and McLay, 1998; Sternberg,
1996; Taylor et al., 1999; and Taylor and
Schram, 1999). For reasons we feel are inappropriate
for discussion in a review and compilation of
this nature (mostly differences in how we would
score certain morphological characters and the low
number of specimens examined), we have not followed
Scholtz and Richter here. In fairness, some
of the characters proposed by Scholtz and Richter
are well beyond our ability to comment on (such
as the shape of thoracic and cephalic ganglia and
the development of embryonic growth zones) and
possibly provide fertile ground for further investigations.
And we acknowledge and compliment
them on an attempt to place decapod classification
in a phylogenetic context, which our classification
clearly does not do. But concerns raised by their
questionable (to us) use of morphological characters
caused sufficient doubt as to their overall
scheme, and we have not accepted the Scholtz and
Richter (1995) arrangement in the current classification.
The date of establishment of the name Decapoda
has been changed to Latreille (1802) rather than
Latreille (1803) (L. Holthuis, pers. comm.; see earlier
comments in the section Names, Dates, and the
ICZN).
SUBORDER DENDROBRANCHIATA
Christoffersen (pers. comm.) would rather we employ
the name Penaeidea Dana instead of Dendrobranchiata
Bate, as the former name is older and
‘‘perfectly legitimate.’’ Holthuis (pers. comm.)
agrees but notes that ‘‘since Dendrobranchiata
seems to [have] become generally accepted, I am
quite willing to go along.’’ Within the group, there
have been no significant family-level or higher
changes proposed (to our knowledge) since the
Bowman and Abele (1982) classification. Authorship
of the family Solenoceridae has been credited
to Wood-Mason rather than to Wood-Mason and
Alcock (Kensley, pers. comm.). Thus, our classification
of the Dendrobranchiata is the same as that
44 Contributions in Science, Number 39 Rationale