An Updated Classification of the Recent Crustacea

the Amphipoda are deserving of status separate
from all other peracarids and should constitute
their own superorder as a sister group to the remaining
taxa, which would then constitute a reduced
Peracarida sensu stricto. (Interestingly, if the
Mysidacea and Thermosbaenacea are removed
from Watling’s (1981) fig. 1, then the Amphipoda
would indeed appear as the sister group to all other
‘‘true’’ peracaridans in that diagram.) But this is not
in agreement with Wagner (1994), who depicted
amphipods and isopods as closely related and depicted
amphipods, isopods, cumaceans, and tanaidaceans
as a monophyletic clade. Wagner (1994)
also suggested affinities between the Thermosbaenacea
and Mictacea and between those two groups
and the Spelaeogriphacea, whereas Pires (1987)
treated amphipods and mysidaceans as related taxa
that were in turn the sister group to all other peracarids.
In Wagner’s phylogenies, the mysids (both
Mysida and Lophogastrida) are shown as the sister
group to the other Peracarida. Depending on where
the line is drawn, Wagner’s phylogeny could be
used as an argument for inclusion or exclusion of
the mysids within the Peracarida.
Spears and Abele (1997, 1998) have suggested,
on the basis of molecular data, that the two groups
of mysidaceans are not monophyletic (suggested
earlier by Dahl, 1983a, and others based on morphological
features), with the Lophogastrida grouping
with other peracarids but with the Mysida falling
outside that clade (see below). Jarman et al.
(2000) also concluded (on the basis of 28S rDNA
sequence data) that the Mysida and Lophogastrida
are not closely related but posited the Mysida closer
to the Euphausiacea. Thermosbaenaceans, treated
as true peracarids by us (see arguments below and
also Richter and Scholtz, in press), have in the past
been treated by some workers (e.g., Bowman and
Abele, 1982; Pires, 1987) as the separate order Pancarida,
which we have abandoned. A more radical
departure is suggested by Mayrat and Saint Laurent
(1996), who suggested a phylogeny (their fig. 342)
of the Malacostraca in which the peracarids are
polyphyletic, with amphipods depicted as the sister
taxon to all other malacostracans (except the leptostracans)
and with cumaceans and mysids associated
with the higher eumalacostracans. This, to
us, seems unlikely. Richter (1999), after a thorough
analysis of characters of the compound eyes of malacostracans,
felt that ‘‘Lophogastrida and Mysida
are clearly members of the Peracarida.’’ These are
only a few of the suggestions to be found in the
rather confusing literature on the diverse peracarid
crustaceans. The most recent coverage is a wonderful
in-depth treatment of the entire Peracarida
in Tome VII, fascicule IIIA of the Traité de Zoologie
edited by J. Forest (see especially the review by Hessler
and Watling, 1999).
The suggestion that the orders Spelaeogriphacea,
Cumacea, Tanaidacea, and Thermosbaenacea constitute
a grouping termed the ‘‘Brachycarida’’ that
is the sister group to the Isopoda, first suggested by
Schram (1981) and supported by Watling (1983,
1999b) [although note that the suggested placement
of isopods and amphipods differs in these two papers],
is not followed here. However, removal of the
thermosbaenaceans from the ‘‘Pancarida’’ and
grouping them with the other peracarids, which we
have done, could be seen as supportive of that
move (see below under order Thermosbaenacea).
Gutu (1998) and Gutu and Iliffe (1998) have suggested
a novel reorganization of the peracarids,
where both the spelaeogriphaceans and mictaceans
would be treated as suborders of a new peracarid
order, the Cosinzeneacea (Gutu, 1998). The mictacean
family Hirsutiidae would be removed to the
new order Bochusacea (Gutu and Iliffe, 1998). We
have not followed this suggestion.
Thus, our Peracarida contains the two orders of
former ‘‘mysids’’ treated as the separate orders Lophogastrida
and Mysida (as in many earlier treatments
as well; see below), plus the Thermosbaenacea,
in addition to the Spelaeogriphacea, Mictacea,
Amphipoda, Isopoda, Tanaidacea, and Cumacea.
Additional comments on each group are
given below.
ORDER SPELAEOGRIPHACEA
To date, there are only three known extant species
of this group, from South America (Brazil), South
Africa, and Australia (Pires, 1987; Poore and Humphreys,
1998; see also Shen et al., 1998). Pires
(1987) suggested that spelaeogriphaceans and mictaceans
might be sister taxa. A recent cladistic analysis
stemming from the discovery of a new genus
and species from the Upper Jurassic of China (Shen
et al., 1998) indicates that the Spelaeogriphacea
may be paraphyletic. Although Shen et al. treat the
Spelaeogriphacea as a suborder under the order
Hemicaridea Schram, we have not followed that
suggestion. This may change if fossil taxa are incorporated
into the next edition of this classification.
All species are currently considered members
of a single extant family, the Spelaeogriphidae, and
the group has been reviewed recently by Boxshall
(1999). Gutu (1998) has suggested recently that
spelaeogriphaceans and some former mictaceans
(the family Mictocarididae, not the Hirsutiidae)
should be treated as suborders within the newly
created order Cosinzeneacea. We have not followed
this suggestion, as most other workers seem to be
in agreement that the two groups are deserving of
separate status within the Peracarida.
ORDER THERMOSBAENACEA
The former order Pancarida (as used in Bowman
and Abele, 1982), erected to accommodate the order
Thermosbaenacea, has been eliminated in light
of suggestions that thermosbaenaceans are members
of a redefined Peracarida clade (see discussion
in Wagner, 1994; see also Monod and Cals, 1988;
Cals and Monod, 1988; Spears and Abele, 1998;
Richter and Scholtz, in press; and above under Per-
Contributions in Science, Number 39 Rationale 33