| Abstract |
Gill morphology, traditionally, has played an important role in attempts to reconstruct the phylogenetic history of
the Crustacea Decapoda. We examined the gills of dendrobranchiate shrimps (Crustacea, Decapoda, Dendrobranchiata)
to test the assumption that all members of the clade have gills that are ‘‘dendrobranchiate’’ (highly branching)
in form, from whence the taxon name Dendrobranchiata comes. Currently, the Dendrobranchiata consists of two
superfamilies and seven families. Specimens from two genera in each of the known families were examined using light
and scanning electron microscopy. Members of the family Luciferidae, all of which lack gills as adults, were not
examined. Only one genus was examined for the Penaeidae (because they have been the subject of numerous previous
studies) and Sicyoniidae (a monogeneric family). All gills examined have secondary branches that are further
subdivided, conforming to existing and rather broad definitions of dendrobranchiate gills. Families with ‘‘typical’’
dendrobranchiate gills, which consist of curved secondary branches that in turn bear branched (dendritic) tubular
tertiary elements on their distal surfaces, include the Penaeidae, Aristeidae, and Solenoceridae. In other families,
secondary and tertiary gill elements are sometimes quite flattened, and the tertiary elements are not dendritic, giving
the gill a distinctly non-dendrobranchiate appearance. Flattened biserial secondary branches and their flattened
tertiary elements are particularly obvious in gills of the monogeneric family Sicyoniidae (Sicyonia). Within the family
Sergestidae, gills of the genus Sergestes are unusual in having secondary branches that arise from the main gill axis in
an alternating pattern; these gills also have distinctly oval tertiary elements that are not further subdivided and are
directed basally rather than distally. Another sergestid genus, Petalidium, displays gills that differ from those of
Sergestes; in Petalidium the secondary branches also come off the main gill axis in an alternating pattern, but these
branches are more widely spaced and have relatively larger and broader tertiary elements when compared with gills of
Sergestes. The family Benthesicyemidae also contains species with different gill types; Gennadas is shown to have
flattened, plate-like tertiary elements, whereas Benthesicyemus has more typical dendrobranchiate gills. The
significance of this variation in gill morphology within families and within the Dendrobranchiata as a whole is
unclear at this point; rearrangements of the currently accepted phylogeny and resulting classification based solely on
gill morphology are not recommended at this time. |
