Genus
Elasmopus Costa, 1853
Remarks
Schellenberg (1938) stabilized the
Elasmopus
generic concept by including the character mandibular palp article 3 falcate with pectinate setae along the anterior margin, which clearly distinguished
Elasmopus
from
Maera Leach, 1814
. With nearly 100 described species,
Elasmopus
has become cumbersome and the only subgenus
Dentelasmopus Ledoyer, 1983
, is monotypic, including only
E. (D.) spinipalpus Ledoyer, 1983
. In this paper we discuss three discrete informal species groups that account for 21 of the 99 known species.
The
Elasmopus pectenicrus
group
The
E. pectenicrus
group is defined by the characters: mandibular palp article 3 short, length less than three times as long as broad; male gnathopod 2 propodus with long slender bunches of setae; pereopods 5–7 basis posterior margin with at least one margin crenulated, without long setae and telson lobes apically truncate.
The
E. pectenicrus
group includes 10 species:
E. brasiliensis (Dana, 1853)
;
E. canarius Krapp-Schickel and Ruffo, 1990
;
E. carteri
sp. nov.;
E. crenulatus Berents, 1983
;
E. leveque
sp. nov.;
E. nanshaensis Ren, 1998
;
E. otus
sp. nov.;
E. pectenicrus (Bate, 1862)
;
E. spinibasus Sivaprakasam, 1970
and
E. yunde J.L. Barnard, 1974
. The
E. pectenicrus
group is an example of a species complex with lost type material and vague species descriptions. The species
E. pectenicrus
was originally described from material collected in Papua New Guinea, but there are now four species in the geographic region that conform to the type description, which identifies a crenulated pereopod 6 basis with a quadrate posterodistal corner:
E. carteri
sp. nov;
E. leveque
sp. nov;
E. pectenicrus
(of Lowry and Hughes 2009) and
E. crenulatus
. Material from Torres Strait attributed to
E. pectenicrus
by Lowry and Hughes (2009) are the closest specimens to the type locality; however, a neotype was not established in the hope that material from Papua New Guinea would be obtained.
The
Elasmopus rapax
group
The
E. rapax
group is defined by: mandibular palp article 3 short, length less than three times as long as broad; gnathopod 2 male propodus with two or more palmar teeth; pereopods 5–7 with long, stiff, slender setae along the basis posterior margin and telson with rounded inner lobes.
The group includes 11 species:
E. arafura
sp. nov.;
E. bampo J.L. Barnard, 1979
;
E. calliactis Edmondson, 1951
;
E. hooheno J.L. Barnard, 1970
;
E. integer Myers, 1989
;
E. mayo J.L. Barnard, 1979
;
E. molokai J.L. Barnard, 1970
;
E. mutatus J.L. Barnard, 1962
;
E. ocoroni J.L. Barnard, 1979
;
E. pseudinteger Appadoo and Myers, 2003
and
E. rapax Costa, 1853
.
The
E. rapax
species complex was discussed at length by Barnard (1979) and recently reviewed by Hughes and Lowry (2010). Although some identifications of
E. rapax
(sensu stricto) may be dubious, the extensive citation of material attributed to this species at least acknowledges a closely related fauna with a worldwide distribution.
The
Elasmopus delaplata
group
The
E. delaplata
group is defined only by the mandibular palp article 3 elongate, at least three times as long as broad. Other characters within this group are more varied with the male gnathopod 2 propodus palm with either setal bunch, teeth or sculpturing, pereopods 5–7 posterior margin smooth, crenulated or setose, without setae and telson lobes truncate, rounded or concave. The
E. delaplata
, elongate mandibular palp, group includes 15 species:
E. aduncus Myers, 1995
;
E. alalo Myers, 1986
;
E. balkomanus Thomas and Barnard, 1988
;
E. bollonsi Chilton, 1915
;
E. delaplata Stebbing, 1888
;
E. hawaiensis Schellenberg, 1938
;
E. karamani
Souza- Filho and Senna, 2009;
E. neglectus Chilton, 1915
;
E. piikoi J.L. Barnard, 1970
;
E. shepherdi
sp. nov.;
E. slatyeri Lowry and Hughes, 2009
;
E. thomasi Ortiz and Lalana, 1994
;
E. varanocephalensis Lowry and Hughes, 2009
;
E. wahine J.L. Barnard, 1972
and
E. woodjonesi
sp. nov. Most species in the group occur in the Indo-Pacific region, the exception is
E. thomasi
from the Caribbean Sea.
The elongate mandibular palp may be a shared derived character, particularly where it occurs in conjunction with other features such as the unicarinate urosomite 1, as in
E. neglectus
,
E. shepherdi
sp. nov. and
E. woodjonesi
sp. nov., species from southern New Zealand and southern Australia. Although the elongate mandibular palp can be used to define a group within
Elasmopus
, this character may have limited value as an evolutionary homology because it represents a lengthening of a feeding appendage and it is highly plausible that there were multiple independent origins of this character. Therefore we have chosen to define this fauna as an informal grouping, which can facilitate species identification.
Morphological variation
Material examined for this paper further demonstrated that some
Elasmopus
species show juvenile and adult forms where extreme examples of developing characters could cause adults and juveniles to be misidentified as separate species. Characters that are affected by maturation and vary with growth stage include: gnathopod 2 propodus palmar and subpalmar sculpturing becoming more pronounced / exaggerated; uropod 3 short inner ramus becoming more subequal in length to the outer ramus with increasing size; elongation of telson with reduction in number of apical robust setae with increasing age ( Barnard 1970).
Elasmopus
species that show some or all of the development changes include
E. alalo
(see Ledoyer 1983; Myers,1995),
E. dubius Walker, 1904
(see Ledoyer 1983),
E. hooheno
,
E. carteri
sp. nov.,
E. pectenicrus
,
E. pocillimanus (Bate, 1862)
(as reported by Barnard 1970) and
E. rapax
(see Hughes and Lowry 2010).
Informative species level characters within
Elasmopus
outlined by Barnard (1979) are: eyes, size and colour in live specimens; mandibular palp article 3 length; the lower lip, which can have one or two pair of ducts (cones); male gnathopod 1 propodus teeth and setation; pereopods 5–7 setation and breadth; epimeron 3 sculpturing and telson form. We further recognize the following characters as useful for species level identifications: mandibular palp article 3 length, gnathopod 1 propodus medial surface with or without setae comb and uropod 1 peduncle with one or two basofacial robust setae.
The presence / absence of the gnathopod 1 setal comb and variation of either a single or paired ducts on the lower lip within
Elasmopus
is also known within
Mallacoota J.L. Barnard, 1972 a
closely related maerid genus. The presence of two basofacial robust setae on uropod 1 has not been reported previously; however this character may have been overlooked by earlier workers. Many specimens were examined to confirm that this character was not an aberration or misinterpretation of individuals penultimate to moulting.
Australian fauna
Australia now has nearly 25% of the described world species of
Elasmopus
. Twelve species occur in tropical Australia, compared with the 10 species reported by Ortiz et al. (2007) for the western tropical Atlantic Ocean. Ten species are known from temperate Australia, twice as many as reported by Karaman (1982) from the Mediterranean Sea. There appears to be no species overlap between temperate and tropical Australia except
E. menurte J.L. Barnard, 1974
with a distribution extending along the Western Australian coast. Fifteen species of
Elasmopus
are endemic to Australia. Of the seven non-endemic species, five species are confined to the Indo- West Pacific and two species,
E. pectenicrus
and
E. rapax
, have been reported from the tropical Atlantic Ocean and the Mediterranean Sea.
