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196 Family Alpheidae
Genus Alpheus Fabricius, 1798
Key to species
[Adapted from Chace, 1972]
1. Frontal region evenly convex dorsally, adrostral depressions lacking; fingers of
minor first chela strongly curved in vertical plane (rostrum short, subrectangular,
not elevated in midline; ocular hoods subrectangular, frontal margin broadly
tridentate; major first chela subcylindrical, without marginal notches on palm;
proximal article of carpus of second pereopod longer than second segment; third
and fourth pereopods with dactylus biunguiculate, merus without distal tooth on
inferior margin, ischium without movable spine on lateral surface)
A. cylindricus
Ocular hoods mesially delimited by adrostal depressions or furrows; fingers of
minor first chela not noticeably curved in vertical plane 2
2. (1) Rostrum dorsally flat, at least in distal portion; ocular hood armed with spine
arising from surface of hood, not from margin, although appearing marginal in A.
malleator because of receding ventral portion of hood (adrostral furrows sharply
defined and partially delimited posteriorly; marginal lobe or projection between
rostrum and ocular hood; proximal segment of carpus of second pereopod longer
than second segment) 3
Rostrum either rounded or carinate in dorsal midline, not flat; ocular spine, if
present, arising from margin of hood 5
3. (2) Spine on ocular hood arising from mesial slope, overhanging adrostral furrow; meri
of third and fourth pereopods armed with distal tooth on inferior margin (fingers of
minor chela of male not "balaeniceps"-shaped; third and fourth pereopods with
simple dactyli and movable spine on lateral surfaces of ischia. Small tooth or
tubercle in midline of carapace in line with posterior limits of adrostral furrows;
palm of major first chela with superior and inferior margins entire, not notched,
immovable finger notched on opposable margin distal to socket; distolateral spine
on exopod of uropod dark-colored in male) A. armatus
Spine on ocular hood arising from anterior slope, overhanging frontal margin; meri
of third and fourth pereopods unarmed at distal end of inferior margin (immovable
finger of major first chela notched on opposable margin distal to socket; distolateral
spine on exopod of uropod dark-colored in male) 4