n.1.(Zool.) The second joint of the antennæ of crustaceans.
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Antennal scale generally oval with distal margin obliquely truncate, distolateral tooth absent; dorsal surface of antennal scale with prominent middorsal carina; basicerite with acute or subacute ventrolateral tooth, lateral surface concave in proximal part to accommodate expanded pterygostomial part of carapace.
4C) not tightly fitting against antennular peduncle, with small, subacute distolateral tooth far exceeded by broadly rounded distal lamella; basicerite (Fig.
5C) becoming broader, but still not tightly fitting against antennular peduncle, with trace of distolateral tooth; basicerite (Fig.
6B, C) tightly fitting against antennular peduncle, without distolateral tooth but with short transverse groove distolaterally; basicerite partially covered by pterygostomial projection of carapace.
Antennal scale generally oval with distal margin broadly rounded, blunt distolateral tooth present; short transverse suture extending mesially from base of distolateral tooth; dorsal surface with prominent mid-dorsal carina; basicerite with subacute ventrolateral tooth.
9A to D) with anterior part sloping anteriorly; no longitudinal depression on either side of midline; antennal lobe broadly rounded; pterygostomial expansion directed rather ventrally, exceeding beyond tip of antennal basicerite, rounded.
12A to C) with anterior part not strongly sloping anteriorly even in spawning females; shallow longitudinal depressions, ornamented with irregular pattern of longitudinal striae, present on dorsal surface either side of midline in ovigerous females; antennal tooth showing as small, blunt prominence; pterygostomial projection directed forward, somewhat tapering distally, reaching tip of ventrolateral tooth of basicerite, terminating in rounded tip.