clypeus

An unpaired dorsal unit of the cephalon bearing the labrum medially and the mandibular fossae laterally. The fossae articulate with the dorsal condyle of the mandibles [Wilson, 1989].

Part of head carrying labrum; plate on anterior medial part of head formed by fusion of basal segments of antennae (e.g., Branchipus, also Hexapoda) [Moore and McCormick, 1969].

(Order Anostraca):

Part of cephalon carrying labrum; plate anteromedially on head formed by fusion of basal segments of antennae [McLaughlin, 1980].

(Order Anostraca):

Plate-like structure fromed by medial fusion of bases of antennae. (with/without digiform process). (Syn. frontal plate) [Stachowitsch, 1992].

(Order Tanaidacea):

On underside of head, plate-like structure bearing upper lip (labrum). Separated from labrum by suture [Stachowitsch, 1992].

(Order Isopoda):

In most (but not all) isopods the labrum consists of two pieces; the anteriormost (proximal) piece is referred to as the clypeus, the posteriormost (distal) piece as the labrum proper [Wetzer et al. 1997].

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^{Nomenclature of isopod cephalon (A). Examples of isopod mouth appendages: Idoteidae (B, C, F, H); Cirolanidae (D, E, G, I). [Wetzer et al. 1997]}

(Order Isopoda):

Part of head (cephalon) bearing upper lip (labrum) [Stachowitsch, 1992].

(Order Isopoda):

Platelike structure of cephalon, anterior to upper lip or labrum, sometimes fused with frontal lamina [Kensley and Schotte, 1989].

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^{Schematic representation of an isopod illustrating morphological terms. [Kensley and Schotte, 1989]}