Riethia Kieffer



Moderate-sized larvae, to 8 mm long.

Dorsal Head

Frontal apotome separate from clypeus, isolated labral sclerite 2, labral sclerites 3 and 4 fragmentary.


Antenna with 5 segments, either successively shorter, 3rd longer than 2nd, or 4th longer than 3rd Pedestal rounded. Ring organ in basal 1/4 of basal antennal segment. Lauterborn organs on apex of 2nd segment, well developed but no longer than half segment length, without pedicels. Antennal blade as long or longer than flagellum.


SI seta broadly plumose, SII elongate, finely feathered, arising from strong pedestal, SIII closely approximated, fine, simple, SIVa simple sensillum. Chaetae laterales deeply serrate on inner margin. Labral lamellae broad, single, pectinate. Pecten epipharyngis of 3 subequal scales, or middle tooth smaller. Premandible with several teeth, brush strong; seta premandibularis very long.


Mandible often with differentiation in colour between pale apical tooth and darker inner teeth, or all teeth pale. Apical tooth subequal in length to, or slightly longer than, longest of three inner teeth, without dorsal tooth or pecten mandibularis. Seta subdentalis long, extending to base of apical tooth, inserted on mid-surface of mola, but lying along the inner surface. Seta interna of 4-6 plumose branches. External surface of mandible smooth, molar margin with or without spines.


Mentum rather variable in depth of pigment but uniform in structure, with single, shallow-domed median mental tooth, first pair of laterals long, second short, remaining outer four on even line of slope. Ventromental plates slender, broad, gently curved, only narrowly separated medially; striae numerous linear, parallel, fine.


Anterior parapods with dense spines, posterior parapods with fewer hooked claws. Procercus large, conical, with strong procercal seta at about mid-point, and 6-9 strong apical setae.


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