Nereis (Ceratonereis) aequisetis Augener, 1913.

https://www.marinespecies.org/polychaeta/aphia.php?p=taxdetails&id=324869.

Hartmann-Schröder (1985); Bakken and Wilson (2005).

Neurochaetae dorsal fascicle simple chaetae (fused falcigers) present; palpophore barrel-shaped, approximately equal width from base to palpostyle (not overly large compared with palpostyle); maxillary ring paragnaths present (minimal diagnosis; secondary diagnosis not attained).

Palpophore barrel-shaped, approximately equal width from base to palpostyle (not overly large compared with palpostyle). Palpophore surface with a single transverse groove (palpophores well developed).

Jaws with dentate cutting edge.

Maxillary ring of pharynx with papillae absent. Maxillary ring paragnaths present. Area I conical paragnaths present, or absent; II conical paragnaths present; III conical paragnaths present; III rod-like paragnaths absent; IV paragnaths present; IV conical paragnaths present; IV rod-like paragnaths absent. Oral ring papillae absent. Oral ring paragnaths absent.

Dorsal notopodial ligule not markedly elongate on posterior chaetigers; not markedly broader on posterior chaetigers (rarely markedly reduced on posterior chaetigers). Prechaetal notopodial lobe present, or absent; smaller than dorsal notopodial ligule on anterior chaetigers, usually reduced or absent posteriorly; restricted to a limited number of anterior chaetigers. Notopodial acicular process present, or absent. Dorsal cirrus not sub-terminally attached to dorsal notopodial ligule on posterior chaetigers; not terminally attached to dorsal notopodial ligule on posterior chaetigers; not terminally attached throughout all chaetigers.

Neuropodial postchaetal lobe absent, or present; projecting beyond end of the acicular ligule; restricted to anterior chaetigers; digitiform. Ventral neuropodial ligule of anterior chaetigers present. Ventral neuropodial ligule of anterior chaetigers approx. as long as acicular neuropodial ligule. Ventral neuropodial ligule on posterior chaetigers present. Ventral neuropodial ligule on posterior chaetigers similar to length of acicular neuropodial ligule, or short, up to half length of acicular neuropodial ligule.

Notoaciculae on chaetigers 1 and 2 absent. Notochaetae: homogomph spinigers present. Neurochaetae dorsal fascicle: heterogomph spinigers present, or absent (only in S.lizardensis); homogomph spinigers present; heterogomph falcigers in anterior chaetigers present; on posterior chaetigers present; simple chaetae (fused falcigers) present. Neurochaetae ventral fascicle: heterogomph spinigers present; homogomph spinigers present (only in Simplisetia sp. from Phuket), or absent; heterogomph falcigers present; anterior chaetigers heterogomph falcigers with long blades absent; anterior chaetigers heterogomph falcigers with extra-long blades present; anterior chaetigers heterogomph falcigers with short blades absent; posterior chaetigers heterogomph falcigers with long blades present, or absent; posterior chaetigers heterogomph falcigers with extra-long blades present, or absent; posterior chaetigers heterogomph falcigers with short blades present, or absent; heterogomph falcigers blade lacking distinct tendon on terminal tooth.

Anal cirri form cirriform or conical.

Simplisetia is a genus of estuarine nereidids characterised by the presence of fused neuropodial falcigers in posterior chaetigers and absence of oral ring paragnaths. The fused falcigers are also present in another estuarine genus, Hediste, and the two genera may be related (Bakken and Wilson 2005) although they are easily separated by the presence of numerous oral ring paragnaths in Hediste.

Simplisetia currently includes ten species, seven of which occur in Australian estuaries. Significant differences occur among Simplisetia species in the form of the fused falcigers.

The interactive key of Wilson et al. (2003) allowed identification of the Australian species.