Dawsonius Manning and Felder, 1991

Poore, Gary C. B., Dworschak, Peter C., Robles, Rafael, Mantelatto, Fernando L. & Felder, Darryl L., 2019, A new classification of Callianassidae and related families (Crustacea: Decapoda: Axiidea) derived from a molecular phylogeny with morphological support, Memoirs of Museum Victoria (Mem. Mus. Vic.) 78, pp. 73-146 : 119

Dawsonius Manning and Felder, 1991

Dawsonius Manning and Felder, 1991: 785 .— Sakai, 2005b: 245.— Sakai, 2011: 508.

Gourretia .— Sakai, 2017a: 1128–1129 (partim).

Type species. Callianassa latispina Dawson, 1967 , by original designation and monotypy.

Diagnosis. Cardiac prominence present. Rostrum sharply triangular, produced to near apex of ocular lobes. Pleomere 6 with lateral projections. Male major cheliped merus with straight or weakly convex blade on lower margin bearing a short proximal curved spine and 1 or more distal spines; propodus rectangular, fingers fine, fixed finger smooth. Minor cheliped merus lower margin with erect proximal spine (as in major cheliped); propodus tapering, about 3 times as long as wide, with long narrow fingers. Pereopod 3 propodus triangular, with straight upper margin, expanded proximally on lower margin. Male pleopod 1 article 2 with lobed distomesial margin, distal notch, sharp curved distolateral apex. Telson parallel-sided over anterior half, then tapering to evenly rounded apex.

Remarks. Dawsonius latispina differs from other ctenochelids (except Paragourretia biffari Blanco Rambla and Liñero Arana, 1994 ) in having lateral projections on pleomere 6.

Manning and Felder (1991) differentiated Dawsonius from Gourretia on the absence of an exopod on maxilliped 3 and the sharp lateral projections on pleomere 6. We ( DLF) can confirm that maxillipedal 3 exopod is absent ( Dawson, 1967; Manning and Felder, 1991) and that Biffar’s (1971a) figure and Sakai’s (2011) observation of an exopod are in error. Biffar’s figures are a composite from types and Honduran material but the latter is P. biffari .

Sakai (2005b) treated the genus first as a synonym of Callianopsis and in an addendum as a separate genus that he differentiated from Callianopsis . Callianopsis is a member of another family. He did not explain what he meant by “sensu Sakai (not Manning and Felder, 1991)” before his new diagnosis. Sakai (2011) included Dawsonius in Gourretiidae . Sakai’s (2011) observations of a “ paratype ” and a “ lectotype ” ( USNM 103755, 172310) were not made on the holotype and paratype designated by Dawson (1967); these specimens may well have been misidentified. Sakai’s (2011: fig. 69E) figure of the apex of the male pleopod 2 is impossible to reconcile with Manning and Felder (1991: fig. 16i), which is typical of the family, nor with any ctenochelid.

Sakai (2017a) synonymised Dawsonius with Gourretia on the basis of the same male pleopods 1 and 2. In fact, Dawsonius is unique in pleopod 1 possessing a distomesial rounded blade and acute apex, whereas in Gourretia and Paragourretia the distomesial lobed is acute and smaller than the apical lobe.