Microphoxus cornutus

Microphoxus cornutus (Schellenberg)

(figures 10–12)

Metharpinia cornuta Schellenberg, 1931: 68–69, figure 35.

Paraphoxus cornutus: Barnard, 1960: 271.

Microphoxus cornutus: Barnard, 1980: 110–115, figures 3 (part), 4.

Material examined The material examined is detailed in table 3.

Remarks

All the material examined from the different south-west Atlantic localities, encompassing Buenos Aires and Chubut provinces, agree closely with the description and illustrations given by Barnard (1980) (figures 10, 11a–e). Barnard redescribed a female from Punta Arenas (Chile) which he borrowed from the Swedish State Museum. The material deposited in the Swedish collections had been described by Schellenberg (1931) from Punta Arenas (Chile) and Ushuaia (Argentina), but his illustrations are inadequate and there are no fine details of character states to be found in literature to assist in accurate identification of the species. Comparing the female redescribed by Barnard (1980) with the Argentine females examined herein, some differences were observed related to number of spines and setae on appendages and mouthparts, with all variations represented in various combinations in the specimens, and it was impossible to discover a single individual displaying all the attributes described for the female from Punta Arenas (Schellenberg, 1931). Thus, while some specimens have the same spine formula for antenna 2, they display uropods with dissimilar spine formulae, and vice versa, as seen in table 4. The number of setae on peduncle article 2 of antenna 1 ranges from five (some sockets are not clear) to nine. Epimera 1–3 are similar in shape, but the number of marginal and facial setae varies from individual to individual, although this variation is not very conspicuous. Barnard (1980) pointed out that the terminal male of M. cornutus was unknown. In the present study mature males were morphologically similar to mature females, except in certain morphological characters which denote sexual dimorphism, such as eyes remarkably larger (figure 11f); antenna 1, peduncle article 1 with medial patch of fine setae; primary flagellum, composed of eight articles, bearing one calceolus each on articles 1–3 and one aesthetasc each on articles 4–7 (figure 11g); antenna 2, peduncle articles 3 and 4 ornamented with dorsomedial brushes of sensory fine setae; article 4 facial spine formula: 3-4-3, and ventral margin with few setae; peduncle article 5 about as long as article 4, dorsal margin with three sets of male setae and one distal calceolus, facial spine formula 2; flagellum elongate, composed of 32 articles, bearing one calceolus each on articles 1–3 and then on every other article: 5, 7..., 29 (figure 12a); uropod 3, inner ramus as long as outer ramus article one, medial and lateral margins profusely plumose setose; outer ramus article 1, medially setose, lateral margin with two acclivities, spine formula: 2-2-0, setal formula: 0-0-2; article 2 of outer ramus shorter than in female, 0.13, apex with longer plumose setae (figure 12b).

Microphoxus cornutus was recorded in Buenos Aires and Chubut provinces, inhabiting very fine to fine sand from shallow waters to 19 m depth.