Exogone anomalochaeta Benham 1921

Exogone anomalochaeta Benham, 1921

Figures 4–5

Exogone anomalochaeta Benham, 1921: 24, pl. 5, figs 11–13; 1927: 62, pl. 1, figs. 9– 10; Blankestein & Lana 1986: 62, figs 30–31 San Martín & Parapar 1997: 291; Barroso et al. 2017: 403, figs. 1–2.

Exogone (Parexogone) tridentata Hartmann-Schröder, 1993: 143, figs. 20–21.

Material examined. Livingston Island, South Shetlands (Antarctica), id. G. San Martín, 17 February 1994, 1 specimen (MNCN 16.01 /1518); same location, 19 February 1994, 24 specimens (MNCN 16.01 /1518), (4 SEM); same location, 7 February 1994, 4 specimens (MNCN 16.01 /1517); same location, 30 January 1995, 1 specimen (MNCN 16.01 /3540); same location, 18 January 1995, 3 specimens (MNCN 16.01 /3541).

Remarks and additions to description. The new species herein described, Exogone yagan, share the lack of spiniger-like chaetae with E. anomalochaeta, an Antarctic species. For this reason, we examined specimens deposited in the MNCNM, collected and reported by San Martín & Parapar (1997). These specimens agree with the previous descriptions, except for the absence of dorsal cirri on chaetiger 2 (Figs 4A, 5A); this character is described in the previous descriptions but in Benham 1921, fig. 11, the drawing shows dorsal cirri on chaetiger 2; at that time, the importance of the presence or absence of dorsal cirri on chaetiger 2 was not known to separate species of Exogone, and usually they were figured although not present. The compound chaetae are all thick, with distally enlarged shafts and numerous distal and subdistal spines (Figs 4C, E, G), and very short, almost included inside the distal, spinose part of the shafts, named as “gomphotric chaetae” by Benham 1921, 1927. The dorsal simple chaetae are the typical of the genus (Figs 4B, F, 5B, C, E), but some in the mid-body are distally enlarged, and having a spatulate appearance (Fig. 4D). Apparently, this species lacks ventral simple chaetae, since they have not been described by any author and we have not found these in the material examined.

Barroso et al. (2017) recently redescribed this species in bases of material collected in Brazil between 749 and 1050 m depth. These specimens agree well with the Antarctic specimens, except by having ventral simple chaetae and longer proventricle (3.5–5 segments instead of 2–3 segments); it is possible that they could belong to two different species, but would be necessary more detailed studies to separate them.

Habitat. In mud. Intertidal to 1000 m.

Distribution. Antarctic and sub-Antarctic seas. Brazil.