Exogone (Paraexogone) cf. wolfi San Martín, 1991  

Exogoninae Langerhans, 1879

Exogone (Parexogone) Mesnil and Caullery, 1918

Exogone (Paraexogone) cf. wolfi San Martín, 1991

Vouchers. VINSON WEST: Station 38 MFB and Sea Lion: station 7MFC.

Diagnosis. Both vouchers posteriorly incomplete; very small, slender species; 1.1 and 5mm long, 0.15mm wide for anterior fragment with 10 and 40 chaetigers. Integument smooth; colour in alcohol pale yellow. Prostomium about twice as wide as long bearing three antennae and two palps. Palps distinctly longer than prostomium; fused throughout their length. Antennae smooth, arising nearly at same level near posterior margin of prostomium; lateral antennae distinctly shorter, spindle-shaped; median antenna very long (reaching back to chaetiger 3), slender, cirriform. Eyes present as a pair of tiny red eyespots (voucher 38MFB) or as two pairs, anterior pair as large spherical eyes (composed of several small eyespots), posterior pair as large rod-shaped eyes (composed of several small eyespots). Pharyngeal tube extending through 4 chaetigers, proventricle with around 20 muscle rings extending through chaetiger 4-6. First segment achaetous laterally with a pair of smooth, short, ovoid tentacular cirri.

Parapodia uniramous with smooth dorsal cirri similar to tentacular cirri in anterior chaetigers, becoming slightly longer digiform in latter chaetigers; dorsal cirri present in all chaetigers; ventral cirri conical, inserted near parapodial base.

Chaetae of 3 different types: type 1. as simple chaetae (usually one dorsal and one ventral) lacking in anteriormost chaetigers; long, slender, distally bidentate with several long aristae; type 2. as compound falcigerous chaetae with bidentate blades, their lengths decreasing inferiorly; type 3. as compound spinigerous chaetae with long bidentate blades; all compound chaetae distally bidentate; with the teeth widely separated in morphotype with eyes, but this gap appear much smaller in morphotypes with small eyes; all blades serrated with long spines over entire length of margin. Pygidium not observed.

Remarks. Falkland Island specimen belongs to two morphotypes with 2 pairs of large eyes (from ~500m depth) or pair of tiny eye spots (~1000m depth). Some minute differences were also observed in the degree of distal dentation of falciger and spiniger-like compound chaetae. Until molecular evidence becomes available, we consider these to be the same species. Both morphotypes correspond well with Exogone wolfi, which in turn has been reported from widespread geographical and bathymetrical ranges showing similar variation in eye development to the one observed here (see comparative Table below). This may possibly represent a species complex and molecular evidence is needed to clarify status of different morphotypes. Exogone minuscula Hartman, 1953 is Southern Ocean species, which is superficially also very similar to FI specimens (morphotypes with eyes), however Hartman reported unidentate not bidentate tips and simple chaetae show subdistal serration, but lack aristae. E. parasexoculata Hartmann-Schröder, 1993 from Argentinean part of the South Atlantic Ocean lack dorsal cirri on 2^nd chaetiger.

Variation reported in morphotypes of E. (P.) wolfi reported from wide geographical and bathymetric area.