cf. Perkinsiana sp. 2

Perkinsiana Knight-Jones, 1983

Perkinsiana? sp. 2

Voucher. NIMROD: N11FA.

Diagnosis. Voucher is a complete specimen; small to medium sized species, with 8 thoracic and approximately 52 abdominal chaetigers; body 9 mm long and 0.8 mm wide, branchial crown 6.5mm long. Thoracic and abdominal chaetigers similar, rather narrow, intersegmentally incised.

Branchial crown with 7 pairs of radioles; radioles lacking pigmentation; with long tips; with many pinnules; palmate membrane absent; ventral radioles shorter than dorsal ones; the base of the crown high. Radiolar appendages of dorsal lips prominent as long, narrow, lobe; with long, thin pinnular appendage. Collar somewhat oblique, covering the base of the crown; not developed dorsally and with two rounded lappets of medium height ventrally.

Thoracic notochaetae mostly missing (broken off), superior chaetae not observed , inferior paleate (mucronate) chaetae with short tips observed. Thoracic tori short, not indenting the thoracic ventral shields; thoracic uncini avicular with rounded breasts and likely short handles (handle length not clearly observed, but appear to be no longer then distance between crest and breast); approximately 10 arranged in single row; companion chaetae with a flat and very long tapered blade at right-angles, with several minute teeth. Abdominal neurochaetae long, narrowly limbate, 5 per fascicle; additionally about 2-3 extremely narrow limbate shorter chaetae observed. Abdominal uncini with equally-sized teeth above main fang, covering half the length of the main fang, with long necks, only slightly enlarged breasts and short handles.

Pygidium as rounded lobe; no cirri or pygidial eyes observed. Tube not observed.

Remarks. The genus Perkinsiana resembles other genera, particularly Potamilla Malmgren, 1866 and Parasabella Bush, 1905; while Potaspina Hartman, 1969 can be distinguished with relative ease by replacement of typical thoracic uncini by acicular spines (Giangrande and Gambi, 1997). Knight-Jones (1983) re-define some of these (i.e. Potamilla lacks well developed radiolar appendages supporting the dorsal lips), while establishing genus Perkinsiana. Even though a clear synapomorphy for this genus is still missing (Rouse 1996, Capa 2007), the length of handle of thoracic uncini and development of hood of abdominal neurochaete has been considered of taxonomic importance. The genus Perkinsiana is particularly diverse in Antarctic and sub-Antarctic waters and has a confused taxonomic past (good regional summary and key provided by Giandgrande and Gambi, 1997 and more recently updated by Tovar-Hernandez et al. (2012). Falkland Island specimen agrees well and shows similarities with Sabellomma minuta (Treadwell, 1941) (type locality: Atlantic Ocean, Sao Sebastio, Brazil), which was considered to be Perkinsiana by Knight-Jones (1983), they agree in small size, possessing 7 pairs of radioles, around 10 thoracic uncini per ramus each with very short handles and possessing elongated, narrowly limbate abdominal neurochaetae. The new genus Sabellomma Nogueira, Fitzhugh & Rossi, 2010 was however recently established to house this and related species to account for presence of unpaired, simple eyespots along entire lengths of outer radiole margins. These were not observed in Falkland Is. specimen.

Some characteristics of valid Perkinsiana species known from the region and specimens collected from Falkland Is.