Perkinsiana sp. 1

Perkinsiana Knight-Jones, 1983

Perkinsiana sp. 1

Voucher. SEA LION: station 5MFA.

Diagnosis. Voucher is a complete specimen; medium sized species, with 8 thoracic and 65 abdominal chaetigers; body 25 mm long and 1.8 mm wide, branchial crown 15mm long. Thoracic chaetigers longer than wide, abdominal chaetigers narrow, crowded.

Branchial crown with approximately 12 pairs of radioles; radioles with two pigmented area thoughout their length; with short 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 very long, narrow, pigmented lobe; with short pinnular appendage. Collar somewhat oblique, covering the base of the crown; with a wide gap middorsally and with two high rounded lappets ventrally.

Thoracic notochaetae with long broadly limbate superior chaetae and inferior paleate (mucronate) chaetae with long tips; arranged with about 10 + 8 per fascicle. Thoracic tori long, slightly indenting the thoracic shields; thoracic uncini avicular with very large, somewhat angular breasts and long handles (handle length at least twice the distance between crest and breast); about 40 arranged in single row; companion chaetae with a flat and very long tapered blade at right-angles, with several minute teeth. Abdominal neurochaetae long, with a basal broad knee and distal end narrowing abruptly, about 10 per fascicle; additionally very few, extremely narrow, shorter, limbate 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 low, wide 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. 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)). Of the known species of Perkinsiana, there are currently 5 species recorded from the area with large number of thoracic uncini (40+). Morphospecies Perkinsiana sp. 1 shows differences to those species as well as to Perkinsiana? sp. 2 also found in this study and likely represents a new species (see Table below). The main differences are its relatively small size and neurochaetae with a basal broad knee, distally narrowing abruptly.

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