Pista Malmgren, 1866
Pista sp. 4
Voucher. TOROA: station T5FA.
Diagnosis. Voucher incomplete specimen in good state of preservation, 9mm long and 1mm wide with 17 thoracic chaetigers and at least 14 abdominal uncinigers (posteriorly incomplete). Body cylindrical, thorax somewhat inflated, with dorsal “hump” on segment 5-7 and abdomen tapering; segments 1-7 crowded, then getting longer form segment 8.
Prostomium triblobed; eyes absent.
Segment 1 dorsally incomplete, well developed ventrally without prominent lobes. Segment 2 also low, but more developed then segment 1, best developed ventrally, with enlarged, rounded ventrolateral lobes, dorsally as low ridge without any prominent lobes (attachment of 1st pair of branchial pair). Segments 3 similar to segment 2 with enlarged lobes placed laterally; dorsally segment 3 forming a low rim without any lobes (attachment of 2nd branchial pair). Segments 4 thickened laterally otherwise similar to subsequent segments. Genital papillae on segments 6–7, located posterior to notopodia and dorsally aligned with them.
Two pairs of branchiae on segments 2–3; first pair present, with left brachia much smaller than right branchia, both positioned close together; arborescent with “Christmas tree-like” shape; second branchial pair missing/regenerating with stem present on right side; inserted ventrally compared to first pair, separated by a wide gap.
Pygidium unknown.
Seventeen pairs of notopodia, starting from segment 4 and extending until segment 20 (the last thoracic segment/unciniger); first pair of notopodia about same size as following pairs, all notopodia vertically aligned. Notochaetae narrowly bi-limbate, distally smooth, arranged in two rows.
Neuropodia starting from chaetiger 2 (segment 5); in thorax as low rectangular ridges slightly raised from surface of body until segment on which notopodia terminate; in abdomen as short rectangular pinnules situated laterally on body, internal neuropodial shafts present. In thorax uncini arranged in a single row in chaetigers 2–7 (segments 5 – 10) and in intercalated double rows from chaetiger 8 (segment 11) until the end of thorax. Thoracic uncini with elongated handle originating from heel, with sharp rostral tooth situated at mid-length between base of main fang and tip of prow, distally rounded prow and crest with 3–4 rows of secondary teeth. Abdominal uncini from chaetiger 18 (= segment 21), short-handled with rostral tooth situated at mid-length between base of main fang and tip of prow, distally rounded prow and crest with up to 4 rows of secondary teeth.
Remarks. There are several species found in the Falkland Islands material, which are likely new to science and are here assigned morphospecies name only. Pista is a large genus, reported worldwide and comparisons with these are not provided here as further work by specialists will be needed. This genus is characterized by the presence of lobes on anterior segments, long-handled uncini occurring for variable number of segments on the region with biramous parapodia, and 17 pairs of notopodia with broadly winged notochaetae, starting from segment 4. Santos et al. (2010) also proposed that morphology of lobes in this group, especially with regard to the shape of lobes on segment 1, is important for distinguishing species. Those characters were used here to separate different morphospecies of Pista (see comparative table).
