Pista Malmgren, 1866
Pista sp. 3
Voucher. LOLIGO: station L14FB.
Diagnosis. Voucher incomplete specimen in good state of preservation, 15mm long and 1mm wide with 17 thoracic chaetigers and at least 11 abdominal uncinigers (posteriorly incomplete). Body with thorax somewhat dorsoventrally flattened and abdomen cylindrical, tapering; segments never crowded, of similar length throughout. Dark brown pigmentation dorsally on prostomium, peristomium, segments 1-4 (and slightly on segment 5) and stem of branchia; ventrally only horizontal brown patch present on segment 1; the rest of light to dark yellow in alcohol.
Prostomium triblobed, with peristomium forming wide, dorsally incomplete collar; eyes absent.
Segment 1 dorsally high, forming a high single lobe (on which pair of branchia is attached), ventrally also well developed, with large rounded lateral lobes. Segment 2 extremely small, only slightly visible laterally. Segments 3 similar to segment 1 with rounded lateral lobes aligned with those of segment 1; dorsally segment 3 forming a high rim with two low rounded dorsal lobes. Segments 4 and 5 thickened laterally otherwise similar to subsequent segments.
One pair of branchiae present on segment 2; left hand side branchia detached (scar observed), right hand side branchiae present; branchia plumose with the ratio of stem to crown length about 2:1.
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, notopodia of chaetigers 1–3 (segments 4–6) inserted progressively more laterally, than vertically aligned. Notochaetae widely 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. 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 rounded 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).
