Pectinariidae Malmgren 1866

Family Pectinariidae Malmgren, 1866

Description. Typical ice cream cone shaped tubes, composed of sand grains and small stones cemented in mucus. Conical short body, with 26 segments. Prostomium fused to peristomium, forming circular to ovate membranous cephalic veil, with smooth or cirrate distal margin; relatively few, short, broad and tapering distally, almost triangular buccal tentacles, located ventrally at base of cephalic veil. Segment 1 distinctly short to poorlydeveloped ventrally, well-developed laterally and dorsally, forming cushion-like rounded operculum with low marginal lobe of even length, smooth or cirrate distal margin, and large golden and flattened notopodial paleae tapering to tips, arranged in two dorso-lateral arched rows, near proximal (= ventral) margin of operculum. Segment 1 with pair of digitiform tentacular cirri located ventro-laterally, one cirrus at each lateral margin of opercular lobe. Segments 2–6 forming distinctly raised crests ventrally, as ventral ridges, first crest more developed, sometimes with ventral lobe(s), cirrate or smooth; segment 2 also with pair of digitiform tentacular cirri, usually aligned ventrally to cirri of segment 1. Two pairs of lamellate branchiae on segments 3 and 4, branchial filaments originating in pectinate arrangement from dorso-lateral to lateral basal stalks; branchial lamellae relatively loosely packed, flat and smooth. Notopodia from segment 5 to segments 20–21; neuropodia beginning on segment 8 and continuing to segment 20–21; 1–2 achaetous or only notopodia-bearing segments may be present at base of scaphe. Narrowly-winged notochaetae throughout in both rows, or only on posterior row, and those of anterior row have narrow limbation from base, terminating by finely serrated alimbate blade; sometimes blades of bases with modifications, which shape of varies among taxa. Neurochaetae as uncini, arranged in single, straight tori; uncini with anterior peg made of densely packed denticles; uncinal teeth long and thin, arranged in longitudinal rows, main fang absent (pectinate) or main fang present and secondary teeth in transverse rows and progressively shorter distalwards (avicular); uncini with base extending posteriorly as stout handle. Last 5 segments fused into sucker-like scaphe, with pair of transverse rows of stout notopodial hooks dorsally at base, paired lateral lamellae and longer anal flaps distally, frequently with terminal cirrus in-between (Rouse & Pleijel 2001; Hutchings & Peart 2002; Zhang & Qiu 2017).

Remarks. Pectinariids differ from members of all other families of Terebelliformia in regards to the body regions. Terebelliforms typically have the body divided into a thoracic region with some achaetous segments, followed by a few segments with only notopodia and then biramous parapodia, and an abdomen with segments bearing only neuropodia, although when notopodia extend until posterior body the demarcation between thorax and abdomen is not clearly defined (Nogueira et al. 2010, 2013).

Members of Pectinariidae, in contrast, have only 26 segments arranged in a thoracic region with some achaetous segments and then a few segments bearing only notopodia, an abdomen with biramous parapodia, frequently terminating by 1–2 segments achaetous or bearing only notopodia, and then a sucker-like scaphe, consisting of five fused segments (Rouse & Pleijel 2001; Hutchings & Peart 2002; Zhang & Qiu 2017).

The family Pectinariidae is composed of five genera distinguished mostly by the morphology of the cephalic veil, opercular margin, scaphe and uncini. In members of Amphictene Savigny, 1822 both the cephalic veil and the opercular margin are cirrate, the scaphe is well separated from the abdomen, and the uncini are pectinate, with at least two longitudinal rows of teeth (Hutchings & Peart 2002). Specimens belonging to Cistenides Malmgren, 1866 have cirrate cephalic veil, but the opercular margin is smooth, the scaphe is well separated from the abdomen, and the uncini are pectinate, with single longitudinal row of teeth (Hutchings & Peart 2002). Individuals of Lagis Malmgren, 1866 also have cirrate cephalic veil and smooth opercular margin, but their cephalic veil is laterally fused to the operculum; among members of Lagis, the uncini are also pectinate and have at least two longitudinal rows of teeth, while the scaphe is also well separated from the posterior body segments (Hutchings & Peart 2002). Among members of Pectinaria Lamarck, 1818, the cephalic veil is also cirrate and the opercular margin is smooth, the uncini have at least two longitudinal rows of teeth, and the scaphe is well separated from the abdomen (Hutchings & Peart 2002). Animals belonging to Petta Malmgren, 1866 have smooth cephalic veil, except for a medial extension, the opercular margin is also smooth, the uncini are breviavicular rather than bipectinate (sensu Holthe 1986a), with transverse series of progressively shorter distalwards secondary teeth on top of the main fang, and the transition between the posterior body segments and the scaphe is not as clearly marked as among members of the other genera of the family (Hutchings & Peart 2002).