Polycirrus minutus, Nogueira, João Miguel Matos, Hutchings, Pat & Carrerette, Orlemir, 2015

Nogueira, João Miguel Matos, Hutchings, Pat & Carrerette, Orlemir, 2015, Polycirridae (Annelida, Terebelliformia) from Lizard Island, Great Barrier Reef, Australia, Zootaxa 4019 (1), pp. 437-483 : 450-453

Polycirrus minutus n. sp.

( Figs 6–7 )

Type material. Holotype: AM W.47640, MacGillivray Reef, 14°39'23"S, 145°29'3"E, coarse coral rubble, 22 m, 29 Aug 2010, CReefs, posteriorly incomplete, 2 mm wide, 6 mm long, gravid, in good condition. Paratype: AM W.47638 (1 mounted on SEM pin), between small patch reefs just inside Lizard Island lagoon entrance, 14°40'S, 145°28'E, medium to fine sand, 18 m, coll. Jones & Short, hand corer, 9 Oct 1978.

Other material examined. AM W.47639, Mermaid Cove (buoy), 14°38'46"S, 145°27'13"E, coral rubble, 7 m, 27 Aug 2010, CReefs; AM W.47641, North Direction Island, 14°44'43"S, 145°30'18"E, coral rubble, 8.5 m, 4 Sep 2010, CReefs.

Description. Transverse prostomium attached to dorsal surface of base of upper lip; basal part as thick, curved crest, distal part poorly developed, as low lobe of uniform length at base of upper lip ( Fig. 6 A–D, G–H). Buccal tentacles of two types, both spatulated at tips, with deeper groove, long ones with thinner uniformly cylindrical peduncle before spatulated tip ( Fig. 6 A–I). Peristomium forming lips; short, circular upper lip, hood-like, heavily ciliated; short, swollen lower lip, divided in two parts, inner region button-like, almost rectangular, distal half heavily ciliated, outer region short and narrow, rectangular, shelf-like, also ciliated ( Fig. 6 A–D, G–H, J). Segment 1 reduced, visible mid-dorsal and ventrally, laterally covered by expanded prostomium; segment 2 visible all around, distinctly narrower than following segments, with relatively large, rectangular mid-ventral shield ( Fig. 6 A–D, G–J). Tessellated, highly papillated ventro-lateral pads of anterior segments, present until segment 10, last 2 pairs progressively less developed ( Fig. 6 A–D, G–K). Notopodia extending for 9 segments, until segment 11; elongate, bilobed notopodia, lobes of equal size, last 2 pairs of notopodia markedly shorter, especially last one ( Figs 6 A–E, G– I, K; 7B). Narrowly-winged notochaetae in both rows ( Fig. 7 B–C). Neuropodia beginning from segment 10, penultimate with notopodia; sessile neuropodia on first two pairs, on segments 10–11, at bases of notopodia, as short, raised pinnules after notopodia terminate, with scattered tufts of cilia ( Figs 6 A–C, L; 7A, D–G). Minute, type 1 uncini throughout, with elongate, distally pointed prow, crest with single elongate and sharp tooth on first row above main fang, surrounded by single row of shorter, irregularly sized teeth at base, medial tooth larger, and short neck ( Fig. 7 D– H). Nephridial and genital papillae only present on segments 3–6, lateral to bases of notopodia ( Fig. 6 A–D, G–I, K). Pygidium with rounded ventral papilla and crenulated rim, anus heavily ciliated ( Figs 6 A–C; 7A, I–J).

Remarks. Polycirrus minutus n. sp. is a small species, with distal part of prostomium restricted to the base of the upper lip; circular upper lip; button-like lower lip, divided in two parts; tessellated ventro-lateral pads; few pairs of notopodia, 9 pairs only, extending until segment 11, with evenly-sized lobes and bearing narrowly-winged, acicular notochaetae; neuropodia beginning from the penultimate thoracic segment, segment 10, with type 1 uncini; and nephridial and genital papillae present on segments 3–6, ventral to the bases of notopodia, the last pair almost inconspicuous.

Glasby & Hutchings (2014) suggested a variation of up to 5 segments in the number of pairs of notopodia present, and 4 segments for the beginning of neuropodia. Currently among known species of Polycirrus , only nine have up to 14 pairs of notopodia and neuropodia beginning near to the termination of notopodia. Of these, six have type 1 uncini, as in P. mi nut us n. sp. Those species are P. breviuncinatus Carrerette & Nogueira, 2013 , P. broomensis Hartmann-Schröder, 1979 , P. dodeka Hutchings, 1990 , P. hesslei Monro, 1930 , P. latidens Eliason, 1962 , and P. ro s e a Hutchings & Murray, 1984; of these P. broomensis and P. ro s e a were originally described from Australian waters.

Polycirrus breviuncinatus differs from P. minutus n. sp. in having a large, cushion-like lower lip, not divided in regions; smooth ventro-lateral pads; 13 pairs of notopodia, extending until segment 15 and bearing winged notochaetae, wings conspicuous under light microscopy; neuropodia beginning on the last thoracic segment, segment 15; and nephridial and genital papillae inconspicuous or absent ( Carrerette & Nogueira 2013).

Members of P. minutus n. sp. differ from P. broomensis because this latter species has a holotype of 35 mm in length, and is incomplete, with 32 segments, with a cushion-like and deeply corrugated lower lip; 12 pairs of notopodia, extending until segment 14, with post-chaetal lobe longer and bearing winged chaetae in anterior row of notochaetae, pinnate chaetae in posterior row; neuropodia beginning from the last thoracic segment, segment 14, with pectinate uncini; and nephridial and genital papillae present until segment 11 ( Glasby & Hutchings 2014).

Polycirrus dodeka is also small, with a body ~ 1 cm long; with a large, cushion-like outer region of the lower lip; 12 pairs of notopodia, extending until segment 14, with longer post-chaetal lobe and bearing winged chaetae in both rows of notochaetae, wings conspicuous under light microscopy; neuropodia beginning from the last thoracic segment, segment 14; and nephridial and genital papillae present until the last pair of notopodia ( Glasby & Hutchings 2014).

Polycirrus hesslei differs from P. m i nu t us n. sp. as the holotype of the latter is 5 cm long, and it has the distal part of prostomium extending along the upper lip and terminating near the anterior border of the lip; cushion-like and deeply corrugated outer region of the lower lip; smooth, inflated and transversely wrinkled ventro-lateral pads; 13 pairs of notopodia, extending until segment 15, with longer post-chaetal lobe and probably bearing pinnate chaetae in both rows, according to the line drawings provided by Glasby & Hutchings (2014: 61, Fig. 30C); neuropodia beginning from the last thoracic segment, segment 15; and nephridial and genital papillae present until segment 9 ( Glasby & Hutchings 2014).

Polycirrus latidens is also larger than P. m i nu t us n. sp., the holotype of P. latidens is 1.7 cm long, with larger, cushion-like and deeply grooved outer region of the lower lip; smooth, inflated and transversely ridged ventrolateral pads; 12 pairs of notopodia, extending until segment 14, with longer post-chaetal lobes and probably bearing pinnate chaetae in both rows, according to the line drawings provided by Glasby & Hutchings (2014: 65, Fig. 33c); neuropodia beginning from the last thoracic segment, segment 14; and nephridial and genital papillae present until segment 8, ventral to the bases of notopodia ( Glasby & Hutchings 2014).

Polycirrus rosea described from New South Wales, Australia is perhaps the species most similar to P. m i nu t u s n. sp. Both taxa share similar dimensions of the body, type of notochaetae, and beginning of neuropodia from segment 10, with few uncini per torus, of type 1. These species are distinguished, however, because among members of P. ro s e a the outer region of the lower lip is cushion-like, rectangular, extending across entire ventrum; the ventro-lateral pads are almost smooth; there are 12 pairs of notopodia, extending until segment 14, with longer post-chaetal lobe; neuropodia begin on the fifth segment before the termination of notopodia, segment 10; and nephridial and genital papillae are inconspicuous or absent ( Glasby & Hutchings 2014), which differs from P. minutus n. sp.

Etymology. The specific name refers to the small size of the species.

Habitat. In course coral rubble in 22 m.

Type locality. MacGillivray Reef, 14°39'23"S, 145°29'31"E, Great Barrier Reef, Australia.

Distribution. Known only from the Lizard region.

Figures

FIGURE 6. Polycirrus minutus n. sp., paratype AM W. 47638. A – C. Entire worm, left lateral, ventral and right lateral views, respectively; D – E. Thorax right lateral and dorsal views, respectively, arrow points to last notopodium; F. Tips of some tentacles; G – I. Close ups of the anterior end, right lateral, ventral and left lateral views, respectively; J. Close up of the oral area; K. Notopodia of segments 3 – 7, ventral view; L. Close up of the transition between thorax and abdomen. Numbers refer to segments. Abbreviations: i = inner region of lower lip, ll = lower lip, o = outer region of lower lip, P = basal part of prostomium, ul = upper lip. Scale bars: A – C = 300 µm, D, G – I = 100 µm, E = 200 µm, F = 30 µm, J – K = 40 µm, L = 50 µm.

FIGURE 7. Polycirrus minutus n. sp., paratype AM W. 47638. A. Posterior end, left lateral view; B – C. Notochaetae, segment 7; D – E. Progressively closer views of abdominal neuropodia; F – H. Uncini, segment 10, anterior and posterior abdominal segments, respectively; I – J. Progressively closer views of the posterior end, frontal view. Scale bars: A = 100 µm, B, D = 20 µm, C = 3 µm, E = 7 µm, F – H = 2 µm, I = 40 µm, J = 10 µm.