Polycirrus cruciformis Nogueira, Hutchings & Carrerette, 2015, n. sp.

Polycirrus cruciformis n. sp.

(Figs 1 B–C, 18–19)

Type material. Holotype: AM W.47663, MacGillivray Reef, 14°39'23"S, 145°29'31"E, CReefs, posteriorly incomplete, 5 mm in length, 1.5 mm in width. Paratype: AM W.47664, MI QLD 2380 (on SEM pin).

Description. Minute worm, a few mm in length; in life, orange to reddish body, with red buccal tentacles (Fig. 1 B–C). Transverse prostomium attached to dorsal surface of base of upper lip; basal part as thick, curved to inverted V-shaped crest, distal part poorly developed, as low lobe of uniform length at base of upper lip (Figs 1 B; 18A–J, L–M; 19A). Buccal tentacles of three types, short and intermediate tentacles narrower at bases and distally blunt, long tentacles densely papillated at tips, with narrow, cylindrical peduncle, distally widening towards cylindrical swelling and blunt, deeply grooved tip (Figs 18 A–M; 19K–L). Peristomium forming lips; short, circular upper lip, hood-like; short, swollen lower lip, button-like, restricted to oral area (Fig. 18 A–J, L–M). Segment 1 inconspicuous all around; segment 2 conspicuous, distinctly narrower than following segments, with relatively large, rectangular mid-ventral shield (Figs 18 A–J, L–M; 19A). Highly papillated ventro-lateral pads of anterior segments, pads present until segment 9, less papillated posteriorly (Figs 18 B–G, L–M; 19A). Notopodia extending for 8 segments, until segment 10, last pair much shorter; elongate, bilobed notopodia, lobes of equal size (Figs 18 A–J, L–M; 19A–E). Narrowly-winged notochaetae in both rows (Fig. 19 A–E). Neuropodia beginning from segment 11, first after termination of notopodia (Fig. 19 A–B); type 1 uncini, with short, triangular heel directed posteriorly, single, elongate and sharp tooth in first row above main fang, with another row of shorter, irregularly sized teeth at base, medial tooth larger, and short neck (Fig. 19 F–J). Nephridial and genital papillae present at bases of notopodia of segments 3–9, inconspicuous on last pair of notopodia (visible in life, Fig. 1 B–C), genital papillae anterior and slightly ventral to notopodia (Figs 18 B–G, L–M; 19A–B). Pygidium with rounded ventral papilla and crown of evenly sized rounded papillae (Figs 18 A–C; 19M–O).

Remarks. Polycirrus cruciformis n. sp. is another minute worm, with the distal part of prostomium restricted to the base of the upper lip; button-like lower lip; highly papillated, not clearly defined ventro-lateral pads; only 8 pairs of notopodia, on segments 3–10, with narrowly-winged, acicular chaetae in both rows, wings inconspicuous under light microscopy; neuropodia beginning immediately after the termination of notopodia, on segment 11, and bearing type 1 uncini throughout; and nephridial and genital papillae conspicuous at bases of all notopodia, except for the last pair, which is distinctly shorter than the preceding ones. In addition, the long buccal tentacles of the holotype of Polycirrus cruciformis n. sp. are highly modified, progressively widening towards cylindrical papillate swelling, with blunt tip.

Among the species of Polycirrus known previously to the present study, 11 have up to 13 pairs of notopodia terminating up to segment 15, and neuropodia beginning after termination of notopodia; out of those, seven [P. antarcticus (Willey, 1902), P. medusa Grube, 1850, P. papillosus Carrerette & Nogueira, 2013, P. parvus Hutchings & Glasby, 1986, P. paucidens Hutchings & Glasby, 1986, P. tesselatus Hutchings & Glasby, 1986, and P. variabilis Hutchings & Glasby, 1986] have type 1 uncini throughout.

Polycirrus antarcticus has a large, rectangular lower lip extending across ventrum; 11 pairs of notopodia, until segment 13; neuropodia beginning three segments after the termination of notopodia, on segment 16; and inconspicuous or absent nephridial and genital papillae (Glasby & Hutchings 2014).

Polycirrus medusa is the type species of this genus and, although reported worldwide, for a long time it remained a largely unknown taxon, until Glasby & Hutchings (2014) designated a neotype from the type locality and provided a redescription for the species. However, several characters remain unknown due to the state of preservation of the neotype, such as the morphology of the buccal tentacles and the anterior end. Members of P. medusa differ from P. cr u c i f or m i s n. sp. as they have 12 pairs of notopodia, extending until segment 14, with longer post-chaetal lobe and bearing pinnate chaetae in anterior row of notochaetae; and nephridial and genital papillae only extend until segment 8 (Glasby & Hutchings 2014).

Members of P. papillosus differ from those of P. cruciformis n. sp. in having the distal part of prostomium extending along the upper lip until near the anterior margin of the lip and spatulated long buccal tentacles. In addition, they also differ from P. cruciformis n. sp., as they have 11–14 pairs of notopodia, with pinnate chaetae in anterior row of notochaetae, and inconspicuous to absent nephridial and genital papillae (Carrerette & Nogueira 2013).

Polycirrus parvus originally described from Western Australia is separated from P. c r uc i f o r m i s n. sp., because P. parvus has long buccal tentacles spatulated; larger, cushion-like lower lip; 10 pairs of notopodia, extending until segment 12; uncini somewhat intermediate between types 1 and 2, with elongate neck, but otherwise as type 1; and inconspicuous to absent nephridial and genital papillae (Glasby & Hutchings 2014).

Polycirrus paucidens was also originally described from Australian waters, from Bass Strait, southern Australia. Members of this species are different from those of P. cruciformis n. sp. as the former have the distal part of prostomium extending until near the anterior margin of the upper lip; notopodia with longer post-chaetal lobe; neuropodia bearing intermediate uncini between types 1 and 2, with elongate neck but otherwise as type 1; and inconspicuous to absent nephridial and genital papillae (Glasby & Hutchings 2014).

Polycirrus tesselatus is another Australian species, only known from Victoria. Members of this species also differ from those of P. crucif ormi s n. sp. in having the distal part of prostomium extending until near the anterior margin of the upper lip; larger lips, the lower lip cushion-like across ventrum, reaching segment 3; 10 pairs of notopodia, extending to segment 12; and neuropodia beginning from segment 15, with a gap of two achaetous segments between termination of notopodia and beginning of neuropodia (Glasby & Hutchings 2014).

Finally, P. variabilis was originally described from material from the Lizard Island Group and differs from the holotype of P. cruciformis n. sp. because P. variabilis has the distal part of prostomium extending until near the anterior margin of the upper lip; the long buccal tentacles are spatulated; larger lower lip, cushion-like, extending across ventrum; 10–15 pairs of notopodia, with longer post-chaetal lobe; and nephridial and genital papillae inconspicuous or absent (Glasby & Hutchings 2014).

Etymology. The specific name “ cruciformis ” refers to the shape of the tips of long buccal tentacles, with subdistal cylindrical inflation and blunt tip, from the Latin “crucis” = cross.

Habitat. Found in amongst beds of Halimeda at 12 m.

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

Distribution. Known only from the Lizard Island region.