Iphione treadwelli Pettibone, 1986

Figs 12–14

Iphione treadwelli Pettibone, 1986: 19–21, Fig. 7; Hanley & Burke 1991: 43–45, Fig. 13A–F; Imajima 2005: 55–59, Figs 15–17; Imajima 2011: 153.

Type material. Hawaii. Holotype (USNM 5435), Auau Channel, Maui Island, Lahaina, RV Albatross, unnumb. Sta. (20 51 35 N, 156 42 35 W), 51–79 m, 14 Apr. 1902 . Paratype (USNM 81934), off Laysan Island, USFCS Albatross, Sta. 3936, 142– 234 m, 16 May 1902 (body 9 mm long, 5 mm wide, probably 28 chaetigers, not manipulated to avoid further damage) .

Additional material

Philippines. One specimen (ECOSUR 3-117), Musorstom 3, Sta. DR 117 (12°31’ N, 120°39’ E), 92 m, 3 Jun. 1985 (markedly bent ventrally; elytra with macrotubercles short, digitate, in a single row; not measured to avoid further damage) . Two specimens (ECOSUR 3-131), Musorstom 3, Sta. CP 131 (11°36.6’ N, 121°43.0’ E), 111–113 m, 5 Jun. 1985 (bent ventrally, some elytra detached and one specimen distorted by compression; elytra yellow with abundant brownish spots; macrotubercles arranged in a single row, as fragile blunt spines, eroded to low, cushion-shaped tubercles; median cirrigerous segments with a projected basal tubercle to dorsal cirrophores; neurochaetae unidentate; undamaged specimen 13 mm long, 7 mm wide, 29 chaetigers) . One specimen (ECOSUR 3-137), Musorstom 3, Sta. DR 137 (12°03’ N, 111°06’ E), 56 m, 6 Jun. 1985 (markedly bent ventrally; right elytron 6 removed for observation (kept in container); macrotubercles cushion-shaped, in a single row; not measured to avoid further damage) .

Mariana Islands. One specimen (UF 133), Guam, Hagatna Bay, East side (13°30’00” N, 144°48’00” E), 115 m, reef tallus, 14 Jul. 1997, G. Paulay & B. Smith, coll. (markedly bent ventrally, dried-out; not measured to avoid further damage; left parapodium of chaetiger 14 removed for observation, kept in container; elytra yellowish, with sessile to pedunculate fimbriae, and macrotubercles along a single row, darker than other areas with oblique illumination) .

Australia. One specimen (NMV F185639), Western Australia, RV Southern Surveyor, L 30 Transect (12°25’57” S, 123°35’47” E to 12°26’04” S, 123°35’52” E), 111 m, Sherman sled, 7 Jul. 2007, D. J. Bray, coll. (bent ventrally; most elytra previously removed; elytra yellowish with 4–7 short macrotubercles in a single row; body 8 mm long, 5.5 mm wide, 29 chaetigers) .

Taupo Seamount. Two specimens (AM 21762), 500 km ENE off Sydney (33°06’11.9999” S, 156°09’18.00” E), 164 m, 7 Oct. 1982, R.T. Springthorpe & W.F. Ponder, coll. (bent ventrally, several elytra previously removed; elytra yellowish, with a small central black spot, better defined in smallest specimen; macrotubercles in a row, with up to five macrotubercles per row, progressively smaller middorsally; cirrigerous segments with basal tubercle slightly projected, glandular area not pigmented, if present; body 5–7 mm long, 3.5–5.0 mm wide, 27–29 chaetigers) .

Coral Sea. One specimen (MAGNT 5456), RV Corail, Sta. 94DW (19°86’ S, 158°58’ E), 36–53 m, 27 Aug. 1988, J.R. Hanley, coll. (all right elytra and left anterior ones previously removed, two parapodia previously removed (all kept in container); elytra yellowish with spread black dots medially, 6–7 macrotubercles in a row; cirrigerous segments with basal tubercle of dorsal cirrophores projected; neurochaetae unidentate, barely falcate, some with distal keel; body 8.5 mm long, 5 mm wide, 29 chaetigers) . One specimen (MAGNT W 5457), RV Corail, Sta. 26DW (20°21.98’ S, 161°04.87’ E), 62 m (after cruise data; 88 m on label), 22 Jul. 1988, J.R. Hanley, coll. (markedly bent ventrally; some elytra previously detached (kept in container) and 3 parapodia (lost); elytra yellowish, with spread black spots medially, macrotubercles in a single row with 6–7 macrotubercles, each one blunt conical, directed or bent middorsally; fimbriae minute, restricted to outer margin; cirrigerous segments with basal tubercle of dorsal cirrophores bilobed; cirrostyles tapered, not subdistally swollen; neurochaetae unidentate, slightly falcate, some with a distal keel reaching tip; not measured to avoid further damage) .

Papua New Guinea. One specimen (NMV F227776), Gulf of Papua, Stat. unnumbered (08°36’08” S, 144°54’32” E), trawl, 96 m, 7 Nov. 2015, M. Wright, coll. (slightly bent ventrally; elytra yellowish, with sessile to pedunculate fimbriae, macrotubercles in a single row; basal tubercle of dorsal cirrophores projected; neurochaetae subdistally expanded, unidentate; body 12 mm long, 7.5 mm wide, 29 chaetigers) .

New Caledonia. One specimen (ECOSUR 6-458), Îles Loyauté, Musorstom 6, Sta. DW 458 (21°00.93’ S, 167°28.96’ E), 415 m, 20 Feb. 1989 (complete; data used for variation; body 10 mm long, 6 mm wide, 29 chaetigers) . One specimen (MNHN IA 2015-73), Mission KANACONO, Sta. DW 4732 (22°34’ S, 167°36’ E), 194– 168 m, 22 Aug. 2016, S. Hourdez et al., coll. (juvenile; markedly bent ventrally; a few elytra previously removed, kept in container; elytra yellowish, with one row of falcate macrotubercles; body width 5 mm) . One specimen (MNHN IA 2015-74), Mission KANACONO, Sta. DW 4763 (23°17’ S, 168°15’ E), 192–260 m, 27 Aug. 2016, S. Hourdez et al., coll. (juvenile; markedly bent ventrally; elytra mottled, middorsal longitudinal band brownish, ill defined, with some brownish spots along posterior region; macrotubercles in one row, low digitate; cirrigerous segments with basal tubercle of dorsal cirrophore projected; not measured) .

French Polynesia. One specimen (MNHN IA 2013-154), Palliser Islands, Mission TARASOC, SW off Raitahti, Sta. CP 3386 (15°42’ S, 146°54’ W), 400–440 m, 5 Oct. 2009, S. Hourdez, et al., coll. (slightly bent ventrally; elytra brownish, macrotubercles cushion-shaped, in a single row, slightly raised along the inner side; cirrigerous segments with basal tubercle of dorsal cirriphore projected, with abundant black globular glands; body 18 mm long, 13 mm wide, 29 chaetigers) . Two specimens (MNHN IA 2013-163), Palliser Islands, Mission TARASOC, NNW off Niau Atoll, Sta. DW 3362 (16°07’ S, 146°23’ W), 198–280 m, 5 Oct. 2009, S. Hourdez et al., coll. (bent ventrally; elytra blackish along chaetigers 1–7, posterior ones yellowish, without black spots; macrotubercles in a single row, cushion shaped, falcate in smallest specimen; cirrigerous segments with basal tubercle of dorsal cirrophore projected, with black globular glands, less defined in smallest specimen; body 13–15 mm long, 6–9 mm wide, 29 chaetigers) . Two specimens (MNHN IA 2013-166), Palliser Islands, Mission TARASOC, among Apataki, Aratika and Toau atolls, Sta. DW 3372 (15°39’ S, 145°55’ W), 326–540 m, 3 Oct. 2009, S. Hourdez et al., coll. (smaller markedly bent ventrally; elytra brownish, macrotubercles cushion-shaped in a single row; body 12 mm long, 9 mm wide, 29 chaetigers) .

Diagnosis. Iphione with median antenna reduced to nuchal papilla; elytra fimbriate, fimbriae short, globose; macrotubercles cushion-shaped without distal spines, in a single row; cirrigerous segments with dorsal cirrophores with basal tubercle projected, tip blackish; neurochaetae unidentate; ventral cirrostyles bases pale.

Description. Holotype (USNM 5435) markedly bent ventrally (Fig. 12A); most elytra and right parapodia of chaetigers 13–15 previously detached, left parapodium of chaetiger 12 removed for observation (kept in container). Elytra yellowish, with macrotubercles arranged in a single row, without black spots; notochaetae whitish, neurochaetae golden; midventrally paler than lateral areas; ventral cirrophores pale. Body length not measured, body width 5.5 mm; chaetigers not counted.

Elytra with fimbriae small (Fig. 12C), each fimbria globular, reduced, present along external lateral margins; macrotubercles conical, distal spines present in many macrotubercles, directed middorsally, slightly decreasing in size middorsally.

Prostomium oval, wider than long (Fig. 12B), with a deep longitudinal depression along anterior prostomial fourth. Anterior lobes projected into ceratophores, slightly longer than prostomium, pale, ceratostyles pale, directed ventrally, slightly longer than ceratophores, tips tapered, thread-like. Palps pale, twice longer than lateral antennae. Eyes black, positioned in posterior prostomial half; anterior eyes directed laterally, slightly larger than posterior eyes, directed dorsolaterally; anterior and posterior eyes not close to each other along same side. Nuchal papilla not visible dorsally.

Tentacular segment reduced dorsally, tentacular cirrophores and cirrostyles pale, without chaetae. Facial tubercle visible dorsally, pale.

Segments 2–4 directed anteriorly. Second segment visible dorsally, with a projected semicircular nuchal lappet, about as wide as long, completely covering nuchal papilla. Ventral buccal cirri inserted ventrally, almost twice longer than following ones. Dorsal nodules indistinct. Segments 2–3 with finer neurochaetae, barely swollen subdistally, with a longer region with transverse denticulations.

Median cirrigerous segments with dorsal cirri broken (Fig. 12D); dorsal cirrophore smooth, with projected basal tubercle. Notochaetae whitish, very abundant, delicate capillaries with series or transverse funnel-shaped spinose rows, tips bare. Neuropodia with neuracicular lobe about twice longer than wide, truncate; neurochaetal lobe with short papillae. Neurochaetae thick, abundant, basally smooth, subdistally swollen, with series of fine denticulations along swollen region, tips falcate, unidentate.

Anus not seen.

Variation. The paratype (USNM 81934) is dried out, bent ventrally (Fig. 13A, B), nine elytra were previously removed (kept in container); median elytra with a single row of tubercles, dark brown, bent, tips broken, without large spines (Fig. 13C); fimbriae globose, short, mostly sessile or with very short peduncles (Fig. 13D, E), a single long one in one of the 9 elytra. The paratype has a transverse anteroventral dissection.

A non-type specimen (ECOSUR 6-458) has the first five pairs of elytra darker than following ones, and elytra pairs 4–5 forming a wide transverse black band, and darker inner margins forming a longitudinal wide band (Fig. 14A). Elytra are brittle (Fig. 14B), with large cushion-shaped macrotubercles (Fig. 14C), each longer than wide, arranged in a single row, lateral margins with deciduous tiny fimbriae (Fig. 14D). Cirrigerous segments with basal tubercle to dorsal cirrophore projected, with brownish glands (Fig. 14E, inset); neurochaetae unidentate, tips slightly falcate (Fig. 14F).

The additional specimens were 5–18 mm long, 3.5–13.0 mm wide. Macrotubercles are arranged in a single row, and this does not change with body size; each macrotubercle is cushion-shaped with a distal tip, and this is better seen in smaller specimens. Older ones have macrotubercles variably eroded.

Remarks. Iphione treadwelli Pettibone, 1986 resembles I. corbariae sp. nov. from the Indian Ocean (see below), because they are the only species having elytra with cushion-shaped macrotubercles (once the distal spine is broken) arranged in a single row, and minute fimbriae. The main differences can be noted in the type of neurochaetae, and in the pigmentation pattern of some parapodial features. In I. treadwelli neurochaetae are unidentate, and the basal tubercles of dorsal cirrophores have blackish tips and pale bases, whereas in I. corbariae neurochaetae are bidentate, and the basal tubercle is basally blackish and distally pale. Further, the ventral cirrostyles of I. treadwelli are pale, whereas they are blackish in I. corbariae . An additional difference is in elytral pigmentation. In I. treadwelli elytra are rather homogeneously pigmented, either yellowish or blackish, without spots, whereas in I. corbariae median elytra have 2–3 darker spots each.

Iphione treadwelli Pettibone, 1986 and I. henshawi were described from Hawaii, and they include the Iphione specimens provided with elytral fimbriae, previously often recorded from the Hawaiian Archipelago as I. muricata (Savigny in Lamarck, 1818).

Besides pigmentation, which can be lost after long time preservation in ethanol, there are several differences between the type specimen described from Hawaii, and the specimens from New Caledonia. As indicated in the key above, the type has distinct nuchal lappets, whereas they are not well-developed in the New Caledonia specimens, but these features are often modified after preservation. In the elytra, the macrotubercles are blackish in the Hawaiian type specimens, but pale in the New Caledonian ones, and lateral fringe papillae also differ, being mostly sessile in the type, and with short stems in the other specimens. Further, neurochaetae from median chaetigers are straighter, and less swollen subdistally in the New Caledonia specimens than in those from Hawaii. The only difference found in Japanese specimens, as illustrated by Imajima (2005: 55–59, Figs 15–17) is that the series of rows of denticles do not completely cover chaetae but apparently leave the dorsal surface smooth. However, this might be an artifact because tips of the series of spines are visible along the dorsal surface in his figures.

Distribution. From western Australia and Philippines, east to Hawaii and the Tuamotu Islands, on deep reefs and in rocky or mixed bottoms at moderate depths (36–540 m).