Macellicephala patersoni, Neal & Brasier & Wiklund, 2018

Neal, Lenka, Brasier, Madeleine J. & Wiklund, Helena, 2018, Six new species of Macellicephala (Annelida: Polynoidae) from the Southern Ocean and south Atlantic with re-description of type species, Zootaxa 4455 (1), pp. 1-34 : 18-19

Macellicephala patersoni sp. nov.

( Figures 2F and Figures 9 , 10 ; Table 2.)

Macellicephala sp. B in Neal et al. (2017) [record].

Material examined. Holotype, NHMUK.2018.1009, Pine Island Bay , Amundsen Sea, Southern Ocean, cruise JR 179, station BIO4 -EBS-3D, collected on 07/03/2008, epibenthic sledge, epi-net, 74°23'25.836''S, 104°46'4.512''W, 506 m depth.

Description (based on holotype). Medium sized species; holotype complete specimen in good condition, 13.5 mm long, 2 mm wide excluding parapodia and 6.55 mm wide including parapodia, 18 segments (segment 1 = tentacular segment); body dorsoventrally flattened, tapering anteriorly and posteriorly; live specimen not observed; dorsum and everted proboscis purple in alcohol ( Fig. 9A ), remaining body pale yellow ( Fig. 9A, B ); ceratophore of median antenna and tentacular cirrophores with distinct purple pigmentation ( Fig. 9C ).

Prostomium bilobed with wide and deep median notch; prostomial lobes slightly pronounced, anteriorly tapering ( Figs. 2F and 8C ). Frontal filaments distinct, basally slightly inflated, distally slender, extending from tapering prostomial lobes where medially inserted ( Figs. 2F and 9C ). Eyes absent. Facial tubercle trilobed, composed of three inflated oval lobes, with median lobe larger than lateral lobes ( Figs. 2F and 9C ). Ceratophore of median antenna massive, bulbous, with purple pigmentation, inserted medially on prostomium (near the base of anterior notch) ( Figs. 2F and 9C ); style of median antenna very long (longest of all appendages, reaching to beginning of segment 10), smooth and slender. Palps thick, smooth, tapering into slender tips; moderately long (extending to the beginning of segment 6).

Tentaculophores large, cylindrical, equal-sized, with purple pigmentation ( Fig. 9C ), inserted laterally to prostomium, achaetous; all tentacular styles attached, long slender smooth, similar in form, but shorter in length (about 2/3) than style of median antenna; dorsal tentacular cirrus slightly longer than ventral tentacular cirrus. Pharynx everted, purple, with 9 pairs of equal-sized, triangular papillae distally ( Fig. 9D ); two pairs of dark ambercoloured jaws, with smooth margins. Second segment with elytrophores, biramous parapodia, chaetae and ventral cirri.

Nine pairs of prominent, bulbous elytrophores, on segments 2, 4, 5, 7, 9, 11, 13, 15 and 17; all elytra missing.

Parapodia biramous. Notopodia reduced to elongate acicular lobe ( Fig. 10A ), starting on mid-dorsum as two raised ridges, extending into slender elongated acicular lobes, tip of notoacicula not penetrating epidermis; two distinct, narrow, white lines across dorsum of each segment ( Fig. 9A ), connecting raised ridges; dorsal tubercules not developed. Neuropodia large ( Fig. 10A ), approaching subtriangular to rectangular shape, with elongate slender acicular lobe, tip of neuroacicula not penetrating epidermis. Cirrigerous segments with prominent, cylindrical cirrophores, inserted basally on notopodia; styles mostly missing, 8 remaining styles very long (much longer than neuropodial acicular lobe), smooth slender, similar in form to styles of median antenna and tentacular cirri. Ventral cirri smooth, slender, tapering; present from segment 2 to last segment; inserted basally on segment 2, where very long, (slightly longer than associated neuropodia lobe); inserted medially on subsequent segments ( Fig. 10A ), where very short (not reaching distal margin of neuropodial lobe).

Notochaetae about as slender as neurochaetae ( Fig. 10B, C ); few (<10 observed per ramus); short to very long, straight to slightly convex, with faint serration across convex side ( Fig. 10C ). Neurochaetae numerous ( Fig. 10A, D–E ), all translucent, very long and slender; neurochaete of two forms: either flattened subdistally with faint serrations along margins, with bidentate tips (secondary tooth minute) ( Fig. 10H ), these neurochaetae are few in number and easily overlooked or neurochaete slender with faint serration along margins, with bluntly rounded tips ( Fig. 10D–F ).

Two distinct white lines running through ventral side of neuropodia and ventrum of each segment (except for tentacular segment). Nephridial papillae on ventrum of segments 10, 11 and 12 small, globular, inconspicuous in other segments, present from segment 5. Reduced parapodia of segment 18 lateral to pygidium, consisting of large notopodia only. Pygidium somewhat truncated, dorsally with two large loops ( Fig. 10E ). Anal cirri not observed ( Fig. 10E, F ).

Remarks. Of the Southern Ocean Macellicephala species, M. patersoni sp. nov. is most similar to M. brenesorum sp. nov. It differs from the latter species in having a massive, bulbous and pigmented ceratophore of median antenna, in lacking dorsal tubercules, in possessing two dorsal loops on the pygidium and in having neurochaetae with bidentate tips. For comparison with other known Macellicephala species, including those described in this publication, see Table 2.

Molecular Information. 16S (434 bp) and 18S (676 bp) were obtained from the holotype. Based on 16S, this species was closest to Macellicephala brenesoru m sp. nov. with uncorrected 'p' distance 0.156, and distance to M. violacea was 0.166.

Etymology. Macellicephala patersoni sp. nov. is named after Dr. Gordon Paterson, who recently retired from the Natural History Museum London after a long and successful career in deep-sea research with the focus on polychaete ecology and systematics.

Distribution. Known only from its type locality, Pine Island Bay, Amundsen Sea, Southern Ocean, depth of 507 m.

Figures

FIGURE 2. Drawings of prostomia and anterior ends in dorsal view of species described and redescribed in this study: A) M. mirabilis (holotype, BMNH: 1885: 12: 1: 100); B) M. macintoshi sp. nov. (holotype, BMNH: 1924: 7: 21: 12); C) M. monroi sp. nov. (paratype, BMNH: 1930: 1930: 10. 8. 440), historic specimen collected from South Georgia by Monro (1930); D) M. monroi sp. nov. (holotype, NHMUK.2018.53), specimen collected from South Georgia during BIOPEARL I expedition to Scotia Sea; E) M. brenesorum sp. nov. (holotype, NHMUK.2018.830); F) M. patersoni sp. nov. (holotype, NHMUK.2018.1009); G) M. gloveri sp. nov. (holotype, NHMUK.2018.211); H) M. linseae sp. nov. (holotype, NHMUK.2018.9354). All scale bars 1 mm.

FIGURE 8. Macellicephala monroi sp. nov. (holotype, NHMUK.2018.53, unless stated otherwise): A) mid body cirrigerous parapodium with dorsal cirrus attached; B) mid body cirrigerous parapodium with ventral cirrus attached, C–D detail of neurochaetae (modern specimen); E) drawing of parapodium from historic specimen, after Monro (1930) (paratype, BMNH 1930: 10. 8. 440); F) drawing of neurochaeta from historic specimen, after Monro (1936) (paratype, BMNH 1930: 10. 8. 440). Scale bars: A–B) 500 µm; C) 100 µm; D) 50 µm; E) 1 mm; F) 100 µm.

FIGURE 9. Macellicephala patersoni sp. nov. (holotype, NHMUK.2018.1009): A) specimen in dorsal view; B) specimen in ventral view; C) detail of prostomium and anterior end; D) detail of everted proboscis; E) detail of pygidium in dorsal view, showing two large loops; F) detail of pygidium in ventral view. Scale bars: A–B) 5 mm; C) 1.5 mm; D) 2.5 mm; E) 1.5mm.

FIGURE 10. Macellicephala patersoni sp. nov. (holotype, NHMUK.2018.1009): A) mid body parapodium; B) notochaetae; C) detail of notochaetae; D–H) neurochaetae. Scale bars: A) 500 µm; B) 300 µm; C–E) 100 µm; F–G) 50 µm and H) 15 µm.