Marphysa yunbenun sp. nov. LSID urn:lsid:zoobank.org:act: 492840B0-5B82-45D1-BC40-D8B3A68BA754 Figures 5–7, Table 2 Material examined. Holotype (AM W.33021) Arcadia, Magnetic Island, Great Barrier Reef, Queensland, 19.15°S 146.87° E, hand collected by P.A. Hutchings, 17 Aug. 2006, intertidally on mud flats. Description. Preserved, complete specimen, 100 mm length, length to chaetiger 10, 6.5 mm, width at chaetiger 10 (excluding parapodia) 5 mm, with 234 chaetigers, pale yellow in colour, no pigmentation present. Body elongate, and tapered gradually at both ends, anteriorly first nine chaetigerous segments rounded in cross-section (Fig. 5A), following chaetigers becoming flattened (Fig. 5A) until pygidium, posterior segments with mud-filled gut visible through body wall, no sign of any gametes. Posterior segments very compact. Prostomium strongly bilobed anteriorly with two dorsoventrally flattened buccal lips and an anterior notch between them (Fig. 5B, C). Two palps and three antennae slender and tapering with tips damaged, each with short palpophores (Fig. 5B, D), arranged in a slightly curved arc on posterior margin of prostomium, all slightly wrinkled, palps shorter than antennae, less than half length of the one complete antenna which extends to chaetiger 2 and longer than length of prostomium; ratio c. 1.0/1.8/1.6 (Fig. 5B). Eyes present, minute, on outer edge of palps (Fig. 5A). First peristomial ring 4x longer dorsally than 2 nd, with shallow notch on anterior margin, ventrally (Fig. 5B, C). Maxillary apparatus not everted, dissected out (Fig. 5E). Maxillae with carriers, four paired elements and one single one, light brown except for dark brown edges on carriers and base of MIV, formula as follows: MF=1+1, 5+6, 7+0, 4+5, 1+1. MI approximately 2.5x longer than maxillary carrier; carriers rectangular anteriorly with a pair of oval wings situated at posterior-lateral margins. MI forceps-like, without attachment lamellae, well-developed, sub-right angle falcal arch. Closing system approximately 6x shorter than MI. Ligament between MI and MII rectangular, same colour as MI. MII wide without an attachment lamella, teeth triangular pointed downward, and distributed along half length of plate. Ligament between MII and MIII absent. MIII single, slightly shorter than right MIV, curved forming part of distal arc with recurved equal-sized triangular teeth. Left MIV about 2/3 length of right MIV with a wide, rounded base, with dark brown edge. MV paired, rectangular, as long as wide, with broad cutting edge and no clearly defined teeth (but following tradition to score a 1+1). Mandibles (Fig. 5E) darkish with darker longitudinal strip on inner margin, slightly shorter than MI plus carriers, cutting plates whitish, without distinct growth rings. First few parapodia located below middle line of body wall, but gradually positioned dorsally to about midline in subsequent segments. Notopodial cirri (Figs 5A, B, 6A) slender, tapering, anterior ones faintly annulated with base swollen (Fig. 6A), extending laterally slightly further than both post-chaetal lobe and ventral cirri; extending slightly further than chaetal lobes in midbody chaetigers onwards. Ventral cirri swollen cylindrical with rounded tips, initially slightly longer than parapodial lobes, gradually becoming shorter than lobes, and posteriorly cylindrical and glandular. Parapodia comprising low rounded pre- and post-chaetal lobes, strongly contracted due to preservation in 95% ethanol (Fig. 6B). Branchiae palmate (Fig. 7A) commencing from chaetiger 19 and continuing to chaetiger 223, 1st branchiate chaetiger with 2 filaments increasing to a maximum number of 7 on chaetiger 81 and numbers decreasing on posterior chaetigers, last chaetiger with branchiae with single filament. Filaments robust and wrinkled (Fig. 7A). Branchiae longer than notopodial cirri and the longest filament is longer than the branchial stem. Dorsal cirri longer than ventral cirri (Fig. 6A) and slightly lobulate. Compound chaetae absent (Fig. 6A). Subacicular bidentate hooks begin on parapodia on segment 40, yellow-brown, one per parapodium (Fig. 6D), and present to posterior. Acicula brown to dark brown 2–3 per chaetiger anteriorly, reducing to one per chaetiger in posterior half of body, almost 2x wider than subacicular hook (Fig. 6A, C). Pectinate chaetae present, two kinds: isodont pectinate wide with long and slender teeth, about 33 teeth and isodont wide with about 19 long teeth (terminology of Molina-Acevedo & Carrera-Parra 2017). First parapodia with confirmed pectinate chaetae chaetiger 42 and present until at least chaetiger 220 although anterior chaetae mostly broken. The holotype has been stored in 95% alcohol for 18 years, and this has caused the chaetae to become very brittle as evidenced in the SEM (Fig. 7A–F) where most of the capillaries are broken, but the more robust posterior comb chaetae have survived. Pygidium with two pairs of anal cirri—dorsal pair ~4x longer than ventral pair. Remarks. Fauchald (1970) divided the genus Marphysa into several groups. Group A was characterised by lacking compound chaetae; it only included one species M. mossambica (Peters, 1854) described from Mozambique. Since then, M. moribidii Idris, Hutchings & Arshad, 2014 described from Malaysia (considered here a junior synonym of M. mossambica, and not compared below), and M. fijiensis nom. nov. (see Molina-Acevedo & Idris 2021) described from Fiji have been added to this group; and they also included M. novaehollandiae (Kinberg, 1865) described from Sydney Harbour, Australia (see Table 1 in Molina-Acevedo & Idris 2021). More recently, another species M. kertehensis Che Engku Abdullah, Idris, Fahmi, Flaxman & Hutchings, 2024, also known only from Malaysia has been described. The new species M. yunbenun sp. nov. also belongs to this group (the lack of compound chaetae was also recorded by J. Zanol (pers. comm.) when she examined the specimen in 2014) and can be distinguished from M. kertehensis in having sub-acicular hooks, which are absent in the latter species. Marphysa yunbenun sp. nov. can be separated from M. mossambica by having only two types of pectinate chaetae (IWSS and IWLS; requires confirmation, as many chaetae were broken), whereas the other two species have four types (but see below). Regarding the dentition of the pectinate chaetae, the new species has 33 teeth (n = 2) on the IWSS, compared to 41 (n = 3) in the Kenyan specimen and 47 (n = 1) in the lectotype of M. mossambica as counted by Fauchald (1987) and 41 as counted by Idris et al. 2014); the IWLS pectinates have 23 teeth (n = 3) compared to 19 teeth (n = 6) in the Kenya specimen, 20 in the lectotype counted by Fauchald (1987), and 28 as counted from images in Idris et al. (2014, Fig. 6d,e) (Table 2). Note that M. mossambica is now shown to have four types of pectinate chaetae in total (INLS, IWSS, IWLS, AWLT), with the INLS only present in anterior chaetigers, and the other three types present in middle and posterior chaetigers (Molina-Acevedo & Idris, 2021). Earlier reports of only three types (e.g., Idris et al. 2014) appear to be because the ones occurring anteriorly were overlooked. Further, Fauchald (1987) claimed that ‘fan chaetae’ [=pectinate chaetae] did not appear until after chaetiger 100, but Idris et al. (2014) reported them after 30. Notably, studies on Marphysa species utilising SEM images based on a series of parapodia from along the body have often detected fewer and smaller pectinate chaetae in the first few chaetigers, whereas they are likely overlooked in LM studies, particularly if the parapodium is mounted posterior side up. Marphysa yunbenun sp. nov., can also be distinguished from M. mossambica by the peristomial ring 4.0x longer dorsally than the second one in the new species cf. 2.3x longer dorsally than second one in M. mossambica; branchiae commence from chaetiger 19 in the new species cf. chaetiger 34–42 in M. mossambica (chaetigers 37–49 according to Fauchald 1987); subacicular bidentate hooks beginning on segment 40 and are continuous in every chaetiger after they begin in the new species cf. beginning on segment 43–50 and discontinuous in M. mossambica; 2 or 3 aciculae per chaetiger in the new species cf. and 4 or 5 aciculae per chaetiger in M. mossambica; and the acicula being only slightly wider than the subacicular hooks in the new species (cf. ~2x wider in M. mossambica). As some of these characters are size-related, further specimens of the new species need to be studied to better understand morphological variation. Marphysa novaehollandiae and M. fijiensis can be separated from M. yunbenun sp. nov. by the maxillary formulae, 1+1, 4-5+6, 7+0, 5+8-9, 1+1 and 1+1, 5+5-6, 9+0, 2+8, 1+1 (as per Table 1 in Molina-Acevedo & Idris 2021) in comparison to 1+1, 5+6, 7+0, 4+5, 1+ 1 in the new species. The specimen of M. mossambica (Peters, 1854) identified by Glasby & Hutchings (2010) from the Low Isles, Great Barrier Reef (Fig. 4) in the report of Monro (1931) may instead represent this new species, extending the distribution of the species about 330 km northward; unfortunately, the two specimens (AM W.2956), lack heads and tissue sampling was not possible, preventing positive identification. Etymology. The species is named after the First Nation people’s name for Magnetic Island, Yunbenun in the language of the Wulguru people—the traditional owners of the island. The species epithet is an unmodifiable noun in apposition. Habitat. Mud flat. Distribution. Magnetic Island, Great Barrier Reef, Australia. Known only from the type locality.

Published as part of Glasby, Christopher J., Biriukova, Olga, Hutchings, Pat, Daffe, Guillemine & Lavesque, Nicolas, 2025, Redescription of the enigmatic Marphysa mossambica (Polychaeta: Eunicidae) and description of two new Marphysa species from northern Australia, pp. 151-179 in Zootaxa 5717 (2) on pages 161-166, DOI: 10.11646/zootaxa.5717.2.1, http://zenodo.org/record/17890174