Magelona cf. cornuta Wesenberg-Lund, 1949

Magelona cf. cornuta Wesenberg-Lund, 1949 View in CoL

Figs 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

Material examined. JAPAN, Off Shirahama , Wakayama ( NMW.Z.2022.001.0013, af), R. V. Janthina Stn 4 (33.7040, 135.3418), dredge, 27/05/2015, collected by NJ, sandy sediments, 31 m depth GoogleMaps .

Diagnosis. Prostomium slightly wider than long, rounded, with distinct frontal horns, anterior margin straight, crenulate. Notopodia of chaetigers 1–8 with large foliaceous postchaetal lamellae, and long superior dorsal lobes. Neuropodia with slender cirriform ventral lamellae. Chaetiger 9 with triangular notopodial lamellae, superior dorsal lobes absent. Neuropodia of chaetigers 8 and 9 with additional triangular postchaetal lobes. Thoracic chaetigers with unilimbate chaetae. Abdominal lateral lamellae spatulate, basally constricted, with small triangular processes. Hooded hooks tridentate, in two groups, vis-à-vis.

Dimensions. A moderately sized species: with a very slight constriction between thorax and abdomen ( Figs 2A View FIGURE 2 ; 3C View FIGURE 3 ), thorax slightly dorsoventrally flattened, and marginally thinner (when viewed laterally), but wider than the rounded abdomen (when viewed dorsally). Chaetigers 5–6 marginally wider than rest of thorax (when viewed dorsally, Fig. 3C View FIGURE 3 ). Specimen, anterior fragment: prostomium 0.9 mm long, 1.0 mm wide; thorax 6.25 mm long (including prostomium), 0.8 mm wide; total length 21.5 mm for 31 chaetigers (last chaetiger dissected and slidemounted).

Description. Prostomium marginally wider than long (L:W ratio 0.9), rounded with distinct frontal horns, anterior margin straight, crenulate, with three triangular crenulations ( Figs 2B View FIGURE 2 ; 3B View FIGURE 3 ). Two prominent dorsal longitudinal muscular ridges, diverging at distal tips and extending into frontal horns. Two outer muscular ridges either side, marginally shorter and abutting inner pair for entire length. Distinct muscular patterned markings either side of ridges as roughly oblong sections (approximately four to five each side). Burrowing organ [previously termed ‘proboscis’, see Mortimer et al. (2012) for discussion on terminology] heart-shaped ( Fig. 3A, C–F View FIGURE 3 ), with distinct longitudinal ridges inferiorly, upper surface a distinct pad ( Fig. 3C View FIGURE 3 ) showing lighter longitudinal ridges. Both palps partially retained (regenerating), short, reaching chaetiger 7–8 ( Fig. 3A–F View FIGURE 3 , length of non-regenerating palps unknown), non-papillated region reaching chaetiger 3. Papillae, digitiform, two rows either side an indistinct longitudinal line medially, three rows either side proximally (distally unknown). Achaetous region, approximately one and a half times the size of chaetiger 1 ( Fig. 2A View FIGURE 2 ).

Chaetigers 1–7 similar: notopodia with large foliaceous and distally pointed postchaetal lamellae increasing marginally in size along thorax, inferiorly encircling chaetae, forming low triangular prechaetal lamellae ( Fig. 2C–I View FIGURE 2 ). A long, slender superior dorsal lobe (SDL) present on each chaetiger, marginally shorter in posterior thorax. Neuropodia with slender cirriform lamellae directly under chaetal bundle, decreasing gradually in size along thorax. Low pre- and postchaetal ridges encircling chaetae, cuff-like.

Notopodia of chaetiger 8 similar to preceding chaetigers ( Fig. 2J View FIGURE 2 ). Neuropodial lamellae of same chaetiger short, and in a marginally prechaetal position, additional postchaetal expansion of neuropodia distinct and triangular.

Chaetiger 9 notopodial postchaetal lamellae shorter than those of preceding chaetigers, triangular, with rounded distal tips, prechaetal lamellae low triangular, superior dorsal lobes absent. Neuropodia similar to that of chaetiger 8 ( Fig. 2K View FIGURE 2 ).

Very light ventral swellings present between chaetigers 6 and 8, paired and reniform ( Fig. 3E View FIGURE 3 ). All thoracic chaetae simple, smooth edged, unilimbate, capillary chaetae ( Fig. 2M View FIGURE 2 ), of a similar size in notopodia and neuropodia throughout ( Fig. 2C–K View FIGURE 2 ). Chaetae of chaetiger 9 with slightly curved tips.

Abdomen with basally constricted lateral lamellae, large and rounded spatulate, distally pointed, in both rami ( Figs 2L View FIGURE 2 ; 3G View FIGURE 3 ). Long triangular dorsal (DML) and ventral (VML) processes evident throughout at inner margins of chaetal rows ( Figs 2L View FIGURE 2 ; 3G View FIGURE 3 ). Abdominal hooded hooks tridentate (superior two fangs parallel, above main fang) ( Figs 2N, O View FIGURE 2 ; 4C–E View FIGURE 4 ), those towards middle of ramus slightly longer, although approximately similar in size. Hooks in two roughly equal groups, vis-à-vis, initially 12 per ramus, reducing to ten by chaetiger 31 ( Figs 2L View FIGURE 2 ; 3G View FIGURE 3 ). Hooks protruding from definite ridge, with a distinct triangular postchaetal expansion ( Fig. 2L View FIGURE 2 ). Small, curved support chaetae (‘aciculae’, abdominal support chaetae of Müller & Bartolomaeus 2022) present, one per ramus, basal areas overlapping in region between notopodial and neuropodial rami of each parapodium; distal regions small with rudimentary hooded hook. No pouches observed (although pouches only recorded from chaetiger 41 for M. cornuta , see Mortimer & Mackie 2009).

Pygidium unknown.

Colour. No live specimens observed. Specimen cream-white in alcohol with distinct interparapodial abdominal patches. Methyl Green staining pattern inconspicuous, diffusely stained all over ( Fig. 3B, D–G View FIGURE 3 ). When much time has passed, light speckling occurs dorsally between chaetigers 4–8, and ventrally between chaetigers 3–8, and the dorsal muscular ridges of the prostomium.

Distribution. Magelona cornuta was originally described from Iranian waters, Gulf of Oman, in clay sediments at a depth of 12 m ( Wesenberg-Lund 1949) and has since been recorded in the area by Taheri & Foshtomi (2009) and Miri et al. (2014). Further records of the species include: the Red Sea ( Amoureux 1983), Gulf of Aden ( Hartman 1974, 1976), the Ivory Coast ( Intès & Le Loeuff 1975, 1984), Kuwait ( Al-Yamani et al. 2012; Al-Rifaie et al. 2012), Nigeria, Zaire, Angola ( Kirkegaard 1959, 1996), and Hong Kong ( Zhou & Mortimer 2013). Magelona cornuta was additionally recorded in Hong Kong by Mortimer & Mackie (2009) during a redescription of the species, and although minute differences were noted these were attributed to the poor condition of the type material. The need for fresher material from the type locality recognised at the time. The material from the Red Sea recorded by Amoureux (1983) was later described as an additional species Magelona montera Mortimer, Cassà, Martin & Gil, 2012 , and that recorded by Kirkegaard (1959) was shown to be incorrectly identified ( Mortimer et al. 2011). Personal observations of the second author indicate that there are several new species off Western Africa which share morphological similarities with both M. cornuta and M. crenulifrons . It is therefore likely that previous records of M. cornuta off Western Africa as noted above relate to new species, the current authors do not consider it to occur in that region. Mortimer (2010) stated that Hartman’s specimens from the Gulf of Aden should be revisited given the morphological similarity with M. crenulifrons .

Magelona cornuta is a species which has relatively few records ( Fig. 5 View FIGURE 5 ). Whilst this may have been previously attributed to information lacking in the original description, the species was redescribed by Mortimer & Mackie (2009). The morphologically similar species M. crenulifrons has been extensively recorded ( Fig. 5 View FIGURE 5 ) from the NorthWestern Indo-Pacific to Central Indo-Pacific ( Mortimer & Mackie 2009; Mortimer et al. 2012; Shakouri et al. 2017; Vijapure et al. 2019; Nateewathana & Hylleberg 1991; Gallardo 1968; Phan 2015; Thompson & Shin 1983; Rosita et al. 1991, 1998; Oliver 1993; Shin 1998, 2003; Yan 2007; Wang 2008; Du et al. 2011, 2013; Zhong et al. 2020; Al-Hakin & Glasby 2004; Glasby et al. 2016; Pamungkas 2020). Given the morphological similarity between these two species previous records should be verified. However, if previous identifications are correct the lack of records of M. cornuta may indicate that the species occurs in a much more restricted region around the Arabian Sea. Further analysis would be needed to verify the latter.

The records of M. cornuta from Hong Kong by Mortimer & Mackie (2009), and a specimen approaching M. cornuta off Shirahama, Japan from the current study call into question the known distribution of the species. Whilst Mortimer & Mackie (2009) concluded that the Hong Kong material agreed well with the type material, the overall condition of the latter was poor and the need for fresher material from the type locality highlighted. Certain magelonid species are known to have wide distributions (e.g., Magelona alleni Wilson, 1958 , see Mortimer et al. 2021b), however, the Japanese specimen herein observed was collected a significant distance from the type locality. The material of Mortimer & Mackie (2009) from Hong Kong was compared with the Japanese specimen and they agree well. This may suggest that Northern Pacific records may be a distinct species. However, without further material from both the type locality and Japan this cannot be verified at this time. For this reason, we refer the Japanese specimen to M. cf. cornuta , until verifications can be made. We suggest that M. cornuta should be considered a predominantly Western Indo-Pacific (sensu Spalding et al. 2007) species. Central Indo-Pacific and Temperate Northern Pacific records should be treated with caution until further material can be studied.

Habitat. The following specimen was collected from off Shirahama, Wakayama in sandy sediments at 31 m ( Fig. 1 View FIGURE 1 ).

Remarks. The Japanese material closely resembles the holotype previously observed and redescribed by the second author. The main difference relates to the shape of the prostomium, being somewhat more rounded in the latest material and subtriangular in the type. Mortimer & Mackie (2009) noted that the prostomial shape of the holotype was likely altered by its condition, with the lateral margins somewhat squashed inwards. The only other difference is slightly more pointed tips of the thoracic notopodial lamellae of the Japanese material. As noted above, until further material can be examined, we refer this specimen to M. cf. cornuta .