Magelona armatis, Taylor & Mortimer & Jimi, 2022

Taylor, Abbie, Mortimer, Kate & Jimi, Naoto, 2022, Unearthing the diversity of Japanese Magelona (Annelida: Magelonidae); three species new to science, and a redescription of Magelona japonica, Zootaxa 5196 (4), pp. 451-491 : 470-473

Magelona armatis sp. nov.

[Japanese name: Misaki-morote-gokai]

Figs 4 ; 12–13

Type locality: Kanagawa, Japan

ZooBank LSID: urn:lsid:zoobank.org:act:AFFFAFF6-3120-4A2B-B591-33723F47BCB0

Material examined. JAPAN, off Misaki, Kanagawa (Holotype, NMW.Z.2022.001.0011, af), off Misaki (35.1641, 139.6250), dredge, 16/10/2014, collected by NJ, sandy sediments, 3–5 m depth .

Diagnosis. A large, stout species. Prostomium wider than long, squared anterior margin. Chaetigers 1–8 with foliaceous, smooth-edged lamellae, with superior dorsal lobes. Chaetiger 9 with triangular postchaetal lamellae in both rami, with superior dorsal lobes in the notopodia and small prechaetal lamellae at base of neurochaetal bundle. Thoracic chaetigers with capillary chaetae only. Abdominal lateral lamellae spatulate. Hooded hooks tridentate, in two groups, vis-à-vis.

Dimensions. A large, stout species; abdomen of similar width to thorax when viewed dorsally, difference between the two regions not marked ( Figs 12A ; 13G ). When viewed laterally, the slightly dorsoventrally flattened thorax is thinner than the more rounded abdomen ( Fig. 13E ). Chaetigers 4–6 marginally wider than anterior and posterior thorax ( Fig. 13D, F ). Holotype, anterior fragment: prostomium 2.2 mm long, 2.3 mm wide (measurements an estimate due to the edges being curled under; flattening of prostomium would cause damage to specimen, particularly the burrowing organ); thorax 8.5 mm long (including prostomium), 1.35 mm wide (between chaetigers 5 and 6); abdominal chaetigers 1.5 mm wide: total length 21.0 mm for 24 chaetigers (last chaetiger dissected and slide mounted).

Description. Prostomium slightly wider than long (L:W ratio 0.96), rounded-triangular, lateral edges rounded, wavy, and curled due to large size of prostomium ( Figs 12A, B ; 13A, B ). Base of prostomium extends around palp bases, as seen in species like M. capax . Holotype, anterior fragment with a squared anterior margin forming very rudimentary prostomial horns. Prostomium with two pairs of prominent longitudinal dorsal muscular ridges, carrying transverse ridging. Inner pair diverging at distal margin and marginally at proximal margin. Outer pair abutting the inners for entire length. Distinct highly patterned markings either side of ridges, forming rows of arched lines ( Fig. 12B ). Burrowing organ partially everted ( Figs 12A ; 13A–F ), with heavy longitudinal ridges inferiorly, appearing as wavy lines, having a wrinkled appearance. Superior surface largely obscured by prostomium but appears smoother than inferior. No palps attached, unknown.

Achaetous region, marginally longer than chaetiger 1 ( Figs 12A ; 13A, B ). Chaetigers 1–8 similar ( Figs 12A ; 13D–F ); parapodia biramous with low notopodial prechaetal lamellae confluent with large, foliaceous postchaetal lamellae, which gradually increase in size towards the mid thorax ( Fig. 12C–J ). Slender, long, cirriform prechaetal superior dorsal lobes present, increasing in size until mid-thorax before decreasing again towards chaetiger 9. Neuropodial lamellae initially large and spatulate but decreasing in size from mid thorax to chaetiger 8. Those of chaetiger 1 more postchaetal in position, whilst remaining lamellae directly beneath chaetal bundle and attached to low pre- and postchaetal lamellae, cuff-like. Postchaetal expansion of neuropodia expands along thorax, becoming distinctly triangular on chaetiger 8 ( Fig. 12J ).

Notopodial postchaetal lamellae of chaetiger 9 triangular, smaller than on preceding chaetigers, with low prechaetal lamellae ( Fig. 12K ). Very small superior dorsal lobe present on left ramus (not observed on right). Neuropodial postchaetal lamellae broad triangular, with additional small, triangular prechaetal lamellae towards base of chaetal bundle. All thoracic chaetae simple, smooth edged unilimbate capillaries, those of neuropodia longer than notopodia ( Fig. 12C–K ). Those of chaetiger 9 not specialised but appearing marginally thicker than those on preceding chaetigers. Distinct ventral swellings present on thorax ( Fig. 13E, F ). The transverse boundaries between chaetigers enlarged and overlap preceding chaetiger, obvious from chaetiger 2 but distinct from chaetiger 3 onwards ( Figs 12A ; 13A, D ). Surface of thorax appearing rugged, armour-like.

Abdominal chaetigers with large rounded to oblong lamellae, of about equal size in both rami, basally constricted ( Figs 12L ; 13H ). Triangular processes (DML, VML) present sporadically at inner margins of chaetal rows. Minute rounded postchaetal expansion on chaetigers 11–14, behind chaetal rows.

Abdominal chaetae tridentate hooded hooks of similar size, superior two fangs parallel above main fang ( Figs 4F, G ; 12M ). Hooks long, approximately 18 to 20 per ramus, in two roughly equal groups ( Fig. 12L ), vis-à-vis. Those towards mid ramus longer, chaetae forming an arch, hook at base of each lamella slightly smaller. No abdominal support chaetae (‘aciculae’) or pouches observed.

Posterior unknown.

Colour. No live material observed, preserved specimen cream in alcohol. Cream interparapodial patches abdominally. Staining with Methyl Green shows speckling between chaetigers 1 and 7, particularly from chaetiger 4 ( Fig. 12A ). Overlapping borders between chaetigers often not staining.After much time has passed, a band of stain remains around mid-thorax (chaetigers 5–7, Fig. 13C ).

Habitat. Type specimen found between 3 and 5 m depth off Misaki , Kanagawa, Japan ( Fig. 1 ) .

Distribution. Magelona armatis sp. nov. is currently only known from Japan.

Etymology. The specific name armatis comes from the Latin for armoured, referring to the rugose nature of the epidermis, giving the species a distinct armoured appearance.

Remarks. Magelona armatis sp. nov. shares morphological similarities with nine species in terms of prostomial and lamellar shape. It differs from two West African species M. nanseni and M. picta in possessing rudimentary horns, whilst in the latter two species horns are absent. Similarly, the new species differs from Magelona methae Nateewathana & Hylleberg, 1991 from the Western Indo-Pacific; Magelona lenticulata Gallardo, 1968 from the Central Indo-Pacific; and Magelona berkeleyi Jones, 1971 from the Temperate Northern Pacific in possessing rudimentary and not distinct prostomial horns. The new species most closely resembles Magelona wilsoni Glémarec, 1967 from Temperate Northern Atlantic; Magelona cepiceps Mortimer & Mackie, 2006 from the Western Indo Pacific (given the morphological similarity of the thoracic parapodia of this and the new species, figures of the anterior of M. cepiceps are included ( Fig. 11G, H ), a species which has not previously been imaged); Magelona nonatoi Bolívar & Lana, 1986 from Temperate South America; and Magelona sp. J of Uebelacker & Jones (1984) from the Gulf of Mexico. Magelona cepiceps differs in terms of prostomial shape, being rounded and of a similar length to width ( Fig. 11G ); as opposed to triangular, and wider than long as in the new species. Magelona nonatoi and M. wilsoni differ in the nature of chaetiger 9, the parapodia of which are almost identical in size and shape in both rami for each species, whereas in the new species the notopodia is larger. The new species shares many morphological similarities with Magelona sp. J . but differs in the nature of the parapodia of chaetiger 9, which are more elongate in the Gulf of Mexico species. The new species is also distinguished from Magelona sp. J in possessing more foliaceous neuropodial lamellae of the anterior thorax.

Figures

FIGURE 1. Map highlighting the sampling locations around Japan where all observed material was collected.

FIGURE 4. Tridentate abdominal hooded hooks of Magelona alba sp. nov. (A–B), Magelona cf. cornuta (C–E) and Magelona armatis sp. nov. (F–G). A–C, F & G lateral views; D, frontal view; E, posterolateral view.

FIGURE 11. Magelona alba sp. nov. (NMW.Z.2022.001.0012, A–F), Magelona cepiceps Mortimer & Mackie, 2006 (NMW. Z.2000.020.0208, Holotype, G & H). A, prostomium, dorsal view; B, anterior, dorsal view; C, entire specimen, ventral view; D, prostomium and first five chaetigers, ventral view; E, thorax, ventral view; F, chaetigers 4 and 5, ventral view; G–H, entire specimen, dorsal and ventral views respectively. B–D, F–H, stained with Methyl Green.Ab = abdomen, BO = burrowing organ, PH = prostomial horns, Pp = palp, Pr = prostomium, Th = thorax, Noto = notopodia, Neuro = neuropodia, SDL = superior dorsal lobe, VS = ventral swellings, numbers indicate chaetiger.

FIGURE 12. Magelona armatis sp. nov. (NMW.Z.2022.001.0011). A, anterior, dorsal view showing Methyl Green staining pattern; B, prostomium, dorsal view (N.B. lateral edges folded under and distal tip directed upwards as seen in A); C–K, lefthand parapodia from chaetigers 1–9 respectively (anterior views, arrowed figure shows the ventral view of the neuropodial lamellae of chaetigers 2–8 respectively, that of chaetiger 9 anteroventral; L, right-hand parapodium of chaetiger 10, anterior view; M, tridentate abdominal hooded hook from chaetiger 24, lateral view. Pr = prostomium, BO = burrowing organ, Noto = notopodia, Neuro = neuropodia, SDL = superior dorsal lobe, numbers indicate chaetiger.

FIGURE 13. Magelona armatis sp. nov. (NMW.Z.2022.001.0011,A, D–G, stained with Methyl Green).A, prostomium and first five chaetigers, dorsolateral view; B, prostomium and first two chaetigers, dorsal view; C, anterior 20 chaetigers, dorsolateral view, retained stain present between chaetigers 4–7; D, anterior, dorsolateral view; E, anterior thirteen chaetigers, ventrolateral view, showing burrowing organ; F, anterior, ventral view showing ventral swellings; G, thoracic-abdominal junction, dorsal view; H, abdominal chaetigers, dorsolateral view. Ab = abdomen, BO = burrowing organ, Pr = prostomium, VS = ventral swellings, Th = thorax, numbers indicate chaetiger.