Magelona sinbadi Mortimer, Cassà, Martin & Gil, 2012, sp. nov.

Magelona sinbadi sp. nov.

Figures 2, 13 F

Material examined. Holotype: Persian Gulf, IRAN, Stn. B4-20A (27°41.908'N, 52°11.497'E), shelly muddy sand, 20 m (NMW.Z.2010.037.0001; af), Van Veen grab, August 2005.

Diagnosis. Prostomium longer than wide, with distinct prostomial horns. Notopodia of chaetigers 1–8 with subspatulate postchaetal lamellae expanded as cirriform dorsal superior processes; neuropodia with digitiform ventral lobes. Neuropodia of chaetiger 8, with additional triangular postchaetal lamellae. Notopodia of chaetiger 9 with triangular postchaetal lamellae and digitiform lateral processes; neuropodia with triangular postchaetal lamellae and smaller digitiform prechaetal lobes. All thoracic chaetae capillary. Abdominal lateral lamellae rounded triangular, basally constricted. Hooded hooks tridentate, in two groups, vis-à-vis.

Description. A moderately stout species; difference between abdomen and thorax not marked (Figure 2 A). Specimen dimensions: prostomium 1.0 mm long, 0.8 mm wide; thorax (including prostomium) 4.5 mm long, 0.9 mm wide (measured at widest point around chaetiger 4 – 5); abdomen 0.8 mm wide, 10.8 mm long; total length 15.3 mm for 27 chaetigers.

Prostomium longer than wide (L:W ratio 1.25); anterior margin smooth, triangular, with conspicuous prostomial horns (Figures 2 B, 13F); distal tip folded upwards (Figure 2 C) (Note: figured prostomium appears slightly shorter due to distal folding of prostomium); lateral edges undulating. Two pairs of prominent longitudinal dorsal muscular(?) ridges, outer pair shorter and abutting inners for entire length; inner pair diverging only distally, into corners of horns. Outer pair moderately thick, with heavy transverse ridges. Distinct quadrangular (muscular?)

areas present either side of ridges. Proboscis not everted. Both palps attached, long (distal tips broken?), thinner at point of attachment but increasing in thickness by chaetiger 2; arising ventrolaterally from base of prostomium. Palps reaching at least chaetiger 20, non-papillated region reaching chaetiger 4 or 5. Papillae long, digitiform; proximally with two rows of papillae either side of inconspicuous groove, one row either side medially and distally.

Achaetous region behind prostomium, roughly twice the size of chaetiger 1. Chaetigers 1–8 similar; parapodia biramous; notopodia with low triangular prechaetal lamellae confluent with subspatulate postchaetal lamellae of similar size throughout thorax; single long, slender cirriform prechaetal superior processes (DML) present (Figures 2 D–G). Neuropodia of chaetigers 1–8 with low pre- and postchaetal ridges; ventral cirriform lobes (VNL) underneath chaetae, decreasing slightly to mid-thorax. Small postchaetal expansions present by chaetiger 6, becoming well-developed and triangular on chaetiger 8, apexes of which are broadly rounded. Ventral neuropodial lobes of chaetiger 8 short, slender triangular, in distinctly prechaetal positions.

Chaetiger 9: Notopodial prechaetal lamellae low and rounded, adjoined to lateral digitiform processes underneath chaetae; distal tips papilla-like (Figures 2 H–J). Processes also confluent with broadly rounded triangular postchaetal lamellae, much smaller than on preceding chaetigers. No superior processes (DML) observed. Neuropodia of chaetiger 9 (Figure 2 H) with triangular postchaetal lamellae of similar size to notopodial; apexes broadly rounded; confluent with low prechaetal ridges and short digitiform prechaetal lobes (VNL). Chaetae of all thoracic chaetigers simple winged capillaries.

Abdominal chaetigers with large, basally constricted and broadly rounded triangular lateral lamellae (in profile, somewhat toad-stool shaped) of about equal size in both rami (Figures 2 K and L); edges undulating (often folded over and appearing crinkled); overlapping in anterior abdomen. Postchaetal extensions of the lateral lamellae behind chaetal rows well-developed, rounded. Triangular processes (DML and VML) present at inner margins of chaetal rows, long in anterior abdomen.

Abdominal chaetae tridentate hooded hooks (Figure 2 M) of similar size. Hooks in two groups, main fangs visà-vis (Figures 2 K–L). Around 10–14 hooks per rami. No pouches observed, posterior unknown.

Colour. Preserved colour uniformly cream/white in alcohol, conspicuous glandular areas noticeable interparapodially in the abdomen. Staining with methyl green shows no distinct pattern, but a diffuse overall stain. After much of the stain has dissipated, light stain between chaetigers 4–7 remains.

Habitat. Holotype found in shelly muddy sand, 20 m, Iran, Persian Gulf.

Etymology. From the name Sinbad, the fictional sailor of traditional Arabic and Persian tales who sailed extensively around the Persian Gulf (and beyond) during his mythical voyages, referring to the region in which this species was first sampled.

Remarks. Magelona sinbadi sp. nov., shares many morphological similarities with M. gemmata originally described from the Seychelles. In particular, the prostomia of both species, which are: longer than wide; undulating laterally and which possess distinct quadrangular regions either side of thick, highly ribbed ridges. Both species further share similarities in the shape of the thoracic lamellae. However, the two species differ in the shape of the lamellae of the 9th chaetiger. This is particularly true for the notopodia, with M. gemmata possessing subtriangular lamellae with swollen bud-like tips (Mortimer & Mackie 2003: figure 4E), whilst M. sinbadi sp. nov., possesses digitiform lateral processes in addition to triangular postchaetal lamellae. The two species further differ in the neuropodia of the same chaetiger, M. gemmata possessing postchaetal lamellae that are distinctly pointed, and prechaetal lobes that are long and slender. In M. sinbadi sp. nov., these are broadly rounded (postchaetal lamellae) and shorter, thicker and more blunt (prechaetal lobes). Magelona sinbadi sp. nov., further differs in possessing thoracic neuropodial lobes which reduce in size to the mid-thorax.

As in M. sinbadi sp. nov., the methyl green staining pattern of M. gemmata shows no clear pattern (new observations), however, distinct transverse bands of white speckles across the dorsum, level with the parapodia are present. These bands were heavily stained with Rose Bengal when the type specimen was first examined; similar bands were not observed in M. sinbadi sp. nov.

Magelona sinbadi sp. nov., shares similarities with a further 14 species which possess prostomial frontal horns and rounded sub-spatulate thoracic lamellae: M. tehuanensis, M. pacifica, M. nonatoi, M. marianae, Magelona lenticulata Gallardo, 1968, Magelona longicornis Johnson, 1901, M. cornuta, M. crenulifrons, Magelona cepiceps Mortimer & Mackie, 2006, M. berkeleyi and four unnamed species (Magelona spp. G, J, K and L of Uebelacker & Jones 1984) from the Gulf of Mexico.

Magelona tehuanensis, M. marianae, M. lenticulata, M. cornuta, M. crenulifrons and Magelona sp. L differ from M. sinbadi sp. nov., in possessing prostomia which are either as long as wide, or only marginally longer than their widths. All but M. marianae possess crenulate anterior prostomia. Magelona marianae and M. crenulifrons further differ in possessing bidentate abdominal hooded hooks, not tridentate as in M. sinbadi sp. nov., Magelona lenticulata possesses dorsal superior processes on chaetiger 9 and M. tehuanensis, M. cornuta and Magelona sp. L further differ in the nature of the lamellae of the same chaetiger.

Magelona nonatoi, M. cepiceps, M. berkeleyi and Magelona sp. J all possess rudimentary prostomial horns, unlike the well-developed horns seen in M. sinbadi sp. nov. Apart from M. berkeleyi they further differ from M. sinbadi sp. nov., by possessing dorsal superior processes on chaetiger 9. However, M. berkeleyi differs in possessing a prostomium, which is broader than long and possessing low postchaetal lamellae on chaetiger 9.

Magelona longicornis differs in possessing a prostomium wider than long, with some degree of crenulation of the anterior margin; dorsal superior processes and larger triangular postchaetal lamellae on chaetiger 9; and bidentate abdominal hooded hooks.

Magelona pacifica, and Magelona spp. G and K resemble M. sinbadi sp. nov., in possessing prostomia which are longer than wide with well-developed frontal horns. However, M. pacifica and Magelona sp. G, differ in possessing bidentate abdominal hooded hooks. All three species differ from M. sinbadi sp. nov., in the shape of the chaetiger 9 lamellae.