Magelona cinthyae sp. nov.

Figures 2 (C‒E), 3 and 4

Material examined. Holotype: Hawaii, Oahu, EMAP, Sta. HI02-0008, Paukauila Stream, 21°34'21.35" N, 158°5'47.7" W, 2002 (USNM 1494157). Paratypes: Same locality and station as holotype (2 complete specimens, USNM 1494158; 4 specimens, two complete and two af; two of them with eyespots, BPBM-R 3871). Additional material examined: Hawaii, Oahu, 2.3 km offshore of Ewa Beach, in the vicinity of threadfin Polydactylis sexfilis mariculture cages, Cage Project, April/2002, Sta. U-2 (1 af), Sta. U3 (1 af), Sta. W1 (5 complete specimens, three with eyespots), Sta. W2 (3 af, two with eyespots); Sta. FW-3 (1 af with eyespots), Sta. FW-2 (1 complete specimen with eyespots), 31‒ 39 m.

Diagnosis. Prostomium slightly longer than wide, with distinct prostomial horns. Notopodia of chaetigers 1‒8 with elongate foliaceous postchaetal lamellae with smooth upper edges. Superior processes present from chaetigers 1‒8, more elongate towards posterior thorax. Chaetiger nine with only bilimbate simple capillaries. Abdominal hooded hooks tridentate. Posterior abdominal lateral pouches (C configuration) present from chaetiger 39, paired.

Description. Holotype: complete specimen, both palps attached; prostomium 0.38 mm long, 0.30 mm wide; thorax 2.59 mm long (including prostomium), 0.34 mm wide; abdomen 0.41 mm wide; total length 17.93 mm for 68 chaetigers. Paratypes: Two complete specimens (palps attached) measured; prostomium 0.40‒0.42 mm long, 0.29‒0.30 mm wide; thorax 1.95‒2.69 mm long (including prostomium), 0.22‒0.25 mm wide; abdomen 0.33‒0.34 mm wide; total length 10.29‒11.54 mm for 59‒60 chaetigers.

Prostomium slightly longer than wide (L:W ratio 1.26‒1.43), round; anterior margin smooth, anterior with conspicuous prostomial horns; horns distinctly separated from antero-lateral margins of prostomium (Figs 2C; 3A, B; 4A‒I). Two pairs of prominent longitudinal dorsal ridges; outer pair, reaching further basally and approaching achaetous segment with indistinct transverse ridges; inner pair diverging anteriorly into horn corners and posteriorly towards prostomial base, with slight medial gap both anteriorly and posteriorly (Fig. 3A, B); prostomium with lateral convoluted markings. Black eyespots present on posterior region of prostomium of several individuals, in between inner pair of prostomial ridge (Figs 2C; 3B; 4A‒I); shape and number of eyespots variable, some specimens with a pair and other with two or three eyespots in a row (Fig. 4A‒I). Burrowing organ partially everted in four specimens, saclike, ridges not observed. Palps arising ventro-laterally from base of prostomium and extending to chaetigers 15‒20 (Fig. 3A); palps measuring 6 mm long in holotype and ranging from 3.26‒4 mm long in paratypes; non‒papillated region approximately 1/7 of total length of palp (Fig. 3A). Papillae short proximally but long for majority of length, digitiform; proximally and medially with four rows and distally with two rows of papillae. Achaetous segment approximately twice the size of chaetiger one (Fig. 3B).

Thoracic segments slightly longer than wide; chaetigers 1‒8 similar; parapodia biramous; notopodia with subchaetal prechaetal lamellae confluent with foliaceous postchaetal lamellae of similar size throughout thorax (Fig. 3E‒H), those of chaetiger eight slightly shorter; notopodial lamellae with smooth upper edges; prechaetal lamellae joins far down postchaetal lamellae length. Prechaetal superior processes present (DML), digitiform on anterior thoracic chaetigers and becoming elongate on posterior thoracic segments. Neuropodial pre- and postchaetal lamellae as low ridges; ventral lobes (VNL) lobes elongate to conical (Fig. 3E‒H). Chaetiger nine shorter but not distinctly constricted with triangular postchaetal lamellae and digitiform prechaetal lobes; superior processes (DML) absent (Fig. 3H). Chaetae of thoracic chaetigers 1‒9 bilimbate simple capillaries; number of capillaries similar throughout thorax, approximately 8‒10 per rami, chaetiger nine with 18‒20 per rami with the latter having slightly broader distal blades (Fig. 3C).

Abdominal segments of posterior third of body longer than wide. Abdominal parapodia with foliaceous lateral lamellae, lacking basal constriction and with postchaetal expansion behind chaetal rows; DML and VML present, digitiform. Abdominal chaetae tridentate hooded hooks of similar size throughout but outer hook of a group usually shorter; two same-sized teeth above main fang (Fig. 3D); a pair of internal arcuate chaetae present sensu Fiege et al. (2000) in abdominal chaetigers, possessing broad tips (Fig. 3I). Hooks in two groups, main fangs vis–à–vis; outer groups with usually one more hook than inner group (Fig. 3I). Anterior abdominal segments with 5‒6 hooks per ramus, posterior abdominal segments with 3‒4 hooks per ramus.

Anterior abdominal lateral pouches (Σ configuration) absent and posterior abdominal lateral pouches (C configuration) present from chaetiger 39 on holotype, paired.

Pygidium rounded with a pair of digitiform, short, lateral anal cirri (Fig. 3J).

All preserved specimens lacking pigmentation, pale yellow. A pair of brown spots present on posterior prostomial region of several specimens, presumably eyespots.

Methyl Green Staining. Prostomium with sparse green speckles (Fig. 2D). Posterior prostomial region, achaetous segment and dorsal region of thorax stained with dark green speckles; decreasing in intensity from chaetigers five through nine. Ventral region of chaetiger four intensely stained with green speckles (Fig. 2E). Abdomen staining round pigmented regions in between two subsequent parapodia (Fig. 2D), interparapodial.

Remarks. Magelona cinthyae sp. nov. is unique among its congeners in that several of the examined adults still retained a pair or more of eyespots. A total of nine out of 17 examined specimens had eyespots (Fig. 4A‒I); these specimens ranged from 50‒59 chaetigers and all of them had adult characteristics (i.e. shape of prostomium, chaetiger 9, types of chaetae, and presence of lateral pouches). Eyespots were recorded in larval stages of M. alleni, M. filiformis and M. mirabilis (Wilson 1982) and up until now they were considered to be absent in adult animals (Mortimer in press). Because only about half of the examined specimens presented eyespots and the chosen holotype was the largest specimen lacking eyesposts, it is possible that benthic individuals of M. cinthyae have a delayed loss of eyespots. The eyespots in the magelonid larvae observed by Wilson (1982) were cup-shaped with brownish pigments and forming a primitive lens, similar to those in M. cinthyae (Fig. 4C‒F). Wilson (1982) showed that an additional pair of eyespots was added to a 6-day-old larva and late stage larvae collected in the plankton also presented eyespots.

Magelona cinthyae sp. nov. belongs to a group of species ( M. annulata, M. berkeleyi, M. crenulifrons, M. lenticulata, M. longicornis, M. methae Nateewathana & Hylleberg, 1991, M. pacifica, and M. pulchella Mohammad, 1970) sharing the following characters: 1) prostomium with distinct frontal horns; 2) foliaceous notopodial thoracic lamellae and superior processes; 3) shape of chaetiger 9. Magelona annulata has oval rather than digitate ventral processes on thoracic parapodia and bidentate rather than tridentate abdominal hooks.. It differs from M. berkeleyi on the shape of the prostomium, the latter having prostomium broader than long with inconspicuous horns, not clearly separated from the prostomium. Magelona cinthyae sp. nov. differs from M. methae and M. crenulifrons in having a smooth anterior prostomial margin rather than crenulate. Magelona lenticulata has a slightly crenulate anterior prostomial margin and prostomium distinctly broader than long. Magelona longicornis and M. pacifica have bidentate hooks and while the hooks in the former are organized in one unidirectional group, this has not been confirmed in M. pacifica due to the condition of the syntypes examined by Mortimer et al. (2012). Magelona pulchella has similar prostomial characteristics to M. cinthyae but differs in having bidentate hooks and on the shape of parapodial lamellae of chaetiger 9.

Etymology. This species is named after Dr. Cinthya S.G. Santos, a polychaete researcher that has collaborated with the authors on describing Hawaiian polychaetes and has also been an example for her dedication to the study of polychaetes and great work ethics.

Distribution. This species is known from the north and south shores of Oahu, Hawaii, 31‒ 39 m.