Magelona anuheone, Magalhães & Bailey-Brock & Watling, 2018

Magalhães, Wagner F., Bailey-Brock, Julie & Watling, Les, 2018, Four new species of Magelona (Annelida: Magelonidae) from Easter Island, Guam and Hawaii, Zootaxa 4457 (3), pp. 379-396 : 391-394

Magelona anuheone sp. nov.

Figures 7 (D‒F) and 8

Material examined. Holotype: Easter Island, Hanga Roa, 27°08'45.60" S, 109°26'06.00" W, Sta. HB3, 5 November 2015, coll. L. Watling ( USNM 1494162). Paratypes: Easter Island, same date and collector as holotype: Vare Vare, Sta. Bajo B4 (1 af, USNM 1494163); Vare Vare, Sta. Ariba A3 (4 af, SCBUCN-7281; 1 af, MNHNCL ANN-15018; 1 af, MNHNCL ANN-15019; 1 af, MNHNCL ANN-15020). Additional material examined. Hanga Roa, Sta. HB3 (1 af); Sta. Ariba A1 (1 af); Vare Vare, Sta. Ariba 1 (1 af); Sta. Ariba 2 (1 af); Sta. Ariba 3 (1); Ariba 4 (6 af and 1 pf); Sta. Ariba 5 (3 af); Sta. Bajo B1 (3 af); Sta. Bajo B2 (3 af); Sta. Bajo B3 (2 af); Sta. Bajo B5 (4 af and 1 pf).

Diagnosis. Prostomium much longer than wide, with distinct prostomial horns. Notopodia of chaetigers 1‒8 with elongate postchaetal lamellae with minutely crenulate upper edges. Low, rounded pre-chaetal lamellae. Superior processes present from chaetigers 1‒8. Thoracic chaetae simple bilimbate capillaries. Abdominal hooded hooks tridentate. Lateral pouches (Ʃ configuration) present between chaetigers nine and ten.

Description. Holotype: incomplete posteriorly; prostomium 1.84 mm long, 1.14 mm wide; thorax 8.3 mm long (including prostomium), 0.61 mm wide; abdomen 0.79 mm wide; total length 26.4 mm for 45 chaetigers. Four paratypes measured, all posteriorly incomplete; prostomium 0.84‒1.05 mm long, 0.63‒0.8 mm wide; thorax 3.97‒5.3 mm long (including prostomium), 0.36‒0.43 mm wide; abdomen 0.35‒0.45 mm wide; total length 13.4‒24.5 mm for 31‒61 chaetigers.

Prostomium much longer than wide (L:W ratio 1.25‒1.61), rounded laterally; anterior margin smooth, rounded triangular, with conspicuous prostomial horns, bulbous; horns distinctly separated from antero-lateral margins of prostomium ( Figs 7D ; 8A, B ). Two pairs of prominent, thick longitudinal dorsal ridges; outer pair, reaching further basally and approaching achaetous segment and with transverse rings; inner pair diverging anteriorly into horn corners and posteriorly towards prostomial base, medially fused along their length ( Fig. 8A ). Burrowing organ partially everted in several specimens including holotype and paratypes, oval with distinct ridges ( Fig. 8A ). Holotype with both palps attached. Palps arising ventro-laterally from base of prostomium, short, marginally longer than thoracic region ( Fig. 8A ); palps measuring 5.52‒5.78 mm long; non‒papillated region short reaching as far as chaetiger 3 ( Fig. 8A ). Papillae short proximally but long for majority of length, digitiform; proximally and medially with eight rows of papillae reducing to four rows distally. Achaetous segment slightly longer than chaetiger 1 ( Fig. 8A ).

Thoracic segments longer than wide; chaetigers 1‒8 similar; parapodia biramous; notopodia with low rounded prechaetal lamellae confluent with elongate postchaetal lamellae with rounded tips of similar size throughout thorax ( Fig. 8E‒H ); notopodial lamellae minutely crenulated ( Fig. 8E‒G ). Digitiform prechaetal superior processes present (DML), digitiform. Neuropodial pre- and postchaetal lamellae as low ridges; ventral lobes (VNL) lobes digitiform anteriorly, becoming triangular on posterior thoracic segments ( Fig. 8E‒H ). Chaetigers nine and ten short. Chaetiger 9 ( Fig. 8H ): notopodial prechaetal lamellae rounded, postchaetal lamellae slightly shorter than preceding thoracic chaetigers, triangular; superior processes (DML) absent. Neuropodia of chaetiger nine similar to chaetiger eight ( Fig. 8G, H ). Chaetae of all thoracic chaetigers simple bilimbate capillaries ( Fig. 8C ); number of capillaries increasing towards posterior thorax, 10‒18 notopodial capillaries initially, increasing up to 24 on chaetiger nine; 6‒10 increasing to up to 18 in the neuropodia.

Anterior 6‒8 abdominal segments as long as wide and becoming longer posteriorly. Abdominal parapodia with elongate lateral lamellae ( Fig. 8I, J ), well-developed postchaetal extension of lateral lamellae behind chaetal rows in anterior abdomen; DML and VML present, distinct, long. Abdominal chaetae tridentate hooded hooks of similar size throughout, long; two same-sized teeth above main fang ( Fig. 8D ); a pair of internal arcuate chaetae present sensu Fiege et al. (2000) present ( Fig. 8I ). Hooks in two groups, main fangs vis–à–vis; groups with same number of hooks and all hooks of similar size ( Fig. 8I, J ). Anterior abdominal segments with 4‒6 hooks per ramus, reducing to 3‒5 in posterior abdominal segments. One smaller tridentate hook present at the bases of lateral lamellae ( Fig. 8I ).

Anterior lateral pouches (Σ configuration) present between chaetigers 9 and 10, paired ( Fig. 8A ); simple (C configuration) pouches not observed. Round patch of glandular structures darker than body present throughout abdominal region but more evident on anterior 8‒10 chaetigers.

Pygidium observed on one posterior fragment (presumed to be same species), rounded with a pair of digitiform, lateral anal cirri ( Fig. 8K ).

All preserved specimens lacking pigmentation, pale yellow.

Methyl Green Staining. Anterior and median region of prostomium unstained ( Fig. 7E ). Proximal prostomial region, achaetous segment and thoracic region stained with a uniform green; abdominal segments staining slightly darker than thoracic ones. Dorsal transverse bands present from chaetigers 3‒7 just posterior to parapodia ( Fig. 7E ). Mid-ventral region of thorax with green speckles along longitudinal lines ( Fig. 7F ).

Reproduction. Holotype an ovigerous female with eggs present in body cavity. Eggs densely packed from chaetiger 48. Eggs become larger along the body reaching about 65 µm in diameter from chaetiger 55.

Remarks. Magelona anuheone sp. nov., belongs to a small group of five species ( M. berkeleyi , M. cornuta , M. montera Mortimer, Cassà, Martin & Gil, 2012 , M. nonatoi Bolívar & Lana, 1986 , and M. tehuanensis Hernandez- Alcantra & Solis-Weiss, 2000) all sharing the following characters: 1) prostomium with frontal horns; 2) distally crenulate notopodial lateral lamellae; 3) chaetiger nine possessing only winged capillaries, and 4) tridentate abdominal hooks. Magelona berkeleyi and M. nonatoi have rudimentary prostomial horns whereas the new species, M. montera , M. tehuanensis , and M. cornuta have well-developed frontal horns. Magelona cornuta and M. tehuanensis have a crenulated margin of the prostomium and the new species M. anuheone sp. nov. and Magelona montera have a smooth margin of the prostomium and distinct bulbous horns.

Magelona anuheone sp. nov. shares many similarities with M. montera from the Red Sea especially on the prostomial characteristics and methyl green staining pattern, both species having unique prostomial horns with bulbous distal tips ( Mortimer et al. 2012). It differs most noticeably on the shape of the abdominal parapodial chaetal lobes and presence of anteriorly opening lateral pouches in between chaetigers 9 and 10.

Although several species have been described with anteriorly open pouches, only M. parochilis Zhou & Mortimer, 2013 also lack modified chaetae on chaetiger 9. It differs from M. anuheone sp. nov. on the segmental origin of the open pouches (in between chaetigers 9/ 10 in M. anuheone and chaetiger 11/ 12 in M. parochilis ), and by having a rounded prostomium without prostomial horns.

Etymology. The new species epithet derives from the Rapa Nui language and is a combination of anuhe (caterpillar) and one (sand). The implied meaning being ‘caterpillar of the sand’ and the new name was chosen by Sergio Rapu from Rapa Nui (Easter Island).

Distribution. This species is only known from shallow waters of Easter Island, Southeastern Pacific Ocean.

Figures

FIGURE 7. A–C, M. cf. symmetrica, A, prostomium stained with shirlastain A; B and C, MGSP, dorsal and ventral views, respectively, with arrows indicating distinctive staining regions of thorax and abdomen; D–F, M. anuheone sp. nov., D, prostomium of holotype stained with shirlastain A; E and F, MGSP of holotype, dorsal and ventral views, respectively, with arrows indicating distinctive staining regions of thorax and abdomen.

FIGURE 8. Magelona anuheone sp. nov. A, anterior end and thoracic region, dorsal view of holotype; B, anterior region, ventral view of holotype; C, thoracic simple bilimbate capillaries; D, tridentate abdominal hooded hooks, lateral and frontal views respectively; E, parapodium of chaetiger 3, anterior view; F, parapodium of chaetiger 7, anterior view; G, parapodium of chaetiger 8, anterior view; H, parapodium of chaetiger 9, anterior view; I, parapodium of chaetiger 10, anterior view; J, parapodium of chaetiger 12, anterior view; K, posterior end and pygidium with anal cirri. Abbreviations: ch, chaetiger; lp, lateral pouch; pa, palp; ph, prostomial horn; pr, prostomium; bo, burrowing organ.