Magelona fasciata, Mortimer & Kongsrud & Willassen, 2022

Mortimer, Kate, Kongsrud, Jon Anders & Willassen, Endre, 2022, Integrative taxonomy of West African Magelona (Annelida: Magelonidae): species with thoracic pigmentation, Zoological Journal of the Linnean Society 194 (4), pp. 1134-1176 : 1160-1165

MAGELONA FASCIATA SP. NOV.

( FIGS 13–15 )

Z o o b a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: C0848517-9D34-48BB-95B9-52819F88949D.

Type locality: Ghana, 4.9169°N 2.6495°W, 40 m depth .

Type material: Holotype, Ghana: St. 7GH–02, af in 75% Etoh ( ZMBN132144 ) . Paratypes, Mauritania: St. 2011410–SL20, 1af in 96% Etoh ( ZMBN107337 , DNA-voucher) ; St. 2012404–SL20, 1af in 96% Etoh ( ZMBN115741 , DNA-voucher) . Senegal: St. 2011410– SL11, 1af in 96% Etoh ( ZMBN115738 , DNA-voucher) ; 1af in 96% Etoh ( ZMBN115739 , DNA-voucher) ; St. 2011410–SL12, 15af in 75% Etoh ( ZMBN132149 ) ; 236af, 27f, 7pf, 79 palps in 96% Etoh ( NMW.Z.2021.001.0007) ; 1c, 230af, 34f, 10pf, 55 palps, in 96% Etoh ( ZMBN132151 ) ; 1c, 1af in 96% Etoh ( NMW.Z.2021.001.0008, imaged), 3af, pf in 96% Etoh ( NMW.Z.2021.001.0009, imaged), 1af in 96% Etoh ( ZMBN107311 , DNA-voucher) . Guinea Bissau: St. 7GB-06, 1af in 75% Etoh ( ZMBN107287 ) ; St. 2012404–SL06, 1af in 96% Etoh ( ZMBN107339 , DNA-voucher) ; St. 2011410–SL09, 1af in 96% Etoh ( ZMBN107340 , DNA-voucher) . Guinea (Conakry): St. 7GU–05, 1af in 75% Etoh ( ZMBN132159 ) ; 1af in 75% Etoh ( NMW.Z.2021.001.0010) . Sierra Leone: St. 7SL–08, 1af 96% Etoh ( ZMBN107329 , DNA-voucher) ; St. 7SL–09, 1af in 75% Etoh ( NMW.Z.2021.001.0011) . Ghana: St. 7GH–01, 1af in 96% Etoh ( ZMBN115743 ) ; St. 7GH–02, 1af in 96% Etoh ( ZMBN107330 , DNAvoucher) ; 3af, 1f, 2p, in 75% Etoh ( ZMBN132145 ) ; 3af in 75% Etoh ( NMW.Z.2021.001.0012) ; 16af in 75% Etoh ( ZMBN132147 ) ; St. 7GH–07, 1af in 75% Etoh ( NMW.Z.2021.001.0013) ; St. 2009105–GP2/51, 8af in 75% Etoh ( ZMBN107282 ) ; St. 2009105–GW2/52, 8af in 75% Etoh ( ZMBN107283 ) . Nigeria: St. 5N–12, 5af in 75% Etoh ( ZMBN107286 ) ; St. 6N–15, 1af in 96% Etoh ( ZMBN107333 , DNA-voucher) ; 8af in 75% Etoh ( NMW.Z.2021.001.0014) ; 1afin75% Etoh ( ZMBN132164 ) ; St. 6N–23, 1af in 96% ( ZMBN115742 ) . Gabon: St. 5G–01, 1af in 96% Etoh ( ZMBN107304 , DNA-voucher) ; St. 5G–03, 1af in 96% Etoh ( ZMBN107308 , DNAvoucher) ; St. 5G–15, 3af in 75% Etoh ( ZMBN107281 ) ; 1af in 75% Etoh ( NMW.Z.2021.001.0015) ; St. 7GA– 07, 1af in 96% Etoh ( ZMBN107306 ) ; St. 7GA–26, 1af in 96% Etoh ( ZMBN107307 , DNA-voucher) . Republic of the Congo: St. 7CR–04, 1af in 96% Etoh ( ZMBN115747 , DNA-voucher) . Angola: St. 7AN–01, 3af in 75% Etoh ( ZMBN132154 ) ; St. 7AN–02, 3af 75% Etoh ( NMW.Z.2021.001.0016), 1af in 96% Etoh ( ZMBN115744 , DNA-voucher) ; St. 7AN– 04, 1af in 96% Etoh ( ZMBN115740 , DNA-voucher) ; 1af 96% Etoh ( ZMBN107332 ) ; St. 7AN–08, 1af in 75% Etoh ( ZMBN107284 ) ; St. 1997–20, 5af in 75% Etoh ( ZMBN107285 ) .

Other examined material: Guinea (Conakry): St. 2011410–GR01, 1af, juvenile, in 75%Etoh (ZMBN132170). Ghana: St. 7GH–06, 1af in 75% Etoh (ZMBN132169). Nigeria: St. 6N–14, 13af in 75%Etoh (ZMBN132171).

Etymology: From Latin fascia, meaning band, referring to the distinct banded patterns along the body in this species.

Diagnosis: Prostomium as wide as long. Chaetigers 1–9 with slender lamellae, although neuropodial lamellae of chaetigers 1–3, broader, almost scoopshaped. All thoracic chaetae capillary. Abdominal lateral lamellae triangular, without basal constrictions. Abdominal hooded hooks bidentate, in two groups, vis-à-vis. Simple posteriorly open pouches present, pygidium with two short projections.

Description: A stout species; with marked distinction between thorax and abdomen ( Figs 13A , 14C , 15A ), thorax dorsoventrally flattened, thinner (when viewed laterally), but marginally wider than the rounded abdomen. Holotype, anterior fragment; prostomium 0.65 mm long, 0.65 mm wide; thorax 3.0 mm long (including prostomium), 0.75 mm wide; abdomen 0.6 mm wide; total length 20 mm for 43 chaetigers. Largest DNA-voucher specimen (ZMBN107311), anterior fragment: prostomium 0.8 mm long, 0.9 mm wide; thorax 3.3 mm long (including prostomium), 1.0 mm wide; abdomen 0.8 mm wide; total length approximately 8.5 mm for 24 chaetigers (width measurements not including parapodia). Thoracic chaetigers slightly bulbous, particularly in midthoracic region ( Figs 13A , 14A, B , 15E ), thoracic width fairly uniform but tapering from chaetiger 6 to 9. Other specimens (complete and anterior fragments) 2.5–30 mm for 8–65 chaetigers.

Prostomium triangular ( Figs 13B, C , 14A, B , 15B, E ), width similar to, or marginally larger than, length (L: W ratio 0.89–1.00). No prostomial horns, anterior margin straight and square, lateral margins slightly rounded. Two pairs of longitudinal dorsal muscular prostomial ridges. Inner pair abutting for majority of length, diverging only at distal tips; outer pair abutting inners for entire length, fairly thin and indistinct (see RH side of Fig. 13B , for instance). Light diagonal striations apparent on inner ridges and indistinct markings present either side of ridges. Burrowing organ, partially to fully everted in 185 specimens, oval when partially everted ( Fig. 14B, C ), heart-shaped when fully everted (e.g. ZMBN132149); longitudinally ridged inferiorly, superior surface appearing smooth. Palps retained, at least partially, on 77 specimens, arising ventrolaterally from base of prostomium, short and thick, with a ‘frilly’ appearance due to presence of numerous long papillae. Palps reaching approximately chaetigers 13–17 (when folded backwards), nonpapillated region short, reaching approximately chaetiger 2. Papillae short proximally, increasing in size in mid and distal regions, becoming long at tips. Proximally three to five rows of papillae either side of an inconspicuous mid-palp line, devoid of papillae, medially two to four rows and distally one to two rows either side. Exact number of rows difficult to discern due to length and abundance of papillae, and due to neighbouring rows overlapping each other. A higher number of rows of papillae occur on larger specimens.

Achaetous region behind the prostomium, marginally longer than chaetiger 1 ( Figs 14A , 15E ). Chaetigers 1–8 similar ( Fig. 13D–Q ); parapodia biramous. Notopodia with low prechaetal lamellae, which encircle the chaetal bundle and are confluent with smooth-edged, pointed, triangular lamellae, in a slightly subchaetal position. Notopodial lamellae of a similar size throughout the thorax. Minute prechaetal superior dorsal lobes present on thoracic chaetigers, difficult to discern in smaller specimens and on all chaetigers due to size. Neuropodia with low pre- and postchaetal lamellae, encircling chaetae cuff-like and confluent with ventral lamellae underneath chaetal bundle. Those of chaetigers one to three/four broader spatulate with bluntly rounded tips, slightly scoopshaped ( Fig. 13D–K ), but not as marked as those seen in M. cincta . Neuropodial lamellae reducing in length and breadth along thorax.

Chaetiger 9 shorter and narrower than preceding chaetigers ( Fig. 14A ): noto- and neuropodial postchaetal lamellae similar ( Fig. 13R ), marginally larger than on preceding chaetigers. Prechaetal lamellae low, no notopodial superior dorsal lobes observed, however, small, triangular prechaetal processes present in the neuropodia. Chaetae of chaetigers 1–9 simple bilimbate winged capillaries ( Fig. 13W ).

Abdominal lateral lamellae triangular, not basally constricted, and with no obvious postchaetal expansion of lamellae behind chaetal rows ( Fig. 13S–U ). Minute, sporadic processes (DML, VML) observed at inner margins of chaetal rows. (NB not occurring on all chaetigers and more difficult to discern in smaller specimens.) Abdominal chaetigers of mid-body region approximately twice as long as wide. Abdominal chaetae bidentate hooded hooks ( Fig. 13W–Y ) all of a similar size, one superior fang above main fang. Hooks in two approximately equal groups for each ramus, main fangs vis-à-vis ( Fig. 13U ). Approximately ten to twelve hooks per ramus in the anterior abdomen. Posteriorly open, abdominal lateral pouches observed on several specimens towards the posterior region ( Figs 13U , 14D ). Pouches simple, C-shaped, alternating from one side of the body to the other, and on alternating chaetigers, starting, for example, on chaetigers 32R and 34L for complete imaged paratype (NMW.Z.2021.001.0008). Pouches observed starting from 24 segments from the pygidium. Pygidium rounded with two slight, lateral projections ( Fig. 14E ). Anus almost terminal [as has been shown for M. alleni , see: Mills & Mortimer (2019)], but tilted towards the ventral surface [as has been shown for M. equilamellae , see: Mortimer et al. (2020)]. Holotype ovigerous, eggs approximately 80 μm in diameter ( Fig. 13Z ).

T h e p ar a t y p e f r o m St. 7 G H – 0 7 (NMW.Z.2021.001.0013) clearly shows sediment grains within the body cavity.

Colour: No living material observed. Preserved specimens cream to beige in colour with obvious brown pigmentation as transverse stripes along the body to the pygidium ( Fig. 14 ). Pigmentation of the posterior thorax wider and darker than the rest of the body, occurring as a pigment band ( Fig. 14A–C ). No prostomial pigmentation. Brown transverse lines present on non-papillated side of palps. Darker pigmentation running alongside the outer row of papillae, in mid-palp region ( Fig. 14F ) and occurring as sporadic spots towards the distal tips. Additional infrequent pigment spots amongst papillae. Specimens collected in 2005/2006 now entirely without, or with distinctly faded, pigmentation. Pigmentation around the posterior thorax is retained for the longest period of time. White dorsal speckles (glandular?) present between chaetigers 2–4, just behind parapodia, more obvious in stained specimens ( Fig. 15C ). Methyl green staining pattern ( Figs 13A , 15 ) generally indistinct, but the dorsal thoracic surface, prostomium ( Fig. 15B ) and ventral posterior thorax ( Fig. 15D ) become speckled with darker stain. Stain remaining the longest in the posterior thorax, even for several months after initial staining.

Distribution: Collected at 32 stations from ten countries (from Mauritania in the north, to northern Angola in the south, Fig. 1 ), at depths of 19– 106 m.

Remarks: The most important distinguishing feature separating this species from all other pigmented species in the region is the presence of distinct striped or banded pigmentation along the length of the body (but note that pigmentation may fade over time). In possessing bidentate hooded abdominal hooks M. fasciata differs from M. alleni , M. guineensis , M. picta and M. nanseni , in which they are tridentate. In possessing scoop-shaped ventral neuropodial lamellae of the anterior abdomen, and only minute/ sporadic superior dorsal lobes in the thoracic region, Magelona fasciata differs from M. mackiei in which the neuropodial lamellae have more pointed tips and the notopodial superior dorsal lobes are more distinct. They further differ in terms of prostomial shape (width similar to length in the former species but wider than long in the latter) and the presence of two pairs of prominent dorsal prostomial muscular ridges in the latter species (outer pair of which are thinner and less distinct in M. fasciata ).

Magelona fasciata co-occurred at several localities alongside M. alleni within the sampling region, for example, St. 2011410–SL12 off Senegal. When present together, the former species was seen to occur in much higher numbers than the latter. The two can be easily separated within the same sample by the distinct stripy pigmentation of M. fasicata and the presence of subequal abdominal lamellae in M. alleni . The pigment band of M. alleni additionally being somewhat darker and browner in colour. The presence of papery, sediment-covered tubes was observed for M. alleni in these samples but not noted for M. fasciata .

Of the other magelonid species known to carry posterior thoracic pigmentation, M. fasciata shares most similarities with M. cincta described from South Africa. However, it can be distinguished from this species, M. equilamellae , M. japonica , M. symmetrica , M. polydentata and M. variolamellata in the nature of the hooded hooks, being bidentate as opposed to tridentate or polydentate.

Of all the other previously described African species, M. fasciata shares some similarities with M. cepiceps and Magelona mahensis Mortimer & Mackie, 2006 , from the Seychelles. However, it differs from the former in terms of prostomial shape and in possessing only minute superior dorsal lobes of the thoracic region (those of M. cepiceps being somewhat longer and wider, particularly in the posterior thorax), and to the latter based on the presence of abdominal processes at the end of chaetal rows (DML, VML; absent in M. mahensis ).

Figures

Figure 1. Map showing the MIWA sampling area between Morocco in the north and Angola in the south, indicating the position of all sampling stations and current known distributions and depths for all magelonid species carrying posterior thoracic pigmentation off the western and southern coasts of Africa.

Figure 13. Magelona fasciata. (Ghana St.7GH–02) (A, B, D–Z,holotype,ZMBN132144;C, paratype(NMW.Z.2021.001.0012): A, anterior region (dorsal view); B, C, prostomia (dorsal views); D, parapodium of chaetiger 1 (anterior view); E, ventral neuropodial lamella of chaetiger 1 (dorsal view); F, parapodium of chaetiger 2 (anterior view); G, ventral neuropodial lamella of chaetiger 2 (dorsal view); H, parapodium of chaetiger 3 (anterior view); I, ventral neuropodial lamella of chaetiger 3 (dorsal view); J, parapodium of chaetiger 4 (anterior view); K, ventral neuropodial lamella of chaetiger 4 (dorsal view); L, parapodium of chaetiger 5 (anterior view); M, ventral neuropodial lamella of chaetiger 5 (dorsal view); N, parapodium of chaetiger 6 (anterior view); O, ventral neuropodial lamella of chaetiger 6 (dorsal view); P–T, parapodia of chaetigers 7, 8, 9, 14 and 40, respectively (anterior views); U, abdominal chaetiger showing posteriorly open lateral pouch (lateral view); V, capillary chaeta from thoracic segment (lateral view); W–Y, bidentate abdominal hooded hooks (oblique lateral, lateral and posterolateral views, respectively, hoods omitted in X and Z for clarity); Z, eggs observed in the abdominal cavity.

Figure 14. Magelona fasciata (Senegal St. 2011410–SL12: A–C, NMW.Z.2021.001.0009; D, E, NMW.Z.2021.001.0008; F, Senegal St. 2011410–SL12_5; G, St. 2011410–SL11: ZMBN115739): A, anterior region (dorsal view); B, anterior region (ventral view, showing partially everted burrowing organ); C, anterior region (lateral view, showing thoracic/abdominal junction);D, nine abdominal chaetigers, towards posteriorregion, showing two posteriorly openlateral pouches (ventrolateral view); E, posterior region (ventral view, showing pygidium and several lateral pouches); F, middle section of palp, showing pigmentation of the non-papillated side; G, anterior region (dorsal view).

Figure 15. Magelona fasciata. Holotype (Ghana St. 7GH–02, ZMBN132144) stained with methyl green: A, anterior region (dorsal view); B, anterior region (dorsolateral view); C, prostomium and first eight chaetigers (dorsoanterior view); D, anterior region (ventral view, showing buccal region); E, detail of thoracic region (dorsal view).