Magelona mackiei, 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 : 1166-1170

MAGELONA MACKIEI SP. NOV.

( FIGS 16 , 17 )

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: 92162557-7671-41A5-938A-332EA6AC397B.

Type locality: Nigeria, 3.9828°N 6.2157°E, 41 m depth .

Type material: Holotype, Nigeria: St. 5N–14, af in 96% Etoh ( ZMBN107309 , DNA-voucher) . Paratypes: Sierra Leone: St. 7SL–06, 1af in 75% Etoh ( ZMBN132189 ) . Liberia: St. 7LI–01, 1af in 75% Etoh ( NMW.Z.2021.001.0017, imaged) ; 6af in 75% Etoh ( ZMBN132176 ) ; St. 7LI–07, 1af in 75% Etoh ( NMW.Z.2021.001.0018, imaged) . Ghana: St. 7GH– 05, 1af in 75% Etoh ( ZMBN 132172 ) ; 2af in 75% Etoh ( NMW.Z.2021.001.0019) ; St. 7GH–08, 1af in 96% Etoh ( ZMBN115735 , DNA-voucher) ; 1af in 75% Etoh ( ZMBN132174 ) ; St. 2011404–GE1/249, 1af in 96% Etoh ( ZMBN107341 , DNA-voucher) ; St. 2009105– GE1/28, 14af in 75% Etoh ( ZMBN107290 ) ; St. 2009105–GP1/28, 2af in 75% Etoh ( ZMBN107288 ) ; St. 2009105–GW4/252, 5af in 75% Etoh ( ZMBN107289 ) . Nigeria: St. 5N–14, 1af in 96% Etoh ( ZMBN115746 , DNA-voucher) ; 11af in 96% Etoh ( ZMBN107291 ) ; St. 6N–11, 3af, 3f, in 75% Etoh ( NMW.Z.2021.001.0020) . São Tomé and Príncipe: St. 2009-T2, 3af in 75% Etoh ( NMW.Z.2021.001.0021) . Gabon: St. 5G–03, 1af in 75% Etoh ( ZMBN132180 ) ; St. 5G–16, 1af in 75% Etoh ( ZMBN132181 ) ; St. 8G–01, 1af in 75% Etoh ( ZMBN107292 ) , 1af in 96% Etoh ( ZMBN132118 ) . Republic of Congo: St. 8CR–01, 1af in 96% Etoh ( ZMBN115745 , DNA-voucher) ; 4af in 75% Etoh ( ZMBN107293 ) ; 9af in 96% Etoh ( ZMBN132115 ) ; 17af in 75% Etoh ( NMW.Z.2021.001.0022) ; St. 7CR–02, 1af in 96% Etoh ( ZMBN107312 , DNAvoucher) ; 3af in 96% Etoh ( ZMBN132116 ) ; 1af in 96% Etoh ( ZMBN132117 , imaged) ; St. 7CR–05, 1af in 96% Etoh ( ZMBN107310 ) . Angola: St. 1997– 13, 1af in 75% Etoh ( ZMBN132119 ) ; St. 1997–15, 1af in 75% Etoh ( ZMBN132120 ) ; St. 1997–23, 1af in 75% Etoh ( ZMBN132121 ) ; St. 1997–28, 1af in 75% Etoh ( ZMBN132122 ) ; St. 1997–29, 2af in 75% Etoh ( ZMBN132123 ) .

Etymology: This new species is named in honour of Dr Andrew Mackie, who has contributed much to our understanding of magelonids and who has provided advice and support to the first author during the last 20 years.

Diagnosis: Prostomium wider than long, with rudimentary prostomial horns. Chaetigers 1–8 with slender sinuous postchaetal lamellae, those of the notopodia with minute superior dorsal lobes. Chaetiger 9, notopodia similar but without superior dorsal lobes, neuropodia with sinuous postchaetal lamellae and additional small triangular ventral processes. All thoracic chaetae capillary. Abdominal lateral lamellae triangular. Abdominal hooded hooks bidentate, in two groups, vis-à-vis. No pouches observed, pygidium unknown.

Description: A large stout species; junction between thorax and abdomen ( Fig. 17B ), noticeable. Holotype, anterior fragment: prostomium 0.6 mm long, 0.8 mm wide; thorax 5 mm long (including prostomium), 1.0 mm wide; abdomen 0.75 mm wide; total length 7.75 mm for 14 chaetigers. Largest DNA-voucher specimen (ZMBN107312), anterior fragment: prostomium 0.90 mm long, 1.25 mm wide; thorax 5.25 mm long (including prostomium), 1.2 mm wide; abdomen 1.1 mm wide; total length approximately 13.5 mm for 23 chaetigers (width measurements not including parapodia). Thoracic chaetigers characteristically bulbous ( Figs 16A , 17B ), width greatest around chaetigers 5–6, body tapering towards chaetiger 9 ( Fig. 17A, B ). Other measured anterior fragments: 4.0– 18.5 mm for 8–30 chaetigers.

Prostomium subtriangular ( Fig. 16B ), wider than long (L: W ratio 0.72–0.75). Rudimentary prostomial horns, anterior margin straight and square. Anterior prostomial margin of holotype with several minute notches, but not so distinct as crenulations, and otherwise smooth for remaining type material. Two pairs of prominent longitudinal, prostomial, dorsal muscular ridges, relatively thick; inner pair abutting for majority of length, diverging at distal tips. Outer pair, slightly shorter, abutting inners for entire length. Weak prostomial markings present either side of the muscular ridges ( Fig. 16B ), slightly more distinct in larger specimens. Burrowing organ, everted in four specimens, oval when partially everted. Nearly entirely everted in one specimen (ZMBN107312), heart-shaped, transversely ridged inferiorly, appearing smooth superiorly. Palps retained on several specimens, arising ventrolaterally from base of prostomium, short and thick, appearing ‘frilly’ with long numerous papillae. Specimens from the Republic of Congo (St. 8CR–01) with a short, nonpapillated region, reaching approximately chaetiger 1, but in larger specimens it reaches approximately chaetiger 3. Papillae short proximately but increasing rapidly in size, becoming extremely long and slender by chaetiger 2. Largest palp retained on Nigerian specimen (St. 6N–11, NMW.Z.2021.001.0020, left hand palp), approximately 0.4 mm wide and 9.0 mm long, reaching approximately chaetiger 20 (when folded backwards), other palps reaching approximately chaetigers 12–14. Proximally with three to six rows of papillae either side of an inconspicuous mid-palp line, devoid of papillae, medially four or five rows either side and distally one or two rows. Exact number of rows extremely difficult to count due to length of papillae and the overlapping of neighbouring rows.

Achaetous region behind the prostomium, roughly twice the length of chaetiger 1 ( Fig. 16A ). Chaetigers 1–8 similar ( Fig. 16C–M ); parapodia biramous. Notopodia with low prechaetal lamellae confluent with slender smooth-edged sinuous postchaetal lamellae with pointed tips, of similar size throughout the thorax. Small to minute prechaetal superior dorsal lobes present on all thoracic chaetigers (except chaetiger 9) in a slightly prechaetal position (NB these are more difficult to see on more bulbous specimens, due to parapodia occurring in furrows, or on smaller specimens). Neuropodia with low prechaetal lamellae, confluent with long slender triangular, ventral lamellae with pointed tips, which reduce in size along the thorax. Postchaetal expansion, triangular and adjoining ventral lamellae (e.g. Fig. 16D–F ) approximately halfway along their length (postchaetal expansion greater in larger specimens). Ventral lamellae initially slightly prechaetal but becoming more postchaetal by chaetiger 7.

Chaetiger 9 ( Figs 16A , 17B ): shorter and narrower than preceding chaetigers. Notopodial prechaetal lamellae low, confluent with slender, triangular, postchaetal lamellae, slightly larger than on preceding chaetigers ( Fig. 16N ). No superior dorsal lobes observed. Neuropodia similar to notopodia, however, postchaetal lamellae slightly larger; chaetae emerging below lamella, from a definite ridge that terminates in a small triangular process. Chaetae of chaetigers 1–9 simple bilimbate, winged capillaries, those of chaetiger 8, slightly longer and characteristically splayed.

Parapodia of abdominal chaetigers ( Fig. 16O ) with long, triangular, lateral lamellae with pointed tips (NB tips easily broken). Lamellae slightly constricted basally, but with no obvious postchaetal expansion behind chaetal rows. Tiny sporadic processes (DML, VML) observed at inner margins of chaetal rows. Abdominal chaetae bidentate hooded hooks ( Fig. 16P– Q ) 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. 16O ). Approximately ten to 14 hooks per ramus in the anterior abdomen. No abdominal pouches observed, although posterior chaetigers unknown (no specimens with more than 30 chaetigers examined). Posterior region and pygidium unknown. Distinct sediment covered, layered tubes present on several specimens ( Fig. 17I ), inner layers often difficult to remove from specimens.

Colour: No living material observed. Preserved specimens creamy orange in colour with faint reddish pigment in the posterior thorax ( Fig. 17C, D ). Pigment strongest between chaetigers 5–7 but not as strong as other magelonid species in the MIWA region. However, the majority of material examined has been preserved for over 10 years, and personal observations have shown pigmentation in magelonids can fade within a similar time frame. Observation of live or freshly preserved specimens is needed to clarify whether this species has darker pigmentation. Many specimens have an orange tint ( Fig. 17A, B ). Light dorsal speckles (glandular?) present between chaetigers 2–5 ( Fig. 16A, F, H ), more obvious in stained specimens. Staining with methyl green ( Fig. 17F–H ) shows a weak overall stain, with no distinct pattern.

Distribution: Collected from 23 stations in the Gulf of Guinea (from Sierra Leone in the north to northern Angola in the south, Fig. 1 ), at depths of 8– 340 m.

Remarks: Of all the pigmented species in the MIWA region, Magelona mackiei differs from M. alleni , M. guineensis , M. nanseni and M. picta by possessing bidentate and not tridentate abdominal hooded hooks. As noted above, M. mackiei differs from M. fasciata in terms of prostomial shape, pigmentation patterns (although note fading of pigmentation) and the nature of the thoracic neuropodial lamellae. Although the two species share many similarities, they can be easily separated in samples by observing the neuropodial lamellae of chaetigers 1–3, being broad almost scoopshaped in M. fasciata and distinctly slender and pointed in M. mackiei .

Of the other magelonid species known to carry posterior thoracic pigmentation, M. mackiei differs from M. cincta , M. equilamellae , M. japonica , M. variolamellata , M. symmetrica and M. polydentata in the nature of the hooded hooks, which are bidentate as opposed to tridentate or polydentate. It further differs from M. symmetrica in possessing neuropodial lamellae in a distinctly ventral position, as opposed to a postchaetal position. The pigmentation of M. mackiei is noticeably faint in comparison to other MIWA magelonid material. Whilst it is unclear, at present, whether pigmentation is darker in live or freshly preserved specimens, M. symmetrica is a species in which pigmentation was similarly observed to be pale and sporadic, even in freshly preserved specimens ( Mortimer et al., 2012).

KEY TO ADULT SPECIMENS OF MAGELONA FROM WESTERN AFRICA CARRYING POSTERIOR THORACIC PIGMENTATION The geographical region included within the following key runs from Morocco in the north to Algoa Bay, South Africa in the south ( Fig. 1 ).

1. Thoracic superior dorsal lobes absent to minute............................................................................................. 2 – Distinct thoracic superior dorsal lobes clearly developed............................................................................... 5 2. Abdominal hooded hooks bidentate.................................................................................................................. 3 – Abdominal hooded hooks tridentate ................................................................................................................ 4 3. Ventral neuropodial lamellae of anterior thorax scoop-shaped, distinct stripy pigmentation along length of animal (NB this may fade over time)................................................................................................... M. fasciata – Ventral neuropodial lamellae of anterior thorax not scoop-shaped. Pigmentation light and limited to posterior thorax..................................................................................................................................... M. mackiei 4. Abdominal lateral lamellae of roughly equal size in each ramus...................................................... M. cincta – Abdominal lateral lamellae subequal, notopodial being noticeably larger than the neuropodial .... M. alleni 5. Thoracic superior dorsal lobes short, thoracic notopodial lamellae slender and in a slightly subchaetal position. Small, triangular processes below neurochaetae on chaetiger 9..................................... M. guineensis – Thoracic superior dorsal lobes long, thoracic notopodial lamellae more foliaceous, postchaetal. No processes below neurochaetae on chaetiger 9 ...................................................................................................................... 6 6. Foliaceous abdominal lateral lamellae heavily pigmented (NB this may fade over time), with only a slight basal constriction. Thoracic notopodial lamellae foliaceous, neuropodial lamellae of a similar length along the thorax (only marginally shorter towards posterior thorax). Abdominal lamellae with obvious postchaetal expansion behind chaetal rows, distinct, triangular ................................................................................ M. picta – Spatulate abdominal lateral lamellae without pigmentation, basal constriction distinct. Thoracic notopodial lamellae slender foliaceous, marked reduction in the length of neuropodial lamellae along the thorax. Abdominal lamellae without postchaetal expansion behind chaetal rows in the abdomen ............. M. nanseni The minimum, maximum and mean depths from which all MIWA pigmented species were collected are given in Table 6 . The results indicate that whilst M. mackiei can be found in shallow waters, it appears to more abundant in waters over 100 m deep. The remaining five pigmented species in the region were encountered more frequently at depths of 26– 58 m.

Of all the other previously described African Magelona species, M. mackiei shares some similarities with M. cepiceps and M. mahensis . However, it differs from M. cepiceps , which has an onion-shaped prostomium and tridentate abdominal hooded hooks, and from M. mahensis in which thoracic superior dorsal lobes are absent. Magelona mackiei shares affinities with Magelona capax Hartman, 1965 described off the mouth of theAmazon River. However, it differs in the shape of the prostomium, having a more distinct anterior prostomial margin, which is almost horn-like for M. capax .

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 16. Magelona mackiei. Holotype (Nigeria St. 5N–14, ZMBN107309):A, anterior region (dorsal view); B, prostomium, dorsal view; C, neuropodium of chaetiger 1 (anterior view); D, parapodium of chaetiger 2 (anterior view); E, F, neuropodial lamella of chaetiger 2 (ventral and lateral views, respectively); G, parapodium of chaetiger 3; H, parapodium of chaetiger 4 (anterior view); I, neuropodial lamella of chaetiger 4 (ventral view); J–O, parapodia of chaetigers 5–9, and 11, respectively (anterior views); P, Q, bidentate hooded hooks of chaetiger 15 (oblique lateral view; P, outermost hook of ramus next to process).

Figure 17. Magelona mackiei. (A, B, Liberia St. 7LI–01, NMW.Z.2021.001.0018; C–H, Liberia St. 7LI–07, NMW.Z.2021.001.0017; I, Nigeria St. 6N–11, ZMBN132179): A, anterior region (ventral view); B, anterior region (dorsal view); C, anterior region (dorsal view); D, anterior region (ventral view); E, anterior region (lateral view); F, anterior region (dorsal view); G, anterior region (ventral view); H, prostomium and first three chaetigers (dorsolateral view); I, section of sediment tube. F–H, stained with methyl green.