A further review of European Magelonidae (Annelida), including redescriptions of Magelona equilamellae and Magelona filiformis Author Mortimer, Kate Author Mills, Kimberley Author Jordana, Esther Author Pinedo, Susana Author Gil, João text Zootaxa 2020 2020-04-23 4767 1 89 114 journal article 22645 10.11646/zootaxa.4767.1.4 829a29de-aa93-4196-bb5d-79e9d6ce8744 1175-5334 3770151 urn:lsid:zoobank.org:pub:7B5EC00B-44DA-4A09-8B0A-3DCA78CD7C37 Magelona filiformis Wilson, 1959 Figures 7–9 , Table 1 Magelona filiformis minuta : Wilson (1959 ) (juvenile M. filiformis specimens, see Mills & Mortimer 2018 and Fig. 10 ) Material examined. ENGLAND , Mill Bay , Salcombe : Holotype ( BMNH 1959.4.2.1 , c, slide mounted); paratypes ( BMNH 1959.4 .2.2, af, slide mounted; BMNH 1959.4.2.2-5, 4af, fluid preserved, poor preservation; BMNH 1959.4.2.6–10, 6af, fluid preserved). East Portlemouth , Mill Bay ( NMW .Z.2003.0.35.2003, c) 16.05.2003 . Diagnosis. A moderate species. Prostomium longer than wide, with a squared anterior margin. Chaetigers 1–8 with slender, smooth-edged, filiform lamellae, with superior dorsal lobes. Lamellae of chaetiger 9 triangular, without dorsal lobes. Thoracic chaetigers with capillary chaetae only. Abdominal lateral lamellae spatulate. Hooded hooks tridentate, in two groups, vis-à-vis . Dimensions. Holotype complete (mounted on two slides: slide 1, majority of specimen; slide 2, posterior fragment of eight chaetigers and pygidium): prostomium 0.7 mm long (not possible to measure width of prostomium or thorax due to orientation on slide); thorax 4.5 mm long (including prostomium); abdomen 0.45 mm wide; 143 chaetigers. Slide mounted paratype (BMNH 1959.4.2.2): prostomium 0.75 mm long, 0.47 mm wide; thorax 0.36 mm wide, 5.45 mm long (including prostomium); abdomen 0.3 mm wide; 119 chaetigers long. Other paratypes 14–51.5 mm for 32–78 chaetigers (width measurements not including parapodia). Description . A slender to moderate species, very long; thorax of similar width (when viewed dorsally, Figs 7A, D ) but marginally thinner than abdomen (when viewed laterally, Figs 7E, G ), difference between the two regions not marked ( Figs 7F, G ). Prostomium longer than wide (L:W ratio 1.6), with a squared anterior margin (often termed “rudimentary horns” but not as distinct as in other species), anterior margin smooth ( Figs 7 A–E). Prostomium with two pairs of prominent longitudinal dorsal muscular ridges, relatively thin. Inner pair abutting medially but diverging at either end, outer pair less distinct, shorter and thinner, abutting inners for entire length. Faint markings present on either side of ridges ( Fig. 7B ), indistinct, but generally present. Burrowing organ either partially or fully everted on holotype ( Figs 8A, B ) and five paratypes (BMNH 1959.4.2.6–10, Figs 7A, B ), oval when partially everted, heart-shaped when fully everted. Longitudinally ridged inferiorly, appearing smooth superiorly. Both palps retained on holotype ( Figs 8A, B ), long (approximately 5.2 and 7.5 mm in length) and slender ( Figs 8C, D ). Palps of slide mounted paratype approximately 6.8–8.9 mm in length. Two further paratypes with palps retained. Papillae ampulliform ( Fig. 8D ); proximally and medially in two rows either side of an inconspicuous ventral region, distally with 1–2 rows either side. Non-papillated region reaching chaetiger ~2 when folded backwards. Achaetous region behind prostomium approximately one and a half times the size as chaetiger one ( Figs 7 B–D). Chaetigers 1–8 similar ( Figs 7D, E ; 8 E–Q); parapodia biramous with low triangular notopodial prechaetal lamellae confluent with slender triangular lamellae, postchaetal to subchaetal in position. Postchaetal lamellae increase slightly in size along thorax, becoming more sinuous shaped by approximately chaetiger 6. Single, digitiform superior dorsal lobe present on all thoracic chaetigers except chaetiger 9; increasing slightly in size to chaetiger 8. Neuropodia with single slender triangular ventral lamella with pointed tip, directly below each chaetal bundle, marginally longer in mid-thoracic region. Ventral lamellae confluent with low pre- and postchaetal ridges, which encircle the chaetae cuff-like. Postchaetal lamellae of chaetiger 8 ( Fig. 7G ) slightly expanded and triangular. Notopodial postchaetal lamellae of chaetiger 9 ( Fig. 7F ) triangular, slightly smaller than on preceding chaetiger. Postchaetal lamellae confluent with, and adjoining the low prechaetal lamellae toward distal tips, thus appearing almost lateral in position. Neuropodia ( Figs 7F, G ) with triangular to digitiform postchaetal lamellae, pointing laterally, and appearing behind the upper part of the chaetal bundle, a smaller digitiform process below chaetal bundle on both sides. Thoracic chaetae simple, smooth-edged, winged capillaries, of similar size in both rami; those of the anterior thorax thinner. Distinct reniform ventral swellings, level with parapodia from chaetiger 5 ( Fig. 7E ), paired. Abdominal chaetigers with broad spatulate lateral lamellae, of about equal size in both rami, basally constricted and stalked ( Figs 7G ; 9 A–C). Lateral lamellae not extended behind chaetal rows ( Fig. 9H ). Large digitiform processes present at inner margins of chaetal rows ( Fig. 9G ), of a similar size to, or slightly shorter than abdominal chaetae in anterior abdomen. Abdominal chaetae tridentate hooded hooks, superior two fangs parallel above main fang ( Fig. 9G ). Hooks in two groups, main fangs vis-à-vis . Approximately 7–10 hooks per ramus initially, reducing to 5–6 on later chaetigers. Hooded hook adjacent to lateral lamellae smaller than rest ( Fig. 9H ). No aciculae observed. Posteriorly opening pouches at extreme posterior end. Pouches, simple C-shaped and pocket-like, fairly convoluted, pattern irregular but essentially alternating from one side of the body to the other and on alternate chaetigers. Pouches evident on holotype on chaetigers 119 and 121, and on chaetigers 116L, 118R, 120L, 121R, 123L, 126R and 127L of a 135 chaetiger entire specimen (NMW.Z.2003.035.2003). Pygidium with two long, slender anal cirri ( Fig. 9F ), with a small ventral anus. Colour . Live animals pinkish/white in colour, preserved specimens beige/white in alcohol ( Figs 7A, B ). Paratypes (BMNH 1959.4.2.6–10) described as “pink” females ( Figs 7A, B ) and “dark” males ( Figs 7 C–G), although the label suggested “?cork staining” [sic], proposing the dark worms were possibly so because of leaching from the cork that had stoppered the vial. Dark colouration not observed in any other material. Distinct dorsal transverse bands just behind parapodia in the thorax, comprised of cream to yellow speckles, very characteristic of the species ( Figs 7A, D ). On chaetigers 1–4, the band is medially interrupted, appearing as two separate circular areas. Behind the parapodia of chaetiger 9, the speckled areas are the largest and occur on almost half of the segment. Speckles continuing into anterior abdomen. Speckling also present on ventral surface, although not as conspicuous as those of the dorsal surface particularly in the anterior thorax. Interparapodial ‘glandular’ regions apparent as speckled areas ( Fig. 7A ), relatively thin and appearing as a stripe in the posterior thorax. Staining with methyl green shows no clear pattern, although highlights the transverse bands as described above. The transverse bands of the thoracic region stain with Rose Bengal and can be a helpful identifier for this species in benthic samples (but note the similarity of the pattern in M. minuta noted by Mills & Mortimer 2018 ). Dorsally, level with the parapodia of chaetiger 1, the stained buccal region can be seen as a large spot of stain through the epidermis of the specimen. Abdominally, staining behind the parapodia, and patches along the mid ventral line is present. Habitat. Wilson (1959) stated that M. filiformis “lives in fragile tubes, which may be no more than the walls of burrows lined with a secretion to which sand grains adhere”. Observations of live animals within a laboratory setting by the first two authors, showed that whilst M. filiformis was the most inactive of the species under observation (see also Mortimer & Mackie 2014 ), as with other magelonid species, they move more or less continuously through the sediment. They do not inhabit burrows for any length of time and do not construct tubes such as is known for species such as M. alleni ( Mills & Mortimer 2019a ) and M. equilamellae ( Fig. 4E ). Meissner & Darr (2009) suggested the species in general has a preference for fine sands with low mud content (below 10%), and can be found from the intertidal zone to 45 m . Mortimer & Mackie (2014) collected large numbers of the species in fine sands of Oxwich Bay, South Wales. Distribution. Distributed around the UK , Irish Sea, North Sea, English Channel, Bay of Biscay to Morocco , Mediterranean Sea. Remarks. Several differences compared to the original description by Wilson are noted herein. Firstly, Wilson (1959) stated that the species had only one pair of prostomial ridges. However, there is an additional pair of thin out- er ridges alongside the inner pair previously reported. There are light markings either side of the ridges, not drawn or mentioned in the original description. Although indistinct, they are noticeable in the majority of specimens. Wilson, made no mention of the presence of lateral abdominal pouches and Fiege et al. (2000) later stated they were absent in this species. However, as detailed by Mortimer & Mackie (2014) , posteriorly open pouches are present in the extreme posterior region of the species. Wilson described the neuropodium of chaetiger 9 as possessing “two fingerlike processes, the dorsal moderately long the ventral short, and 25–30 curved double-winged bristles arising from a setal sac anterior to the processes.” This implies that both lamellae are postchaetal. However, the lower lamella of this chaetiger is ventral in position, directly underneath the chaetal bundle. Furthermore, the “dorsal” neuropodial lamella, is more triangular, wider based than described or drawn by Wilson. The smaller abdominal hooded hook, adjacent to the lateral lamellae is a feature not previously reported for the species, although, hinted at in Wilson’s drawing of abdominal chaetigers. As highlighted by Mills & Mortimer (2018) , M. filiformis shares many morphological similarities with M. minuta (also originally described from north European waters), such as distinctive transverse bands of the thoracic region and a similar prostomial shape. However, they can be distinguished in terms of presence/absence of thoracic superior dorsal lobes (lacking in M. minuta ), dentition of abdominal hooded hooks (bidentate in M. minuta versus tridentate in M. filiformis ) and lamellar shape. FIGURE 7. Magelona filiformis , paratypes (BMNH 1959.4.2.6–10, (A, B) “pink female” individual; (C–G) “dark male” individual. N.B. Wilson’s original label stated “?cork staining” [sic], suggesting the dark worms were so because of leaching from the cork that stoppered the vial: (A) anterior and many abdominal segments (initially dorsal view becoming lateral in more abdominal chaetigers); (B) prostomium and first two chaetigers (dorsal view, burrowing organ partially everted, oval. Abdominal segments visible underneath prostomium); (C) prostomium and first three chaetigers (dorso-lateral view); (D, E) anterior and first few abdominal segments (dorso-lateral and ventro-lateral views respectively); (F, G) thoracic-abdominal junction (dorsolateral and ventro-lateral views respectively). (BO) Burrowing organ; (No) Notopodium; (Ne) Neuropodium. FIGURE 8. Magelona filiformis , holotype (BMNH 1959.4.2.1A–B, slide mounted, thorax in a lateral position): (A) prostomium and first two chaetigers (lateral view, burrowing organ partially everted, both palps attached); (B) prostomium (lateral view); (C, D) palp sections (lateral views, proximal and distal respectively); (E, G, I, K, M, P, R) notopodial lamellae of chaetigers 1, 3, 4, 5, 6, 8, 9 respectively; (J, S) neuropodial lamellae of chaetigers 4 and 9 respectively; (F, H, L, N, O, Q) parapodia of chaetigers 1, 3, 5, 6, 7, 8 respectively. (BO) Burrowing organ; (Ne) Neuropodia; (No) Notopodia; (Pp) Palp; (Post) Postchaetal; (Pr) Prostomium; (Pre) Prechaetal; (SDL) Superior dorsal lobe. Scale bars (E–S) = 100 µm. FIGURE 9. Magelona filiformis , holotype (BMNH 1959.4.2.1A–B): (A) LH parapodia of chaetigers 9 and 10 (ventro-lateral view); (B) LH parapodia of chaetigers 11–13 (ventro-lateral view); (C) LH abdominal parapodia from chaetiger 19 (ventrolateral view); (D) chaetigers 24–25 (ventral view); (E) LH parapodia of chaetiger 64 (ventral view); (F) pygidium and last four chaetigers (ventral view, anus just visible); (G) tridentate abdominal hooded hooks (frontal view) from chaetiger 43; (H) tridentate abdominal hooded hooks (lateral view) from chaetiger 45 (small hook visible adjacent to lateral lamellae). (A) Anus; (AC) Anal cirri; (Ne) Neuropodia; (No) Notopodia; (Pre) Prechaetal; (STH) Small tridentate hook. FIGURE 10. Magelona filiformis minuta , syntype (BMNH 1959.4.2.11–13): (A, C) anterior (dorsal view, latter stained with methyl green); (B) anterior (ventral view). Right hand palp retained, broken. FIGURE 11. European Magelona species: M. minuta , M. filiformis , M. lusitanica , M. johnstoni , M. mirabilis , M. alleni , M. equilamellae and M. wilsoni (adapted from Mills & Mortimer 2018 ; Mortimer & Mackie 2014 and Mills & Mortimer 2019a and current study ( M. lusitanica , paratype NMW.Z.2010.010.0004; M. wilsoni , NMW.Z.2010.010.0008)). (Photos of M. johnstoni , M. mirabilis , M. alleni by Andrew Mackie). TABLE 1. Characters of European magelonid species (adapted from Fiege et al. 2000 ). Species grouped according to similarity of character sets to facilitate comparison.

Species/ Characters	M. minuta Eliason, 1962	M. filiformis Wilson, 1959	M. lusitanica Mortimer et al., 2011	M. johnstoni Fiege et al., 2000	M. mirabilis ( Johnston, 1865 )
Size/Dimensions	Small, slender	Moderate	Moderate	Moderate	Moderate
Prostomium
Horns	Absent	“Rudimentary horns”	Distinct triangular horns	Absent	Absent
Shape	Anterior margin straight	Squared anterior margin	Spatulate	Long, rounded	Long, rounded
L:W ratio	Equal	L>W	L>W	L>W	L>W
No. of ridges	1 pair	2 pairs	2 pairs	2 pairs	2 pairs
Thorax
No. of thoracic cha- etigers	Nine	Nine	Nine	Nine	Nine
Notopodial lamellae	Triangular, postchaetal	Filiform, postchaetal	Slender foliaceous, postchaetal	Foliaceous, postchaetal, crenulate upper edge	Foliaceous, postchaetal, smooth upper edge
Superior Dorsal Lobe (SDL)	Absent	Present 1–8	Present 1–8	Present 3–8	Absent
Neuropodial lamellae	Triangular, postchaetal	Slender triangular, ventral	Slender triangular, ventral	Slender triangular, ventral	Small foliaceous, prechaetal 1–5, small digitform, ventral 6–8
Chaetae	Smooth, unilimbate	Smooth, capillary	Simple, capillary	Smooth, capillary	Smooth, bilimbate
Chaetiger 9
Notopodial lamellae	Triangular, postchaetal	Triangular	Low, triangular	Low, cuff-like encircling chaetae	Low, cuff-like encircling chaetae
Superior Dorsal Lobe	Absent	Absent	Absent	Absent	Absent
Neuropodial lamellae	Triangular, postchaetal	Triangular postchaetal, fili- form subchaetal	Triangular postchaetal, small digitiform prechaetal	Low, cuff-like encircling chaetae	Low, cuff-like encircling chaetae
Chaetae	Smooth, unilimbate	Smooth, capillary	Simple, capillary	Specialized, mucronate	Specialized, mucronate

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Species/ Characters	M. minuta Eliason, 1962	M. filiformis Wilson, 1959	M. lusitanica Mortimer et al., 2011	M. johnstoni Fiege et al., 2000	M. mirabilis ( Johnston,1865 )
Abdomen
Lamellae	Slender foliaceous	Spatulate	Spatulate	Spatulate	Spatulate
Postchaetal expansion	Absent	Triangular	Triangular	Absent	Triangular
Medial lobes	Small	Present	Present	Small	Present
Hook orientation	Vis-à-vis	Vis-à-vis	Vis-à-vis	Unidirectional	Unidirectional
Hook dentition	Bidentate	Tridentate	Tridentate	Tridentate	Tridentate
Lateral pouches— Anteriorly opening	Absent	Absent	Absent	Present, paired, from ch. 9/10	Absent
Lateral pouches— Posteriorly opening	Absent	Present, extreme posterior end ~chaetiger 116	Present, alternating from ~ch.36	Present, alternating, from ~ch. 20	Present, posterior chaetigers (~ch. 78) alternating
Pygidium	2 long, slender cirri	2 slender anal cirri	Unknown	2 small anal cirri	2 small, anal cirri
Anus	Small, ventral	Small, ventral	Unknown	Small, ventral	Small, ventral
Colour	Pale, pinkish white, distinct dorsal and ventral thoracic stripes	Distinct dorsal and ventral thoracic stripes	Cream when preserved, light transverse thoracic bands	Creamy yellow	Creamy/pink, stripy palps
Tube building	No	No	No	No	No
Type locality	Sweden, Öresund	Salcombe, UK	Southwestern Portuguese conti- nental shelf	St Andrews, Scotland, UK	St Andrews, Scotland, UK
Habitat/Ecology	15 m to at least 160 m, muddy and sandy sediments, offshore, ( Mills & Mortimer 2018 )	Intertidal ( Fiege et al. 2000 ) to at least 40 m, fine sands ( Meissner & Darr 2009 )	49–327 m, sandy mud-sand ( Mortimer et al. 2011 , Martins et al. , 2013 )	Intertidal to 88 m, sandy sediments, ( Fiege et al. 2000 )	Intertidal to 32 m, sandy sediments ( Fiege et al. 2000 )
Distribution	Norway to West Africa ( Mills & Mortimer 2018 )	NE Atlantic to Mediterranean	Bay of Biscay to S Portugal ( Mortimer et al. 2011 ; Martins et al. 2013 ; JG, pers. obs.)	North Sea to Mediterra- nean ( Fiege et al. 2000 )	North Sea to Mediterranean ( Fiege et al. 2000 )
Species	M. minuta	M. filiformis	M. lusitanica	M. johnstoni	M. mirabilis

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Species/ Characters	M. alleni Wilson, 1958	M. equilamellae Harmelin, 1964	M. wilsoni Glémarec, 1967	O. bizkaiensis Aguirrezabalaga et al., 2001
Size/Dimensions	Stout	Stout	Stout	Stout
Prostomium
Horns	Absent	Absent	Distinct triangular horns, anterior margin minutely crenulated	“Rudimentary horns”
Shape	Triangular, anterior margin straight	Triangular, anterior margin straight	Rounded triangular	Truncate, squared anterior margin
L:W ratio	Roughly equal	W>L	W>L	W>L
No. of ridges	1 pair	1 pair	2 pairs	1 pair
Thorax
No. of thoracic cha- etigers	Nine	Nine	Nine	Eight
Notopodial lamellae	Triangular, postchaetal	Triangular, postchaetal	Slender, foliaceous, postchaetal	Slender, cirriform, reducing in size to ch. 8
Superior Dorsal Lobe (SDL)	Absent	Absent	Large, foliaceous	Absent
Neuropodial lamellae	Triangular, ventral	Triangular, moving from prechaetal to postchaetal along thorax	Slender triangular, ventral, decrease in size to ch. 8	Slender, cirriform on ch. 1, much reduced or absent thereafter
Chaetae	Smooth, bilimbate	Bilimbate, irregular blade	Simple, capillary	Smooth, bilimbate
Chaetiger 9
Notopodial lamellae	Triangular, postchaetal	Triangular, postchaetal	Triangular	N/A
Superior Dorsal Lobe	Absent	Absent	Present, small	N/A
Neuropodial lamellae	Long, slender, ventral process	Triangular, postchaetal	Triangular, postchaetal	N/A
Chaetae	Smooth, bilimbate	Bilimbate, irregular blade	Simple, capillary	N/A

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Species/ Characters	M. alleni Wilson, 1958	M. equilamellae Harmelin, 1964	M. wilsoni Glémarec, 1967	O. bizkaiensis Aguirrezabalaga et al., 2001
Abdomen
Lamellae	Sub-equal, notopodial larger	Triangular	Spatulate	Lanceolate
Postchaetal expansion	Absent	Absent	Absent	Absent
Medial lobes	Absent	Absent	Small	Ventral only
Hook orientation	Vis-à-vis	Vis-à-vis	Vis-à-vis	Vis-à-vis
Hook dentition	Tridentate	Tridentate	Tridentate	Tridentate
Lateral pouches— Anteriorly opening	Absent	Absent	Absent	Absent
Lateral pouches— Posteriorly opening	Absent	Absent	Present, alternating from ~ch. 24 (absent on type),	Absent
Pygidium	2 stout, lateral projections	No cirri observed	Unknown	Unknown
Anus	Large, terminal	Large, terminal	Unknown	Unknown
Colour	Dark pigment band chaetigers 5–9	Dark pigment band chaetigers 5–9	Yellowish white, transverse dorsal thoracic stripes	White specks dorsally, transverse bands ventrally
Tube building	Paper-like tube, covered in sand	Paper-like tube, covered in sand	Unknown	Unknown
Type locality	Plymouth, UK	Rade de Villefranche & Golfe de Marseille, France	South of Brittany, ‘Grande Vasière’, France	Capbreton Canyon, Bay of Biscay
Habitat/Ecology	Intertidal to 115 m, sandy mud to sandy gravel, (Mills & Mortimer in prep)	0–50 m, muddy sediments, with seagrass in euryhaline, shallow enclosed, transitional waters	10–225 m, mud to sand ( Mortimer et al. 2011 )	1000–1040 m, soft sediments ( Aguirrezabalaga et al. 2001 )
Distribution	Norway to Nigeria (Mortimer et al. in prep.)	Mediterranean	Bay of Biscay to Mediterranean ( Mortimer et al. 2011 )	Bay of Biscay to Mediterranean ( Aguirrezabalaga et al . 2001 : JG, pers. obs.)
Species	M. alleni	M. equilamellae	M. wilsoni	O. bizkaiensis

Fiege et al . (2000) stated that the abdominal hooded hooks of M. filiformis were in “one group in each ramus, all facing laterally”. The original description does not state their orientation, with the figure of the 13th parapodium showing the majority of hooks facing laterally, however, those nearest the lamellae, particularly in the neuropodium, appear twisted and facing anteriorly. The hooks of M. filiformis , as shown herein, for type and additional material are not unidirectional as stated by Fiege et al . (2000) , they are vis-à-vis in two groups. Wilson (1959) stated that the first nine pairs of parapodia carry only double-winged bristles, which he stated were most readily seen in formalin preserved material examined in water. His figure 1J showed two adjacent, distinctly bilimbate bristles, although not stating the chaetiger from which they were observed. As noted above the bristles of the anterior thorax are much thinner than those of the posterior thorax. Whilst the latter look distinctly bilimbate, as was noted by Wilson, the limbations of the anterior chaetae are much more difficult to observe and appear unilimbate. Variation in the thickness of chaetae is also evident in the posterior thorax, those toward the edge of the bundle being somewhat thinner. This is something which warrants further investigations, but it appears there is greater variation within the capillary chaetae than was previously reported.