Myxicola infundibulum ( Montagu, 1808 )

Darbyshire, Teresa, 2023, Designation of a neotype for Myxicola infundibulum (Montagu, 1808) (Annelida: Sabellidae) and a new species from the UK, European Journal of Taxonomy 900 (1), pp. 106-137 : 115-122

Myxicola infundibulum ( Montagu, 1808)

Figs 1–6 , 11 , Table 1

Terebella buccina [ Renier, 1804a]: 19.

Sabella gelatinosa [ Renier, 1804b]: xiii.

Terebella infundibulum [ Renier, 1804b]: 13.

Tuba divisa [ Renier, 1807]: tab. vi.

Amphitrite infundibulum Montagu, 1808: 109–110 , pl. viii.

Sabella villosa Cuvier, 1830: 192 .

Myxicola villosa Koch in Renier, 1847: 52.

Eriographis borealis Grube, 1850: 88 , 140.

Leiobranchus modestus Quatrefages, 1850: 371 .

Amphitrite floscula Dalyell, 1853: 245 , pl. xxxi fig. 9.

Myxicola grubii Krøyer, 1856: 9 .

Myxicola sarsii Krøyer, 1856: 9 .

Myxicola steenstrupi Krøyer, 1856: 35–36 .

Myxicola parasites Quatrefages, 1866: 480 .

Myxicola platychaeta Marenzeller, 1884: 213–214 , pl. iii fig. 6.

Sabella viridis McIntosh, 1874: 206 .

Myxicola pacifica Johnson, 1901: 431–432 , pl. 19 figs 193–198.

Myxicola affinis Bush, 1905: 218 , pl. xxxviii figs 17–20.

Myxicola conjuncta Bush, 1905: 217–218 , pl. xxvi figs 1, 4, pl. xxxviii figs 1–11. Myxicola michaelseni Augener, 1918: 589–593 , pl. vii figs 263–264, textfig. cv. Myxicola monacis Chamberlin, 1919: 20 .

Sabella infundibulum – Delle Chiaje 1841: 72, fig. 5.

Tuba infundibulum – Renier 1847: pl. 9 figs 1–22.

Terebella infundibulum – Renier 1847: 51–54, figs 1–2.

Myxicola infundibulum – Grube 1855: 122. — Claparède 1870: 141, pl. xiv fig. 2. — de Saint-Joseph 1898: 433, pl. xxiii figs 241–247. — Soulier 1902: 20–25, fig. 5. — Rioja 1917: 71.

Arippasa infundibulum – Johnston 1865: 252, 346.

Myxicola modesta – Quatrefages 1866: 480.

Mixicola infundibulum – Panceri 1875: 533. — Cosmovici 1880: 325, pl. xxvii fig. 1.

Leptochone parasites – Langerhans 1884: 272–273.

Myxicola steenstrupi – Cunningham & Ramage 1888: 672. — Bidenkap 1894: 137. — Hofsommer 1913: 348, pl. i figs 23–24. — Eliason 1920: 79.

Myxicola viridis – McIntosh 1923: 319, pl. cxvi fig. 1, pl. cxxi fig. 4, pl. cxxx fig. 6.

Material examined

Neotype ENGLAND • Kingsbridge estuary , Saltstone; 50.2540° N, 3.7588° W; low shore; 1 Oct. 2019; T. Darbyshire leg.; mud; GenBank: OQ343676 (16S), OQ341617 (COI); NMW.Z.2019.023.0001.

Topotypes ENGLAND • 3 spec.; same collection data as for neotype; GenBank: OQ343673–5 (16S), OQ341614–6 (COI); NMW.Z.2019.023.0002–0004 .

Other material

WALES – Pembrokeshire • 4 specs; Gann Flats ; 51.7124° N, 5.1661° W; low shore; 27 Nov. 2019; T. Darbyshire leg.; muddy sand; GenBank: OQ343670–2 (16S), OQ341611–3 (COI); NMW.Z.2019.023.0005 to 0008 • 7 specs; same collection data as for preceding; NMW.Z.2019.023.0009 to 0012 • 1 spec.; Milford Haven ; 51.6861° N, 4.9769° W; depth 9.9 m; 15 Oct. 1996; S.J. May leg.; medium silt; NMW.Z.2011.045.0037 • 7 specs; Gann Flats ; 51.7124° N, 5.1661° W; low shore; P. Knight-Jones leg.; muddy sand; NMW.Z.2009.038.0671 .

ENGLAND – Dorset • 2 specs; Portland Harbour ; 50.5817° N, 2.4663° W; depth 1.9 m; 29 Jul. 2019; T. Darbyshire leg.; sandy mud; GenBank: OQ343677–8 (16S), OQ341618–9 (COI); NMW.Z.2019.023.0013 to 0014 • 1 spec.; Kingsbridge estuary ; 50.2540° N, 3.7588° W; low shore; mud; NHMUK1980.390 – Cornwall • 2 specs; Helford estuary ; 50.0983° N, 5.1178° W; depth 9 m; 16 Sep. 2012; T. Darbyshire leg.; maerl; NMW.Z.2012.058.0065 to 0066 • 3 specs; St Anthony ; low shore; P. Knight-Jones; mud and sand; NMW.Z.2009.038.0675 .

IRELAND – County Galway • 2 specs; Ballynakill Harbour, Fahy Bay ; 53.5604° N, 10.0157° W; low shore; 21 Mar. 1988; A.S.Y. Mackie leg.; muddy gravel; NMW.Z.1988.069 .

Description

Neotype complete with 123 chaetigers, 8 thoracic and 115 abdominal; body length 58 mm, crown length 20 mm. Topotypes with 130–149 chaetigers, body length 58–65 mm, crown length 19–22 mm. Preserved colour pale brown over body, darker on chaetigers 1–10 except around parapodia. Dark brown pigmentation present on basal ¼ of radiolar crown, internal side of ventral lobe, radiolar appendages and on radiolar tips, cream elsewhere. Colour when alive with pale orange-brown body, white, pink or purple radioles and dark brown radiolar tips ( Fig. 3A–E ). Body flattened dorso-ventrally, widest around chaetiger 4, then tapering posteriorly to a blunt pygidium ( Fig. 3D ).

Radiolar crown with semicircular radiolar lobes bearing 26 pairs of radioles ( Fig. 4A, B ). Radioles connected by basal membrane along #/5 of their length (measured from base to lower margin of membrane between radioles) with broad radiolar flanges ( Fig. 4C ); with long tapered tips (measured from end of pinnulae to tip of radiole), ¹/5 of the total radiole length. Dark brown pigmentation occurs over last ¼ of radiole, from just below start of radiolar tip, spreading outward to where basal membrane connects to rachis, then continuing to tip, creating a lanceolate appearance ( Figs 3–E , 4A–C, E , 6A ); radiolar tip triangular, elongating evenly to tip ( Fig. 4E ). Radioles supported by two rows of vacuolated cells ( Fig. 6B ); radiolar eyes absent. Pinnulae slender, with blunt ends in basal region, becoming finer, tapered and longest in distal part of radiole ( Fig. 4A ), 0.25 × total length of radiole, then rapidly decreasing in length to start of radiolar tip; pinnulae terminate at or just above lower margin of basal membrane.

Dorsal lips with fleshy, large, triangular radiolar appendages, oriented transversely and arising from ventral internal border of ventral lips; surrounded by enlarged ventral lips connected to radiolar lobes dorsally ( Figs 4D , 6C ); pinnular appendages absent; ventral radiolar appendages absent; parallel lamellae and ventral sacs both absent.

Posterior peristomial ring collar absent. Anterior peristomial ring with ventral, triangular lobe, high with concave indentation ( Fig. 4B ). Lateral notches present, deep, impacting chaetiger 1 ( Fig. 4F ). Glandular girdle present, toward posterior boundary of chaetiger 2 ( Figs 3D , 4A–C ). Ventral shields inconspicuous. Interramal eyespots present, one or two, from chaetiger 3 to chaetiger 8; lateral eyespots present in abdominal region to end of body, minute, 1–2 per segment ( Fig. 4F ).

First notopodia as oval cushions with dense, fine, narrow-hooded notochaetae ( Fig. 5A ), up to 150. Second notopodia twice the size of the first, then reducing in size gradually along thorax ( Fig. 4F ); notochaetae of same form as on first notopodium ( Figs 5B , 6D ), 150–200 per fascicle. Thoracic neurochaetae acicular uncini with long handles, mostly non-emergent; long elongate fang, not greatly hooked, with several minute teeth above and a slight constriction at top of shaft ( Figs 5C , 6E ). Companion chaetae absent. Neuropodia small, oval with narrow-hooded neurochaetae. Abdominal notopodial tori forming almost complete cinctures around body, with avicular uncini with 1–2 large teeth and 1–3 smaller teeth over main fang; upper teeth 0.5–0.65× length of main fang ( Figs 5D , 6F ); breast rounded, equal to or slightly longer than main fang, handle absent ( Fig. 6F ).

Pygidium rounded, eyespots present in a transverse line across tip. Pygidial cirrus absent. Tube semi-transparent, gelatinous, with light covering of fine sand grains, some pale brown colouration toward proximal end ( Figs 3E , 4E ).

Methyl green staining pattern

Peristomial ring and ventral lobe with solid staining followed by complete rings on the posterior border of each segment.

Variation

Radiolar pinnulae 0.13–0.25 × total length of radioles. Interramal eyespots present on thorax from chaetiger 3 or 4; lateral eyespots present or absent on abdomen for a variable number of chaetigers, minute and easily missed. Pygidial eyespots present or absent (usually present). Data from photos submitted by divers or taken by the author, along with the examination of museum specimens confirmed as M. infundibulum , show a range in the number of radioles from 13 to 37 pairs. The tube has a slightly firmer feel to it than that of M. polychroma sp. nov., which is softer.

Remarks

Myxicola infundibulum and M. violacea ( Langerhans, 1884) (the latter described from Madeira) are the only current taxa in the genus described with dark coloured tips to the radioles of the crown. Records of M. infundibulum are only verified here (through genetics and morphology) for the UK, Adriatic and Australia although darkly-tipped Myxicola are reported from elsewhere in the Mediterranean (see Discussion). Myxicola violacea is only recorded from Madeira and no other records of the species have been found. Langerhans’ description and figures bear strong resemblance to those of M. infundibulum , particular those of the radiole tip and thoracic chaetae ( Langerhans 1884). However, Langerhans also described and figured two sets of peristomial eyes for M. violacea , as well as abdominal uncini that are alternately large or small in each cincture; these features are not reflected in M. infundibulum as described here and are the main distinctions available between the two taxa at this time. It should be noted that Langerhans described his specimens as immature; all were small, no more than 15 mm in length or with no more than 11 pairs of radioles, and some radioles were not darkly-tipped, giving rise to the potential that Langerhans may have been looking at more than one species at the time as well as juveniles that might exhibit modified characters, although juvenile M. infundibulum observed during this study did not exhibit peristomial eyes or more than one type of uncinus and all had dark radiole tips. Type material for M. violacea was enquired of from museums in Germany but was not found, and so further investigation needs to be done to determine whether the taxa that exist around the island are, or include, true M. infundibulum . If they do, then M. violacea would become a junior synonym of M. infundibulum . For now, both names are retained until their relationship can be resolved and morphological characters confirmed.

The pigment present in the tips does not break down easily as in some taxa and can still be identified in specimens over 200 years old, as was evident in the specimens from NHMUK. The presence or absence of darkly pigmented radiole tips can therefore be used as a diagnostic character for this taxon, although other characters should be taken into account as well. Other pigment features such as the abdominal (lateral) eyespots and pygidial eyespots are not so consistent and are unreliable as characters. Thoracic (interramal) eyespots were consistent in their presence across all body sizes.

In addition to the dark radiole tips, Myxicola infundibulum can be distinguished from all other current members of the genus using a range of other characters. Myxicola aesthetica , with which it overlaps in distribution, and M. nana Capa & Murray, 2015 (described from Australia) are both smaller, with fewer thoracic chaetigers ( M. infundibulum : 8; M. aesthetica : 3–4; M. nana : 6) and fewer pairs of radioles ( M. infundibulum : 13–33; M. aesthetica : 7–10; M. nana : 6). Around the UK, M. infundibulum is distinct from the newly described M. polychroma sp. nov. by the radiolar pinnulae which, in M. infundibulum , are 0.13–0.25 × the length of the radiole and terminate around the lower margin of the basal membrane, whereas in M. polychroma sp. nov. pinnulae are 0.22–0.3 × the length of the radiole, at their longest, and terminate below the lower margin of the basal membrane.Additionally, the dorsal lips of M. infundibulum are oriented transversely and arise from the ventral internal border of the ventral lips, whereas in M. polychroma sp. nov. the dorsal lips are oriented dorsal-ventral and arise centrally. Finally, the abdominal uncini in M. infundibulum have a rounded breast, whereas those of M. polychroma sp. nov. show a more angled profile. Of the remaining larger species, which are more geographically removed, M. sulcata Ehlers, 1912 ( Antarctica) has only 10–20 thoracic chaetae, on inconspicuous notopodia, on each segment ( Tovar-Hernández et al. 2017), in comparison to over 100 for M. infundibulum on large notopodial pads, M. ommatophora Grube, 1878 ( Philippines) has a clay tube (not gelatinous) and paired subdistal radiolar eyes (absent in M. infundibulum ), and M. fauveli Potts, 1928 (Suez Canal) has only around 12 pairs of radioles and a sharply delineated filiform radiolar tip (triangular tip, not sharply delineated in M. infundibulum ).

Distribution

Present on the west and southwest coasts of the UK only as far north as southern Scotland and the south and west coasts of Ireland; also Adriatic Sea ( Croatia) and Australia, confirmed through genetic sequencing. All records from the UK and Ireland of ‘black-tipped’ Myxicola are attributed to M. infundibulum . Records of ‘black-tipped’ Myxicola also exist from Penpoull (Brittany, France; De Saint-Joseph 1894) and additional locations in the Mediterranean ( Grube 1850; Claparède 1869; Soulier 1902) but need confirmation as to whether they are M. infundibulum or another taxon that has dark radiole tips. All records of Myxicola infundibulum without black tips on the radioles should be re-evaluated and those with black tips but from outside the northeast Atlantic region should be considered suspect and re-evaluated according to the new description and genetic information available.

Ecology

From intertidal to shallow waters (15–20 m) in mud, muddy sand and muddy gravel.

Figures

Fig. 1. Map showing the distribution of Myxicola infundibulum (Montagu, 1808) (closed circles) and M. polychroma sp. nov. (open circles) around the British Isles, based on validated specimens and photographs. Grey circles indicate an undetermined species of Myxicola in northeast England. Type locality of Myxicola infundibulum indicated by black arrow.

Fig. 2. Map showing the type localities of both valid (bold type) and invalid species of Myxicola in Europe.

Fig. 3. Images of live Myxicola infundibulum (Montagu, 1808) demonstrating different colour morphs. A. White crown, Portland Harbour, England. B. Pink crown, Portland Harbour, England. C. Red crown, Gann Flats, Wales. D. Cream-yellow body, Kingsbridge estuary, England. E. Orange body, Kingsbridge estuary, England.

Fig. 4. Myxicola infundibulum (Montagu, 1808). A–D. Neotype (NMW.Z.2019.023.0001). A. Antero-dorsal view. B. Anteroventral view. C. Radiolar tips. D. Dorsal and ventral lips, anterior view. E. NMW.Z.2019.023.0003. Live specimen in tube, entire. F. Neotype (NMW.Z.2019.023.0001). Anterolateral view. Scale bars: A–B, E–F = 10 mm; C–D = 1 mm.

Fig. 5. Myxicola infundibulum(Montagu, 1808), NMW.Z.2019.023.0002. A. Thoracic chaetae, chaetiger 1. B. Thoracic chaetae, chaetiger 4, white arrow indicates thoracic uncini. C. Thoracic uncini, chaetiger 4. D. Abdominal uncini, chaetiger 9. Scale bars: A = 200 µm; B = 20 µm; C–D = 10 µm.

Fig. 6. Myxicola infundibulum (Montagu, 1808). A–C. Neotype (NMW.Z.2019.023.0001). A. Radiole tip illustrating basal membrane, pigmentation pattern and extent of pinnulae.B. Cross-section of radiole. C. Ventral and radiolar lobes, anteroventral view. D–F. NMW.Z.2019.023.0002. D. Thoracic chaeta, chaetiger 5. E. Thoracic uncinus, chaetiger 5. F. Abdominal uncinus, chaetiger 12. Scale bars: A, C = 1 mm; B = 100 µm; D–E = 50 µm; F = 20 µm.

Fig. 11. Bayesian inference trees. A. 16S rRNA dataset. B. Cytochrome oxidase I gene dataset. The first value at each node represents maximum likelihood bootstrap support, the second the Bayesian posterior probabilities and the third the maximum parsimony bootstrap support.