Amphitritides gracilis ( Grube, 1860 )

Lavesque, Nicolas, Daffe, Guillemine, Londoño-Mesa, Mario H. & Hutchings, Pat, 2021, Revision of the French Terebellidae sensu stricto (Annelida, Terebelliformia), with descriptions of nine new species, Zootaxa 5038 (1), pp. 1-63 : 16-19

Amphitritides gracilis ( Grube, 1860)

Figures 5 and 6

Terebella gracilis . Grube 1860: 99.

Amphitrite gracilis .— Saint-Joseph 1894: 198–201, pl. VIII, figs. 224; Fauvel 1927: 252–253, fig. 87, a–e; Jirkov 2020: 332– 334, figs 2B, 16–17.

Amphitritides gracilis .— Holthe 1986: 104–106, fig. 45; Arvanitidis & Koukouras 1995: Table 1.

Other synonyms. Physelia scylla Quatrefages, 1866 ; Terebella gelatinosa Keferstein, 1862 ; Terebella laevirostris Claparède, 1869 .

Material examined. MNHN-IA-PNT 128, posteriorly incomplete, Northeastern Atlantic , Bay of Biscay , Bay of Brest , 48°21’54”N 4°26’00”W, depth 5 m, February 2013. SMA-BR-Amphi-01, posteriorly incomplete, Northeastern Atlantic , Bay of Biscay, Bay of Brest, 48°21’54”N 4°26’00”W, depth 5 m, February 2013, mounted for SEM .

Description. Small specimens, all incomplete, largest specimen 14.7 mm long and 1.9 mm wide, for 33 segments.

Prostomium at base of upper lip without eyespots, distal part forming a shelf-like tentacular membrane from which long, thin and non-grooved buccal tentacles originate (few remaining) ( Fig. 5B ), continuing ventrally as a thin lobe ( Fig. 5C ). Peristomium forming lips; upper lip, hood-like, broader than high; lower lip swollen, very glandular and ridged, slightly broader than high ( Figs 5A, C ; 6A–B ).

Segment I dorsally narrow, more developed ventrally, forming protruding lobe below ventral lobe of prostomium and lower lip ( Fig. 5C ). Segments II–IV without lateral lobes ( Figs 5A–B ; 6A–B ). Ventral shields on SG II–XII (n=11), rectangular, wide and thin, shields separated by deep incision ( Fig. 5C ); replaced by groove posteriorly.

Two pairs of short, arborescent branchiae on SG II–III, both pairs with short, thick main stem, with dichotomous ramifications starting from close to base and ending with short wrinkled filaments ( Fig. 5D ); the two pairs inserted dorso-laterally, at the level of the following notopodia ( Fig. 6A–B ).

Notopodia beginning from SG IV and extending for 19 segments. Notopodia well-developed, approximately rectangular, all similar in size, first two pairs aligned more dorsally, laterally aligned from SG VI ( Figs 5A–B ; 6A– B ). Notochaetae in two rows with symmetrical limbation and curved serrated tips, first row shorter ( Fig. 5E–F ).

Neuropodia starting from SG V, thoracic neuropodia as long lateral ridges slightly raised from surface of body, not reaching ventral groove ( Figs 5B–C ; 6A–B ); abdominal neuropodia as short fleshy ridges, close to mid ventral groove. Uncini arranged in double rows from SG XI until end of body, in a face-to-face arrangement, with rows completely separated from each other. Uncini avicular, with short triangular heel, distally pointed prow downwardly directed, short dorsal button inserted halfway between base of main fang and tip of prow, convex base, and main fang surmounted by crest of five rows of secondary teeth ( Figs 5G ; 6C–D ).

Nephridial and genital papillae on SG III and SG VI–XII, inserted laterally and slightly anteriorly to branchial stem on SG III, and anteriorly to base of notopodia on SG VI–XII (NP).

Pygidium not seen.

Type locality. Scilly Isles , off southwest England, approx. 49°56’02”N 6°18’44”W .

Type material. ZMB Q.5045, 2 syntypes .

Distribution. Along all the French coasts ( Fauvel 1927, this study, Resomar database). In Europe, from Scotland to Black Sea ( Gil 2011; Jirkov 2020). Also recorded from Ivory Coast ( Holthe 1986), but this record is considered to be doubtful.

Habitat. Shallow waters, in maërl (rhodolith) beds (this study), soft muddy bottoms and sandy mud, under stones and among Posidonia , Zostera and algae, eulittoral to 80 m ( Fauvel 1927; Holthe 1986; Gil 2011).

Remarks. Our material corresponds closely to the recent description by Jirkov (2020), including the variation in the number of nephridial papillae and notopodia (specimens from UK and Black Sea).

Two morphological differences can be perceived between the present description and the data by Arvanitidis & Koukouras (1995: Table 1, based on the original descriptions and French specimens from the “Collection des Polychètes d’Angers”). Indeed, our specimens, and those of Jirkov, do not show any eyespots (which may fade with time when stored in alcohol), and they also show “rugose” branchial tips, i.e. wrinkled (as in A. kuehlmanni Arvanitidis & Koukouras, 1995 ). This last character was not described by Jirkov (2020) and could be related to method of fixation.

Genus Eupolymnia Verrill, 1900

Type-species: Terebella danielsseni Malmgren, 1866 , by monotypy.

Diagnosis. (after Hutchings et al. 2021b). Prostomium transverse, attached to dorsal surface of upper lip; basal part as a thick crest, eyespots usually present; distal part shelf-like. Buccal tentacles all uniformly cylindrical. Peristomium restricted to expanded lips; relatively short upper lip, hood-like, wider than long, distal margin rounded, frequently undulated; lower lip button-like, mid-ventrally, almost completely covered by lobes of SG I. Segment I conspicuous all around, dorsally narrow, with pair of low ventro-lateral lobes connected to each other by mid-ventral lobe marginal to mouth. Segments II–IV with pairs of progressively shorter and more laterally inserted lobes, those on SG II ventro-lateral and frequently connected to each other by low collar-like lobe across ventrum.Anterior segments highly glandular ventrally, with discrete rectangular shields, anterior shields frequently corrugated. Three pairs of branchiae, on SG II–IV, each one with a single short and thick main stem, dichotomously branching to short distal filaments. Conical to roughly rectangular notopodia from SG IV, extending 17 segments, until SG XX; notochaetae all narrowly-winged, wings slightly broader basally on one side and with smooth tips. Neuropodia beginning on SG V, as low, sessile ridges in conjunction with notopodia as conical to rectangular pinnules posteriorly; neurochaetae as short-handled avicular uncini, in completely intercalated double rows in face-to-face arrangement from SG XI until end of notopodia. Nephridial and genital papillae present, from SG II or III, extending for few anterior segments, between parapodial lobes or equivalent position on anterior segments. Pygidium crenulate to papillate.

Remarks. Currently, only two valid species (but with long lists of synonymized species) of this genus occur in European waters, both without any extant type material: Eupolymnia nesidensis ( Delle Chiaje, 1828) (described from Gulf of Naples, Italy) and Eupolymnia nebulosa ( Montagu, 1819) (described from Cornwall, UK). The main problem with these two species is that in spite of being widely referred to in the taxonomic literature and used in dichotomous keys, we do not believe that there is a good recent morphological description of any of them as both of the original descriptions are brief. For example, following Holthe (1986), E. nebulosa would have “anterior branchiae with long stems” and a “buccal segment forming a broad cushion-like lip”, but this author only observed specimens from Norway. After examination of several specimens from near the type locality (Cornwall, UK), Hutchings & Glasby (1988) concluded that this species has “branchiae with virtually no main stalk” and “peristomium expanded as a discrete narrow elongated raised ventral collar”, though, knowing that there are other species present in the area (as shown in this study) it is possible that the studied material could also belong to a different species. Capa & Hutchings (2006) after observing two specimens sampled close from the type locality (AM W.200882 and BMNH ZK 1950.6.6.21) provided more details concerning this species: presence of 10 ventral shields, branchiae with no stalk and few branches, small spherical lateral lobes on SG II and IV, bilobed on SG III, dental formula of uncini MF:2:3 with dorsal button in the middle of uncini. This species has been widely reported because of its particular “strawberry” colour (e.g. Fauvel 1927) but at least two other species (and probably more) seem to exhibit this pattern of red colour with white spots (see below). Concerning E. nesidensis, Delle Chiaje (1828) briefly wrote that the species was yellow, with three pairs of red arborescent branchiae and with parapodia bearing chaetae. There is also a variety, differing from the former by its green colour, the yellowish-red branchiae and the thinner body ( Delle Chiaje, 1828). Until a neotype from the Gulf of Naples is selected and described, it is recommended that this name should not be used.

Figures

FIGURE 5. Amphitritides gracilis (Grube, 1860) MNHN-IA-PNT 128 (A, C, E–G), SMA-BR-Amphitritides-01 (B, D). A. Anterior end, lateral view; B. Anterior end, lateral view, MG staining; C.Anterior end, ventral view; D. Branchia; E–F. Notochaetae, SG XV; G. Uncinus, SG XV. Abbreviations: Ll, lower lip; Pr, prostomium; Ul, upper lip. Numbers referring to segments.

FIGURE 6. Amphitritides gracilis (Grube, 1860) SMA-BR-Amphitritides-01, SEM. A–B. Anterior end, lateral view; C–D. Uncini, SG XIV.