Sphaerodoridium cf. minutum (Webster & Benedict, 1887)

Capa, Maria, Nygren, Arne, Parapar, Julio, Bakken, Torkild, Meissner, Karin & Moreira, Juan, 2019, Systematic re-structure and new species of Sphaerodoridae (Annelida) after morphological revision and molecular phylogenetic analyses of the North East Atlantic fauna, ZooKeys 845, pp. 1-97 : 76-78

Sphaerodoridium cf. minutum (Webster & Benedict, 1887) Figs 5Y, 23M, N, 27B, C, 30

Ephesia minuta Webster & Benedict, 1887: 728-729, pl. IV, figs 64-66.

Sphaerodoropsis minuta .- Imajima 1969: 153-154, fig. 2; Hartmann-Schröder 1996: 237; Moreira 2012: 39-41, fig. 13.

Sphaerodorum minutum .- Berkeley and Berkeley 1948: 27-28, fig. 34.

Sphaerodoridium minutum .- Lützen 1961: 415; Capa et al. 2016b: 19-23, fig. 7.

Type locality.

Off Maine, United States, North Atlantic Ocean, shelf depths.

Material examined.

Lectotype: USNM 393, Eastport, Maine, United States, North Atlantic Ocean, coll. Webster, H. E; Paralectotypes: USNM 1407984 (11 specs and 4 slides), Eastport, Maine, United States, North Atlantic Ocean, coll. Webster, H. E. Paratypes: USNM 22873 (29 specs, 3 for SEM) Eastport, Maine, United States, North Atlantic Ocean, coll. Webster, H. E.

Additional material.

(13 specs) South Greenland, ZMBN 127345 (1 spec.), 63°21'N, 52°35'W, 105,5 m, 07 Nov 2002; Svalbard, ZMBN 127344 (1 spec. for DNA sequencing SPH277), 79°43.434'N, 11°5.55'E, 216 m, 27 Aug 2009; Barents Sea, ZMBN 129500 (1 spec. in SEM stub), Finnmark, 71°20.262'N, 25°13.17'E, 297 m, 23 Apr 2011. Great Britain: ZMBN 127346 (1 spec. for DNA sequencing SPH 320), Plymoouth, Mount Sant Michelle, 50°7.148'N, 5°28.419'W, 15 m, 16 Mar 2011; ZMBN 127347 (1 spec. for DNA sequencing SPH 321), The Sound, Plymoouth, 50°21.5'N, 4°8.9'W, 15 m, 16 Mar 2011; ZMBN 127348 (1 spec. for DNA sequencing SPH 322), The Sound, Plymoouth, 50°21.5'N, 4°8.9'W, 15 m, 16 Mar 2011.

Diagnosis.

Body short and ellipsoid. Prostomial appendages digitiform, smooth, lacking spurs; median antenna as long as or slightly shorter than other head appendages. Antenniform papillae absent. Ten to twelve longitudinal rows of spherical and stalked macrotubercles in one transverse row per segment, in mid-body segments. Additional spherical papillae arranged in three transverse rows per segment, in dorsum and ventrum. Parapodia with acicular lobe from chaetiger 3, digitiform; ventral cirri digitiform, project ing well beyond acicular lobe; four spherical parapodial papillae. Compound chaetae with medium length blades (6-7 times as long as wide), showing little dorso-ventral gradation.

Description of NEA material.

Measurements and general morphology. Body with oval contour strongly convex dorsum and flat ventrum. Size range of material examined 20-27 chaetigers; 2-5 mm long; 0.8-0.9 mm wide. Segmentation not distinct. Pigmentation absent in live or fixed material (Figs 27B, C, 30A).

Head. Prostomium with five short and digitiform appendages, including a pair of palps and lateral antennae, similar in size and shape, and a shorter median antenna (Fig. 30B). Tentacular cirri shorter than lateral antennae and palps. A few rounded small papillae scattered around head appendages (Fig. 30B).

Tubercles. First chaetiger with eight dorsal macrotubercles; following chaetigers each with one transverse row of dorsal macrotubercles increasing to 10-12 tubercles per segment from chaetiger 5 (Fig. 23M). Macrotubercles spherical to club-shaped with a short and smooth stalk (Fig. 30C, D); all macrotubercles similar in shape and size. Additional spherical and sessile papillae in different sizes over dorsum, arranged in 2-3 irregular transverse rows per chaetiger; 20-30 papillae on each mid-body chaetiger (Fig. 30A, C). Ventral surface with spherical papillae in different sizes, arranged in 2-3 transverse rows in a zig-zag pattern, with ca. 20 per segment in mid-body (Fig. 23N); numbers decreasing towards posterior end (Fig. 30E, F).

Parapodia. Parapodia sub-conical, increasing in size towards chaetiger 3, ca. 2 times longer than wide (Fig. 30F, G). Acicular lobe anterior to chaetae, digitiform to clavate, longer than parapodial papillae and projecting distally (Fig. 30G, H). Ventral cirri digitiform projecting 1/2 to 2/3 as long as acicular lobe on anterior and mid-body segments, almost as long as in posterior segments (Fig. 30 F–I). Parapodia with three spherical to clavate papillae: one on antero-dorsal surface, one on antero-basal position, and one on the posterior surface (Fig. 30 F–I).

Chaetae. All parapodia with 4-7 compound chaetae, arranged in a curved transverse row around acicular lobe (Fig. 30 G–I). Serrated, long blades, 4-5 times longer than maximum width, with a curved tip (Fig. 30J, K), similar throughout.

Pygidium. Pygidium terminal, with one mid-ventral digitiform anal cirrus projecting beyond parapodia, and one pair of clavate anal cirri, at base on median cirrus.

Internal features. Specimens are all opaque after fixation and preservation and internal features not observable.

Reproductive features. Sexual structures or eggs not seen in type specimens.

Remarks.

Sphaerodoridium minutum (as re-described by Capa et al. 2016b) is characterized by having up to 10-12 macrotubercles in mid-body, a parapodium that bears three (sometimes four) parapodial papillae and compound chaetae with blades 4-5 times as long as maximum width on mid-body chaetigers. Furthermore, the macrotubercles have a short stalk that was overlooked until Capa et al. 2016b reported their morphology. This species was originally described from NW Atlantic coasts ( Webster and Benedict 1887) and since then has been reported worldwide (see Capa et al. 2016b for a comparison with related species). However, it is likely that many records from other oceans might refer to other similar, yet undescribed species. Specimens examined from NE Atlantic reported here differ from those of NW Atlantic in having chaetae with slightly longer blades (6-7 times as long as wide) and four parapodial papillae. They might represent a new species but to truly assess this possibility more material from other European localities (both Atlantic and Mediterranean) should be examined. Anyway, NE Atlantic specimens could be distinguished from S. celiae sp. n. and S. guerritai because the latter bear prostomial appendages with spurs, the stalk of the macrotubercles are longer and parapodia are provided with more papillae (6-7 and 7-8 respectively).

Distribution.

Reported as a common species in the North Atlantic and Arctic. However, some records should be reviewed as they could be misidentifications (e.g., Moreira 2012).

Habitat.

Shelf or slope depths ( Moreira 2012, Capa et al. 2016b).