Sphaerodoridium balticum (Reimers, 1933) Reimers, 1933

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 : 64-65

Sphaerodoridium balticum (Reimers, 1933) comb. n. Figs 5T, 23C, D, 24

Sphaerodorum balticum Reimers, 1933: 41-110, 45 figs

Type locality.

Kiel, Baltic Sea, 6-8 m.

Material examined.

(16 specs) Barents Sea: ZMBN 127332 (1 spec. used for DNA sequencing, SPH 280), 70°17.79'N, 31°18.83'E, 217 m, 18 Aug 2013; Norwegian Sea: ZMBN 127331 (11 spec.), Mørebanken, 62°45.5'N, 5°31.56'E, 91 m, 04 Oct 2012; ZMBN 127329 (1 spec. used for DNA sequencing, SPH281), Mørebanken, 62°45.5'N, 5°31.56'E, 91 m, 04 Oct 2012; ZMBN 127330 (1 spec. used for DNA sequencing SPH282), Mørebanken, 62°45.5'N, 5°31.56'E, 91 m, 04 Oct 2012; ZMBN 129499 (1 spec. on SEM stub), Mørebanken, 62°45.5'N, 5°31.56'E, 91 m, 04 Oct 2012. Kattegat: NHMD 302862 (1 spec.), Kattegat, Samsø, NW of Bosserne, 23-26 m, 18 Jul 1969; NHMD 302861 (1 spec.), Kattegat, Samsø, NW Møgelskår, Nordby, 14 Jul 1979.

Diagnosis.

Body short and ellipsoid. Prostomial appendages digitiform, smooth, longer than wide. Palps and lateral antennae with basal spurs or basal papillae, the later with 3-4 spurs. Median antenna as long as or slightly shorter than other head appendages. Antenniform papillae absent. Eight to nine longitudinal rows of spherical and sessile macrotubercles in one transverse row per segment. 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, projecting well beyond acicular lobe; four spherical parapodial papillae. Compound chaetae with me dium length blades (6-7 times as long as wide), showing little dorso-ventral gradation; unidentate, finely serrated.

Re-description of NEA material.

Measurements and general morphology. Body ellipsoid, with rounded anterior and posterior ends, with convex dorsal surface and slightly flat ventrum; cross section almost circular (Fig. 24A). Segmentation inconspicuous and pigmentation absent. Measuring 1.3-2.2 mm in length and near 0.5 mm wide; with 10-18 chaetigers.

Head. Prostomium fused to first segment. Prostomial appendages including palps and lateral antennae digitiform, similar in shape and size (Fig. 24B). Palps and lateral antennae with 3-4 basal papillae or spurs (Fig. 24C, D). Median antenna shorter than lateral appendages, or similar to other rounded prostomial papillae, without spurs. Tentacular cirri, similar in size and shape to median antenna (Fig. 24C).

Tubercles. Dorsal macrotubercles, sessile, spherical, smooth. Arranged in 8-9 longitudinal rows from second chaetiger to posterior segments, and one transverse dorsal row per segment (Fig. 24A). All macrotubercles similar in size. Additional spherical dorsal papillae arranged in two or three irregular transverse rows, ca. 20 papillae in mid-body segments (Figs 23C, 24A). Ventral papillae, similar to dorsal in shape and size, arranged in three transverse rows per segment (Figs 23D, 24A).

Parapodia. Parapodia conical, as long as wide. Ventral cirri digitiform. Acicular lobe similar or slightly shorter, similar in shape and size to parapodial papillae. Four parapodial papillae, two dorsal and two posterior, one behind the chaetal fascicle and another one closer to the base (Figs 5T, 24 F–I).

Chaetae. Five to seven compound chaetae on each parapodium, with fine and medium size blades (ca. 5-8 times as long as wide), unidentate, finely serrated (Fig. 24 F–H, K, L). A single straight acicula per parapodium.

Pygidium. Pygidium with paired anal cirri resembling macrotubercles and medio-ventral digitiform anal papilla.

Internal features. Two dark eyes visible dorsally inside the head. Pharynx extending over two chaetigers.

Reproductive features. Sexual structures between parapodia of chaetigers 8 and 9. They resemble a large ventral cirrus or a hemispherical knob (Fig. 24A, H, J).

Remarks.

This species has been widely recorded across the North and Baltic seas ( Hartmann-Schröder 1996) but giving the similarity with other species also present in the area these records require revisions. Other similar species reported from European waters are Sphaerodoridium cf. minutum (Webster & Benedict, 1887) (see below) that bears 10-14 stalked macrotubercles per segment. One of the diagnostic features of this species is the presence of spurs in palps and lateral antennae. These are only clearly recognised in specimens with a relaxed head and appendages (e.g., Fig. 24C, D) but are not obvious on specimens with contracted anterior end (e.g., Fig. 24B)

Distribution.

New records for the Barents Sea, Norwegian Sea, and Kattegat. Reported in the North and Baltic seas ( Hartmann-Schröder 1996).

Habitat.

Sandy and muddy sediments, 6-200 m ( Hartmann-Schröder 1996, present study).