Euritmia nordica Capa & Bakken

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 : 26-28

Euritmia nordica Capa & Bakken sp. n. Figs 4 I–J, 5E, 10

Type locality.

Greenland Sea, off eastern Greenland in Denmark Strait, 321 m.

Material examined.

Holotype: SMF 25281, Greenland, Denmark Strait, 67°38.77'N, 26°44.78'W, 321 m, 14 Sep 2011. Paratype: ZMBN 127261 (1 spec. on SEM stub), Norwegian Sea, 63°2.232'N, 4°41.34'E, 760 m, 30 Sep 2013.

Diagnosis.

Body short and ellipsoid, up to 1.5 mm long. Head with short appendages, without spurs or basal papillae; antenniform papillae absent. Dorsum with sessile spherical papillae arranged in three transverse rows, and up to 18, per segment. Ventrum with a pair of papillae near each parapodial bases and two additional longitudinal rows. Parapodia without papillae; digitiform acicular lobe and spherical ventral cirrus. Six or seven simple chaetae with serrated edges, enlarged subdistally, with a distal spine and filament in opposite directions.

Description.

Measurements and general morphology. Holotype 0.9 mm long, 0.5 mm wide, with 12 chaetigers. Body ellipsoid, with strongly convex dorsum and flattened ventrum (Fig. 10A). Epithelium with transverse wrinkles, segmentation not noticeable (Fig. 10A, D). Pigmentation absent on preserved material.

Head. Head fused to first chaetiger (Fig. 10B, C). Prostomial appendages digitate, with a pair of palps, a pair of lateral antennae slightly longer than palps, a median antenna half as long as lateral antennae (Fig. 10B, C). Dorsal antenniform papillae absent or not conspicuous. Few small hemispherical papillae scattered on head surface, ca. 5-6 confined among palps and antennae. Tentacular cirri, digitate, shorter than palps, similar in size and shape to median antenna (Fig. 10C). Eyes not observed.

Tubercles. Dorsum with about eight rows of similar sized and ellipsoid papillae, in three irregular transverse rows of per segment (Fig. 10A, D–F); adding up to ca. 15-18 per segment on mid-body chaetigers (Fig. 4I). Ventrum with fewer spherical papillae, arranged at base of parapodia with two parallel papillae (Fig. 10B, F), and additional two longitudinal rows (10B, C), in total ca. six papillae per segment (Figs 4J, 10B, C). Mid-dorsal body bare of papillae (Fig. 10B).

Parapodia. Parapodia conical, as long as wide in all chaetigers (Fig. 10F, H), similar throughout. Acicular lobe digitate longer than ventral cirri; ventral cirri ellipsoid (Fig. 10 F–H). Most segments with no additional papillae or parapodial appendages, exceptionally one or two small parapodial papillae near the base of ventral cirrus (Fig. 5E, 10F).

Chaetae. Large, recurved hooks in the first chaetiger absent. All parapodia with 6-7 simple chaetae; blade serrated on cutting edge and a recurved distal tip (Fig. 10C, G–K).

Pygidium. Pygidium with two small and spherical tubercles and a small digitiform ventral cirrus.

Internal features. A pair of rounded eyes observed under the epithelium, in the head. Muscular pharynx not observed.

Reproductive features. Two large eggs are visible in the coelom of the holotype.

Variation.

Paratype 1.5 mm long, 0.6 mm wide, with 19 chaetigers (anterior end on SEM stub). Papillae on ventrum in three transverse rows per segment, positioned as two parallel at base of parapodia and one towards mid-body (Fig. 10B). Parapodia are smooth in most chaetigers of both holo- and paratype but variation has been observed, with one parapodium with one small papilla and the following with two papillae, located at the base of the ventral cirrus (Fig. 10F). Sexual structures (unknown gender) observed as inflated ventral cirri with pore openings in first chaetiger in the paratype (Figs 4J, 10G).

Etymology.

The epithet of this species, nordica , refers to the geographical region where this species has currently been found. Nordic or The North gathers the north-western European countries, including Scandinavia and Fennoscandia.

Remarks.

Euritmia nordica sp. n. is characterized by a unique combination of features: dorsum provided with similar sized, ellipsoid tubercles arranged in three transverse rows per segment, leaving a conspicuous longitudinal bare mid-dorsal area; two longitudinal zig-zag rows of small and ellipsoid papillae on ventrum (with ca. six papillae per segment); parapodia lacking papillae (with some exceptions). Euritmia nordica sp. n. resembles E. carolensis due to the arrangement of dorsal papillae in three transverse rows per segment and the absence of parapodial papillae. Differences between members of these two species rely on size and number of dorsal epithelial papillae, larger and more abundant in E. carolensis (covering most of the dorsum, while in E. nordica sp. n. the dorsum is mainly smooth); chaetae in E. nordica sp. n. are broader subdistally and recurved at the distal end, while E. carolensis has a slim appearance and a straighter distal tip. Moreover, E. nordica sp. n. presents an inflated cirrus in the first chaetiger, with pore openings on its base (Fig. 10G), similar to what was described in Sphaerodoropsis halldori , on chaetiger 6 of males ( Moreira and Parapar 2012). This is the first time that potentially sexual structures are described in members of Euritmia , and therefore it is unknown if the attributes described herein are species specific.

Euritmia nordica sp. n. is distinguished from E. bipapillata , described from Alaska, in the absence of parapodial papillae, while E. bipapillata has one papilla on anterior surface of parapodia (Kudenov, 1987). Euritmia hamulisetosa from southern Spain has dorsal papillae in four transverse rows per segment and parapodial papillae ( Sardá-Borroy 1987), unlike E. nordica sp. n. with three transverse rows of dorsal papillae and smooth parapodia. Euritmia capense , from South Africa, bears two transverse rows of papillae per segment and five parapodial papillae ( Day 1963).

Distribution.

The species is known from Denmark Strait, East of Greenland (holotype), and the Norwegian Sea.

Habitat.

The specimens were found in soft bottom, in areas influenced with cold water (approximately 0 °C). The paratype was found inside the tube of an undescribed species of Ampharete .