Sphaerephesia multichaeta Capa, Moreira & Parapar

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 : 48-51

Sphaerephesia multichaeta Capa, Moreira & Parapar sp. n. Figs 5N, 15I, J, 18, 19

Type locality.

Borgenfjorden, Trondheimsfjord, 25 m.

Material examined.

Holotype: NTNU VM 24856, Norway, Trondheimsfjord, Borgenfjorden, 63°53'N, 11°20'E, 25 m, 14 July 1970. Paratypes (10 specs): Norwegian Sea, Trondheimsfjord, Borgenfjorden NTNU-VM 24809, 63°53'N11°20'E, 10 m, 04 May 1971 (1 spec. on SEM stub); NTNU-VM 24810 (2 specs, 1 on SEM stub), 10 m, 11 Aug 1970; NTNU-VM 24852 (1 spec.), 10 m, 02 Jun 1971; NTNU-VM 24854 (1 spec.), 20 m, 11 Aug 1970; NTNU-VM 24851 (1 spec.), 10 m, 13 May 1970; NTNU-VM 24853 (1 spec.), 15 m, 06 Oct 1970; NTNU-VM 24855 (1 spec.), 20 m, 06 Oct 1970; NTNU-VM 24857 (1 spec.), 25 m, 16 Jun 1970; NTNU-VM 24858 (1 spec.), 25 m, 09 Feb 1971; NTNU-VM 24859 (1 spec.), 25 m, 02 June1971.

Additional material.

(1 spec.) Skagerrak ZMH P13351, 58°07'N, 10°34'E, 196m, (1 spec. on SEM stub).

Diagnosis.

Body ellipsoid, with convex dorsum and slightly flattened dorsoventrally, up to 1 mm long. Palps and antennae smooth, lacking spurs. Four longitudinal rows of dorsal macrotubercles, in a single transverse row per segment. Macrotubercles sessile, spherical to pear-shaped. Additional minute spherical papillae scattered on dorsum (approx. seven transverse rows with ca. 100 low papillae per segment), often inconspicuous. Ventrum with even smaller papillae in four transverse rows per segment, often inconspicuous. Parapodia with 20-40 spherical papillae. Acicular lobe from segment 1, small and rounded. Compound chaetae, numerous (up to 40 per fascicle), with blades slightly decreasing in length dorso-ventrally (3-8 times their width), unidentate, with finely serrated edge.

Description.

Measurements and general morphology. Holotype with ellipsoid body, 0.7 mm long, 0.1 mm wide and with 27 segments; with blunt ends, with a convex dorsum and flattened ventrum. Segmentation not conspicuous. Pale, with brownish granules in some macrotubercles, in fixed material.

Head. Head fused to first chaetiger (Fig. 18 A–C). Palps and lateral antennae conical, 2-3 times longer than wide, wrinkled, and lacking spurs or basal papilla (Fig. 18 A–C). Median antenna conical, slightly shorter than lateral antennae (Fig. 18 A–C). Antenniform papillae absent (Fig. 18 A–C). Head papillae rounded, apparently randomly arranged. Tentacular cirri conical, similar to lateral antenna (Fig. 18 A–C).

Tubercles. Medium-sized dorsal macrotubercles arranged in four longitudinal rows, one transverse row per segment, with exception of first chaetiger with only two macrotubercles (Fig. 18 A–C). Macrotubercles sessile, spherical and smooth in anterior segments, and pear-shaped in posterior segments (Fig. 18 A–E). Distance between dorsalmost rows is larger than these to lateralmost longitudinal rows. Additional dorsal papillae, low, rounded, arranged in approximately seven irregular transverse rows per segment along dorsal surface (Figs 15I, 18D), and in four transverse rows per segment in ventrum (Figs 15J, 18F). Papillae are not conspicuous in all segments; consequently epithelium seems smooth in some parts of the body.

Parapodia. Parapodia subtriangular, with wide dorso-ventral base as long as wide at mid-body segments (Figs 18 D–H, 19A). Ventral cirri conical, small, not protruding from parapodia (Fig. 18H). Acicular lobe from chaetiger 1. Numerous (ca. 20 in mid-chaetigers) small and spherical papillae distributed randomly over parapodial surfaces (Fig. 5N).

Chaetae. All chaetae compound, with unidentate and finely serrated blades. First chaetiger with blades 7-9 times longer than wide. Midbody chaetigers with blades ranging 3-6 times longer than wide within each parapodia. Number of chaetae from 11-13 in first segment to 25-30 in mid-body segments (Figs 18 G–H, 19 B–D). One straight acicula per parapodia.

Pygidium. A pair of piriform anal cirri, similar to posterior macrotubercles and digitiform medio-ventral anal papilla (Fig. 18D, E).

Internal features. Pharynx slightly protruded though mouth in some specimens. Pharynx and internal organs not discernible.

Reproductive features. Sexual structures or genital openings not observed. Preserved specimens opaque and gametes not detected.

Variation.

Size range of material examined: 0.6-0.9 mm long, 0.08-0.15 mm wide, with 21-30 chaetigers. The holotype is somehow more inflated and elongated than the paratypes. These are more flattened dorso-ventrally and bodies seem to be more ellipsoid. This could be due to body collapse or perhaps the holotype is inflated from preservation. Head appendages are small and conical in all specimens examined; antenniform papillae not observed. Paratypes are homogenous in the general shape of the body, presence of large parapodia, small ventral cirri and presence of numerous, medium length blade falcigers. They differ in the number of epithelial papillae observed, in part probably due to the different conditions of the epithelium. We suspect the body and parapodia bear numerous small spherical papillae but these are only conspicuous in well-preserved specimens, otherwise they look almost smooth. Nuchal organs pits observed in several specimens (e.g., Fig. 18C). Sexual structures not seen.

Etymology.

The specific epithet, multichaeta (masculine), refers to the extraordinary number (multi) of bristles (chaetae, Greek origin) present in the fascicles of, at least, some specimens.

Remarks.

Sphaerephesia multichaeta sp. n. belongs to the group of spherodororids with four longitudinal rows of dorsal and macrotubercles (i.e., Sphaerephesia after the present study). It is characterised by a unique combination of features: macrotubercles at least in posterior segments are pear-shaped, parapodia bear a great number of papillae (20-40) and chaetae (20-40). Only Sphaerephesia sibuetae and S. similisetis have been reported with 20-25 chaetae per fascicle ( Fauchald 1972, Desbruyères 1980, Moreira et al. 2011). Likewise, also these two species have been reported with 20-30 parapodial papillae ( Fauchald 1972, Desbruyères 1980, Moreira et al. 2011), but these numbers do not reach those accounted in the new species. Sphaerephesia multichaeta sp. n. is distinguished from these two congeners in the chaetal morphology (with blades up to eight times as long as wide) while S. sibuetae and S. similisetis have longer blades (7-13 and 20-25 times as long as wide, respectively).

Distribution.

Most specimens were collected in the Trondheimsfjord, but also from Skagerrak.

Habitat.

Habitat soft bottom with mud, 10-25 m deep.