Nephtys assimilis Örsted, 1843

Ravara, Ascensão, Cunha, Marina R. & Pleijel, Fredrik, 2010, Nephtyidae (Annelida, Polychaeta) from southern Europe 2682, Zootaxa 2682 (1), pp. 1-68 : 30-34

Nephtys assimilis Örsted, 1843

Figures 10 , 11

Nephthys assimilis Örsted, 1843a: 33 , pl. VI, figs. 93 and 100; Malmgren 1865: 105, pl. XII, fig. 19; not Treadwell 1914:

192; not Berkeley 1924: 290; not Hartman 1940: 239, pl. 39, figs. 87–88. Nephtys assimilis Rainer 1989: 877 , fig. 1A–E; Rainer 1991: 66, fig. 2A; Hartmann-Schröder 1996: 218, fig. 94;

Böggemann 1997: 80, fig. 53; Dnestrovskaya and Jirkov 2001: 195,1 fig; Laborda 2004: 396, fig. 146A, B.? Nephtys cuvieri Quatrefages, 1865: 421 .? Nephthys assimilis Malm 1874: 78 . Nephthys hombergii Saint-Joseph 1894: 3 , pl. 1, figs. 1–13 (partim) (not Savigny in Lamarck, 1818). Nephthys hombergi Augener 1913: 197 (partim). Nephtys hombergii Kirkegaard 1969: 47 (partim); Hartmann-Schröder 1971: 215, fig. 70a, b (partim); Hartmann-

Schröder 1974: 206 (partim); Hartmann-Schröder 1977: 88 (partim); Hartmann-Schröder 1981: 31 (partim);

Hartmann-Schröder 1982: 10 (partim). Nephtys scolopendroides Michaelsen 1896: 57 (partim). Nephtys hombergii var. vasculosa McIntosh 1908: 21 (partim). Nephtys caeca Heinen 1911: 13 (partim). Nephtys incisa var. bilobata Heinen 1911: 25 (partim); Fauvel 1923: 370, fig. 144B. Nephthys breogani Laborda and Viéitez, 1984: 211 , figs. 2–6; Laborda 1987: 131.

Type locality. Hellebaek , Øresund, Denmark. (neotype from off Hornbaek Bay, coll. 05.07.1963, stns 225– 227, 18 m, designated by Rainer 1989) .

Material examined. Atlantic Ocean. Kattegat, Denmark, Hornbaek Bay: Jul 1963, 1 complete spm, neotype (ZMUC-Pol-1470). North Sea, Scotland, Monterose Bay: 1870, 3 complete and 1 incomplete spms ( NHM 1921.5.1.810-813 as N. hombergii var. vasculosa , syntypes). Portugal, off Aveiro: cruise Aveiro 94, RV Côte d’Aquitaine, 40º41.125’N, 8º46.303’W, 13.6 m, grab, Jul 1994, 3 incomplete spms ( DBUA 00060-02 ) ; 40º39.631’N, 8º45.705’W, 11.2 m, grab, Jul 1994 ,1 complete and 1 incomplete spms ( DBUA 00060-03 ) ; 40º39.600’N, 8º45.714’W, 11.1 m, grab, Jul 1994, 1 complete and 2 incomplete spms ( DBUA 00060-04 ) ; 40º38.626’N, 8º48.636’W, 21.9 m, grab, Jul 1994, 3 incomplete spms ( DBUA 00060-05 ) ; 40º38.533’N, 8º48.235’W, 48.2 m, grab, Jul 1994, 1 incomplete spm ( DBUA 00060-06 ) ; 40º37.683’N, 8º47.575’W, 18.0 m, grab, Jul 1994, 1 incomplete spm, ( DBUA 00060-07 ) ; 40º37.657’N, 8º50.151’W, 33.1 m, grab, Jul 1994, 2 complete and 1 incomplete spms ( DBUA 00060-08 ) ; cruise Aveiro 95, RV Côte d’Aquitaine , 40º43.489’N, 8º45.210’W, 12.7 m, grab, 27 Jul 1995, 1 complete and 5 incomplete spms ( DBUA 00060-01 ) ; 40º33.468’N, 8º48.232’W, 28.7 m, grab, 28 Jul 1995, 3 incomplete spms ( DBUA 00060-09 ) ; Figueira da Foz , mouth of Mondego estuary : 40º08’43.352”N, 08º52’06.218”W, 8.5 m, 7 Dec 2005, 2 complete and 1 incomplete spms (in collection of M. Pardal); off Cascais: 38º39’– 38º42’N, 9º25’– 9º30’W, 40 m, Jul 2005, 3 complete and 2 incomplete spms ( DBUA 00842-01 ) and 1 complete spm ( MB36000105 ) ; Jan 2006, 7 complete and 2 incomplete spms ( DBUA 01054-01 ) ; Lagos : 37º06.824’N, 08º38.500’W, 8 m, Apr 2006, 1 complete spm ( DBUA 01061-01 ) .

Mediterranean Sea. Naples: 1 complete spm ( NHM 1919.11.6.31-33 as N. hombergii ).

Atlantic/Indian Ocean. South Africa: South African Collection of Prof. J. H. Day, Nov 1960, 1 incomplete spm ( NHM 1961.9.71/79 as N. hombergii ); 4 incomplete spms ( NHM 1961.19.76/81 as N. hombergii ).

Description. Examined specimens up to 124 mm long for up to 117 chaetigers. See Fig. 11 for length and width measurements. Body slightly wider anteriorly, gradually tapering from median region to pygidium. Colour in ethanol cream; some larger specimens brownish mid-dorsally on anterior segments, with green pigment near prostomium and anteriormost segments; prostomium with brown pigment spot medially in anterior region; chaetae amber in anterior chaetigers, darker in posterior ones; aciculae amber with dark tips, surrounded by red pigment on anterior segments. One pair of eyes visible in smaller specimens at level of chaetiger 2. Pharynx distal region with 10 pairs of terminal bifid papillae, separated by dorsal and ventral gap ( Fig. 10A ); middorsal papilla cirriform, long ( Fig. 11D ); midventral papilla if present, small, similar in size and shape to distalmost subterminal papillae; subdistal region with 20–22 rows of 2–5 conical subterminal papillae (papillae of lateral rows slightly longer than dorsal or ventral ones), extending over 1/3 length of pharynx; proximal region smooth. Jaws conical, slightly incised at base ( Fig. 10B ). Prostomium subrectangular, anterior margin slightly convex, posterior margin V-shaped extending over first chaetiger; antennae conical; palps conical with bulbous bases, subequal in length to antennae, inserted ventrolaterally on prostomium. Nuchal organs rounded, conspicuous. Parapodia biramous; interramal space “U-shaped”, posteriorly with ciliation in raised pads. Parapodia of chaetiger 1 slightly smaller than subsequent ones, directed anteriorly, parallel to prostomium; notopodial acicular lobes conical; pre- and postchaetal lamellae well developed but not extending beyond acicular lobe, rounded; neuropodial pre- and postchaetal lamellae forming a cylinder covering the acicular lobes; dorsal cirri poorly developed, rounded ( Fig. 11C ); ventral cirri conical, with broad base and tapered distally. Acicular lobes of anterior parapodia rounded, with low papilliform outgrowth on interramal side of aciculae ( Fig. 10C ), becoming more conical and without outgrowths posteriorly; notopodial prechaetal lamellae well developed but not extending beyond acicular lobes, rounded in anterior parapodia, bilobed in following ones, postchaetal lamellae extending beyond acicular lobes (much larger in anterior parapodia), rounded; neuropodial prechaetal lamellae not extending beyond acicular lobes, unequally bilobed, with dorsal lobe much larger than ventral one, postchaetal lamellae extending well beyond acicular lobes, asymmetrically triangular in anterior parapodia, broadly rounded in following ones, directed dorsally, with internal vascular structure starting around chaetiger 13 (absent in posterior parapodia); dorsal cirri cirriform; ventral cirri conical ( Fig. 10C–E ). Branchiae recurved, cirriform, lightly ciliated, with conspicuous conical basal projection; present from chaetiger 4 to near posterior end; occupies half of interramal space when fully developed. Chaetae short, of three kinds: barred chaetae in preacicular position ( Fig. 10F ), finely spinulated chaetae in postacicular position ( Fig. 10G ), and capillary chaetae on neuropodia of chaetiger 1 and near interramal space of noto- and neuropodia of other chaetigers. One acicula per ramus, posterior ones with curved tips ( Fig. 10H ).

Remarks. Nephtys assimilis was originally described by Örsted (1843a), but the type material was appearently lost ( Rainer 1989). Consequently, Rainer (1989) designated a neotype from a locality close to the original one. The original description did not mention the vascular structure of the neuropodial postchaetal lamellae or the raised ciliated pads in the interramal region of midbody and posterior chaetigers. Thus Laborda and Viéitez (1984) described N. breogani as a new species from NE Spain using these features to separate the two species. Rainer (1989) re-examined N. breogani and synonymized it with N. assimilis . Specimens of N. assimilis have been frequently identified as N. hombergii (especially in older studies), due to their close morphological similarity. Both species have bilobed prechaetal lamellae, a papiliform outgrowth on the acicular lobes, very large neuropodial postchaetal lamellae, branchiae starting on chaetiger 4 and a similar pattern in the pharynx papillae. Furthermore, they have overlapping geographical distributions and are often collected simpatrically or even in the same sample. However, in N. hombergii the neuropodial postchaetal lamellae are narrower and do not have internal vascularization, the papiliform outgrowth of the acicular lobes are much more developed and the interramal region of midbody chaetigers have low ciliated papillae instead of prominent raised pads. Differences between other morphologically close related species with similar geographical distribution are summarized in Table 5. Nephtys hystricis and N. kersivalensis are smaller species ( Figs. 11 , 19 ) with noto- and neuropodial postchaetal lamellae similar in size, acicular lobes without outgrowths, interramal space of parapodia without raised papillae, and pharynx middorsal papillae much longer than the other subterminal papillae. Furthermore N. hystricis has branchiae from chaetigers 5–7 which are absent in posterior chaetigers. Nephtys hystricis usually occurs at deeper waters, while N. kersivalensis occurs frequently in shallow waters, together with N. hombergii and N. assimilis .

Distribution. Atlantic Ocean (W Baltic, Oresund, Skagerrak, North Sea, English Channel, NW Spain, Portugal, W Africa; Mexico); Mediterranean Sea ( Rainer 1989, 1991; Laborda 2004).

Habitat. Sandy to muddy sediments, most abundant in muddy sand with strong tidal currents, from the intertidal to 100 m depth ( Rainer 1989, 1991; Laborda 2004).

kersivalensis .

Figures

FIGURE 10. Nephtys assimilis. A. Pharynx, prostomium and first chaetiger, dorsal view. B. Jaw. C. Left parapodium of chaetiger 10, anterior view. D. Left parapodium of chaetiger 40, anterior view. E. Left parapodium of chaetiger 80, anterior view. F. Preacicular chaeta from chaetiger 40. G. Postacicular chaeta from chaetiger 40. H. Acicula from chaetiger 40.

FIGURE 11. Relationships between: A. Number of segments and body length. B. Body length and body width. C. Length of ventral cirri (VC) and dorsal cirri (DC) of chaetiger 1. D. Length of pharynx distalmost subterminal papillae and middorsal papilla. Nephtys assimilis. × N. hombergii. N. kersivalensis.

FIGURE 19. Relationships between: A. Number of segments and body length. B. Body length and body width. C. Length of ventral cirri (VC) and dorsal cirri (DC) of chaetiger 1. D. Length of pharynx distalmost subterminal papillae and middorsal papilla. Nephtys hystricis. N. incisa.