Nereis lunulata Ehlers, 1901

Salazar-Vallejo, Sergio I., León-González, Jesús Angel De & Conde-Vela, Víctor M., 2021, Revision of the species confused with “ Nereis falsa ” de Quatrefages, 1866 (Annelida, Nereididae), European Journal of Taxonomy 779, pp. 1-70 : 38-43

Nereis lunulata Ehlers, 1901 stat. nov.

Figs 14–15

Nereis pelagica var. lunulata Ehlers, 1901a: 259 (nomen nudum).

Nereis pelagica var. lunulata – Ehlers 1901b: 103–104, pl. 12 figs 12–17. — Wesenberg-Lund 1962: 77 (records by Ehlers).

Nereis pelagica lunulata – Hartmann-Schröder 1962: 407 (key). — Hartman 1964: 101, pl. 31 fig. 1 (image from Ehlers 1901b).

Nereis falsa – Fauvel 1941: 279. — Wesenberg-Lund 1962: 77 (records by Fauvel; both non de Quatrefages, 1866).

Diagnosis

Nereis with posterior eyes completely exposed; tentacular belt 1.5 × as long as first chaetiger; tentacular cirri short, reaching chaetigers 4–5; jaws with 6–7 teeth; pharyngeal area II with 16 paragnaths in oblique rows, areas VII–VIII with 46 paragnaths in 3 transverse rows; anterior chaetigers with notopodial ligules digitate, longer than wide; ventral ligules in median and posterior chaetigers reaching tip of neuracicular ligules.

Material examined

Syntype CHILE • 1 spec.; Patagonia , Charrua Port; 53º03´S, 073º56´W; stn 1071; 26 Mar. 1896; Nordenskjölds Expedition till Eldslandet och Patagonien 1895–96 leg.; rocky shore, low tide; SMNH Type 513 .

Other material

CHILE • 2 specs (both complete, regenerating posterior end); Punta Arenas , “No. 25, T 59”; 53°10′ S, 70°56′ W; M. Lebrun leg.; MNHN 83-T52 .

Description

Syntype BODY. Complete, 26 mm long, 1.5 mm wide including parapodia, with 70 chaetigers. Dorsum pale brown, anterior chaetigers with two semicircular lateral spots per segment, remaining segments pale. Prostomium with brown pigmentation laterally, close to palps.

PROSTOMIUM. Longer than wide, subpyriform, dorsal groove present. Eyes black, in trapezoidal arrangement, anterior eyes slightly longer than posterior ones. Antennae half as long as prostomium, not reaching tips of palpostyles, with a small gap between them. Palpophores globose, 2 × as long as wide, palpostyles rounded ( Fig. 14A ).

TENTACULAR BELT. 1.5× as long as first chaetiger, anterior margin not covering posterior eyes. Tentacular cirri smooth, longest pair reaching anterior margin of chaetiger 5 ( Fig. 14A ).

PHARYNX. Not everted, observed by dissection. Jaws brown with 6–7 teeth. Paragnath formula: I: 2 in tandem; II: 16 in 3 oblique rows; III: 36 in oval group; IV: 20 in a crescent-shaped group; V: 0; VI: 4– 4 in diamond; VII–VIII: 46 in three bands, basal band with larger paragnaths.

PATTERN OF PARAPODIAL LIGULES. Anterior and median chaetigers with ligules massive, blunt, round, slightly longer than wide, posterior chaetigers with ligules conical, blunt, as long as wide, or slightly longer than wide in posterior chaetigers; ventral ligule reaching tip of neuracicular ligules.

CHAETIGERS 1–2. With neuraciculae only, with both noto- and neuraciculae thereafter.

ANTERIOR PARAPODIA ( Fig. 14B ). With dorsal cirrus inserted medially, longer than ventral ones, dorsal cirrus about 3× as long as dorsal ligule. Dorsal and median ligules subequal; dorsal one subconical, blunt, median ligule rounded. Neuracicular and ventral ligules subequal; neuracicular one subconical, ventral one digitiform, longer than ventral cirrus. Notochaetae 6 homogomph spinigers. Supracicular neurochaetae: 6 homogomph spinigers and 2 heterogomph falcigers, blades 6× as long as wide;

subacicular neurochaetae: 2 heterogomph spinigers and 5 heterogomph falcigers, blades 6× as long as wide.

MEDIAN PARAPODIA ( Fig. 14C ). With dorsal cirrus inserted medially, longer than ventral one, dorsal cirrus 2.8 × as long as dorsal ligule. Dorsal and median ligules subequal, subconical, 1.5× as long as neuracicular ligule. Neuracicular ligule digitiform, slightly longer than ventral ligule; ventral ligule digitiform, longer than ventral cirrus. Notochaetae: 2 homogomph spinigers and 1 homogomph falciger with blade 5.6 × as long as wide, distal tooth incurved and fused to blade, heavily serrated ( Fig. 14E ). Supracicular neurochaetae: 5 heterogomph spinigers and 1 heterogomph falciger, blades 2× as long as wide, inner edge spinulose, distal tooth incurved, fused to blade ( Fig. 5F ); subacicular neurochaetae: 2 heterogomph falcigers with blades barely 2× as long as wide, distal tooth incurved, fused to blade.

POSTERIOR PARAPODIA ( Fig. 14D ). With dorsal cirrus inserted medially, 2.5× as long as ventral one, about 3 × as long as dorsal ligule. Dorsal ligule subconical, slightly longer than median ligule; median ligule subconical, 2× as long as neuracicular ligule. Neuracicular ligule subconical; ventral ligule digitiform, clearly longer than neuracicular ligule, 2× as long as ventral cirrus. Notochaetae: 3 homogomph spinigers and 1 homogomph falciger, similar to those of middle parapodia. Supracicular neurochaetae: 5 heterogomph spinigers and 1 heterogomph falciger, similar to those of middle parapodia; subacicular neurochaetae: 1 heterogomph spinigers and 3 heterogomph falcigers, similar to those of median chaetigers ( Fig. 14E ).

POSTERIOR REGION. Tapered. Pygidium with anus terminal; anal cirri as long as last 5 chaetigers.

Non-type specimens

BODY. Specimens complete (MNHN 83-T52), damaged, slightly macerated (soft, fluffy), integument separated on cephalic appendages ( Fig. 15A ), most chaetae broken or softened. Body 24–26 mm long, 1.8–2.0 mm wide, with 65–80 chaetigers. Body pale, almost colorless, subcylindrical along anterior and medial body thirds, slightly depressed along posterior third.

PROSTOMIUM. 2× as long as wide, dorsal groove present. Eyes blackish, of similar size, anterior ones oval, directed anteroventrally,diameter ⅙–⅐ of prostomial width, slightly more separated than posterior eyes ( Fig. 6B ). Antennae half as long as prostomium, without gap between them, tips reaching palpostyle tips. Palpophores 2 × as long as wide; palpostyles longer than wide (left) or rounded (right).

TENTACULAR BELT. 2 × as long as first chaetiger; anterior margin projected anteriorly (less pronounced in smaller specimen), with an unpigmented irregular area along its right side. Tentacular cirri smooth, integument detached along almost all their length, longest ones reaching chaetigers 3–4.

PHARYNX. Not everted, observed by dissection of largest specimen. Jaws with 7 denticles. Paragnath formula: I: 1; II: 17–18; III: about 36 in oval group; IV: 26–28 in oval groups; V: 0; VI: 4 in diamond; VII–VIII: 2–3 rows in of small and large paragnaths in two bands.

PATTERN OF PARAPODIAL LIGULES. Anterior and median chaetigers with ligules blunt, slightly longer than wide, becoming blunt triangular, slightly longer than wide in posterior chaetigers. Ventral ligules as long as neuracicular ligules, tapered.

CHAETIGERS 1–2. With neuraciculae only ( Fig. 15D ); with both noto- and neuraciculae thereafter. Dorsal cirrus slightly longer and about as wide as ventral cirrus, 1.5× as long as dorsal and ventral ligules. Dorsal ligule wider, as long as ventral one, 2 × as long as neuracicular ligule. Neuracicular ligule subconical, blunt. Supracicular neurochaetae: 4 homogomph spinigers and 3 heterogomph falcigers, blades spinulose, 6× as long as wide, tips incurved; subacicular neurochaetae: 12 heterogomph chaetae (only 2 spiniger and 1 twisted falciger blade remaining).

MEDIAN PARAPODIA ( Fig. 15E ). With dorsal cirrus 1.5× as long as dorsal ligule, slightly longer and wider than ventral cirri, both with sessile ciliates. Dorsal ligules 1.5 × as wide as long, blunt; median ligule rounded, slightly longer than neuracicular ligule, glandular areas unpigmented, extended along ligular bases. Neuracicular ligule digitiform, 2× as long as wide, slightly longer than ventral ligule; ventral ligule digitiform, 3× as long as wide, longer than ventral cirrus. Notochaetae 8 homogomph spinigers, without falcigers. Supracicular neurochaetae: 5 homogomph spinigers and 3 heterogomph falcigers with blades spinulose, 2–3 × as long as wide, distal tooth incurved, fused to blade; subacicular neurochaetae: 3 heterogomph spinigers and 7 heterogomph falcigers with blades spinulose, 2–3 × as long as wide, distal tooth incurved, fused to blade.

POSTERIOR REGION ( Fig. 15F ). With dorsal and ventral cirri 6–8× as long as wide, dorsal cirrus 1.2× as long as dorsal ligule, often with several sessile ciliates transforming their appearance into medially swollen, ventral cirrus shorter than ventral ligule, some with sessile ciliates ( Fig. 15F , inset). Dorsal and median ligules subconical to digitate, about as long as wide, 1.5× as long as neuracicular ligule, glandular areas unpigmented, extended along ligular bases; dorsal one slightly wider than long, median one slightly longer than wide. Neuracicular ligule subconical, blunt, as long as wide, as long as ventral ligule; ventral ligule digitiform, slightly longer than wide. Notochaetae 6 homogomph spinigers, falcigers absent. Supracicular neurochaetae: 2 homogomph spinigers and 2 heterogomph falcigers, blades missing; subacicular neurochaetae: 2 heterogomph spinigers and 8 heterogomph falcigers with blades spinulose, 3× as long as wide, distal tooth incurved, fused to blade.

SUBTERMINAL CHAETIGERS ( Fig. 15G ). With dorsal cirrus slightly longer than dorsal ligule, about 2× as long as ventral cirrus. Dorsal ligule subconical, tapered, slightly longer than wide, 1.5 × as long as median ligule; median ligule subconical, 1.5× as long as wide, 2 × as long as neuracicular ligule. Neuracicular ligule subconical, about as wide as long, as long as ventral ligule; ventral ligule digitiform, slightly longer than wide, 3 × as long as ventral cirrus. Notochaetae: 3 homogomph spinigers and 1 homogomph falciger with blade distorted, bent dorsally, spinulose, distal tooth incurved, tendon visible ( Fig. 15G , inset). Supracicular neurochaetae: 4 homogomph spinigers and 6 heterogomph falcigers with blades spinulose, 1–2× as long as wide, distal tooth barely incurved, tendon visible. Subacicular neurochaetae: 2 homogomph spinigers and 4 heterogomph falcigers with blades spinose, 2× as long as wide, distal tooth incurved, tendon not seen.

POSTERIOR REGION. Tapered into a blunt cone. Pygidium regenerating, almost completed in smallest specimen, anus terminal, anal cirri as long as last 5–6 chaetigers.

Remarks

Nereis pelagica lunulata Ehlers, 1901 differs from the stem species, N. pelagica Linnaeus, 1758 as defined by Chambers & Garwood (1992: 16, figs 17–18), because its ventral ligules are tapered in posterior chaetigers, instead of being blunt, lobate, and because its notopodial homogomph falcigers are spinulose, with a barely defined tendon, as opposed to dentate or smooth in N. pelagica . Consequently, it is herein elevated in rank from subspecies to species.

As indicated in the key below, because of the presence of 2–3 transverse rows of paragnaths in pharyngeal areas VII–VIII, and by having digitate notopodial ligules in anterior chaetigers, N. lunulata stat. nov. resembles N. splendida Grube, 1840 , from the Mediterranean Sea, and “ N. falsa ” sensu Liñero-Arana & Reyes-Vásquez (1979) , from the southeastern Caribbean. These three species differ by the relative size of ventral ligules and by the number of paragnaths in pharyngeal area II. In N. lunulata stat. nov., ventral ligules are as long as neuracicular ligules, and area II has 16 paragnaths, whereas N. splendida and “ N. falsa ” have ventral ligules longer than neuracicular ligules, and there are 22 paragnaths in area II in the former, and about 30 in the latter.

It is worth noting that the presence of some unidentified, solitary peritrich ciliates on the parapodial cirri modifies their appearance, making them look wider, and the surface also becomes more irregular, i.e., it is not as smooth as in other similar species.

Distribution

Souhern Chile, from Punta Arenas to Tierra del Fuego, in shallow water.

Figures

Fig. 14. Nereis lunulata Ehlers, 1901 stat. nov., syntype (SMNH Type 513). A. Anterior region, dorsal view. B. Chaetiger 11, right parapodium, anterior view.C. Chaetiger 30, right parapodium, anterior view. D. Chaetiger 52, right parapodium, posterior view. E. Chaetiger 30, notopodial homogomph falciger. F. Same, neuropodial heterogomph falciger of infracicular fascicle.

Fig. 15. Nereis lunulata Ehlers, 1901 stat. nov., non-type specimen (MNHN 83-T52). A. Anterior region, dorsal view. B. Anterior end, dorsal view. C. Anterior end, ventral view. D. Chaetiger 2, left parapodim, anterior view. E. Chaetiger 14, left parapodium, anterior view. F. Chaetiger 30, left parapodium, posterior view (inset: close-up of dorsal cirrus). G. Chaetiger 56, left parapodium, anterior view (inset: homogomph falciger).

Fig. 5. Nereis splendida Grube, 1840, non-type, female epitoke (MNHN A83), after Shirlastain-A staining. A. Anterior region, dorsal view. B. Anterior end, ventral view. C. Posterior region, dorsal view. D. Chaetiger 2, right parapodium, anterior view. E. Chaetiger 15, right parapodium, anterior view. F. Chaetiger 30, right parapodium, anterior view. G. Chaetiger 73, right parapodium, anterior view (chaetae omitted).

Fig. 6. Nereis splendida Grube, 1840, non-type, atokous specimens. A–F. MNHN 423-531. A. Anterior region, dorsal view. B. Anterior end, dorsal view. C. Chaetiger 2, right parapodium, anterior view. D. Chaetiger 15, right parapodium, anterior view. E. Chaetiger 30, right parapodium, anterior view. F. Chaetiger 55, right parapodium, anterior view (inset: homogomph falciger tip). G–H. MNHN 495-1. G. Anterior region, dorsal view. H. Posterior region, left lateral view. I. Another specimen (MNHN 423- 531), chaetiger 30, right parapodium, homogomph falciger tip.