Nereis mezianei, Salazar-Vallejo & León-González & Conde-Vela, 2021

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 : 53-59

Nereis mezianei sp. nov.

urn:lsid:zoobank.org:act:9E0D6CE0-F754-4E19-9ACE-6C77485ADBF9

Figs 2 , 18–20

Nereis falsa – Fauvel & Rullier 1959: 162 (non de Quatrefages, 1866).

Diagnosis

Nereis with posterior eyes partially covered by anterior margin of tentacular belt; tentacular belt 1.5× as long as first chaetiger; tentacular cirri long, reaching chaetigers 7–8; pharyngeal areas VII–VIII with 5 large paragnaths in a single row; posterior chatigers with dorsal and median ligules of similar width.

Etymology

This species is named after Dr Tarik Meziane, curator of polychaetes at the Muséum national d’histoire naturelle, Paris, in recognition of his curatorial activities and especially as a means of gratitude for his long-standing support of our research activities.

Material examined

Holotype SENEGAL • atokous ♀ (without posterior region); Sénégambie , 50 km W of Abene; 12°55′30″ N, 17°33′00″ W; R/V Calypso , stn 4; depth 65–75 m; 16 May 1956; MNHN 372-4 .

Paratypes SENEGAL • 2 ♀♀ (without posterior region); same collection data as for holotype; MNHN 372-4b .

Other material

EQUATORIAL GUINEA • 1 spec. (complete, broken in two pieces, anterior end distorted by label, anterior fragment previously dissected, 13.5 mm long, 1.5 mm wide, 42 chaetigers; posterior fragment 5 mm long, 1.5 mm wide, 20 chaetigers, most chaetae broken; jaws with 5 accesory denticles; paragnath formula: I: 0; II: 4–5; III: destroyed; IV: 4–5; V: 0; VI: 3–6; VII–VIII: single row with 5 paragnaths); Annobon; 01°24′04″ S, 05°36′45″ E; R/V Calypso , stn 50; depth 7–10 m; 13 Jun. 1956; MNHN 372-50 .

GUINEA • 1 spec. (anterior end distorted by pressure of the label; 12 mm long, 0.7 mm wide at chaetiger 10 without parapodia, with 52 chaetigers, anal cirri lost; tentacular cirri slightly damaged, reaching chaetiger 5; antennae thick, as long as palps; eyes blackish, round, of similar size, posterior eyes partially covered by anterior margin of tentacular belt; used for glandular patterns in parapodial ligules); 140 km W of Kaloum; 09°16′ N, 14°50′ W; R/V G. Trica, stn 45; depth 45 m; 11 Mar. 1953; J. Forest leg.; MNHN 372-45 .

GUINEA-BISSAU • 1 spec. (without posterior region, 13 mm long, 1 mm wide, 61 chaetigers; anterior eyes oblique, directed anterolaterally; anteroventrally dissected, paragnaths not seen); 100 Km SSW of Uite, Ilha de Orangozinho; 10°19′00″ N, 16°33′40″ W; R/V Calypso , stn 6; depth 73– 60 m; 16 May 1956; MNHN 372-6 .

SÃO TOMÉ AND PRÍNCIPE • 1 spec. (complete juvenile, 8 mm long, 0.8 mm wide, 57 chaetigers), 1 ♀ (anterior end distorted by label); Ilha de São Tomé ; R/V Calypso , stn T28; 23 Jun. 1956; low tide; MNHN 372-T28 • 1 spec. (complete); S of Baía das Agulhas, “Ilha Principe” [Príncipe]; 01°37′00″ N, 07°24′00″ E; R/V Calypso , stn 92; depth 4–8 m; 26 Jun. 1956; MNHN 372-92 .

Description (holotype, except where indicated)

BODY.Mature female, without posterior end ( Fig. 18A ). Body subcylindrical up to chaetiger 15, depressed thereafter to end of fragment; 23 mm long, 1.5 mm wide (without parapodia), with 63 chaetigers. Dorsum brownish, darker along first 10 chaetigers, progressively paler; dorsal pigmentation as a solid transverse bar, paler approaching parapodia. Venter homogeneously brownish, progressively paler medially and posteriorly. Parapodial ligules with brownish glands from chaetiger 5.

PROSTOMIUM. Slightly longer than wide; eyes blackish, of similar size, anterior eyes oval, longer than wide, about ⅙ of prostomial width, slightly more distant from each other than posterior eyes ( Fig. 18B ). Antennae terminal, without gap between them, tips reaching palpophore ends. Palpophores 2× as long as wide; palpostyles rounded, small.

TENTACULAR BELT. 1.5× as long as first chaetiger; anterior margin partially covering posterior eyes. Tentacular cirri corrugate to articulate, tips broken, posterior dorsal cirri lost, remaining ones reaching chaetiger 2.

PHARYNX. Barely exposed, showing paragnaths and tips of jaws, but not dissected to avoid further damage. Another specimen (MNHN 372-50) with jaws with 5 accesory denticles. Paragnath formula: I: 0; II: 4–5; III: destroyed; IV: 4–5; V: 0; VI: 3–6; VII–VIII: single row with 5 paragnaths.

PATTERN OF PARAPODIAL LIGULES. Anterior, median and posterior chaetigers with ligules tapered, slightly blunter in anterior chaetigers, progressively sharper, 3–4 × as long as wide. Ventral ligules progressively smaller. Ligules with contorted glandular tubules ( Fig. 2 ).

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

ANTERIOR PARAPODIA ( Figs 2A–C , 18C ). With dorsal cirrus thicker, slightly longer than dorsal ligule and ventral cirrus. Dorsal and median ligules subequal, dorsal ligule wider than ventral one. Neuracicular ligule digitiform, blunt, 2× as long as wide, slightly longer than ventral ligule. Notochaetae 6 homogomph spinigers. Supracicular neurochaetae: 5 homogomph spinigers and 3 heterogomph falcigers with blades spinulose, 6–7 × as long as wide, distal tooth incurved, fused to blade; subacicular neurochaetae: 5 homogomph spinigers and 4 heterogomph falcigers with blades lost (in MNHN 372-T28 with blades 5–6 × as long as wide, spinulose, distal tooth incurved).

MEDIAN PARAPODIA ( Fig. 18D ). With dorsal cirrus shorter than dorsal ligule, slightly longer than ventral one in MNHN 372-T28. Both dorsal and median ligules subconical, tapered, 2× as long as wide, dorsal ligule slightly longer than median one, glandular areas distinct, expanded inside ligular bases. Neuracicular ligule subconical, as long as wide, shorter than ventral ligule; ventral ligule subconical, blunt, 3× as long as wide, as long as ventral cirrus. Notochaetae 5 homogomph spinigers. Supracicular neurochaetae: 8 homogomph spinigers and 1 heterogomph falciger with blade spinulose, 5× as long as wide, distal tooth incurved, fused to blade; subacicular neurochaetae: 4 heterogomph spinigers, and 7 heterogomph falcigers with blades spinulose, 3× as long as wide, distal tooth incurved, fused to blade. POSTERIOR PARAPODIA ( Fig. 18E ). With dorsal cirrus 1.3× as long as dorsal ligule. Dorsal and median ligules subequal, subconical, tapered, 1.5–2.5× as long as wide, 2× as long as neuracicular ligule, glandular areas distinct, expanded inside ligular bases. Neuracicular ligule subconical, as long as wide, subequal to ventral ligules; ventral ligule digitiform, slightly longer than wide, longer than ventral cirrus. Notochaetae: 4 homogomph spinigers and 1 homogomph falciger. Supracicular neurochaetae: 5 homogomph spinigers and 1 heterogomph falciger (broken); subacicular neurochaetae: 3 heterogomph spinigers and 5 heterogomph falcigers with blades spinulose, 2 × as long as wide, distal tooth incurved and fused to blade.

SUBTERMINAL PARAPODIA ( Fig. 18F ). With dorsal cirrus markedly longer than notopodial ligules. Both dorsal and median ligules subconical, 2× as long as wide, median ligule slightly longer than dorsal one. Neuracicular ligules subconical, as long as wide, tapered; ventral ligules digitiform, slightly longer than wide, slightly longer than neuracicular ligules, longer than ventral cirri. Notochaetae 1 homogomph spiniger, and 2 homogomph falcigers, blades spinulose, 3–4 × as long as wide, tip blunt, tendon well developed. Supracicular neurochaetae 4 homogomph spinigers and 1 larger heterogomph falciger, blade spinulose, 3× as long as wide, tip blunt, tendon well developed. Infracicular neurochaetae 3 heterogomph spinigers, and 3 heterogomph falcigers, blades spinulose, 3 × as long as wide, tip blunt, tendon well developed.

POSTERIOR REGION. Missing. In MNHN 372-T28, posterior end tapered into a blunt pygidium, anus terminal, anal cirri as long as last 5–6 chaetigers.

OOCYTES. Yellowish, visible from about chaetiger 30; each about 150 μm in diameter (distorted, inside parapodium in Fig. 18E ).

Variation

The paratypes are anterior fragments, regarded as mature females due to the presence of oocytes in their coelom ( Fig. 19 ), as damaged as in the holotype. Body with dorsum brownish, especially along anterior third of body ( Fig. 19A–B, E ), and parapodial ligules with brownish glandular regions from chaetigers 3–4, often darker in posterior chaetigers. They are 12–23 mm long, 1–2 mm wide, with 61–62 chaetigers; all parapodial ligules with dark brown glands, many chaetae broken. The left posterior dorsal tentacular cirri in the largest paratype are broken, reaching chaetiger 6 ( Fig. 19E ). The right one is longer, but it was broken during manipulation, such that tentacular cirri might reach chaetiger 8. The tentacular belt partially covers the posterior eyes ( Fig. 19B, F ), and the eyes are of similar size, with the posterior eyes slightly closer to each other than the anterior ones. Both paratypes with oocytes from about chaetiger 30 ( Fig. 19C ), although they can appear from chaetiger 18 (MNHN 372-T28), and continue throughout most segments, even in the smallest paratype ( Fig. 19D ); each oocyte about 150 μm in diameter.

Another mature female (MNHN 372-T28), defined as such by the presence of oocytes in its coelom, is 12 mm long, 1.2 mm wide, with 72 chaetigers, and has an almost complete histolysis such that most of the coelomic space is filled with oocytes ( Fig. 20A ), first visible from chaetiger 8–9, but more abundant from chaetiger 18, each about 150 μm in diameter. Tentacular cirri articulate, broken. Antennae slightly longer than palps. the parapodia do not show any trace of epitokal transformation.

Chaetigers 1–2 With neuraciculae only ( Fig. 20C ). With dorsal cirri slightly longer than ventral ones, and dorsal and ventral ligules of similar shape and size. Neurochaetal ligule conical, blunt, as long as wide. Supracicular neurochaetae: 5 homogomph spinigers and 2 heterogomph falcigers, blades spinulose, 5–6 × as long as wide, tips incurved, tendons barely visible; subacicular neurochaetae: 4 heterogomph spinigers and 4 smaller heterogomph falcigers, blades spinulose, 4–6× as long as wide, tips incurved, tendons indistinct.

Median chaetigers ( Fig. 20D ) with dorsal cirri slightly longer than notopodial ligules and ventral cirri. Neuracicular ligules conical, tapered, wider than long. Ventral ligule slightly shorter than neurochaetal lobe. Notochaetae 5 homogomph spinigers. Supracicular neurochaetae: with 3 homogomph spinigers and one larger heterogomph falciger, blade spinulose, about 3× as long as wide, tips incurved, tendon well defined; subacicular neurochaetae: with 2 heterogomph spinigers and 5 smaller heterogomph falcigers, blades spinulose, almost 3 × as long as wide, tips incurved, tendons well developed. Oocytes 150 μm in diameter.

Subterminal chaetigers with dorsal cirri about 2 × as long as parapodial ligules and ventral cirri ( Fig. 20E ). Notopodial ligules acute, about 2× as long as wide, tapered. Neurochaetal ligule conical, tapered, about 2× as long as wide. Notochaetae: 1 homogomph spiniger and 1 homogomph falciger (broken). Supracicular neurochaetae: 2 homogomph spinigers and 1 larger heterogomph falciger (blade lost); subacicular neurochaetae: 3 heterogomph spinigers and 3 smaller heterogomph falcigers, blades spinulose, about 2× as long as wide, tips incurved, tendons well defined. Ventral ligule digitate, shorter than neuracicular ligule.

Remarks

Nereis mezianei sp. nov. has been recorded as “ N. falsa ” de Quatrefages, 1866 from the Gulf of Guinea, herein regarded as resembling N. splendida instead. However, these two species differ in relevant pharyngeal and parapodial features, and the main difference is that N. mezianei sp. nov. has a single row of paragnaths in areas VII–VIII, whereas N. splendida has 2–3 rows. Furthermore, because the posterior eyes are partially covered by the anterior margin of the tentacular belt, N. mezianei sp. nov. groups with N. marginata Grube & Örsted in Grube, 1857 from the Caribbean Sea, and with N. rava Ehlers, 1868 from the Mediterranean Sea. However, N. mezianei sp. nov. can be separated from these two other species because its tentacular cirri are longer.

Nevertheless, N. mezianei sp. nov. approaches N. rava by having dorsal and median ligules in the posterior parapodia of similar width. Although the depth of the sampling site was not given in the original description of N. rava , the type locality (Gulf of Quarnero) has a maximaum depth of 128 m. There are at least three different morphs regarded as belonging to N. rava in the Mediterranean region, and it has been reported from sediments in depths of 130–1685 m ( Fauvel 1914: 169). Herein, we follow Gravina et al. (2015) regarding the specific features of N. rava . Nereis mezianei sp. nov. and N. rava have corrugate or articulate tentacular cirri. They especially differ in pigmentation pattern, in the relative size of tentacular cirri and in some parapodial features. In N. mezianei sp. nov., anterior segments have a solid brownish pigmentation, their longest tentacular cirri reach chaetigers 7–8, and the ventral ligule is longer than the neuracicular ligule, whereas in N. rava , anterior segments have two transverse brownish bands, their longest tentacular cirri reach chaetigers 2–3, and the neuracicular ligule is as long as the ventral ligule. Another important difference relies on mature females. In N. mezianei sp. nov., there is no metamorphosis or parapodial modification in mature females, whereas female heteronereis are known for N. rava ( Núñez 2004: 374–375) .

Nereis mezianei sp. nov. also resembles N. caparti Fauvel, 1953 described from off Namibia, because they have the longest tentacular cirri reaching chaetiger 7–8, parapodial ligules tapered and pharynx areas VII–VIII with a single row of paragnaths. They differ, however, because in N. mezianei sp. nov. the posterior eyes are partially covered by the anterior margin of first segment, notopodial ligules are of similar length and width, and compound notofalcigers have spinulose blades, whereas in N. caparti , posterior eyes are fully exposed, dorsal ligules are progressively longer than median ones, and the blades of the notofalcigers are smooth.

Distribution

Senegal to Equatorial Guinea, Western Africa, in shallow subtidal sediments in depths up to 75 m.

Figures

Fig. 2. Nereis mezianei sp. nov., non-type juvenile (MNHN 372-45). A. Chaetiger 9, left parapodium, anterior view. B. Same, base of notopodial ligules. C. Same, base of ventral ligule. D. Chaetiger 25, left parapodium, posterior view. E. Same, dorsal ligule. F. Same, ventral ligule. G. Chaetiger 46, left parapodium, posterior view. H. Same, notopodial ligules. I. Same, ventral ligule.

Fig. 18. Nereis mezianei sp. nov., holotype (MNHN 372-4). A. Dorsal view. B. Anterior region, dorsal view. C. Chaetiger 2, left parapodium, anterior view (ventral cirrus lost). D. Chaetiger 16, left parapodium, posterior view (ventral cirrus lost). E. Chaetiger 31, right parapodium, posterior view (notopodial homogomph and supracicular heterogomph falcigers broken). F. Chaetiger 55, right parapodium, posterior view (insets: homogomph falcigers tips). G. Posterior region, dorsal view.

Fig. 19. Nereis mezianei sp. nov., paratypes (MNHN 372-4b). A. Smallest paratype, dorsal view. B. Same, anterior end, dorsal view. C. Same, median segments, dorsal view. D. Same, posterior region, dorsal view. E. Largest paratype, anterior region, dorsal view. F. Same, anterior end, dorsal view.

Fig. 20. Nereis mezianei sp. nov., mature female (MNHN 372-T28). A. Dorsal view. B. Anterior region, dorsal view. Parapodia stained with Shirslastain-A. C. Chaetiger 2, right parapodium, anterior view (dorsal cirrus bent). D. Chaetiger 35, left parapodium, posterior view.E. Chaetiger 52, right parapodium, posterior view.