Terebellides nkossa, Parapar & Martin & Moreira, 2020

Parapar, Julio, Martin, Daniel & Moreira, Juan, 2020, On the diversity of Terebellides (Annelida, Trichobranchidae) in West Africa, seven new species and the redescription of T. africana Augener, 1918 stat. prom., Zootaxa 4771 (1), pp. 1-61 : 38-43

Terebellides nkossa sp. nov.

Figures 11C , 28A , 29–32 , 37 ; Tables 1, 2 urn:lsid:zoobank.org:act:8C262B7A-F8EC-4ABC-A6AE-538652C71D1B

Material examined. Type material. Fifty specimens: holotype ( MNCN16.01 /18594); forty-nine paratypes ( MNCN16.01 /18592, 16.01/18593 and 16.01/18595 to 16.01/18610). Non-type material. Five dried-out specimens ( MNCN16.01 /18611 and MNCN16.01 /18612); one specimen (NHMD-231434) (Table 1) .

Diagnosis. Body small sized (5–15 mm in length); semi-transparent body wall. Branchial anterior lobe absent; posterior lobes not fused; ventral ones thinner and shorter than dorsal ones, with long terminal filament, directly emerging from branchial stem. TC1 notopodia and notochaetae smaller than following ones. Thoracic neurochaetae with rostrum / capitium length about 1/1 and capitium with a first row of 4–7 medium-sized teeth followed by progressively shorter ones.

Description based on holotype

Measurements and general body features. Complete specimen, with coelomic cavity filled with oocytes, 12 mm long and 1.0 mm wide ( Fig. 28A , 29A ); body tapering posteriorly with segments increasingly shorter and crowded towards pygidium. Prostomium compact; tentacular membrane surrounding mouth, with a low number of buccal tentacles ( Fig. 29A ). SGI as an expanded structure below tentacular membrane (lower lip) ( Fig. 29A , 30A ). Lateral lappets weakly developed on SGIII–VII ( CH 1–5).

Branchiae. Branchiae arising as single structure from SGIII, with a single stalked mid-dorsal branch having of one pair of dorsal (upper) lobes not fused along their lengths, and a pair of ventral (lower) lobes much shorter, neither fused together nor to dorsal ones ( Fig. 28A , 29A , 30 A−B, 32A). Anterior projection of dorsal lobes (lobe 5) not present. Pointed projection of posterior region of both upper and lower lobes much longer in ventral ones, becoming a long terminal filament ( Fig. 30 A−B, 32A). Both sides of branchial lamellae with several parallel bent rows of cilia and several ciliated tufts near outer edge ( Fig. 30 C−D).

Thorax. Eighteen pairs of notopodia (SGIII−XX); those in TC1 slightly smaller than subsequent ones ( Fig. 30A , E−F, 32A). Neuropodia as sessile pinnules, from TC6 (SGVIII) to pygidium, with uncini in single rows start- ing from TC7 (SGIX) throughout. First neuropodia (TC6) with 3–4 sharply bent, acute-tipped, geniculate chaetae with well-developed minute teeth forming a capitium ( Fig. 31A ). From TC7, neuropodia with up to 7–9 uncini per torus in one row ( Fig. 31B ), with long-shafted denticulate hooks, rostrum about same length as capitium, with 4−7 medium-sized teeth above main fang, surmounted by 4−6 slightly shorter teeth ( Fig. 31C , 32 C−D).

Abdomen. 29−30 pairs of neuropodia, as erect pinnules with about 20 uncini per torus ( Fig. 31 D−E) having three teeth above main fang surmounted by two teeth above one in middle, an upper crest of two teeth and a variable number of smaller teeth ( Fig. 31F ).

Other features. Paired, mulberry-like nephridial papilla behind first thoracic notopodia and dorsal to each SGVI and VII ( CH 4 and CH 5) notopodium ( Fig. 30A , E−F, 32A−B). Pygidium blunt, as funnel-like depression.

Methyl green staining pattern. Anterior CH 1 to CH 4 solid; CH 5 to CH 11 striped; CH 12 and CH 13 only neuropodia slightly stained; pattern 1 of Schüller & Hutchings (2010) ( Fig. 37 ).

Variability. Most specimens of T. nkossa sp. nov. are complete, with well-defined branchiae, ranging from 5 to 15 mm long, showing intra-coelomic oocytes from 9-mm long specimens ( Fig. 29D ). The digestive tract main parts, especially the hind stomach, can be easily seen by transparency through the delicate body wall ( Fig. 29C ). The only specimen from the Atlantide cruise (NHMD-231434), identified as T. stroemii by Kirkegaard (1959), comes from shallow waters (108 m depth) off Sierra Leone, measures 7 mm in length and overall agrees with T. nkossa sp. nov. description, except in having much shorter, comma-shaped branchiae, both features not present in our specimens of this species, and therefore it was labelled as T. af. nkossa .

Type locality. Gabon; 43 m depth (Table 1) .

Distribution and bathymetry. Gabon and Democratic Republic of Congo; 43−250 m depth ( Fig. 11C ; Table 1).

Etymology. The species is named after the N’Kossa gas field located off Congo, where most specimens were collected.

Remarks. The diagnostic characters above mentioned clearly distinguishes T. nkossa sp. nov. from all other species here described. However, it shares some branchial features with six previously described species: Terebellides mundora Hutchings & Peart, 2000 ( Australia) , Terebellides atlantis Williams, 1984 (New England slope), Terebellides parapari Lavesque, Hutchings, Daffe, Nygren & Londoño-Mesa, 2019 , T. sepultura , T. irinae and T. shetlandica .

Terebellides mundora differs from T. nkossa sp. nov. in having branchiae with posterior ventral lobes almost as long as dorsal ones and thoracic uncini with rostrum shorter than capitium, while the new species has ventral lobes much shorter and rostrum longer than capitium; T. sepultura has a very large branchial stalk (short in T. nkossa sp. nov.), and T. irinae has very long thoracic notopodial chaetae (short in T. nkossa sp. nov.).

The Atlantic species T. atlantis , T. shetlandica and T. parapari closely resemble T. nkossa sp. nov. in their small body size ( T. atlantis : 8–18 mm; T. shetlandica : 06– 19 mm; T. parapari : 8–23 mm and T. nkossa sp. nov.: 5–15 mm) and several other morphological features. Thus, even though the brief original description of T. atlantis ( Williams, 1984) does not allow accurate comparisons, the Icelandic specimens described by Parapar et al. (2011) differ from T. nkossa sp. nov. in the size and shape of dorsal branchial lobes vs. ventral ones (which are all highly deciduous in the former) and the shape of thoracic uncini, which show the capitium endowed with minute and numerous teeth (type 4 in Parapar et al., 2016c) (long and scarce in T. nkossa sp. nov., type 3 in Parapar et al., 2016c). Terebellides shetlandica and T. parapari most closely resemble T. nkossa sp. nov. in general branchial shape with ventral branchial lobes only fused at base with dorsal ones and provided with a terminal filament and thoracic uncini. Furthermore, all three species were found at a similar depth range: 100–160 m for T. shetlandica , 120 m for T. parapari and 43–250 m for T. nkossa sp. nov. Nevertheless, T. nkossa sp. nov. mostly differs from T. shetlandica in the number of uncini per abdominal neuropodium (6–7 vs. ca. 20, respectively), and from T. parapari in having smaller TC1 notopodial and notochaetae than following (much longer in T. parapari ) and having ciliated papillae dorsal to thoracic notopodia and ciliature in branchial lobes (absent in T. parapari ).

Other species with four-lobed branchiae are: Terebellides ehlersi McIntosh, 1885 ( Fiji Islands), Terebellides intoshi Caullery, 1944 ( Indonesia) and Terebellides lobatus Hartman & Fauchald, 1971 (New England). Nevertheless, all of them are much larger than T. nkossa sp. nov. (30−40 mm vs. 5−15 mm) and T. intoshi also bears two chaetigers with geniculate chaetae (cfr. Imajima & Williams, 1985), instead of one.

Figures

FIGURE 11. Maps of Central and Southern Atlantic African coasts showing the stations where the species of Terebellides described in this work were found. (A) T. africana stat. prom., T. augeneri sp. nov. and T. congolana sp. nov.; (B) T. fauveli sp. nov. and T. kirkegaardi sp. nov.; (C) T. longiseta sp. nov. and T. nkossa sp. nov.; (D) Terebellides sp. 1, Terebellides sp. 2 and T. ramili sp. nov.

FIGURE 28. Terebellides nkossa sp. nov. (holotype, MNCN 16.01/18594): (A) anterior end, left lateral view and detail of branchiae. Terebellides ramili sp. nov. (holotype, MNCN 16.01/18615): (B) anterior end, left lateral view and detail of branchiae. Abbreviations: bldl—branchial left dorsal lobe; blvl—branchial left ventral lobe; brdl—branchial right dorsal lobe; brvl—branchial right ventral lobe; bvltf—branchial ventral lobe terminal filament; TC—thoracic chaetiger.

FIGURE 29. Terebellides nkossa sp. nov. Stereomicroscope images. Holotype (MNCN 16.01/18594): (A) anterior end, left lateral view. Paratypes (MNCN 16.01/18595 and MNCN16.01/18602): (B) anterior end, ventral view; (C) anterior half, right latero-ventral view; (D) anterior end, right lateral view. Abbreviations: bldl—branchial left dorsal lobe; blvl—branchial left ventral lobe; brdl—branchial right dorsal lobe; fst—fore stomach; hst—hind stomach; int—intestine; latlap—lateral lappet; loli—lower lip; ooc—oocytes; SG—segment; TC—thoracic chaetiger; tm—tentacular membrane.

FIGURE 30. Terebellides nkossa sp. nov. SEM micrographs of the paratype MNCN 16.01/18596. (A) anterior end, left dorsolateral view; (B) branchial posterior ventral lobes, ventral view; (C) several dorsal branchial lamellae, inner side, showing ciliature pattern; (D) the same, rows of cilia, detail; (E) TC1–TC5, left lateral view; (F) TC1 nephridial opening. Abbreviations: bct—branchial ciliated tuft; bldl—branchial left dorsal lobe; blvl—branchial left ventral lobe; brdl—branchial right dorsal lobe; brvl—branchial right ventral lobe; bst—branchial stalk; bt—buccal tentacle; bvltf—branchial ventral lobe terminal filament; cr—ciliary row; latlap—lateral lappet; loli—lower lip; no—nephridial opening; np—nephridial papilla; TN—thoracic notopodium; tndp—thoracic notopodium dorsal papilla.

FIGURE 31. Terebellides nkossa sp. nov. SEM micrographs of the paratype MNCN 16.01/18601. (A) TC6, two geniculate chaetae; (B) row of thoracic uncini row and detail of geniculate chaeta capitium (framed in (A); (C) two thoracic uncini, lateroupper view; (D) three abdominal uncinigers in dorsal view; (E-F) abdominal uncini, anterior and fronto-upper view. Circles in (C) and (F) showing number of teeth on capitium. Abbreviations: cap—capitium; ros—rostrum.

FIGURE 32. Terebellides nkossa sp. nov. SEM micrographs of the paratype MNCN 16.01/18599. (A) anterior end, right lateral view showing branchial lobes arrangement; (B) TC4–TC5, nephridial openings; (C–D) several abdominal uncini, upper view. Circles in (C) and (D) showing number of teeth on capitium. Abbreviations: bdltp—branchial dorsal lobe terminal papilla; bldl—branchial left dorsal lobe; blvl—branchial left ventral lobe; brdl—branchial right dorsal lobe; brvl—branchial right ventral lobe; bst—branchial stalk; bt—buccal tentacle; bvltf—branchial ventral lobe terminal filament; cap—capitium; loli—lower lip; no—nephridial opening; TN—thoracic notopodium; tndp—thoracic notopodium dorsal papilla.

FIGURE 37. Body staining patterns—following Schüller & Hutchings (2010)—in ventral view of the species described in this work; chaetigers indicated in Arabic numbers.