Saphobranchia omorpha, Salazar-Vallejo, 2020

Salazar-Vallejo, Sergio I., 2020, Four new deep-water flabelligerid species from Pacific Costa Rica (Annelida Sedentaria, Flabelligeridae), Zootaxa 4885 (4), pp. 560-578 : 571-574

Saphobranchia omorpha n. sp.

urn:lsid:zoobank.org:act:C97609B8-AF2E-413B-80C9-F45CC68CF5A2

Figures 6 , 7 , 8H, I

Diagnosis. Saphobranchia with tunic without sand particles; median chaetigers with notochaetae longer than body width; neurochaetae with tips straight, basal anchylosed region 1/3 chaetal length, articles 4–6 times longer than wide; no gonopodial lobes.

Type material. Holotype ( SIO A9595 ), CR 18-0013, Alvin dive 4972, Jaco Scar (09°07’01.20” N, 84°50’24.00” W), 1784 m, 18 Oct. 2018, G. Rouse & A. Hatch, coll. [ MW 172264 ].

Description. Holotype (SIO A9595) originally with 32 chaetigers ( Fig. 8H ), 12 posterior chaetigers removed for molecular studies; now without posterior region. Body pale, anteriorly swollen, slightly bent laterally, broken along left margins of chaetigers 5–8, tapered medially and posteriorly, anterior chaetigers with notochaetae up to 9 times longer than body width; body wall broken along left size in chaetigers 5–8 ( Fig. 6A ); 13 mm long, 1 mm wide (widest by chaetigers 7–8, 2.8 mm), cephalic cage chaetae 6 mm long, 20 chaetigers (last one removed for a slide).

Tunic thin, without sand particles; papillae long, in about three different lengths, up to 10 times longer than wide, sparse, variably eroded along body, dorsally and ventrally of similar shape, shorter and more abundant ventrally ( Figs 6D ; 8I ), and surrounding chaetal bundle bases ( Fig. 6C, E ).

Anterior end features not seen; one palp barely exposed, brownish; not dissected to avoid further damage.

Cephalic cage chaetae 2–3 times longer than body width. Chaetigers 1–2 forming cephalic cage, chaetae directed anteriorly; chaetiger 3 with notochaetae directed anteriorly, neurochaetae directed laterally. Chaetae arranged in short rows, notochaetae dorsolateral along body.

Chaetiger 1 with 7–8 notochaetae, 3–4 neurochaetae, longest ones basally to medially anchylosed, shorter ones completely articulated, articles 3–4 times longer than wide medially, progressively longer distally. Chaetiger 2 with 7 thinner notochaetae, 4/5 as long as those of chaetiger 1 or of similar size, anchylosed region progressively shorter in smaller chaetae; neurochaetae thicker, 11–12 per bundle, some with adsorbed brownish particles along their length, articles 2–3 times longer than wide, slightly longer distally.

Anterior dorsal margin of chaetiger 1 with several papillae and two small blunt conical projections internal to notochaetae ( Fig. 6B ), also visible in chaetiger 2. Chaetigers 1–4 of similar length. No chaetal transition from cephalic cage to body chaetae; all neurochaetae multiarticulated. Gonopodial lobes not seen ( Fig. 6D ). Testis seen through broken body wall, confirmed by abundant spherical spermatids within gonad.

Parapodia laterally projected from body wall; parapodia lateral, median neuropodia ventrolateral. Notopodia and neuropodia surrounded by several cylindrical papillae ( Fig. 7A ); papillae covered by a very thin tunic ( Fig. 7B ), longest papillae about as 1/13 as long as longest notochaetae, or 1/11 as long as longest neurochaetae.

Median notochaetae arranged in short transverse rows, chaetal fascicles fan-shaped, directed dorsally, at least 5 times longer than body width. All notochaetae multiarticulate capillaries; 14 per bundle, central notochaetae with basally anchylosed region about 1/3 chaetal length ( Fig. 7C ), basal notochaetae with a shorter anchylosed region, not fully articulated; articles 4–6 times longer than wide medially, progressively longer distally. Neurochaetae twice longer than body width, nine per bundle, central neurochaetae with anchylosed region 1/3 as long as chaetal length, medially with articles 3–4 times longer than wide, progressively longer distally ( Fig. 7D ), tips straight ( Fig. 7D , inset).

Posterior region cylindrical, tapered (seen in photos before cropping for molecular studies); pygidium unknown.

Etymology. The specific name is from the Greek ómorphos, beautiful, masculine, latinised and declined in feminine, for referring to the beauty of the specimen. The specific name is regarded as a noun in apposition ( ICZN 1999, Art. 31.2).

Remarks. Saphobranchia omorpha n. sp. groups with S. micans ( Fauchald, 1972) n. comb., and S. ilys n. sp. because their bodies do not have abundant sand particles adhered on tunic, and their notochaetae are longer than body width. Their main difference after the key above is the type of neurochaetal tips. In S. omorpha n. sp. they are straight whereas in S. micans and S. ilys n. sp., they are falcate. Another conspicuous difference is the size of chaetae, because in S. omorpha n. sp. they are very long, more than 10 times longer than body width, whereas in the two other species, they can be up to 5 times as long.

An additional comparison might be needed because S. omorpha n. sp. and S. ilys share pale body wall and brownish chaetae. As indicated above, their main differences are in the development of tunic papillae, associated sediment particles, parapodial development, and chaetal size in median chaetigers. Saphobranchia omorpha n. sp. has a pilose body wall because the scarce dorsal papillae lack sediment particles, or have fine particles forming a thin layer, parapodia are clearly projected laterally, and chaetae are up to 4 times longer than body width. On the contrary, S. ilys n. sp. has a rugose body wall because dorsal papillae are short, blunt mainly with fine sediment, and a few sand particles, parapodia are slightly projected from the body wall, and chaetae are as long as body width.

Distribution. Off Pacific Costa Rica, in 1784 m depth.

Figures

FIGURE 6. Saphobranchia omorpha n. sp., holotype (SIO A9595). A. Dorsal view. B. Anterior region, dorsal view. C. Last chaetigers, dorsal view. D. Anterior region, ventral view. E. Last chaetiger, ventral view. Scale bars.- A: 1.5 mm, B: 0.90 mm, C: 0.60 mm, D: 0.95 mm, E: 0.52 mm.

FIGURE 7. Saphobranchia omorpha n. sp., holotype (SIO A9595).A. Chaetiger 14, right parapodium, anterior view. B. Close up of parapodium. C. Central notochaetae, basal, medial and distal regions. D. Central neurochaetae, basal, medial and distal regions (inset: neurochaetal tip). Scale bars.- A: 0.36 mm, B: 0.21 mm, C: 35 μm, D: 65 μm.

FIGURE 8. Living specimens. A. Lamispina polycerata n. sp., holotype (SIO A9842), anterior fragment, left lateral view. B. Same, posterior fragment, dorsal view. C. Saphobranchia canela n. sp., holotype (SIO A1332), dorsal view. D. Same, ventral view. E. Same, anterior end, frontal view (Br: branchia, Pa: palp). F. S. ilys n. sp., holotype (SIO A 9605), dorsal view. G. Same, ventral view. H. S. omorpha n. sp., holotype (SIO A9595), dorsal view. I. Same, ventral view. Scale bars: A, B: 1.0 mm; C, D: 2.2 mm; E: 0.4 mm; F, G: 3.5 mm; H, I: 3.7 mm (Photos: Greg Rouse).