Octomagelona cf. borowskii Fiege, Knebelsberger and Meissner

Meissner, Karin, Schwentner, Martin, Göưing, Miriam & Fiege, Thomas Knebelsberger and Dieter, 2023, Polychaetes distributed across oceans-examples of widely recorded species from abyssal depths of the Atlantic and Pacific Oceans, Zoological Journal of the Linnean Society 199, pp. 906-944 : 928

Octomagelona cf. borowskii Fiege, Knebelsberger and Meissner

( Fig. 12G, H )

Octomagelona bizkaiensis Aguirrezabalaga, Ceberio and Fiege, 2001 – Fiege et al. 2010: 1338, tables 3 and 5, appendix (name only).

Material examined: SE Atlantic, Angola Basin, M 48-1 (DIVA 1), station 330-3, 5469 m (SMF 30503, SEM 1323; SMF 30506; SMF 30587); station 338-8, 5439 m (SMF 30504); station 340- 1, 5464 m (SMF 30507); station 341-8, 5464 m (SMF 30505). – for details see the Supporting Information, Table S2 .

Description: (Based on specimen SMF 30503.) All specimens incomplete, i.e. anterior fragments with only few abdominal segments. Tentacle fragment (free) found only with one posterior fragment (SMF 30587) showing same characters as described for Octomagelona borowskii sp. nov..

Prostomium wider than long (length/width n.d./ 1.15 mm), truncate, with small, rudimentary frontal horns with free tips, anterior margin smooth. Posterolateral ends of prostomium bent down forming posterolateral flaps. Prostomium pushed up and backwards by bulbous burrowing organ partly everted, longitudinally ridged ventrally. Eyes lacking. Palps broken. First segment achaetous ( Fig. 12G, H ).

Thoracic region with eight chaetigers ( Fig. 12G, H ). Thoracic width decreasing from chaetiger 1 (0.63 mm) to chaetiger 8 (0.50 mm). Constriction between thorax and abdomen. All thoracic parapodia without superior notopodial or ventral neuropodial process ( Fig. 12G ). Notopodial lateral lamellae postchaetal; filiform in chaetigers 1–4; length decreasing gradually posteriorly, absent in chaetigers 5–8. Neuropodial lateral lamellae postchaetal, similar in shape, as long as or longer than notopodial lateral lamellae, likewise gradually decreasing in length from chaetigers 1–4, the laưer as rudimentary knob only, lacking posteriorly. Noto- and neuropodia of thoracic chaetigers 5–8 represented as low ridges encircling chaetal fascicles like cuffs ( Fig.12G ). All thoracic chaetae long, uni- and bilimbate capillaries, similar in length, decreasing in number from chaetiger 1 (12–14 noto-, 15 neurochaetae) to chaetiger 8 (one noto-, two neurochaetae, some broken).

Abdomen starting with chaetiger 9. Width 0.6 mm. Abdominal parapodia without superior notopodial (DML) and ventral neuropodial process (VML) at upper- and lowermost ends of chaetal rows. Notopodial lateral lamellae from chaetiger 9, subchaetal, filiform, gradually increasing in length to chaetiger 12 (abdomen broken). Neuropodial lateral lamellae from chaetiger 11, suprachaetal, filiform, slightly longer in chaetiger 12. Abdominal chaetae tridentate hooded hooks with main fang surmounted by two small teeth, arranged in single line on parapodial ridge. About 10 per parapodial ramus, all about same size, with five each in vis-à-vis arrangement, i. e. noto- and neuropodia with two groups each, teeth facing. Lateral pouches not observed.

Pygidium unknown.

Remarks: Specimens of Octomagelona cf. borowskii from the South Atlantic, are morphologically very similar to specimens of O. borowskii sp. nov. collected in the Pacific. Unfortunately, the limited number of specimens and their poor state of preservation make a detailed morphological distinction difficult. For example, a thoracic ventral neuropodial process is absent in thoracic chaetigers of O. cf. borowskii , whereas it is present in chaetiger 1 in some specimens of O. borowskii sp. nov. but absent in paratype SMF 30528 ( Fig. 12A–F ). Thoracic chaetae are uni- or bilimbate capillaries in O. cf. borowskii and uni- or irregularly bilimbate capillaries in O. borowskii sp. nov.. No conspicuous pigmentation paưern is discernable in specimens of O. cf. borowskii , whereas it is present in some specimens of O. borowskii sp. nov.. Molecular data are highly desirable for distinction among these two taxa. Unfortunately, sequencing of specimens of O. cf. borowskii was not successful.

Distribution: SE Atlantic, Angola Basin, 5439–5473 m.

Figures

Figure 12. SEM and LM studies of Octomagelona borowskii sp. nov. (A–F, I–K), Octomagelona cf.borowskii (G, H), and O. bizkaiensis Aguirrezabalaga, Ceberio and Fiege, 2001 (L): A, anterior end, dorsolateral view.B, thoracic chaetiger, leħ side, posterior view. C, thoracic chaetigers 1–4, right side, lateral view. D, thoracic chaetigers 3–5, right side, lateral view. E, thoracic chaetigers 6–8, right side, lateral view.F, chaetigers 8–11, right side, lateral view. G, anterior fragment, dorsolateral view.H, anterior fragment, ventral view. I, abdominal hooks, lateral view. I’, tip of abdominal hook, frontal view.J, bilimbate thoracic capillary chaeta.K, irregularly bilimbate thoracic capillary chaeta. L, limbate thoracic capillary chaetae, chaetiger 1, right side.—A–F, SMF 30528 (SEM stub 1320), paratype, Peru Basin; G, H, SMF 30503 (SEM stub 1323), Angola Basin; I–K, SMF 30512, Peru Basin; L, O. bizkaiensis, SMF 10026 (SEM stub 604), paratype, Bay of Biscay. Scale Bars: A–F, 100 µm; G, H, 1 mm; I, 20 µm; I’–L, 10 µm.