Asclerocheilus blakei, Mendes & Paiva & Rizzo, 2024

Mendes, Samuel Lucas Da Silva Delgado, Paiva, Paulo Cesar De & Rizzo, Alexandra E., 2024, On species of Asclerocheilus Ashworth, 1901 (Annelida: Scalibregmatidae) from Brazil, European Journal of Taxonomy 947, pp. 88-108 : 97-101

Asclerocheilus blakei sp. nov.

urn:lsid:zoobank.org:act:6088AEC5-0BB2-447F-B09D-B397037F6AF7

Figs 4–6

Diagnosis

Trapezoidal prostomium, with two long horns, both thin and projected laterally with inconspicuous aperture at their basis. Ventral groove present from chaetiger 1 with first pad asymmetrically rounded, bearing up to 4 small lobules on its superior margin, contributing to mouth’s lower lip formation.Acicular chaetae with pointed tips present in chaetigers 1–3 on notopodia and neuropodia. Lyrate chaetae from chaetiger 3 on notopodia and 2 on neuropodia, with unequal tynes. Pygidium present as short crenulated margin with up to 10 small lobes, from which emerges 6 long anal cirri.

Etymology

The specific epithet ‘ blakei ’ was chosen to honour Dr James A. Blake, for his important contributions to polychaete taxonomy, ecology and evolution. Most of the taxonomical issues concerning the family Scalibregmatidae were solved from his contributions, especially on the genus Asclerocheilus , which was revised by him ( Blake 2000). The author also contributed to the second attempt to delimitate the genera within the family ( Kudenov & Blake 1978), in the first work on species from the South Atlantic ( Blake 1981), and in the first work describing the ontogeny and development of a scalibregmatid species ( Blake 2015).

Type material

Holotype

BRAZIL • complete spec.; Rio de Janeiro, Campos Basin ; 23.654317° S, 41.310094° W; depth 693 m; Jun. 2008; box corer; continental slope; UERJ, UERJ-1133 .

Paratypes

BRAZIL • 2 complete specs; Rio de Janeiro, Campos Basin ; 21.186° S, 40.216° W; depth 683 m; Feb. 2009; box corer; continental slope; UERJ, UERJ-6297 • 1 complete spec.; Espírito Santo, Espírito Santo Basin ; 19.970° S, 39.519° W; depth 1908 m; Jun. 2013; box corer; continental slope; UERJ, UERJ-9222 .

Description

Holotype complete, 5 mm long, 1 mm wide over expanded region, 0.25 mm wide on narrowest region, for 36 chaetigerous segments. Moderate-sized species, paratypes measuring 6–13 mm long to 0.15– 2 mm wide for 33–43 chaetigerous segments. Body arenicoliform, weakly expanded over chaetiger 8– 7. Colour in alcohol pale tan to yellowish. Body surface covered by secondarily annulated rings in well preserved specimens. Secondary annuli composed by rounded to quadrangular small pads in both anterior and posterior regions. Annuli’s small pads on anterior region may be weaker in comparison to posterior region. Internal glands not observed.

Trapezoidal prostomium, with two long horns, both thin and projected laterally ( Figs 4A–B , 5A , 6A ). One pair of small eyespots on middle of prostomium in small specimens, but absent in adults. Nuchal organs not observed. Proboscis smooth. Peristomium achaetous, uniannulated dorsally ( Figs 4A , 6A ) and biannulated ventrally ( Figs 4B , 5A ), contributing to mouth’s upper lip formation. Ventral groove present from chaetiger 1 ( Fig. 4B ) with first pad asymmetrically rounded, bearing up to 4 small lobules on its superior margin, contributing to mouth’s lower lips formation. Rectangular triannulated pads present from chaetiger 2, forming ventral mid-ridge up to end of body. Each pad paired to single chaetiger. Posterior pads thinner than anterior ones.

Body chaetigers 1–2 with two secondary annuli connected to parapodial lobe, in addition intermediate annulation between chaetigers ( Fig. 4A–B ). From chaetiger 3, three secondary annuli connected directly to parapodial lobe, in addition intermediate annulation between chaetigers ( Figs 4A–B , 5E ). Interramal papillae present, but inconspicuous on anterior and midbody chaetigers, emerging as blunted projection between noto- and neuropodial lobes on posterior chaetigers ( Fig. 5F ).

Acicular chaetae with pointed tips present in chaetigers 1–3 on notopodia and neuropodia ( Figs 4C , 5C–D , 6B–D ). Lyrate chaetae with unequal tynes (tynes ratio 2.125), present in a single row from chaetiger 3 in notopodia and from chaetiger 2 in neuropodia ( Figs 4D , 5B , 6C ); numbering 3–4 chaetae in both rami on anterior chaetigers, up to 8 in midbody chaetigers, then 4–5 in posterior chaetigers. Short spinous chaetae absent.

Notopodial acicular spines organized in two rows on chaetigers 1–2, numbering 6–7 in anterior row and 8–9 in posterior row ( Figs 4C , 5C–D , 6B ). Notopodial acicular spines on chaetiger 3 organized in single row of 8 transitional acicular spines ( Fig. 6D ), with one row replaced by lyrate chaetae. Neuropodial acicular spines present on chaetigers 1–3, weaker than notopodial ones, organized in single row, numbering 5 per fascicle, being accompanied by anterior row of lyrate chaetae on chaetiger 2.

Notopodial capillaries present in one row on chaetigers 1–2; then in two rows on chaetiger 3, then in three rows on chaetiger 4. Neuropodial capillaries organized in two rows in chaetigers 1–3, then in three rows on chaetiger 4. Noto- and neuropodia on posterior chaetigers with two rows of capillaries, then in single row on last 5–10 chaetigers. Smaller specimens present more posterior chaetigers with single row of capillaries. Notopodial and neuropodial capillaries longer on anterior body, up to chaetiger 8, giving spinous appearance.

Parapodial lobes always asymmetrical, emerging as short and inconspicuous basis ending in rounded tip on anterior chaetigers, forming ‘hill-like’ structure; on midbody chaetigers, parapodial lobes inflate at their basis, transitioning abruptly to pointed tip; on posterior most chaetigers, parapodial lobes become smaller and thinner, emerging as thin basis transitioning smoothly to pointed tip ( Fig. 5F ). Pygidium present as short crenulated margin with up to 10 small lobes, from which emerges 6 long anal cirri ( Figs 5F , 6E ).

Remarks

This species is morphologically similar to A. intermedius , A. shanei , A. abyssalis and A. geiseae sp. nov. by having acicular spines on notopodia of chaetigers 1–3. However, it is set apart from A. abyssalis by the absence of short spinous chaetae on noto- and neuropodia of chaetiger 3. Asclerocheilus shanei differs from A. blakei sp. nov. by the absence of capillaries following the acicular spines on chaetigers 1–3. Asclerocheilus intermedius differs from A. blakei by presenting lyrate chaetae fron chaetiger 4. Asclerocheilus blakei presents a single type of acicular spine on its chaetigers; they are curved with pointed tips, differing from A. geiseae spines, that end in blunt tips. Finally, both species have different prostomial and peristomial morphologies, being triangular with horns directed upwards in A. geiseae , whereas in A. blakei the prostomium is rounded to trapezoidal and its horns are thinner and laterally directed.

Ecology

This species was found living on the continental shelf and slope of the Espírito Santo and Campos basins (Brazilian southern region), from a bathymetric range of 683–2900 m.

Figures

Fig. 4. Asclerocheilus blakei sp. nov., holotype (UERJ-1133), schematic representation. A. Dorsal view of anterior body. B. Ventral view of anterior body. C. Acicular spine. D. Lyrate chaeta. Abbreviations: see Material and methods.

Fig. 5. Asclerocheilus blakei sp. nov., paratype (UERJ-6297), under optical microscope, specimens stained with Shirlastain A. A. Ventral view of anterior body (coll. code). B. Lyrate chaetae. C. Acicular spines on neuropodia of chaetigers 1–3.D. Acicular spines on notopodia of chaetiger 3 in detail.E. Ventral view of mid-body annulation pattern. F. Posterior most chaetigers in lateral view. Abbreviations: see Material and methods.

Fig. 6. Asclerocheilus blakei sp. nov., under SEM. A. Dorsal view of anterior body. B. Acicular spines with terminal arista in detail. C. Lyrate chaetae. D. Acicular spines with pointed tips from chaetiger 3 in detail. E. Pygidium in dorsal view. Abbreviations: see Material and methods.