Euchone mercedesae, Tovar-Hernández & León-González & Hendrickx, 2025

Tovar-Hernández, María Ana, León-González, Jesús Angel De & Hendrickx, Michel E., 2025, Polychaeta collected during the research cruises TALUD aboard the R / V “ El Puma ” in the Mexican Pacific: Sabellidae and Serpulidae, Zootaxa 5663 (1), pp. 1-80 : 29-35

Euchone mercedesae sp. nov.

urn:lsid:zoobank.org:act:8F4D296A-4C96-452F-B8CF-3238DF52709F

( Figs 15–17 , 39T–W , Table 2)

Material examined. Type material. Holotype, ICML-EMU-14028: TALUD X, St. 22, BS, 27°02'46"N 110°52'57"W, 13 February 2007, 1582–1586 m . Additional material. ICML-EMU-14029: TALUD VIII, St. 16, KD, 25º24'48"N 110º34'48"W, 18 April 2005, 1030 m, 1 specimen .

Description. Body pale, whitish glandular ridge on chaetiger 2 ( Fig. 15C–D ). Trunk 24.7 mm long, thorax 1.7 mm wide. Branchial crown 11 mm long with two semicircular lobes, each with 11 radioles. Thorax with eight chaetigers. Abdomen with 42 chaetigers. Dorsal and ventral basal flanges absent. Palmate membrane short, about 1/4 of radiole length. Narrow radiolar flanges along radioles. Radiolar eyes absent. Dorsal lips with short radiolar appendage, dorsal pinnular appendages absent. Ventral lips and parallel lamellae present, ventral sacs absent. Two pairs of ventral radiolar appendages. Posterior peristomial ring collar with dorsal margins fused to faecal groove ( Fig. 15A ), ventral margin with short mid-ventral incision ( Fig. 15D–E ). Anterior peristomial ring lobe entire, triangular. Dorsal pockets of collar present, showing vascular coils inside them ( Fig. 15A ). Body with biannulate segments in thorax ( Figs 15C–D , 16A ). Glandular ridge present on chaetiger 2, slightly broader on dorsal side ( Fig. 15A–F ). Ventral shields rectangular, lateral borders not well defined ( Fig. 15D–E ). Interramal eyespots absent. Thoracic pre-chaetal and post-chaetal lobes well developed. Collar chaetae narrowly-hooded, in two oblique rows. Following thoracic chaetigers with slightly elevated notopodia; superior thoracic notochaetae narrowly-hooded ( Fig. 39T ), inferior, elongated broadly-hooded chaetae ( Fig. 17A , 39U ), additional anterior row of bayonet chaetae present ( Fig. 17A ). Thoracic neuropodial uncini acicular with rows of similar-sized teeth over main fang covering half its length, poorly developed breast and long handle ( Figs 17C–D , 39W ). Companion chaetae absent.Abdominal neuropodia low and inconspicuous, with narrowly-hooded chaetae in transverse rows. Anterior abdominal uncini avicular with rows of similar-sized teeth above main fang, occupying half its length, quadrangular breast, handle absent ( Figs 17E , 39V ); posterior chaetigers with similar-sized teeth over main fang, occupying 3/4 of its length, smaller rectangular breast, handle absent. Pre-pygidial depression ventral, composed by last nine chaetigers, forming a skirt or sheath of same height ventrally and laterally dorsally divided by faecal groove ( Fig. 16C–F ). Pygidium as a triangular lobe without cirrus. Pygidial eyespots not seen. Tube composed of fine sand.

Methyl green staining pattern. Homogenous blue coloration ventrally in thorax, except for anterior collar margin that remains unstained ( Fig. 15E ). Thorax dorsal do not stained with methyl green ( Fig. 15F ). Posterior abdomen with epithelium covered by scattered blue dots dorsally ( Fig. 15E ) and blue triangular areas ventrally ( Fig. 15F ).

Etymology. This species is named after Mercedes Cordero-Ruiz, in recognition to her long trajectory, working and supporting all laboratory activities related to the TALUD Project. The species-group name is a noun in the genitive case ( ICZN 1999, Art. 31.1.2).

Remarks. The pre-pygidial depression of the specimens here reported from the TALUD project is remarkably different to that of other 36 species recognized in Euchone , but in particular to those described from the Californias ( USA and Mexico) ( Table 2). It is ventral, composed by the last nine abdominal chaetigers, forming an entire sheath (or skirt) that, when observed either ventrally or laterally is of the same height. When comparing the new taxon with species described from the Californias, the pre-pygidial depression is: sail-like in E. arenae (six chaetigers) and E. velifera (7–9 chaetigers) ( Hartman 1966; Banse 1972), with a distinct ridge marking anterior and lateral edges without lateral wings in E. limnicola (10 chaetigers) ( Reish 1959); bordered by thickened rim which is continuous anteriorly in E. magna (seven chaetigers) ( Fauchald 1972; Fitzhugh 1989: 18); and with two triangular flaps in the mid-anterior margin of the depression, lateral margins forming wings in E. cortezi ( Table 2). In Euchone hanckocki Banse, 1970 the pre-pygidial depression is composed by three chaetigers only, but the presence of an anterior ridge or lateral wings is not mentioned in the original description. However, E. hancocki lacks ventral shields (present in Euchone mercedesae sp. nov.) and the anterior peristomial ring lobe is bifid (entire in E. mercedesae sp. nov.).

Abiotic conditions. The specimens of E. mercedesae sp. nov., were collected from 1,030 ‒1,586 m deep, under in the following environmental conditions. Temperature: 2.78‒5.00°C; salinity: 34.50‒34.60; dissolved oxygen: 0.20‒0.68 ml O 2 /l; %MO: 7.35; sediments dominated by silt (65.4) ( Table 1).

Distribution. Central and southern Gulf of California, Mexico.

(includes Pacific Ocean only).

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Genus Fabrisabella Hartman, 1969

Figures

FIGURE 15. Euchone mercedesae sp. nov. A) Thorax, dorsal side, B, F) same, dorso-lateral view, C) same, ventro-lateral view, D–E) same, ventral side. E–F) stained with methyl green. Abbreviations: gr2–glandular ridge on chaetiger 2, vc–vascular coils, vsc–ventral shield of collar. Scale bars: A, D–E) 1.7 mm, B) 1 mm, C, F) 0.7 mm. A–F: holotype ICML-EMU-14028.

FIGURE 16. Euchone mercedesae sp. nov. A) Transition between thorax and abdomen, B) medium-abdomen, C–F) prepygidial depression, different views. E–F) Stained with methyl green. Scale bars: A–C, F) 1.5 mm, D–E) 1 mm. A–F: holotype ICML-EMU-14028.

FIGURE 17. Euchone mercedesae sp. nov. A) Thoracic chaetiger 4, B) inferior row of paleate chaetae, C–D) thoracic acicular uncini from chaetiger 4, E) uncini from mid-abdominal. Scale bars: A) 100 μm, B) 15 μm, C) 50 μm, D) 20 μm, E) 25 μm. A–E: holotype ICML-EMU-14028.

FIGURE 39. Line drawings of chaetae and uncini. A–B, F–G, K, Q, T–U, X) Thoracic chaetae. C, H, L, R, W, Z) Thoracic uncini. D, I, N–O, S, V, Z1) Abdominal uncini. E) Companion chaeta. J) Abdominal chaeta. M, Y) Bayonet chaetae. A–E) Bispira beatrizae sp. nov. F–J) Bispira nunezi sp. nov. K–P) Chone tamai sp. nov. Q–S) Claviramus villalobosi sp. nov. T–W) Euchone nmercedesae sp. nov. X–Z1) Jasmineira agustinae sp. nov. Scale bar: 30 μm.