Potamethus pepei, 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 : 55-59

Potamethus pepei sp. nov.

urn:lsid:zoobank.org:act:11632258-41AE-4E59-B879-DF2048D6DF9A

( Figs 30–31 , 40Q–U )

Material examined. Type material. Holotype, ICML-EMU-14048: TALUD XI, St. 1, KD, 16º52'00"N 100º22'00"W, 07 June 2007, 850 m. Additional material. ICML-EMU-14049: TALUD XV, St. 20, BS, 26º30'42"N 113º56'0"W, 01 August 2012, 498 m, 3 specimens .

Description. Body pale with a narrow brownish glandular ridge on chaetiger 2 ( Fig. 30B–C ). Body slightly flattened dorso-ventrally. Body 1.8 mm wide (1.7–1.8 mm in additional specimens). Branchial crown 34 mm long with 11 pairs of radioles (9–11 in additional specimens). Thorax with eight chaetigers ( Fig. 30H ). Abdomen with +9 chaetigers (holotype and additional specimens incomplete). Radioles not fused by palmate membrane ( Fig. 30A–C ), not arranged into a spiral, without eyes or flanges. Radioles filiform, very long tips, as long as 5 mm ( Fig. 30F–G ). Dorsal pinnular appendages absent. Marginal base of crown with parallel lamellae bordering ventrally ( Fig. 30B ). Anterior and posterior peristomial rings distinctly elongated ( Fig. 30A–C ). Anterior peristomial ring fully exposed above dorsal collar margins ( Fig. 30A ). Mid-dorsal margin of anterior peristomial ring triangular ( Fig. 30A ). Peristomial modules present dorsally. Posterior peristomial ring not covering radiolar bases ( Fig. 30A–C ). Dorsal collar margins V-shaped, fused to faecal groove, forming dorsal pockets ( Fig. 30A ). Mid-ventral margin of collar incised, forming two lanceolated lappets ( Fig. 30B, D ) as long as chaetiger 1. Ventral sacs rounded, exposed outside branchial crown and full of sand ( Fig. 30B–C, D ). Lateral collar margin oblique ( Fig. 30C ), elongate toward ventral side, exposing anterior peristomial ring ( Fig. 30C ). Dorsal lips triangular with mid-rib radiolar appendages and lateral lamellae, dorsal pinnular appendages absent. Ventral lips small, rounded. Ventral shield of collar well developed, as bifid molar-shaped ( Fig. 30B, D, H ). Two diagonal dark bands at the base of ventral lappets, separated from each other by mid-ventral incision of collar ( Fig. 30B, D ). Collar chaetae composed of two groups of narrowly hooded chaetae; superior group much longer than two times the length of the inferior group. Ventral thoracic shields well developed, rectangular ( Fig. 30B, D, H ). Glandular ridge on chaetiger 2 brown ( Fig. 30B–C ). Thoracic notochaetae with superior group of elongate narrowly hooded chaetae ( Figs 31A–B , 40S ) and with inferior group of paleate chaetae ( Fig. 31A, C ). Thoracic uncini avicular, with handles 6–7 times longer than crest length ( Figs 31E–F , 40Q ); crest without hood, with 5–6 rows of teeth of nearly equal size above main fang, covering half of main fang ( Fig. 31E ), and with a small hump on the angle between external margin of neck and handle (a slight swelling opposite to breast) ( Figs 31E , 40T ). Companion chaetae teardrop shaped ( Figs 31D, F, G , 40R ), with a narrow dentate head and very long tip (+3 times longer than uncinial main fang). Ventral abdominal shields well developed, rectangular, not well marked lateral margins, separated from each other by faecal groove ( Fig. 30E, H ). Abdominal neurochaetae with two rows of narrowly hooded chaetae, those of inferior row three times shorter than those in superior row ( Fig. 31H–I ). Abdominal uncini avicular without humps on the angle between external margin of neck and handle (a slight swelling opposite to breast) ( Fig. 31J ); breast as a narrow swelling, handles 2.5 times longer than crest length ( Fig. 31J ), main fang surmounted by 4–5 rows of nearly equal-size teeth above main fang, covering half of main fang ( Fig. 31J ). Posterior end unknown. Tubes not preserved.

Etymology. This species is named after José Salgado-Barragán (“Pepe”), a dear friend and colleague that supported not only our activities during the TALUD cruises, but also in coastal fieldwork. The specific epithet is derived from his nickname, “Pepe”, and is a noun in apposition.

Remarks. Potamethus is composed of 13 species ( Tovar-Hernández & Jirkov 2024) and the new species described below. This genus includes species mostly from the deep sea. Potamethus filatovae ( Levenstein, 1961) is the deepest sabellid ever recorded so far, reaching 9,735 m in depth ( Tovar-Hernández & Jirkov 2024). There are only two species described below 100 m: P. breviuncatus Hartmann-Schröder, 1977 and P. japonicus ( Johansson, 1922) . In addition, Hernández-Alcántara & Solís-Weiss (1999) reported an unidentified species of Potamethus from sublittoral zone of the Gulf of California. The genus was recently amended by Tovar-Hernández & Jirkov (2024).

Among the valid species of Potamethus , only three have been described from the Pacific: P. elongatus ( Treadwell, 1906) from Hawaii, USA, at 130 m depth, P. japonicus ( Johansson, 1922) from Sagami Bay, Japan, at 45–60 m depth and P. mucronatus ( Moore, 1923) from Santa Catalina Island, California, USA, at 1,000 m depth. Potamethus mucronatus was reported by Solís-Weiss et al. (2000) in the continental shelf of the Gulf of Tehuantepec (Oaxaca, Mexico). Potamethus elongatus and P. mucronatus were poorly described, but Knight-Jones (1983) reviewed the types of both species. She emphasized that both species lack ventral shields or patches, being the whole epithelium glandular all over. Potamethus pepei sp. nov., has well developed ventral shields, in both the thorax and the abdomen ( Fig. 30B–E, H ).

Original description by Johansson (1922: 8–9, pl. I, figs 3–4, pl. IV figs 4–6) for P. japonicus states that ventral shields are well developed but not distinctly limited at the sides. In contrast, Potamethus pepei sp. nov., has shields and its lateral margins are well defined. Besides, P. japonicus was described with 17 thoracic chaetigers (vs. only eight in Potamethus pepei sp. nov.) and thoracic uncini without humps (small hump in Potamethus pepei sp. nov.). The new species here described has a ventral shield of collar bifid molar-shaped, whereas it is rectangular, in P. japonicus and Potamethus elongatus (unknown in P. mucronatus ). Ventral lappets were described by Moore (1923) as prominent and round in P. mucronatus , small and rounded in P. japonicus , and lanceolated in Potamethus pepei sp. nov. In other species of Potamethus from worldwide localities the ventral lappets of the collar can be triangular in P. breviuncatus as well as in P. filiformis Hartmann-Schröder, 1977 , P. singularis Hartman, 1965 and P. spathiferus ( Ehlers, 1887) ; these are bilobed in P. dubius ( Eliason, 1951) , and rounded in P. filatovae ( Levenstein, 1961) , P. malmgreni ( Hansen, 1879) , P. murrayi ( McIntosh, 1916) , and P. scotiae ( Pixell, 1913) ( Tovar-Hernández & Jirkov 2024: tab. 2).

There is an additional species from California referred to by the Southern California Association of Marine Invertebrate Taxonomists as “ Potamethus sp. A Leslie” and “ Potamethus sp. A Williams” ( SCAMIT, 2025). As in Potamethus pepei sp. nov., the Californian species also features ventral shields in thorax, but the ventral lappets of the collar are long, triangular (short, lanceolate in Potamethus pepei sp. nov.), and a short crown (very long in Potamethus pepei sp. nov.).

Abiotic conditions. The specimens of P. pepei sp. nov., were collected from 498‒850 m deep, under the following environmental conditions. Temperature: 5.00‒8.38°C; salinity: 34.51; dissolved oxygen: 0.14‒0.15 ml O 2 /l; %MO: 5.47; sediments dominated by sand and silt (47.1 and 45.2%) or silt (61.8%) ( Table 1).

Distribution. Off Guerrero and of the West coast of Baja California Sur, Mexico.

Genus Pseudopotamilla Bush, 1905

Figures

FIGURE 30. Potamethus pepei sp. nov. A)Anterior thorax, dorsal view, B) same, ventral view, C) same, lateral view, D) ventral shields of thorax, E) ventral shields, transition between thorax and abdomen, F) branchial crown, G) radiolar tip, H) thorax and anterior abdomen. Abbreviations: apr—anterior peristomial ring, gr2—glandular ridge on chaetiger 2, vs—ventral sacs, vsc—ventral shield of collar, 1, 2, 3…12—refers to the number of chaetiger. D–F, H) Stained with methyl green. Scale bars: A–D, H) 1.8 mm, E–F) 2.2 mm, G) 3 mm. A–E, G–H) holotype ICML-EMU-14048, F) ICML-EMU-14049.

FIGURE 31. Potamethus pepei sp. nov. A) Thoracic notochaetae, B) superior group of notochaetae (elongate, narrowly hooded), C) inferior group of notochaetae (paleate chaetae), D) thoracic uncini and companion chaetae, E) thoracic acicular uncini, arrow points to hump, F) thoracic uncini and companion chaetae, G) companion chaetae, H) abdominal chaetiger, I) short group of narrowly hooded chaetae, J) abdominal uncini. Scale bars: A, F, H) 100 μm; B) 50 μm; C–E, G, I–J) 20 μm. A–J) holotype ICML-EMU-14048.

FIGURE 40. Line drawings of chaetae and uncini. A, G–H, L–M, S) Thoracic chaetae. B, E, J, O, Q, T) Thoracic uncini. C–D, F, K, P, U) Abdominal uncini. I, N, R) Companion chaetae. A–D) Myxicola bruscai sp. nov. E–F) Myxicola dilianae sp. nov. G–K) Perkinsiana araceliae sp. nov. L–P) Perkinsiana nuriae sp. nov. Q–U) Potamethus pepei sp. nov. Scale bar: 30 μm.