Potamethus filatovae ( Levenstein, 1961 ) Tovar-Hernandez & Jirkov, 2024

Tovar-Hernandez, Maria Ana & Jirkov, Igor A., 2024, Jasmineira filatovae Levenstein, 1961, the deepest known sabellid is a Potamethus Chamberlin, 1919: redescription, new combination and generic emendation, Zootaxa 5486 (1), pp. 48-70 : 49-52

Potamethus filatovae ( Levenstein, 1961) , new combination

Figures 1–5

Jasmineira filatovae Levenstein, 1961 , 173, fig. 10.— Hartman, 1965a: 77 (catalogue).— Levenstein, 1966: 75–76.— Levenstein, 1969: 60 (table).— Levenstein, 1973: 132 (table).— Capa & Murray, 2015: 124 (table).— Alalykina, 2020: 200 (table).— Capa et al. 2021: supplementary file (catalogue).

Potamethus filatovae — Belyaev, 1989: 181 (table).

Type material

[ Shirshov Institute of Oceanology] Bering Sea , R / V Vitjaz, St. 618, 25/9/1950, 3940 m, 57°30’N, 168°30 ‘E (lectotype INV0003597 and 7 paralectotypes INV0001520, 3 of them with intact branchiae) and R / V Vityaz, St. 539, 25/8/1950, 3812 m, 58°39’N, 177°43‘E (8 paralectotypes INV0001521). Bottom temperature 1.56°C and 1.62°C, respectively; bottom salinity 34.60‰ and 34.71‰, respectively; sediment composed of fine silt and claydiatom silt, respectively .

Redescription (based on lectotype, with variation of paralectotypes in brackets).

Body slightly flattened dorso-ventrally. Body length excluding crown 66 (15–85) mm, 3 mm wide. Radiolar crown 24 (15–65) mm long. Crown composed of semi-circular radiolar lobes fused dorsally. Twelve (8–25) pairs of radioles not fused by an inter-radiolar membrane, not arranged into a spiral, without eyes or flanges. Radiolar tips entire, filiform ( Fig. 1G ). Marginal base of crown with parallel lamellae bordering ventrally ( Figs 1B , 2D, E ). Anterior and posterior peristomial rings distinctly elongated ( Figs 1C , 2A, B ). Posterior peristomial ring, commonly known as collar, not covering radiolar bases ( Figs 1C , 2D ). Mid-ventral margin of collar incised, forming two rounded lappets ( Figs 1B , 2E ) as long as chaetiger 1. Ventral sacs rounded, exposed outside radiolar crown ( Figs 1B , 2E ). Lateral collar margin oblique ( Figs 1C , 2A ), elongate toward ventral side, exposing anterior peristomial ring ( Figs 1C , 2D ). Dorsal collar margins V-shaped, fused to faecal groove, forming dorsal pockets ( Figs 1A , 2A–C ). Anterior peristomial ring fully exposed above dorsal collar margins ( Figs 1A , 2A–C ). Mid-dorsal margin of anterior peristomial ring triangular ( Fig. 2B ), visible once crown removed. Oval brownish peristomial moldures exposed beyond dorsal collar margins ( Figs 1A , 2A–C ). Dorsal lips with mid-rib (radiolar appendages), dorsal pinnular appendages absent. Ventral lips ear-shaped. Ventral shield of collar well developed, almost trapezoidal ( Figs 1B , 2E ). Two diagonal glandular shields at the base of ventral lappets, separated from each other by mid-ventral incision of collar ( Figs 1B , 2E ).

Collar chaetae (chaetiger 1) composed of two groups of narrowly hooded chaetae ( Figs 3A, B , 4A, B ); superior group more longer than two times the length of the inferior group ( Fig. 3A ). Thorax with 8 chaetigers ( Fig. 1D ). Ventral thoracic shields well developed, rectangular ( Fig. 1D ). Glandular ridge on chaetiger 2 visible only dorsally, broad, brownish in lectotype (in some paralectotypes hardly visible).

Thoracic notochaetae of chaetigers 2–8 with superior group of elongate narrowly hooded chaetae ( Figs 3C, D , 4D ) and with inferior group of paleate chaetae arranged in 3 rows ( Figs 3C, E–H , 4C–E ). Bayonet chaetae absent. Thoracic uncini avicular, with handles 7–8 times longer than crest length ( Fig. 3J ); crest without hood, with 5–6 rows of teeth of nearly equal size above main fang, covering half of main fang ( Fig. 3K ), and with a small hump on the angle between external margin of neck and handle (a slight swelling opposite to breast). Companion chaetae teardrop shaped, with a narrow dentate head and very long tip (+3 times longer than uncinal main fang), some tips distally enrolled ( Fig. 3L–M ).

Abdomen with 51 (26–58) chaetigers. Ventral abdominal shields well developed, oval, with marked brown margins, separated from each other by faecal groove ( Fig. 1E ). Abdominal neurochaetae with two rows of narrowly hooded chaetae, those of inferior row three times shorter than those in superior row ( Fig. 5A–C, E–G ); surface covered with fine bristles visible only under SEM ( Fig. 5D ). Abdominal uncini avicular with a small hump on the angle between external margin of neck and handle (a slight swelling opposite to breast) ( Fig. 5J–K ); breast as a narrow swelling, handles 2.5 times longer than crest length ( Fig. 5J–L ), main fang surmounted by 4–5 rows of nearly equal-size teeth above main fang, covering half of main fang ( Fig. 5J–I ).

Pygidium with terminal anus ( Fig. 1F ) and two lateral rounded papillae, visible in some paralectotypes and mentioned in the original description, and without anal cirrus. Tubes silty, smooth, fragile ( Fig. 2G ). One tube of paralectotype with eggs inside ( Fig. 2F ).

Figures

FIGURE 1. Potamethus filatovae (Levenstein, 1961) n. comb., lectotype stained with methylene blue.A) Peristomial moldures and first three thoracic chaetigers, dorsal view, B) collar and base of radiolar crown, ventral view, C) base of radiolar crown, peristomium and first three thoracic chaetigers, lateral view, D) thorax, ventral view, E) mid-abdominal segments, ventral view, F) posterior end, dorsal view, G) distal ends of radioles.Abbreviations: apr—anterior peristomial ring, fg—faecal groove switch, pl—parallel lamella, pm)—peristomial moldure, vs—ventral sacs, vsc—ventral shield of collar. Numbers: 1, 2, 3 …—number of chaetigers. Scale bars: A–C, F) 500 um, D) 2 mm, E) 1 mm, G) 2.5 mm. White arrow and asterisk in B points to the incised mid-ventral margin of collar.

FIGURE 2. Potamethus filatovae (Levenstein, 1961) n. comb., paralectotypes stained with methylene blue. A) Peristomium and first three thoracic chaetigers, latero-dorsal view, B) peristomium and first three thoracic chaetigers, dorsal view, C) base of radiolar crown, peristomium and first two thoracic chaetigers, dorsal view, D) base of radiolar crown and collar, lateral view, E) base of radiolar crown and collar, ventral view, F) internal wall of tube with oocytes, G) worm partially exposed from tube.Abbreviations: apr—anterior peristomial ring, pl—parallel lamella, pm—peristomial moldure, vs—ventral sacs, vsc—ventral shield of collar. Numbers: 1, 2, 3 …—number of chaetigers. Scale bars:A, B) 1.25 mm, C–E) 500 um, F–G) 2.5 mm. Black arrow in B points to the triangular, mid-dorsal margin of anterior peristomial ring. Black arrow and asterisk in E points to the incised mid-ventral margin of collar, other two black arrows points to the diagonal glandular shields at the base of ventral lappets.

FIGURE 3. Scanning electron and light microscopy of thoracic chaetae and uncini of paralectotypes of Potamethus filatovae (Levenstein, 1961) n. comb. A–B) Narrowly hooded chaetae from collar (chaetiger 1), C) chaetiger 2, D) superior group of elongate, narrowly hooded chaetae from chaetiger 2, E) chaetiger 3, F) inferior paleate chaetae from chaetiger 3, G) chaetiger 4, H) inferior group of paleate chaetae from chaetiger 8, I) companion chaeta of chaetiger 2, J) uncini from chaetiger 2, K) dentition of uncini of chaetiger 2, L) torus of chaetiger 3 (uncini and companion chaetae), M) details of companion chaetae of chaetiger 3. Light microscopy: A–B, I–J. SEM: C–H, K–M. Scale bars: A) 200 μm, B, I) 20 μm, C–E, G, J) 100 μm, F) 10 μm, H, K–M) 30 μm.

FIGURE 4. Light microscopy of thoracic chaetae of paralectotypes of Potamethus filatovae (Levenstein, 1961) n. comb. A) Collar chaetiger, B) narrowly hooded chaetae from collar, C) paleate chaetae, D) chaetiger 3, E) paleate chaetae.

FIGURE 5. Scanning electron and light microscopy images of abdominal chaetae and uncini of paralectotypes of Potamethus filatovae (Levenstein, 1961) n. comb. A) Abdominal chaetiger 8 with inferior group of chaetae remarked with a rectangle, B–D) details of narrowly hooded chaetae of inferior group from abdominal chaetiger 8; E) abdominal chaetiger 3, F) details of narrowly hooded chaetae of inferior group from abdominal chaetiger 3, G) abdominal chaetiger 17, H) dentition of uncini from abdominal chaetiger 7, I) dentition of uncini from abdominal chaetiger 17, J) uncini from abdominal chaetiger 1, K) uncini from abdominal chaetiger 12, L) uncini from abdominal chaetiger 45, L). SEM:A–I. Light microscopy: J–L. Scale bars: A, E, G) 100 μm, B, C, F) 30 μm, D) 3 μm, H–L) 10 μm. Arrows in J and K point to uncinal humps.