Jasmineira filatovae, (Levenstein, 1961)

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 : 61

Comparison of P. filatovae with other species of Potamethus

Potamethus is composed of 12 species including the new combination Potamethus filatovae proposed here ( Capa et al. 2019, 2021, Read & Fauchald, 2024b) ( Table 2 ). Based on the revision of original descriptions and the contribution provided by Knight-Jones (1983), we recognize three features potentially useful to comparative purposes at the interspecific level: the shape of dorsal collar margin and ventral collar lappets, and the presence or absence of ventral shields ( Table 2 ). However, a revision based on types is out the scope of this paper.At the generic level, the presence of oval to circular plates or moldures on each side of the anterior peristomial ring and humps in thoracic and abdominal uncini might be diagnostic as explained below.

Potamethus filitovae , as most species in Potamethus , have pronounced V-shaped dorsal collar margins, exposing the anterior peristomial ring and forming well developed pockets, whereas in P. breviuncatus Hartmann-Schröder, 1977 , P. dubius (Eliason, 1951) and P. japonicus ( Johansson, 1922) dorsal collar margins form two shallow, convex semi-circles and in P. singularis Hartman, 1965 these margins are oblique ( Table 2 ).

The ventral lappets of the dorsal collar in the species of Potamethus can be triangular ( P. breviuncatus , P. filiformis Hartmann-Schröder, 1977 , P. singularis and P. spatiferus Ehlers, 1887 ), rounded ( P. filitovae , P. japonicus , P. malmgreni (Hansen, 1878) , P. mucronatus Moore, 1923 , P. murrayi ( McIntosh, 1916) , P. scotiae ( Pixell, 1913)) or bilobed ( P. dubius ). Within each category, the length of ventral lappets might be diagnostic. For example, in P. spathiferus , the triangular ventral lappets are 2.5 times longer than the chaetiger 1 length, while in the rest of species with triangular lappets, they are short (not longer than chaetiger 1) ( Table 2 ).

The presence of large, brown, oval, semi-circular to circular moldures on each side of anterior peristomial ring is reported for P. murrayi , P. dubius , P. filatovae , P. spathiferus and P. malmgreni ( Table 2 ). The function of these organs is unknown, but McIntosh (1916) suggested that this structure is probably related to feeding in abyssal habitats.

The presence or absence of ventral glandular shields in species of Potamethus was already remarked by Knight-Jones (1983). Whereas some species, such as P. dubious , P. filitovae , P. japonicus and P. scotiae , have well developed shields at least in the thorax, in others ( P. elongatus , P. filiformis , P. mucronatus , P. murrayi , P. singularis and P. spathiferus ) the glandular epithelium of the entire body lacks shields. However, P. malmgreni from the type locality (Norwegian Sea) lacks shields as reported by Knight-Jones (1983), whereas specimens examined in this study from the Norwegian Sea and the Arctic Ocean have well-developed shields in both thorax and abdomen ( Fig. 6D ). Thus, infraspecific variation of ventral shields needs to be accessed not only for P. malmgreni , but also in all species of the genus.

Finally, even though the number of thoracic segments cannot be used to confidently distinguish species within Sabellidae ( Capa 2007, Tovar-Hernández and Dean, 2014, Keppel et al. 2015, Tovar-Hernández et al. 2020), P. japonicus was described with 17 thoracic segments, P. breviuncatus with 10, P. mucronatus with 9 and the rest of species with 8 thoracic chaetigers ( Table 2 ).

Figures

FIGURE 6. Potamethus malmgreni (Hansen, 1878) from the Norwegian Sea stained with methylene blue, light microscopy images. A) Collar and base of radiolar crown, ventral view, B) same, dorsal view, C) same, ventral view, D) ventral shields and transition of thorax and abdomen, E) ventral shields from posterior abdomen, F) thoracic uncini, arrow points to uncinal hump. Abbreviations: 1, 2) number of chaetigers, apr) anterior peristomial ring, pl) parallel lamella, vsa) ventral shields of abdominal segments, vsc) ventral shield of collar, vst) ventral shield of thoracic segments. Scale bars: A–C, E) 500 µm, D) 1 mm, F) not scaled.