Neopleustes Stebbing, 1906

Labay, Vjacheslav S., 2021, Review of amphipods of the family Pleustidae Buchholz, 1874 (Crustacea Amphipoda) from the coastal waters of Sakhalin Island (Far East of Russia). I. Subfamily Neopleustinae Bousfield & Hendrycks, 1994, Zootaxa 4974 (2), pp. 267-306 : 285-286

Genus Neopleustes Stebbing, 1906

Neopleustes Stebbing, 1906: 311 .— Gurjanova 1951: 641.— Gurjanova 1972: 133, 163.— Barnard 1969: 424.— Barnard & Karaman, 1991: 649.— Hendrycks & Bousfield 2004: 94.

Type species. Amphitoe pulchella Krøyer, 1845 : pl. 10.

Species. Including the new subspecies described here, Neopleustes contains 7 species + 2 subspecies ( Gurjanova 1951; Hendrycks & Bousfield 2004; http://www.marinespecies.org; Sars 1877, 1885, 1886; new data): N. boecki boecki ( Hansen, 1887) , N. boecki pacifica ssp. nov., N. carinatus Margulis, 1963 , N. columbianus Hendrycks & Bousfield, 2004 , N. euacanthoides Gurjanova, 1972 , N. euacanthus ( Sars, 1877), 1972 , N. kussakini ( Budnikova, 1995) , N. pulchellus pulchellus ( Krøyer, 1845) , N. pulchellus asiaticus ssp. nov.

Diagnosis (from Hendrycks & Bousfield 2004 with additions). Body middorsally carinate or mucronate, rarely smooth. Rostrum medium to strong, often keeled. Antenna 1 elongate, often longer than body. Antenna 2 distinctly shorter than antenna 1.

Lower lip, outer lobes oblique, widely separated by low flat inner lobes. Mandibular molar process small, thumb-like, without triturating surface; left lacinia 7–10-dentate; palp powerful, length exceeding by 2–3 times that of the mandibular body. Maxilla 2, inner plate, inner marginal seta set apart basally from apical setae. Maxilliped, inner plate truncate, with 3–7 apical button spine-like setae; outer plate slender; palp segments slender; segment 3 with short, outer distal conical projection, dactylus articulated from its medial side.

Coxal plates 1–4 medium, increasing in size posteriorly; coxal plate 1 not bent forwards distally, posterodistally cuspate. Coxal gills medium, sac-lake.

Pereopods 1 and 2 (gnathopods 1 and 2) weak, subchelate, subsimilar; posterodistal tooth of merus weak or lacking; carpus elongate, shorter than propodus, posterodistal lobe shallow; propodus with short, oblique, weakly toothed palmar margin; posterior margin setose.

Pereopods 5–7 regular, homopodous, bases usually convex behind. Epimeral plates 2 and 3, posterior corners acute, produced. Uropod 1 with distolateral peduncular spine-like seta; rami subequal.

Telson with proximal keel.

Distribution. Marine waters of arctic and boreal parts of Northern hemisphere.

Remarks. Stebbing (1906) resurrected Amphitoe pulchella Krøyer, 1845 as the type species of Neopleustes Stebbing, 1906 , that had long been synonymized within genera Pleustes Spence Bate, 1858 and Paramphithoe Bruzelius, 1859 . The main features of the genus after Stebbing (1906) were features of structure of the upper lip (“assymmetrically bilobed, incision oblique”), mandible (“molar weak, palp very large”), maxillae 1 & 2 (“nearly as in Pleustes ”), maxilliped (“dififering by joint 3 of palp distally attenuated, 4th spiniform”), pereopods 1 and 2 (“Gnathopods 1 and 2 feeble to moderately strong”). In the description of Stebbing (1906) the genus Neopleustes included representatives of modern genera Neopleustes , Parapleustes Buchholz, 1874 , Incisocalliope J.L. Barnard in J.L. Barnard & Reish, 1959.

Gurjanova (1951, 1972) adhered to the characteristics from the diagnosis of Stebbing (1906).

Barnard & Karaman (1991) changed the diagnosis of the genus Neopleustes . It was added new main features— the dorsal armament of body, rostrum, coxal plates 1–4 and structure of uropos 1–3: “Body smooth or keeled. Rostrum moderately long”; “Coxae 1–4 ordinary, or slightly acuminate distally, especially coxa 1”; “Rami of uropods 1–3 lanceolate, outer shortened, peduncle of uropod 3 without tooth”.

Hendrycks & Bousfield (2004) added new characteristics to the diagnosis of the genus: the description of lower lip, maxilla 2, epimeral plates (see Diagnosis).

G. Sars (1877) described Pleustes euacanthus sp. nov., which differed from Pleustes pulchello (now Neopleustes pulchellus ( Krøyer, 1845)) in total carination of pereon and pleosome segments. G. Sars later (1885) redescribed this species as Paramphithoe euacantha . Hansen (1887) suggested that the structural features of P. euacantha fit within the morphological variability of the closely related species Paramphithoe pulchella , and combined it with the latter species. G. Sars (1895) supported the opinion of Hansen (1887) and referred P. euacantha to P. pulchella .

Subsequently, the opinions of researchers were divided. A number of authors ( Barnard & Karaman 1991, Hendrycks & Bousfield 2004, Stebbing 1906), following Hansen (1887) and G. Sars (1895), considered Neopleustes euacanthus as one of the morphological variations of N. pulchellus ( Krøyer, 1845) and did not distinguish it as a separate species. Other authors considered it a variation of N. pulchellus ( Krøyer, 1845) ( N. pulchellus ( Krøyer, 1845) var. euacanthus (G. Sars, 1876) ( Gurjanova 1951) or a subspecies of N. pulchellus euacanthus (G. Sars, 1876) ( Wesławski 1990) .

In accordance with the graphic image of G. Sars (1885), N. euacanthus differs from N. pulchellus not only in dorsal carination, but also in the structure of coxal plates 1 and 2, which have a rounded lower margin. Our studies have shown that the number of dorsal teeth and the shape of coxal plates are persistent features within the genus Neopleustes . Therefore, in this article, the species status is restored for N. euacanthus .

Relationships: Neopleustes differs from Shoemakeroides mainly in the more srongly developed rostrum, more strongly cuspate coxal plates 1–3, and smaller pereopods 1 and 2, in which the propodus are subsimilar in form, and elongate carpus ( Hendrycks & Bousfield 2004).