Lepechinella arctica Schellenberg, 1926

Johansen, Per-Otto & Vader, Wim, 2015, New and little known species of Lepechinella (Crustacea, Amphipoda, Lepechinellidae) and an allied new genus Lepesubchela from the North Atlantic, European Journal of Taxonomy 127, pp. 1-35 : 7-10

Lepechinella arctica Schellenberg, 1926

Figs 2–4

Dorbanella sp. Schellenberg, 1925: 206–207, fig. 6.

Lepechinella arctica Schellenberg, 1926: 394 .

Lepechinella sp. Stephensen, 1938: 271–273.

Lepechinella arctica – Barnard 1973: 10. — Barnard & Karaman 1991: 268–269.

non Lepechinella arctica – Gurjanova 1951: 674–677, fig. 465 (= Lepechinella eupraxiella Barnard, 1973: 17 ).

Material examined

Holotype

Parts from peraeon and pleon ( Museum für Naturkunde Berlin: Registration no. 19.848 ). The species is recorded from the Römer & Schaudinn Expedition, st. 41, in the Polar Basin north of Nordaustlandet and Spitzbergen , Svalbard, at position 81 o 20’N, 20 o 30’E, 1000 meters, initially named Dorbanella sp. by Schellenberg (1925), but later the name was changed to Lepechinella arctica by Schellenberg (1926).

The description of L. arctica is based on new drawings of the peraeon and pleon in addition to the text and the original drawing of the head made by Schellenberg (1925). The urosome was missing in the original sample. Schellenberg (1925) briefly described the mouthparts and made a drawing of the head, but these parts have unfortunately not been found in the collections.

Redescription

Holotype

Female with fully developed oostegites, length 5.5 mm without urosome.

BODY. Two mid-dorsal teeth on peraeon segment 1. Peraeon segments 2–7 with one dorsal tooth each, a few setae and spines, primarily on the dorsal part. Coxal plates with some spines and thin setae. Coxal plate 1–7 decreasing in height posteriorly. Peraeon segments 1–7 with distinctly developed lobes above the coxal plates.

HEAD ( Fig. 2 ). According to Schellenberg (1925) (translated from German): “Head short, exclusive of the processes not much longer than 1 st thorax segment. Rostrum shaped as a heavy, acute, horizontal spine, a little wavy, half as long as 1 st joint of antenna 1. Lateral lobe of head not projecting, but provided with 2 marginal spines; postantennal corner acute. No eyes”.

head redrawn after Schellenberg (1925).

MOUTHPARTS. According to Schellenberg 1925 (translated from German): “Oral parts much projecting. Free margin of upper lip rounded, lateral lobes of lower lip distally rounded; mandibular processes very short and blunt; inner lobes well developed. Mandible strong, molar processes broad; incisor and lacinia mobilis strong and of about equal size, with several blunt teeth; spines long and strong; palp slender,

2 nd and 3 rd joints setose, 1 st joint longer than 3 rd, 2 nd joint 4 times as long as 3 rd. Inner plate of maxilla 1 much narrower than outer plate, apically with 2 strong setae; outer plate broad, with 10 dentate spines on the blunt apex; palp strong, apically with short, broad teeth. Maxilla 2 with plates apically densely setose. Inner plate shorter, and only half as broad as outer plate. Maxilliped has inner lobe somewhat oval, apically blunt, beset with setae and a few short heavy denticles; outer lobe oval, reaches to the last third of 2 nd joint of palp; distal part of inner margin beset with short thick teeth apically ending in spines; palp normal, 2 nd joint twice as long as 3 rd joint.”

PERAEON. Gills smooth with distinct distal capillary pattern; Gnathopods with slender setae on both margins. Gnathopod 1 subchelate; coxal plate 1 asymmetrically bifid, anterior process 2x the posterior process; coxal plate 1 medially tapering; propodus subequal to carpus; propodus 0.5x basis; posterior margin of carpus with 5 rows of long setae; medial part of propodus with 3 groups of setae; palm of propodus with serrulations; dactyl curved and 0.5x propodus. Gnathopod 2 subchelate and longer than gnathopod 1; coxal plate 2 tapering to an acute tip; carpus longer than merus and propodus; dactyl curved; palm of propodus serrulate. Anterior part of coxal plate 3 acute, posterior part squarely produced; width of coxal plate 3 is 4x width of basis; peraeopod 3, merus 2x carpus; merus longer than basis; propodus subequal to carpus and dactyl; dactyl lanceolate. Coxal plate 4 pointed anteriorly, posterior part squarely produced; width of coxal plate 4 is 4x width of basis; peraeopod 4, merus is the longest article and 1.3x basis; basis and propodus subequal in length; dactyl and carpus shorter than propodus; dactyl lanceolate. Coxal plate 5 is anteriorly pointed; peraeopod 5, carpus longer than merus and propodus; dactyl is broken. Coxal plate 6 rectangular shaped with an anterior bulge; peraeopod 6, merus shorter than carpus and subequal to propodus; basis longer than carpus; dactyl shorter than propodus; dactyl lanceolate. Coxal plate 7 parallogram-shaped and 2x broader than high; peraeopod 7, merus shorter than carpus and subequal to propodus; basis with a posterior proximal lobe; the tip of the lanceolate dactyl is broken.

PLEON. Segments 1–3 shorter than peraeon segments 1–7; pleon segments 1–3 with one small and large mid-dorsal tooth each; lateral lobes on pleon; epimeral plate1 larger than plates 2 and 3; posterodistal angle of epimeral plates 1–3 acute and forming a sinus, sinus largest in epimeral plates 2 and 3; few setae and some scattered spines on epimeral plates 1–3.

Remarks

L. arctica is characterized by few dorsal and lateral setae and spines. Posterior part of coxal plates 3 and 4 are squarely produced and 4x broader than basis. The shape of coxal plate 3 and 4 and relative length of leg articles of peraeopod 3 and 4 are different from L. schellenbergi and L. norvegica sp. nov. ( Table 1 ). Peraeopod 3 merus / carpus ratio is significantly higher in L. arctica than in the two other species. Schellenberg dissected the mouthparts of specimens from Spitzbergen and described them briefly. However, the mouthparts could not be drawn since we were unable to locate them in the collections. Schellenberg wrote that the postantennal corner of L. arctica was acute and mandible palp article 1 longer than article 3, which is different from L. norvegica sp. nov. Antenna 2 peduncle article 5 is 1.5–2x the length of the penultimate peduncle article in L. schellenbergi and L. norvegica sp. nov. Schellenberg wrote that the two last peduncle articles on the antenna 2 are subequal in length and that the flagellum was broken. However, the exact length of antenna 2 peduncle article 5 is uncertain, because the distal part of peduncle article 5 may also have been lost. Peraeopod 7 carpus of L. arctica is 1.6x propodus. Coxal plate 7 has the shape of a parallelogram and the posterior corner of coxal plate 7 is acute. The Peraeopod 7 carpus / propodus ratio is significantly lower in L. schellenbergi and L. norvegica sp. nov. and the posterodistal part of coxal plate 7 is rounded in these two species.

Figures

Fig. 2. Lepechinella arctica Schellenberg, 1926 (Dorbanella sp.),

Fig. 3. Lepechinella arctica, holotype, ♀. A. Left Gn1. B. Right Gn2. C. Right P3. D. Peraeon and pleon.

Fig. 4. Lepechinella arctica, holotype, ♀. A. Right P4. B. Right P6. C. Right P5. D. Right P7. E. Tooth of peraeon segment 6. F. Gill of P5. G. Ep1. H. Ep2. I. Ep3. J. Spine on Ep3.