Dactylopleustes Karaman & Barnard, 1979

Labay, Vjacheslav S., 2025, Review of amphipods of the family Pleustidae Buchholz, 1874 (Amphipoda) from the coastal waters of Sakhalin Island and Kamchatka Peninsula (Far East of Russia). IV. Subfamily Dactylopleustinae Bousfield and Hendrycks, 1994, Zootaxa 5627 (2), pp. 201-253 : 204-250

Genus Dactylopleustes Karaman & Barnard, 1979

Dactylopleustes Karaman & Barnard, 1979: 112 .— Hirayama 1988: 44.— Barnard & Karaman 1991: 647.— Bousfield & Hendrycks 1994: 38.— Bousfield & Hendrycks 1995: 119.— Tomikawa et al. 2004: 3 .

Type species. Parapleustes echinoicus Tzvetkova, 1975 .

Species. Including the new species described here, Dactylopleustes contains 9 species: D. awatschensis sp. nov., D. echinoicus ( Tzvetkova, 1975) , D. echinoides Bousfield & Hendrycks, 1995 , D. longoantennis sp. nov., D. obsolescens Hirayama, 1988 , D. okhotensis sp. nov., D. ornatus sp. nov., D. tzvetkovae sp. nov., D. yoshimurai Tomikawa et al., 2004 ( Tzvetkova 1975; Karaman & Barnard 1979; Hirayama 1988; Barnard & Karaman 1991; Bousfield & Hendrycks 1994, 1995; Tomikawa et al. 2004; http://www.marinespecies.org; new data).

Diagnosis (from Karaman & Barnard 1979; Barnard & Karaman 1991; Bousfield & Hendrycks 1995, with additions). Body small, smooth, lysianassiform; coxal plates deep, pereopods short. Rostrum short, about equal to latral head lobe. Inferior antennal sinus shallow. Antenna 1 short, not longer than antenna 2; peduncular article 2 shorter than article 1, article 3 very short. Antenna 2 pediform, flagellum shorter than peduncle.

Mouthparts highly modified.Lower lip:inner lobes tall if present, outer lobes large, nearly horizontal.Mandibular molar process small, rounded, without triturating surface; left lacinia 5–9-dentate, right lacinia absent; palp slender, article 1 short, without setae, article 2 weakly setose, article 3 with pectinate setae along inner margin. Maxilla 1: outer plate short, broad, apical setae numerous, slender, innermost seta strongest. Maxilla 2: outer plate with strong spine-like apical setae. Maxilliped: plates weakly armed; inner plate with/without a few tiny button-shape apical setae; outer plate, inner margin concave, apex weakly setose; palp short, article 1 almost as long as article 2, article 3 longest, with medio-distal row of setae, article 4 slender.

Coxal plates 1–4 broad, much deeper than body plates (excluding D. longoantennis sp. nov.), coxal plate 1 distinctly smallest, not expanded distally; postero-distal cusps 2–5 per plate, small. Coxal gills largest on pereopods 3–5, smallest on pereopod 6. Gnathopods short, small, subequal in length, subsimilar, not sexually dimorphic; basis slender, anterior margin variously setose (more strongly in gnathopod 1); merus rounded distally; carpus subequal in length to propodus, variously setose posteriorly; propodus, palm very short, convex, with a few short spine-like setae at postero-distal angle, posterior margin long, with 2–4 groups of setae in gnathopod 1, 2–5 groups of setae in gnathopod 2; dactylus short, smooth.

Pereopods 3–7 short; carpus and propodus with numerous short spine-like setae; dactylus very short, stout, inner margin nearly straight, finely crenulate or pectinate. Pereopods 5–7 regularly homopodous; coxal plate very deep, posterior lobe rounded below, basis broad, evenly rounded or with rounded obtuse angle behind.

Epimeral plates medium deep, broad, ventral margin smooth or with a few tiny spine-like setae, postero-distal corner acuminate. Pleopod peduncle short, rami with variously reduced numbers of articles, not sexually dimorphic. Uropods 1 and 2 short, stout; rami sublanceolate, margins serially “spinose” (with tiny spine-like setae), tips without setae or with single spine-like seta (in D. obsolescens ). Uropod 3: peduncle short, stout, rami broad-lanceolate, inner ramus larger than outer.

Distribution. Marine waters of boreal Pacific.

Remarks. Karaman & Barnard (1979) established a new genus Dactylopleustes with only the type species Parapleustes echinoicus Tzvetkova, 1975 . The main distinguishing features of the genus after Karaman & Barnard (1979) were structures of dactylus of pereopods 3–7 (“swollen, bearing large inferior distal notch and serrate or tuberculate inferior margin”) and maxilla 2 (“apices of maxilla 2 spinose”). Barnard & Karaman (1991) adhered to the characteristics diagnostic of Karaman & Barnard (1979).

Bousfield & Hendrycks (1995) expanded the diagnosis of the genus Dactylopleustes . New main features are: the shape of body, the structure of antenna 1 and 2, mouthparts, gnathopods, pereopods and pleopods.

Bousfield & Hendrycks (1995) mentioned two subgeneric names within the genus Dactylopleustes in their key. These were Apodactylopleustes 1 and Neodactylopleustes, not described in a orinary and formal manner. The two subgeneric names are new to science, and seem to be available, because only one species ascribed to the respective subgenus (monotypy) in their key. Thus the genus Dactylopleustes contains 3 subgenera: Apodactylopleustes Bousfield & Hendrycks, 1995 (type species = D. obsolescens Hirayama, 1988 , by monotypy), Neodactylopleustes Bousfield & Hendrycks, 1995 (type species = D. echinoides Bousfield & Hendrycks, 1995 , by monotypy), and nominal subgenus Dactylopleustes Karaman & Barnard, 1979 (type species = Parapleustes echinoicus Tzvetkova, 1975 , by original designation). The basis for the identification of subgenera was the ratio of the sizes of eyes, segments of the mandibular palp, coxal plates 1 and 2, telson, uropods 1 and 2, and the armament of the outer plate of maxilla 1.

Tomikawa et al. (2004) described D. yoshimurai sp. nov. and provided a new key to all species, but did not adopted the subgenera proposed by Bousfield & Hendrycks (1995).

Key to species of genus Dactylopleustes Karaman & Barnard, 1979

1. Antenna 2, flagellum with 8 or more articles ( Fig. 2j, k, l )..................................................... 2

- Antenna 2, flagellum with 5 or fewer articles ( Fig. 2m –r )...................................................... 4

2. Antenna 1, flagellum with 11–12 or fewer articles ( Fig. 2b, c ); maxilliped, outer plate with 1–2 heavy apical setae ( Fig. 4k, l ) ................................................................................................... 3

- Antenna 1, flagellum with 17–18 articles ( Fig. 2a ); maxilliped, outer plate with 3 heavy apical setae ( Fig. 4j )............................................................................................ D. longoantennis sp. nov.

3. Antenna 1, flagellum with 11–12 articles ( Fig. 2b ); maxilliped, outer plate with 2 heavy apical setae ( Fig. 4k )............................................................................................... D. tzvetkovae sp. nov.

- Antenna 1, flagellum with 8 articles ( Fig. 2c ); maxilliped, outer plate with heavy apical seta ( Fig. 4l ).......................................................................... D. yoshimurai Tomikawa, Hendrycks & Mawatari, 2004

4. Mandible, palp article 3 longer than articles 1 and 2 together ( Fig. 3k ); pereopod 2 (gnathopod 2), posterior margin of propodus with 2 groups of long setae ( Fig. 5r ).............................................. D. obsolescens Hirayama, 1988

- Mandible, palp article 3 shorter than articles 1 and 2 together ( Fig. 3f–j ); pereopod 2 (gnathopod 2), posterior margin of propodus with 3 groups of long setae ( Fig. 5m –q )............................................................ 5

5. Pereopods 2 (gnathopod 2), 3 and 4, basis strongly setose anteriorly ( Fig. 6h )........................................................................................................ D. echinoides Bousfield & Hendrycks, 1995

- Pereopods 2 (gnathopod 2), 3 and 4, basis with or without setae sparsely scattered along anterior margin ( Fig. 6g, i, k, m ).. 6

6. Pereopod 1 (gnathopod 1), posterior margin of propodus with 2 groups of long setae ( Fig. 5g, h )...................... 7

- Pereopod 1 (gnathopod 1), posterior margin of propodus with 3–4 groups of long setae ( Fig. 5d, f ).................... 8

7. Maxilliped, outer plate with 2 heavy and 1 small apical setae ( Fig. 4q ); palp article 3 long and narrow ( Fig. 20d, e )........................................................................................... D. okhotensis sp. nov.

- Maxilliped, outer plate with 1 heavy and 1 small apical setae ( Fig. 4p ); palp article 3 short and wide ( Fig. 26a, g )............................................................................................... D. ornatus sp. nov.

8. Antenna 1, flagellum with 6 or fewer articles ( Fig. 2f ); mandible, palp article 3 as long as article 2 ( Fig. 3h ).............................................................................................. D. awatschensis sp. nov.

- Antenna 1, flagellum with 8 articles ( Fig. 2d ); mandible, palp article 3 2 times as long as article 2 ( Fig. 3f )......................................................................................... D. echinoicus ( Tzvetkova, 1975)

Figures

FIGURE 2. Dactylopleustes spp.: antenna 1—a–i; antenna 2—j–r: a, j—D. longoantennis sp. nov., b, k—D. tzvetkovae sp. nov., c, l—D. yoshimurai (from Tomikawa et al. 2004: fig. 1), d, m—D. echinoicus (from Tzvetkova 1975), e, n—D. obsolescens (from Hirayama 1988: fig. 270), f, o—D. awatschensis sp. nov., g, p—D. okhotensis sp. nov., h, q—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), i, r—D. ornatus sp. nov.

FIGURE 3. Dactylopleustes spp.: mandible—a–k; maxilla 1—l–t: a, b, l—D. longoantennis sp. nov., c, m—D. tzvetkovae sp. nov., d, e, n—D. yoshimurai (from Tomikawa et al. 2004: fig. 1), f, o—D. echinoicus (from Tzvetkova 1975), g, p—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), h, q—D. awatschensis sp. nov., i, r—D. ornatus sp. nov., j, s—D. okhotensis sp. nov., k, t—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 4. Dactylopleustes spp.: maxilla 2—a–i; outer plates of maxilliped—j–r: a, j—D. longoantennis sp. nov., b, k—D. tzvetkovae sp. nov, c, l—D. yoshimurai (from Tomikawa et al. 2004: fig. 1), d, m—D. echinoicus (from Tzvetkova 1975), e, n—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), f, o—D. awatschensis sp. nov., g, p—D. ornatus sp. nov., h, q—D. okhotensis sp. nov., i, r—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 5. Dactylopleustes spp.: pereopod 1 (gnathopod 1)—a–i; pereopod 2 (gnathopod 2)—j–r: a, j—D. longoantennis sp. nov., b, k—D. tzvetkovae sp. nov., c, l—D. yoshimurai (from Tomikawa et al. 2004: fig. 2), d, m—D. echinoicus (from Tzvetkova 1975), e, n—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), f, o—D. awatschensis sp. nov., g, p—D. ornatus sp. nov., h, q—D. okhotensis sp. nov., i, r—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 6. Dactylopleustes spp.: pereopod 4: a, b—D.longoantennis sp. nov., c, d—D. tzvetkovae sp. nov., e, f—D.yoshimurai (from Tomikawa et al. 2004: fig. 2), g—D. echinoicus (from Tzvetkova 1975), h—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), i, j—D. awatschensis sp. nov., k, l—D. ornatus sp. nov., m—D. okhotensis sp. nov., n—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 20. Dactylopleustes okhotensis sp. nov., holotype, male (3.4 mm): a, b—maxilla 1, c—maxilla 2, d—maxilliped, e—palp articles 3–4 of maxilliped, f, g, h—posterodistal angles of coxal plates 1–3, i—pereopod 1, j—propodus and dactylus of pereopod 1, outer side; scales: d, f, g, h—0.2 mm, a, b, c, e, j—0.1 mm.

FIGURE 26. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—maxilliped, b—inner and outer plates of maxilliped, c—pereopod 1, d, e—posterodistal corner of coxal plate 1, f—pereopod 1, inner side; paratype, female (2.9 mm): g—maxilliped, h—inner and outer plates of maxilliped; scale—0.1 mm.