Niphargus polymorphus, Fišer & Trontelj & Sket, 2006

Fišer, Cene, Trontelj, Peter & Sket, Boris, 2006, Phylogenetic analysis of the Niphargus orcinus species- aggregate (Crustacea: Amphipoda: Niphargidae) with description of new taxa, Journal of Natural History (J. Nat. Hist.) 40 (41 - 43), pp. 2265-2315 : 2294-2299

Niphargus polymorphus n. sp. ( Figures 7 , 20–23 )

Type locality. Bileća , Bosnia and Herzegovina

Material examined. Bileća , Bosnia and Herzegovina; September 1956; coll. B. Sket; 2 females.

Holotype: female, 16.1 mm; slide no. 3.

Paratypes: female, 1 specimen dissected, slide no. 2; 5 specimens, not dissected.

Holotype and paratypes deposited in the collection of Oddelek za biologijo, Biotehniška fakulteta, Univerza v Ljubljani ( Department of Biology , Biotechnical Faculty , University of Ljubljana).

Etymology. The name was given on the basis of the mosaic appearance of certain features characteristic of various other species (coxae, bases and number of hooks in retinacles) as well as for the polymorphism of some characters (dorsal setae on carpus of gnathopods I–II, additional spine on dactyl VII), which are usually stable in other species.

Diagnosis

Pleonites I–III with spines and some setae along dorso-posterior margin. Telson with 8–9 apical spines per lobe. Coxal plate of gnathopod I antero-ventrally produced; coxal plates II–IV narrow (width:depth is 1:0.5–0.75); coxal plate IV with well developed posterior lobe. Coxal plates V–VI with posterior lobe much larger than anterior lobe. Bases V–VI with disto-anterior lobe equally developed as disto-posterior lobe; basis VII with extremely large disto-posterior lobe. Pleopods I–III with 3 hooks in retinacles.

Description

Head and trunk ( Figures 7 , 22 ). Body length up to 21.5 mm. Head length 11–13% of body length; rostrum absent. Pereonites I–VI without setae; pereonite VII with 3–4 posteroventral setae.

Pleonites I–III with up to 29 spines and setae along dorso-posterior margin. Epimeral plate II: angle of postero-ventral corner acute; posterior margin straight to concave; ventral margin convex; along ventral margin 3–4 spines; along posterior margin 11–15 setae. Epimeral plate III: angle of postero-ventral corner acute; posterior margin concave; ventral margin convex; along ventral margin 4 spines; along posterior margin 11–15 setae.

Urosomites I–II postero-dorso-laterally with 5 spines; urosomite III without setae and/or spines. At the base of uropod I 1 spine.

Telson length:width is 1:0.75–0.85; cleft 0.7–0.75 of length; apical telson spines 0.3– 0.35 of the length. Plumose setae inserted laterally in the middle part of telson. Only apical spines, 8–9 per lobe, present.

Antennae ( Figure 20 ). Antenna I 0.9 of body length. Flagellum with 50–62 articles; each article with 1–2 aesthetascs. Peduncle articles in ratio 1:0.8–0.9:0.7. Proximal article of peduncle dorso-distally slightly produced. Accessory flagellum biarticulated; distal article shorter than half of proximal article length.

Length ratio antenna I:II is 1:0.25–0.3. Flagellum of antenna II with 13 articles; aesthetascs absent. Antenna II peduncle articles 4 and 5 equally long (1:1); flagellum 0.6– 0.65 of peduncle length (articles 4+5). Article 4 of antenna II peduncle proximally with ventral row of fine setae.

Mouth parts ( Figure 20 ). Inner lobe of labium longer than half of the outer lobe.

Left mandible: incisor with 5 teeth, lacinia mobilis with 4 teeth; between lacinia and molar row of serrated spines, long seta at the base of molar. Right mandible: incisor process with 4 teeth, lacinia mobilis with several small denticles, a row of serrated setae and molar process with a long basal seta. Mandibular palp articles 2:3 (distal) is 1:1.15. Proximal palp article without setae; the second article with 12 setae groups and single setae; distal article with 1 A group of 16 setae; 6 B groups; 41 D single setae; 6 E single setae.

Maxilla I distal palp article with 10–12 apical setae. Outer lobe of maxilla I with 7 uni-, bi- or pluri-toothed spines; inner lobe with 8 setae.

Maxilla II inner lobe slightly smaller than outer lobe; both of them with numerous apical setae.

Maxilliped palp article 2 with 11 rows of setae along inner margin; distal article with a dorsal seta and a group of setae at the base of nail. Outer lobe of maxilliped with 15–16 flattened spines and 6–8 serrated setae. Inner lobe with 5 flattened spines and 9–11 serrated setae apically.

Coxal plates, gills ( Figures 7 , 21–23 ). Coxal plate I antero-ventrally produced; anterior and ventral margin of coxa I with 14–15 setae. Coxal plate II width:depth is 1:0.7–0.73; anterior and ventral margin with 17–18 setae. Coxal plate III width:depth is 1:0.55–0.6; anteroventral margin with 23 setae. Coxal plate IV width:depth is 1:0.7–0.8; postero-distally remarkably widened (postero-distal lobe exceeds 0.2 coxa width); antero-ventral margin with 31 setae. Coxal plates V–VI: posterior lobe much larger than anterior lobe; along posterior margin 6–7 setae, distally spine/very strong seta. Coxal plate VII half-elliptic, ventral margin slightly concave; posterior margin with 2 setae. Gills II–VI large, irregularly ovoid.

Gnathopod I ( Figure 21 ). Ischium with single postero-distal row of setae row. Carpus 0.6– 0.65 of basis length and 0.95–1 of propodus length. Anterior margin of carpus with distal group of setae, additional groups may be present; carpus posteriorly with transverse rows of setae proximally, a row of lateral setae and submarginal setae groups; postero-proximal bulge large (1/3 of carpus length), positioned proximally. Propodus rectangular, palm short, convex and slightly inclined. Posterior margin with 14 rows of denticulated setae. Anterior margin with 35–40 setae in 5 groups; antero-distal group with 14–15 setae. Group of 3–4 facial setae proximally of palmar spine; small groups of surface setae present. Palmar corner with strong palmar spine, 1–2 supporting spines on inner surface and 4 denticulated spines on outer side. Nail length 0.23 of total dactylus length; along anterior margin 7–8 single setae and a distal group of 2 setae; short setae along inner margin present.

Gnathopod II ( Figure 21 ). Basis width:length is 1:0.3. Ischium with single postero-distal row of setae. Carpus 0.6–0.65 of basis length and 1.1–1.15 of propodus length. Anterior margin of carpus with distal group of setae, sometimes additional groups of setae are present; carpus posteriorly with transverse rows of setae proximally, a row of lateral setae and submarginal setae groups; postero-proximal bulge large (1/3 of carpus length), positioned proximally. Gnathopod II propodus small (compared to the body) and larger than propodus of gnathopod I. Propodus rectangular, palm short, convex and slightly inclined. Posterior margin with 17–18 rows of denticulated setae. Anterior margin with 15 setae in 4–5 groups; antero-distal group with 12–15 setae. Group of 4–5 facial setae proximally of palmar spine; small groups of surface setae present. Palmar corner with strong palmar spine, single supporting spine on inner surface and 3 denticulated spines on outer side. Nail length 0.2 of total dactylus length; along anterior margin 6–7 single setae and a distal group of 2 setae; short setae along inner margin present.

Pereopods III–IV ( Figure 22 ). Lengths of pereopods III–IV equal (1:1). Dactylus IV 0.5 of propodus IV length; nail length 0.4 of total dactylus length. Dactyli III–IV with dorsal plumose seta; at the base of nail a spine and a seta.

Pereopods V–VII ( Figure 23 ). Lengths of pereopods V:VI:VII is 1:1.15–1.2:1.01–1.15. Pereopod VII length 0.6–0.65 of body length.

Bases V–VI length:width is 1:0.75–0.8; anterior and posterior margins convex; distoanterior lobe equally large or larger than disto-posterior lobe; posterior margin with 33–34 (basis V) and 24–25 (basis VI) setae; anterior margin with 10–13 single and/or groups of slender spines and/or setae. Dactyla V–VI with 2–3 plumose setae, at the base of nail a spine and a seta.

Basis VII length:width is 1:0.85–0.9; posterior margin convex with large disto-posterior lobe; posteriorly with 21–22 setae and spines; anteriorly with 10–11 single and/or groups of slender spines and/or setae. Propodus:dactylus is 1:0.2–0.25. Dactylus VII with 2–3 dorsal plumose seta; at the base of nail a spine and a seta, additional spine on inner margin may occur.

Pleopods and uropods ( Figure 22 ). Pleopods I–III with 3-hooked retinacles and few setae; occasionally distally of retinacle occurs a spine. Pleopod II rami of 24–27 articles each.

Uropod I protopodit with 7 dorso-lateral spines and 6 dorso-medial spines. Exopodite:endopodite lengths is 1:1.1–1.15; rami straight. Uropod I rami with groups of spines and plumose setae along medial and lateral surface. Endopodite with 10–19 setae and/or spines in 4–7 groups of spines and/or setae; apically 5 spines. Exopodite with up to 24–25 setae and/or spines in 7–8 groups of spine and/or setae; apically 5 spines.

Uropod II exopodite:endopodite lengths is 1:1.1.

Uropod III length 0.17–0.18 of body length. Protopodite with 2 lateral setae; 9–10 apical spines and/or setae. Endopodite 0.55–0.7 of protopodite length; apically with spines and plumose setae; totally with 2–3 setae and/or spines; laterally 2–3 setae and/spines in 1–2 groups. Exopodite of uropod III distinctly flattened; distal article 0.13–0.14 of proximal article length. Proximal article with 7–8 groups of setae, plumose setae and spines along inner margin and 4 groups of spines and/or setae along outer margin. Distal article of exopodite with 0–1 lateral setae groups; setae set along single margin; apically 2–7 setae.

Variability. The paratype is without additional spine on dactyls VII as well as without additional setae groups along anterior margin of gnathopods I–II. Spine distally of retinacles occurs irregularly. Males not known.

Remarks and affinities. Niphargus polymorphus resembles N. carcerarius in most characters, from which it can be distinguished by larger body size, spines along the dorso-posterior margin of pleonites and three hooks in the retinacles of the pleopods. Otherwise N. polymorphus shares some characters with N. longiflagellum (wide bases and structure of distal lobes of pereopods V–VII, large disto-posterior lobe on coxa IV, shape of gnathopods) as well as N. steueri (shape of coxal plate I, much larger posterior lobe on coxae V–VI) and N. pectinicauda (narrow coxal plates of pereopods I–IV, large disto-posterior lobe on coxa IV, much larger posterior lobe on coxae V–VI). However, N. polymorphus can be easily distinguished from all these species by the presence of the three hooks in the retinacle of pleopods and a higher number of apical telson spines.

Figures

Figure 7. N. lourensis sp. n. (above) and N. polymorphus sp. n. (below). Holotypes, lateral view.

Figure 20. Niphargus polymorphus sp. n., holotype. Mouthparts.

Figure 21. Niphargus polymorphus sp. n., holotype. Gnathopod I (above) and gnathopod II (below).

Figure 22. Niphargus polymorphus sp. n., holotype. Pereopods III–IV, detail of pereopod IV dactylus. Retinacle of pleopod II. Uropods I–III. Telson.

Figure 23. Niphargus polymorphus sp. n., holotype. Pereopods V–VII. Details of pereopod VII.