Psammogammarus lobatus, Ariyama, Hiroyuki, 2015

Ariyama, Hiroyuki, 2015, Three new species of the Eriopisa group (Crustacea: Amphipoda: Eriopisidae) from Japan, with the description of a new genus, Zootaxa 3949 (1), pp. 91-110 : 98-103

Psammogammarus lobatus sp. nov.

( Figs 1 C, 6–9)

Material examined. Holotype: male (OMNH-Ar-9717), 4.0 mm, mouth of Higashi River, Misaki Town, Osaka Prefecture, 34°19'20"N, 135°07'09" ( Fig. 1 C), sandy tidal flat, reverse surface of large stone, 14 May 1991, coll. H. Ariyama. Paratypes: 1 male (OMNH-Ar-9718), 4.4 mm, and 2 females (OMNH-Ar-9719, 9720), 4.2 mm, 3.7 mm (ovigerous), same data as holotype.

Description. Male [holotype, 4.0 mm (OMNH-Ar-9717)]. Body ( Fig. 6 ) slender, depressed laterally, smooth; pereonites and pleonites without dorsal setae, urosomites free. Head longer than pereonite 1, rostrum small, eyes absent; lateral cephalic lobe rounded, anteroventral sinus indistinct.

Antenna 1 ( Fig. 7 A, A1) long, with ratio of lengths of peduncular articles 1–3 1:0.7:0.3, article 1 with ventrodistal robust seta; accessory flagellum short, 2-articulated, each article with distal setae; primary flagellum with 11 articles, articles 3–10 with 1, 2, 1, 1, 1, 0, 1, 1 aesthetascs at each distal end, respectively. Antenna 2 ( Fig. 7 B) short, slender, with ratio of lengths of peduncular articles 3–5 1:1.5:1.3; flagellum short, with 6 articles, longer than last peduncular article.

Mandible ( Fig. 7 D, D1, E, E1), each incisor bearing 5 cusps, left lacinia mobilis parallelogramatic, distal margin minutely serrated, right lacinia mobilis with 3 cusps, each accessory blade 6 in number; molar strong; palp article length ratio 1:2.2: 1.2 in left (probably regenerated) and 1:2.5: 1.9 in right, article 2 with 4 setae ventrally, article 3 with 3 and 5 setae in left and right, respectively. Lower lip ( Fig. 7 F) with small inner lobes, distal margins of outer lobes setose. Maxilla 1 ( Fig. 7 G, G1 – 2), inner plate roundish triangular, with several distal setae; outer plate with 9 robust setae apically; palp 2-articulated, tip of article 2 projected in middle, with 3 robust setae. Maxilla 2 ( Fig. 7 H), inner plate as wide as outer, dorsal surface of inner plate with sparse setae, terminal ends of both plates setose. Maxilliped ( Fig. 7 I, I1 – 2), inner plate truncate, distal end bearing 4 short robust setae; outer plate produced distomedially, with 3 long robust setae distally; palp 4-articulated, article 4 with short nail, dorsomedial surface of article 4 covered with thin setae.

Gnathopod 1 ( Fig. 8 A, A1) small, subchelate; coxa short, trapezoidal; basis widened in distal two thirds, posterior margin with 2 long setae; posterior margin of ischium with long seta; posterior margin of merus with long setae, medial surface covered with fine setae; posterior margin of carpus setose; propodus about 1.3 times as long as carpus, palm defined by 2 medial robust setae, bearing 9 minute medial robust setae; dactylus long, curved. Gnathopod 2 ( Fig. 8 B, B1) large, subchelate; coxa short, rectangular, gill curved posteriorly; basis widened in distal two thirds, posterior margin with 3 long setae; carpus lobed, posterior margin setose; propodus dilated, about 3.1 times as long as carpus, posterior margin with several bundle of setae; palm oblique, palmer margin composed of 2 lobes, 1 excavation and 2 large medial robust setae, first lobe with 2 lateral and 3 medial small robust setae, second lobe with 1 lateral and 2 medial small robust setae; dactylus stout, strongly curved.

Pereopods 3–4 ( Fig. 8 C – D) similar, slender; coxae short, trapezoidal, gills large, oval; bases linear, posterior margins with a few long setae; meri slender, widened distally; dactyli narrow, almost straight. Pereopod 5 ( Fig. 8 E, E1), posterior lobe of coxa about 0.6 times as long as anterior lobe; basis rectangular, posterodistal corner projected distally; posterodistal corner of merus with 2 robust setae; anterior margin and anterodistal and posterodistal corners of carpus with 1, 3 and 3 robust setae, respectively; anterior margin and anterodistal corner of propodus each bearing robust seta; dactylus narrow. Pereopod 6 ( Fig. 8 F, F1) about 1.5 times as long as pereopod 5; posterior lobe of coxa 85 % length of anterior lobe; basis rectangular, posterodistal corner projected distally like pereopod 5; posterior margin and posterodistal corner of merus with 1 and 2 robust setae, respectively; anterior margin and anterodistal and posterodistal corners of carpus with 2, 3 and 3 robust setae, respectively; anterior margin and anterodistal and posterodistal corners of propodus each bearing robust seta; dactylus narrow. Pereopod 7 ( Fig. 8 G, G1) about 1.2 times as long as pereopod 6; coxa short triangular, not lobed; basis rectangular, posterodistal corner projected distally like pereopods 5–6; posterior margin and anterodistal and posterodistal corners of merus with 1, 1 and 2 robust setae, respectively; anterior margin and anterodistal and posterodistal corners of carpus with 2, 3 and 2 robust setae, respectively; anterior margin and anterodistal corner of propodus each bearing robust seta; dactylus narrow.

Pleonal epimera ( Fig. 9 A), each posteroventral corner quadrate, each posterior margin with 2 short setae (epimeron 3 probably lost 1 seta), ventral margin of epimeron 3 bearing short seta, posteroventral corners of epimera 2 – 3 minutely projected. Pleopods 1–3 ( Fig. 9 B – D), pleopod 3 shortest; peduncles long, each with 2 coupling hooks and distal projection; inner rami longer than outer, inner and outer rami with 7 and 8 articles in pleopod 1, 6 and 6 articles in pleopod 2, and 4 and 5 articles in pleopod 3, respectively. Uropod 1 ( Fig. 9 E) biramous, long; peduncle bearing 1 ventrofacial and 1 dorsolateral robust setae, distomedial and distolateral corners with 2 (1 long and 1 short) and 2 robust setae, respectively; inner ramus almost same length as peduncle, with 5 distal robust setae; outer ramus 83 % length of peduncle, with 1 lateral and 5 distal robust setae. Uropod 2 ( Fig. 9 F) biramous, short, 65 % as long as uropod 1; peduncle short, bearing dorsolateral robust seta, distomedial and distolateral corners with 2 and 1 robust setae, respectively; inner ramus about 1.1 times as long as peduncle, with 1 medial, 1 lateral and 5 distal robust setae; outer ramus 94 % length of peduncle, with 1 lateral and 4 distal robust setae. Uropod 3 ( Fig. 9 G) very large, about 2.8 times as long as uropod 1, biramous; peduncle short, with 3 ventral robust setae; inner ramus very short, scale-like, 60 % length of peduncle, with seta on tip; outer ramus long, about 6.0 times as long as peduncle; article 1 sparsely setose on medial and lateral margins, distomedial and distolateral corners each with 3 robust setae, article 2 about 1.4 times as long as article 1, sparsely setose on medial and lateral margins, distal margin with many long setae. Telson ( Fig. 9 H), breadth subequal to length, deeply incised; each lateral margin with 2 robust setae; distal margins bearing 1–2 robust setae, dorsal surface with 2 pairs of plumose setae.

Female [paratype, 4.2 mm (OMNH-Ar-9719)]. Generally similar to male except for gnathopods and oostegites. Gnathopod 1 ( Fig. 9 I, I1), carpus wider, propodus longer than that of male; propodus about 1.4 times as long as carpus, palm defined by 2 medial robust setae, bearing 11 minute medial robust setae. Gnathopod 2 ( Fig. 9 J, J1) smaller than that of male; coxa roundish rhomboidal; carpus longer; propodus shorter, about 1.9 times as long as carpus, palm without excavation, defined by 2 medial robust setae, bearing 8 minute medial robust setae. Oostegites present on coxae 2–5.

Etymology. From the Latin lobatus (= lobate), referring to the shape of bases of pereopods 5–7.

Remarks. Psammogammarus lobatus sp. nov. is characterized by (1) male gnathopod 2 with excavated palm, (2) posterodistally projected bases of pereopods 5–7, (3) quadrate posteroventral corner of pleonal epimeron 3, (4) short inner ramus of uropod 3, and (5) article 2 of uropod 3 outer ramus longer than article 1. Although 15 species have been recorded so far in the genus Psammogammarus ( Jaume et al. 2013) , none of the species has this combination of the characters [see Tomikawa et al. (2010), Vonk et al. (2011) and Jaume et al. (2013)]. Psammogammarus mawatarii from Japan can be distinguished from this new species by the shape of posterodistal lobes of bases in the pereopods 5–7.

Habitat. Brackish with fluctuating salinity. Reverse surface of large stone on sandy tidal flat.

Figures

FIGURE 1. Map showing the collecting sites. A – B, Victoriopisa wadai sp. nov.; C, Paraflagitopisa excavata gen. et sp. nov. and Psammogammarus lobatus sp. nov.

FIGURE 6. Psammogammarus lobatus sp. nov. Holotype, male (OMNH-Ar- 9717), 4.0 mm. Habitus, lateral view. Scale: 1 mm.

FIGURE 7. Psammogammarus lobatus sp. nov. All but C, holotype, male (OMNH-Ar- 9717), 4.0 mm; C, paratype, female (OMNH-Ar- 9719), 4.2 mm. A, left antenna 1, lateral view; A 1, accessory flagellum of left antenna 1, lateral view; B, left antenna 2, lateral view; C, upper lip, anterior view; D, left mandible, lateral view; D 1, incisor, lacinia mobilis and accessory blades of left mandible, lateral view; E, right mandible, medial view; E 1, incisor, lacinia mobilis and accessory blades of right mandible, medial view; F, lower lip, ventral view; G, outer plate and palp of left maxilla 1, dorsal view; G 1, inner plate of left maxilla 1, dorsal view; G 2, distal part of left maxilla 1, dorsal view, normal setae omitted; H, right maxilla 2, ventral view; I, right maxilliped, dorsal view; I 1, distal part of inner plate of right maxilliped, dorsal view, normal setae omitted; I 2, distal part of outer plate of right maxilliped, dorsal view, normal setae omitted. Scale: A, 1 mm; A 1, B, 0.5 mm; C – I, G 1, 0.25 mm; D 1, E 1, G 2, I 1 – 2, 0.13 mm.

FIGURE 8. Psammogammarus lobatus sp. nov. Holotype, male (OMNH-Ar- 9717), 4.0 mm. A – B, left gnathopods 1 – 2, lateral views; A 1, B 1, palms of left gnathopods 1 – 2, lateral views, normal setae omitted; C – G, left pereopods 3 – 7, lateral views; E 1, F 1, G 1, posterior parts of carpi of left pereopods 5 – 7, lateral views. Scales: A – G, 0.5 mm; A 1, B 1, E 1, F 1, G 1, 0.25 mm.

FIGURE 9. Psammogammarus lobatus sp. nov. A – H, holotype, male (OMNH-Ar- 9717), 4.0 mm; I – J, paratype, female (OMNH-Ar- 9719), 4.2 mm. A, right pleonal epimera 1 – 3, lateral view; B, left pleopod 1, posterior view; C, left pleopod 2, anterior view; D, left pleopod 3, posterior view; E, left uropod 1, dorsolateral view; F, left uropod 2, dorsomedial view; G, left uropod 3, dorsal view; H, telson, dorsal view; I – J, left gnathopods 1 – 2, lateral views; I 1, J 1, palms of left gnathopods 1 – 2, lateral views, normal setae omitted. Scale: G, 0.75 mm; A – F, I – J, 0.5 mm; H, I 1, J 1, 0.25 mm.