Symmius yamaguchiensis, Shimomura, Michitaka, 2008

Shimomura, Michitaka, 2008, A new species of Symmius Richardson (Crustacea: Isopoda: Chaetiliidae) from Japan, Zootaxa 1719, pp. 61-68 : 63-67

publication ID	https://doi.org/ 10.5281/zenodo.181052
DOI	https://doi.org/10.5281/zenodo.6234391
persistent identifier	https://treatment.plazi.org/id/BF7E878A-3722-FF9C-33B4-34A82698A2E4
treatment provided by	Plazi
scientific name	Symmius yamaguchiensis
status	sp. nov.

Treatment

Symmius yamaguchiensis View in CoL sp. nov.

Figs 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

Material examined. Holotype. Ovigorous female, 11.29 mm ( KMNH IvR 500,229), dissected and mounted on glass slides, St.11, off Yamaguchi Prefecture, 34°36.263’N, 130°32.512’E – 34°36.132’N, 130°32.974’E, 126 m, sand, sledge net, TRV Toyoshio-maru, 18 November, 1999. Paratype. Non-ovigorous female, 8.29 mm ( KMNH IvR 500,230), dissected and mounted on glass slides, same data as holotype.

Description. Body ( Fig. 2 View FIGURE 2 A, B) 2.5 times as long as wide, dorsoventrally flattened. Integument smooth. Head ( Fig. 2 View FIGURE 2 A) 0.46 times as long as wide, with nearly straight frontal margin, with well-defined ocular lobes having yellow rudimentary eye pigment dorsally: ocular lobes not projecting anteriorly. Pereonites each with mid-dorsal projections; pleonite 2 with small mid-dorsal projection. Coxal plates of pereonites 5 and 6 slightly curved posteriorly, with blunt apex. Pereonite 7 and pleonite 1 subequal in width. Pleon 0.45 of total length; pleonite 1 without mid-dorsal projection; pleonite 2 wider than pleonite 1; pleotelson about twice as long as wide, tapering to sharply rounded apex.

Antennule ( Fig. 2 View FIGURE 2 C): peduncular articles 1–3 with many fine setae marginally; article 2 about 1.2 times as long as article 1; article 3 trapezoidal, 0.76 times as long as article 2; flagellum consisting of 1 large and 2 minute articles; article 1 about 1.68 times as long as peduncular article 3, 6.5 times as long as wide, with many fine setae laterally, 1 simple seta and 2 aesthetascs distally; article 2 with 1 simple seta and 1 aesthetasc mesially; article 3 with 5 simple apical setae.

Antenna ( Fig. 2 View FIGURE 2 D) with many fine setae and some bifid, multibranched, plumose and simple setae: peduncular article 3 longest of all articles; flagellum 1.16 times as long as peduncular article 5.

Left mandible ( Fig. 3 View FIGURE 3 A): lacinia mobilis with 3 cusps; incisor with 4 cusps; spine row of 6 spines and 2 pectinate setae. Right mandible ( Fig. 3 View FIGURE 3 B): lacinia mobilis with many small teeth on anterior margin; incisor with 4 cusps; spine row of 9 spine and 2 pectinate setae.

Maxillule ( Fig. 3 View FIGURE 3 C): mesial lobe with 2 plumose apical setae; lateral lobe with 6 simple and 4 denticulate setae apically, and with many fine setae mesially.

Maxilla ( Fig. 3 View FIGURE 3 D): mesial lobe with 5 plumose apical setae and many fine mesial setae; middle lobe with 3 pectinate and 1 fine seta; lateral lobe with 2 pectinate and 3 fine setae.

Maxilliped ( Fig. 3 View FIGURE 3 E) covered with many fine setae ventrally: endite reaching halfway along palp article 2, with 6 plumose setae distally; palp article 1 with 1 bifid mesial seta; article 2 with 10 simple and 3 bifid setae; article 3 with 8 simple mesial and 2 simple lateral setae; article 4 with 7 simple apical setae; epipod about 0.73 length of endite.

Pereopod 1 ( Fig. 3 View FIGURE 3 F) with dense cover of fine setae: ischium 0.58 length of basis; merus 0.45 of ischium, with 2 slender, simple dorsal setae, and 5 slender, simple and 1 robust, plumose ventral setae; carpus with 4 slender, simple mesial and 5 robust, plumose ventral setae; propodus as long as ischium, merus and carpus combined, with 2 slender, bifid, 6 slener, simple and 1 robust, plumose setae dorsally, and with 5 slender, simple and 11 robust, plumose setae ventrally; dactylus with 3 slender, simple distal, 2 subdistal and 4 ventral setae. Pereopods 2–7 ( Figs. 3 View FIGURE 3 G, 4A–C, 5A, B) with dense cover of fine setae: ischia and meri of pereopods 2– 7 with 4–7 long, robust plumose setae dorsally; propodi of pereopods 2–4 broader than those of pereopods 5 and 6. Pereopod 2 ( Fig. 3 View FIGURE 3 G): ischium produced ventrally near at middle. Pereopod 7 (Fig, 5B): ischium 0.68 length of basis; merus 0.74 length of ischium; carpus trapezoidal, 0.43 length of merus; propodus 1.67 times as long as carpus; dactylus as long as carpus.

Pleopod 1 ( Fig. 5 View FIGURE 5 C): peduncle with 1 plumose seta mesially and 4 stout hooks laterally; endopod 0.91 length of exopod, with 28 long plumose setae marginally; exopod with 31 long plumose setae. Pleopod 2 ( Fig. 5 View FIGURE 5 D): peduncle with 2 plumose setae mesially and 3 short hooks laterally; endopod 0.87 length of exopod, with 34 long plumose setae; exopod with 21 long plumose setae. Pleopod 3 ( Fig. 5 View FIGURE 5 E): peduncle with 1 simple mesial seta; endopod 0.92 length of exopod, with 5 short plumose setae. Pleopods 4 and 5 ( Fig. 5 View FIGURE 5 F, G): endopods with short plumose setae mesially, respectively.

Uropod ( Fig. 5 View FIGURE 5 H): peduncle about 3 times as long as wide, with many long multibranched setae; endopod with many multibranched setae and simple scales ventrally, and with 6 long plumose apical setae; exopod 0.76 length of peduncle, with 7 long plumose lateral setae and 3 plumose apical setae, and with 15 short simple, 2 short plumose and many fine setae mesially; multibranched seta with many setules.

Colour. Colour in life yellowish white.

Remarks. Symmius yamaguchiensis sp. nov. is readily distinguished from the other species of the genus except S. caudatus , by a combination of nearly straight frontal margin of the head, the rudimentary eye pigment, 11 plumose setae on the palm of propodus of pereopod 1, the ambulatory pereopod 7, and pereonites 1– 7 and pleonite 2 each with mid-dorsal projection.

Symmius yamaguchiensis View in CoL sp. nov. is similar to Symmius caudatus Richardson, 1904 View in CoL , known from 109– 127 m depth off Osezaki, Izu Peninsula, Japan, in having the ambulatory pereopod 7. The two species, however, differ from one another by the following characters (those of S. caudatus View in CoL in parentheses): body 2.5 times as long as wide (3.1 times as long as wide); pereonites 1–7 and pleonite 2 each with mid-dorsal projection (without mid-dorsal projection); anterior angle of ocular lobe not projecting (strongly projecting anteriorly); peduncular article 3 of antennule 0.76 times as long as article 2 (as long as article 2); coxal plates of pereonites 5 and 6 slightly curved posteriorly, with blunt apex (strongly curved posteriorly, with acute apex); and very setose pereopods (scattered setae).

Etymology. The new species is named after the type locality.