Heterosignum otsuchiensis, Shimomura & Mawatari, 2002

Shimomura, M & Mawatari, SF, 2002, A revision of Heterosignum (Asellota, Isopoda, Paramunnidae) with descriptions of three new species, Journal of Natural History 36 (17), pp. 2103-2126 : 2118-2121

Heterosignum otsuchiensis sp. nov.

(gures 10, 11)

Material examined

Otsuchi Bay , Iwate Prefecture, Japan, 89 m, sand and mud, Smith-McIntyre grab, 11 August 1998: holotype, one ovigerous female, 1.7 mm (ZIHU-01905); paratype, one ovigerous female, 1.8 mm (one juvenile) (ZIHU-01906) .

Description

Female. Body (gure 10A) about twice as long as maximum width (except spine-like processes), widest at pereonite 3. Head narrow with three dorsal setae, with a pair of narrow short preorbital lobes, without dorsal spine; frontal margin of head convex without setae; labrum surpassing head anteriorly; posterior margin of head convex. Eyestalks slender, arising from posterior half of head, reaching proximal one-third of peduncular article 2 of antenna 1. Pereonites 1–7 each with short mid-dorsal spine, and with a few dorsal and lateral setae. Pereonites 1–7 each with a pair of straight single lateral spine-like processes. Pereonite 1 half as long as pereonite 2; pereonite 2 slightly shorter than pereonite 3; pereonites 3 and 4 subequal in length; pereonites 5–7 subequal in length. Pereonites 1–3 increasing in width (except spine-like processes); pereonites 4–7 decreasing in width (except spine-like processes). Coxal plates dorsally invisible on all pereonites. Pleonite 1 small, with a pair of dorsal setae. Pleotelson 1.8 times as long as broad, with scattered small dorsal setae, consisting of two parts; anterior part of pleotelson short, cylindrical, about one-quarter length of posterior; posterior part of pleotelson bulbous, with seven pairs of lateral teeth. Uropod (gure 10B) biramous, cylindrical; ventral ramus, three times as long as broad, distally with ve simple and one pappose setae; dorsal ramus minute, one-tenth as long as ventral ramus, with two apical setae.

Antenna 1 (gure 10C) with three-articulate peduncle and three-articulate agellum. Peduncular article 1 two-thirds length of article 2, distally with two simple and one pappose setae; article 2 longest, distally with one long and six short setae; article 3 half as long as article 2, with one distomesial seta. Flagellum article 1 widest, with one distolateral seta; article 2 as long as article 1, without setae; article 3 longer than article 2, distally with two long, four short setae and one aesthetasc.

Antenna 2 (gure 10D) with peduncle composed of six articles: article 1 shortest, widest, as long as wide, without setae; article 2 twice as long as article 1, with one lateral seta; article 3 slightly longer than article 2, with convex proximal protrusion bearing single seta, one distolateral and two distomesial setae; article 4 half length of article 3, with two mesial setae; article 5 about three times as long as article 4, with six simple setae; article 6 longest, with 14 simple setae. Flagellum slightly shorter than peduncular article 6, composed of seven articles, each with a few setae.

Left mandible (gure 10E) incisor with three cusps; lacinia mobilis with four teeth; spine row with four spines; molar process without setae. Right mandible (gure 10F) lacking lacinia mobilis; incisor with three cusps; spine row with ve spines; molar process with single seta.

Maxilla 1 (gure 10G) with inner lobe bearing six apical setae; outer lobe with ve apical, three lateral and 10 mesial setae. Maxilla 2 (gure 10H) with inner lobe bearing three pectinate and four simple setae apically and about 23 distal setae; outer two lobes each with four apical setae.

Maxilliped (gure 10I) with narrow palp of ve articles; article 1 broader than long, with one mesial seta; article 2 trapezoidal, as wide as article 1, with two distomesial setae; article 3 narrower than article 2, with three mesial and one distolateral setae; article 4 longest, with two distomesial setae; article 5 narrowest, with seven distal setae; endite rectangular, distally with ve pectinate setae and one fan-shaped seta, and two mesial coupling hooks; epipod broad, subtriangular, reaching third article of palp, with acute apex.

Pereopod 1 (gure 11A) shorter than pereopods 2–7: basis very long, 2.1 times as long as ischium, with two ventral and one dorsal setae; ischium twice as long as merus, with two distal setae; merus trapezoidal, with two ventrodistal and one dorsodistal setae; carpus ovate, ventrally with two robust sensory setae, one simple seta and three blunt teeth, and dorsodistally with one simple seta; propodus ovate, ventrally with two robust sensory setae, two simple setae and two blunt teeth, and dorsally with three simple setae; dactylus narrowest, shorter than propodus, with four distal setae, one robust and short unguis, and one acute accessory claw.

Pereopods 2–7 (gure 11B, C) subequal in shape and length; bases longest, with two or four setae; ischia slightly shorter than bases, with two or four setae; meri trapezoidal, half as long as ischia, ventrally with two or three setae, dorsally with one long seta; carpi as long as ischia, dorsally with four setae, ventrally with three robust sensory and one simple setae; propodi slightly narrower than carpi, ventrally with three robust sensory and two simple setae, dorsally with two or three simple and one pappose setae; dactyli shortest and narrowest, with three simple setae, one robust unguis, and one minute accessory claw.

Operculum (gure 11D) ovate, 1.4 times as long as broad, with two apical and a fringe of setae. Pleopod 3 (gure 11E) with endopod bearing three stout plumose setae distally; exopod composed of two articles, eight-ninths of length of endopod, narrower than endopod; article 2 with one terminal seta. Pleopod 4 (gure 11F) with exopod slender, tapering to pointed apex, with about 50 lateral setae; endopod broader than exopod. Pleopod 5 (gure 11G) broad, uniramous, twice as long as broad.

Male. Unknown.

Remarks

Heterosignum otsuchiensis sp. nov. is similar to H. ohtsukai in having pereonites 1–7 each with a mid-dorsal spine. The two species, however, diVer from each other in the following features (those of H. ohtsukai in parentheses): head lacks dorsal spine (with stout dorsal spine), mid-dorsal spine of pereonites 1–7 is short (long), the eyestalks are slender (stout) and basis of pereopod 1 is long (moderately short).