Heterosignum mutsuensis Gamô, 1976

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 : 2105-2108

Heterosignum mutsuensis Gamô, 1976

(gures 1–3)

Heterosignum mutsuensis Gamô, 1976: 39–45 , gures 2, 3.

Metamunna mutsuensis ( Gamô, 1976) . WolV and Brandt, 2000: 130–131.

Material examined

Otsuchi Bay , Iwate Prefecture, Japan, all samples were collected by Smith- McIntyre grab. One male 1.1 mm (ZIHU-01902), 45.3 m, sand, 25 May 1998 ; one ovigerous female, 1.5 mm (ZIHU-01903), one female, 1.5 mm (ZIHU-01904), 62.5 m, sand and mud, 26 May 1998; two males, 1.1 mm (ZIHU-01899), 1.4 mm (ZIHU-01900), one female, 1.2 mm (ZIHU-01901), 59 m, sand, 10 August 1998.

Description

Male. Body (gure 1A, B) about 2.4 times as long as maximum width (except spine-like processes), widest at pereonite 3. Head broad, with four dorsal setae, without preorbital lobes; 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 half of peduncular article 2 of antenna 1. Pereonites 1–7 with scattered small dorsal and lateral setae. Pereonite 1 laterally rounded, without single lateral spine-like processes; pereonite 2 with a pair of short single lateral spine-like processes or not; pereonite 3 with a pair of long lateral spine-like processes; pereonites 4 and 5 without lateral spine-like processes; pereonite 6 with a pair of backwardly curved single lateral spine-like processes; pereonite 7 without lateral spine-like processes. Pereonite 1 shorter than pereonites 2–4; pereonites 2–4 subequal in length; pereonite 5 half as long as pereonite 4; pereonite 6 longer than pereonite 5; pereonite 7 slightly shorter than pereonite 6. 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 consisting of two parts, with scattered small dorsal setae, 1.5 times as long as broad; anterior part of pleotelson short, cylindrical, about one-sixth length of posterior; posterior part of pleotelson bulbous, with six or seven pairs of lateral teeth. Uropod (gure 1E) biramous, cylindrical; ventral ramus, four times as long as broad, bearing six apical and two ventral setae; dorsal ramus one-third as long as ventral ramus, with two apical setae.

Antenna 1 (gure 1F) with three-articulate peduncle and three-articulate agellum. Peduncular article 1 shorter than article 2, with two distal setae; article 2 longest, with one distomesial and ve distolateral setae; article 3 half length of article 2, with one distal seta. Flagellum article 1 shortest, without setae; article 2 longer than article 1, without setae; article 3 longer than article 2, distally with one long and three short setae and one aesthetasc.

Antenna 2 (gure 1G) with peduncle composed of six articles: article 1 not visible dorsally; article 2 widest, as long as wide, without setae; article 3 longest, with convex proximal protrusion bearing single seta, and with two distal setae; article 4 shortest, mesially with two long and one short setae; article 5 twice as long as article 4, with three distal setae; article 6 as long as article 3, with six distal and one proximal setae. Flagellum longer than peduncular article 6, composed of eight articles, each with a few setae.

Left mandible (gure 2A) incisor with four cusps; lacinia mobilis with four teeth; spine row with four spines; molar process without setae. Right mandible (gure 2B) lacking lacinia mobilis; incisor with ve cusps; spine row with three spines; molar process with two setae.

Maxilla 1 (gure 2C) with inner lobe bearing four apical setae; outer lobe with nine apical and three lateral setae. Maxilla 2 (gure 2D) with inner lobe bearing four apical setae; outer two lobes each with four apical setae.

Maxilliped (gure 2E) with narrow palp composed of ve articles; article 1 broader than long, without setae; article 2 trapezoidal, slightly wider than article 1, with one mesial seta; article 3 longest, with three mesial and one distolateral setae; article 4 slightly shorter than article 3, with two distomesial setae; article 5 narrowest, with four apical setae; endite rectangular, bearing four pectinate and two fan-shaped submarginal setae distally, two distomesial pectinate setae and two mesial coupling hooks; epipod broad, subtriangular, reaching third article of palp, with rounded apex.

Pereopod 1 (gure 2F) shorter than pereopods 2–7: basis the longest article, 1.5 times as long as ischium, without setae; ischium twice as long as merus, with one or two stout dorsal setae; merus trapezoidal, with three ventrodistal and one dorsodistal setae; carpus ovate, ventrally with two robust sensory setae and two acute teeth, and dorsally with one simple seta; propodus ovate, ventrally with two robust sensory setae and two simple setae, and dorsally with three simple setae; dactylus narrowest, as long as propodus, with four distal setae, one slender and long unguis, and one acute accessory claw.

Pereopods 2–7 (gure 2G, H) subequal in shape and length; bases as long as ischia, widest, with one or two dorsal and one or two ventral setae; ischia slightly narrower than bases, with one or three dorsal and one or two ventral setae; meri trapezoidal, half as long as ischia, with one long and one or two short setae ventrodistally, unarmed or armed with one simple seta ventroproximally, one long and one short setae dorsodistally; carpi as long as ischia, dorsally with three setae, ventrally with two robust sensory setae and one or two simple setae; propodi half as wide as carpi, ventrally with three robust sensory and one or two simple setae, and dorsally with three or four simple and one pappose setae; dactyli shortest, narrowest, distally with four simple setae, one slender, long unguis and one minute accessory claw.

Pleopod 1 (gure 2I) distally separate, 1.8 times as long as broad, with two pairs of lateral setae and three pairs of apical setae, with a pair of short lateral projections, each projection bearing nine apical setae. Pleopod 2 (gure 3A) with broad protopod and convex lateral margin, with about 12 lateral setae; endopod reaching apex of protopod, with slender second article; exopod stout. Pleopod 3 (gure 3B) with endopod bearing three stout plumose setae distally; exopod composed of two articles, about four- fths as long as endopod, narrower than endopod; article 2 with one terminal seta. Pleopod 4 (gure 3C) with exopod slender, tapering to pointed apex, with about 50 lateral setae; endopod broad. Pleopod 5 (gure 3D) broad, uniramous, 1.7 times as long as broad.

Female. Similar to male in morphology of all pereonal appendages. Body (gure 1C, D) broader than in male, about twice as long as maximum width (except lateral spine-like processes), widest at pereonite 3. Pereonite 1 without single lateral spine-like processes; pereonite 2 with a pair of slightly forwardly curved single lateral spine-like processes; pereonites 3–6 with a pair of single lateral spine-like processes; pereonite 7 with short single lateral spine-like processes or not. Pereonite 1 shorter than pereonites 2– 4; pereonite 2 and 4 subequal in length; pereonite 3 longest; pereonite 5 half length of pereonite 4; pereonite 6 longer than pereonite 5; pereonites 7 and 6 subequal in length. Pereonites 1–3 increasing in width; pereonites 4–7 decreasing in width. Operculum (gure 3E) ovate, 1.2 times as long as broad, with seven apical and a fringe of lateral setae.

Remarks

Twenty- ve years after Gamô described Heterosignum mutsuensis based on a single female specimen from Mutsu Bay, we collected both sexes of the species from Otsuchi Bay, Iwate Prefecture more than 200 km south from the type locality. Features from which the present specimens were identi ed with H. mutsuensis were as follows: no preorbital lobes on head, absence of lateral spine-like process on pereonite 1, and lack of dorsal spines on pereonites 1–7, all of which were originally listed as the diagnostic characters of the species, with illustrations ( Gamô, 1976). The male specimens we collected for the rst time show several features distinct from the females: males have two pairs of long lateral processes on pereonites 3 and 6 (ZIHU-01900, 01902) and sometimes a pair of short additional processes on pereonite 2 (ZIHU-01899), while females possess ve pairs of moderately short processes on pereonites 2–6 (ZIHU-01901, 01904) and occasionally a pair of short ones on pereonite 7 (ZIHU-01903).