Heterosignum elegans, 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 : 2109-2112

Heterosignum elegans sp. nov.

(gures 4–6)

Material examined

TR/ V ‘ Toyoshio-maru ’, St. 10, Umoti-no-Se, oV Yamaguchi Prefecture, Japan, 34° 45.70°N, 130° 45.13°E, 115 m, sand and mud, sledge net (mesh size 0.33 mm), 18 November 1999: holotype, male, 1.1 mm (ZIHU-01907); paratypes, four males, 1.1 mm (ZIHU-01908-10), 1.2 mm (ZIHU-01911), three females, 1.4 mm (ZIHU-01912), 1.2 mm (ZIHU-01913), 1.1 mm (ZIHU-01914), 1.0 mm (ZIHU-01915) .

Description

Male. Body (gure 4A) about 2.6 times as long as maximum width (except spine-like processes), widest at pereonite 3. Head broad, with six dorsal setae, with a pair of long preorbital lobes; frontal margin of head convex, with one or two pairs of setae; labrum surpassing head anteriorly; posterior margin of head convex. Eyestalks slender, very long, arising from posterior half of head, reaching proximal two-thirds of peduncular article 2 of antenna 1. Pereonites 1–7 with scattered small dorsal and lateral setae. Pereonite 1 laterally rounded, without lateral spine-like processes; pereonites 2 and 3 with a pair of long single lateral spine-like processes; pereonites 4 and 6 with a pair of slightly backwardly curved single lateral spine-like processes; pereonites 5 and 7 with a pair of short single lateral spine-like processes. Pereonite 1 shortest; pereonite 2 twice as long as pereonite 1; pereonite 3 longest; pereonite 4 slightly shorter than pereonite 3; pereonite 5 half as long as pereonite 4; pereonite 6 longer than pereonite 5; pereonite 7 as long as 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 1.7 times as long as broad, with scattered small dorsal setae, consisting of two parts; anterior part of pleotelson long, cylindrical, about two- fths as long as posterior; posterior part of pleotelson bulbous, with six pairs of lateral teeth. Uropod (gure 4C) biramous, cylindrical; ventral ramus, 2.6 times as long as broad, bearing six apical and two lateral setae; dorsal ramus one-third length of ventral ramus, with two apical setae.

Antenna 1 (gure 4D) with three-articulate peduncle and three-articulate agellum. Peduncular article 1 shorter than article 2, with two lateral and two mesial setae; article 2 longest, narrower than article 1, with nine distal setae; article 3 about one-third length of article 2. Flagellum article 1 shortest, with one distolateral seta; article 2 longer than article 1, without setae; article 3 as long as article 2, distally with one long, three short setae and one aesthetasc.

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

Left mandible (gure 4F) incisor with four cusps; lacinia mobilis with four teeth; molar process with two setae. Right mandible (gure 4G) lacking lacinia mobilis; incisor with ve cusps; spine row with one spine; molar process with two setae.

Maxilla 1 (gure 5A) with inner lobe bearing four apical and four lateral setae; outer lobe with nine apical and two mesial setae. Maxilla 2 (gure 5B) with inner lobe bearing six apical and three mesial setae; outer two lobes each with two apical setae.

Maxilliped (gure 5C) with narrow palp composed of ve articles; article 1 broader than long, without setae; article two trapezoidal, slightly wider than article 1, with two mesial setae; 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 three apical and one mesial setae; endite rectangular, bearing three pectinate and two simple setae distally, and two mesial coupling hooks; epipod broad, subtriangular, reaching third palp article, with rounded apex.

Pereopod 1 (gure 5D) shorter than pereopods 2–7: basis the longest article, 1.6 times as long as ischium, with two ventral and one dorsal setae; ischium twice as long as merus, with one blunt robust projection, and with one ventral seta; merus trapezoidal, dorsodistally with one simple and one robust setae, and with three ventrodistal setae; carpus ovate, ventrally with two simple, two sensory robust setae and seven acute teeth; propodus ovate, ventrally with one simple, two robust sensory setae and two teeth, and dorsally with one simple seta; dactylus narrowest, shorter than propodus, with four distal setae, one slender unguis and one acute accessory claw.

Pereopods 2–7 (gure 5E, F) subequal in shape and length; bases as long as ischia, with one or two dorsal and one or two ventral setae; ischia twice as long as meri, with two dorsal and one or two ventral setae; meri trapezoidal, with one dorsodistal and two or three ventral setae; carpi as long as bases, with two or three robust sensory and one or two simple setae ventrally, two or three simple setae dorsally; propodi narrower than carpi, with two or three robust sensory and one simple setae ventrally, three simple setae dorsally; dactyli shortest, narrowest, distally with three simple setae, one slender unguis and one minute accessory claw.

Pleopod 1 (gure 5G) twice as long as broad, with two pairs of ventrolateral setae and two pairs of apical setae, with a pair of short lateral projections, each projection bearing ve setae. Pleopod 2 (gure 6A) with narrow protopod and convex lateral margin, with 15 lateral and three ventral setae; endopod surpassing apex of protopod, with slender, long, curved second article; exopod stout. Pleopod 3 (gure 6B) with endopod bearing three stout plumose setae apically; exopod composed of two articles, as long as endopod, narrower than endopod; article 2 with one terminal seta. Pleopod 4 (gure 6C) with exopod, slender, tapering to pointed apex, without setae; endopod broad. Pleopod 5 (gure 6D) ovate, uniramous, twice as long as broad.

Female. Similar to male in morphology of all pereonal appendages. Body (gure 4B) broader than in male, about 2.2 times as long as maximum width (except lateral spine-like processes), widest at pereonite 3. Pereonite 1 without single lateral spine-like processes; pereonites 2–4 with a pair of long, single lateral spine-like processes; pereonites 5 and 7 with a pair of short, single lateral spine-like processes; pereonite 6 with a pair of slightly backwardly curved long single lateral spine-like processes. Pereonite 1 shortest; pereonite 2 twice as long as pereonite 1; pereonite 3 as long as pereonite 2; pereonite 4 longest; pereonite 5 about one-third as long as pereonite 4; pereonite 6 length of pereonite 5; pereonite 7 as long as pereonite 6. Pereonites 1–3 increasing in width; pereonites 4–7 decreasing in width. Operculum (gure 6E) ovate, 1.4 times as long as broad, with a fringe of lateral setae, without apical setae.

Remarks

The absence of dorsal spines on pereonites links Heterosignum elegans sp. nov. to H. mutsuensis ( Gamô, 1976) . The present new species is distinguished, however, from H. mutsuensis by the following features (those of H. mutsuensis in parentheses): a pair of preorbital lobes are present on head (absent); eyestalks are long and reaching to the proximal two-thirds of peduncle article 2 of antenna 2 (relatively short and reaching to the proximal half); cylindrical anterior part of pleotelson is very long (short); pleopod 1 is armed with two pairs of apical setae (three pairs of apical setae), two pairs of ventrolateral setae (without setae) and a pair of lateral projections, each projection bearing ve apical setae (nine pairs of apical setae); second article of pleopod 2 is very long (short); and no apical setae on the operculum (some apical setae).