A redescripton of Lyrosoma pallidum (Eschscholtz) and distributional range extension of Lyrosoma Mannerheim (Coleoptera, Agyrtidae)

Abstract A redescription with illustrations of the species Lyrosoma pallidum and a key to the Korean species of the family Agyrtidae are provided. New distributional data, including a range extension, of the two Lyrosoma Mannerheim species are presented. Lyrosoma pallidum (Eschscholtz) is recorded for the first time in Korea.


Introduction
The genus Lyrosoma Mannerheim, containing two species worldwide, is confined to coastal habitats, such as under stones, seaweeds, and carcasses of various coastal animals along the seashore. They have also been reported in nests of maritime birds, but little is known regarding their immature stages and bionomics. They can be recognized by the combination of the following characters: mandibles without subapical teeth; antennomeres 9-10 each with apical grooves including compact distribution of sensilla; elytron with 9 striae; hind wings absent; pro-and mesotarsi dilated in males; aedeagus without parameres (Newton 1997;Schawaller 1998).
We collected a good series of Lyrosoma pallidum (Eschscholtz) along the seashores of Korea, Hokkaido (Japan), and Kamchatka (Russia). This species is a new addition to the Korean fauna. Newton (1997) classified Lyrosoma under Agyrtinae (one of the three subfamilies, sensu Newton 1997) based on abdominal-elytral interacting system and structure of aedeagus, and discussed its phylogenetic relationships with other genera. Later, Schawaller (1998) revised the genus Lyrosoma, synonymizing six species, thereby reducing the genus from eight species to only two species, and also reported its distributional range along northern Pacific coasts. However, the description of L. pallidum was insufficient, lacking important features such as mouthparts and body sculpture and the distributional data were sparse and incompletely mapped. Here, we present a redescription with a habitus photograph and illustrations of Lyrosoma pallidum, provide improved distribution data for both species, a range extension for L. pallidum, and a key to the Korean species of Agyrtidae.

Material and methods
All L. pallidum specimens used in this study are deposited in the Chungnam National University Insect Collection (CNUIC), Daejeon, Korea. New data for L. opacum are from specimens deposited in the University of Alaska Museum Insect Collection (UAM), Fairbanks, Alaska, USA. These data and all literature records reported here for L. opacum are available online at http://arctos.database.museum/saved/Lyrosoma_opacum. Digital images of habitus were merged using image stacking software (Combine ZP). For measurement, we selected 10 males and 10 females (2♂1♀ from Korea; 5♂6♀ from Japan; 3♂3♀ from Russia) with maximum body size variation. The following abbreviations were used in the text: BL, body length (HL+PL+EL); HL, length of head from the anterior margin of the clypeus to the posterior margin of head; HW, width of head, including the eyes; PL, maximum length of pronotum; PW, maximum width of pronotum; EL, length of elytron from the base to the posterior margin of elytron; EW, width of elytra.   Redescription. Body (Fig 1) general carabid-shape, yellowish brown to reddish brown, surface glossy with microsculpture. Male. BL: 4.3-5.1 mm. Head as long as wide or slightly wider than long (HL/HW: 0.94-1.00); eyes medium and prominent, separated by about 5 times of eye width; eye about 0.8 times as long as temple; short setae present between facets, shorter than facet diameter; vertex of head without pale mounds; epistomal suture indistinct; epicranial suture more or less Y-shaped; dorsal surface with rather dense isodiametric microsculpture, ventral surface with transverse microsculpture. Antenna filiform, about 3 times as long as HW, antennomere 2 shortest, 3 and 11 longest, 4-7 similar in shape and length, 9-10 with dense sensilla in apical grooves, 9-11 very weakly clubbed. Labrum (Fig 2) transverse; anterior margin deeply and broadly emarginate; anterior and each anterolateral margin distinctly membranous and transparent; 4-6 long setae and single very long seta present on membranous part of each side of midline; 3-4 spinose setae present on each anterolateral region of membranous part; anterior margin of membranous part with dense micro setae; sclerotized part with two setae on each side of midline and one seta on each anterior corner; surface of sclerotized part with many pores scattered sparsely. Mandibles (Fig 3) symmetrical, inner regions without tooth; broad at base and pointed at apex; dorsal and ventral surface with many pores on medial area. Maxilla (Fig 4) with 4 palpomeres; palpomeres 2-4 with distinct setae. Labium (Fig 5) with 3 palpomeres; palpomeres 1-2 with long setae, last palpomere asetose; ligula caudal fin-like shape and bilobed, each lobe with 7-10 long setae on subapical region; ligula with many pores on medial and subapical regions of each lobe; paraglossa broadly developed, anterior margin with many setae densely distributed. Mentum trapezoidal narrowing apically; anterior margin straight; single long seta present on each anterolateral region; many pores scattered sparsely and microsculpture transverse. Submentum with many pores, short setae present sparsely. Pronotum broad cordiform, wider than long (PL/PW: 0.81-0.84); pronotum widest near anterior third; anterior corners round, posterior corners angled; pronotum without mid-basal fovea; disc with shallow and broad medial-longitudinal depression. Elytra oval and convex, gradually increased to posteriorly in convexity; longer than wide (EL/ EW: 1.41-1.59); each elytron with 9 striae; intervals as wide as width of first antennomere, weakly convex and impunctate, dense isodiametric microsculpture present; basal lateral margin weakly serrate; epipleura without distinct punctures. Hind wings absent. Mesoventrite glabrous and sculptured strongly; mesoventral process sharp, contiguous to metaventral process. Metaventrite covering many setae sparsely, metaventral process sharp. Pro-and mesotarsi dilated, tarsomere 1−4 with numerous setae ventrally. Metatarsi simple and long; last tarsomere about 1.8 times as long as tarsomere 4. Tarsal claws simple, basal part with very feeble tooth; two empodial setae present, as long as tarsal claws. Abdominal sternites covering many setae, surface with dense isodiametric microsculpture. Aedeagus (Figs 7-10) without paramere; median lobe long and slender, mid- dle part of apex slightly protruded (Fig 9); structure of internal sac as in Figs 8 and 10. Female. BL: 4.6-5.2 mm. Basically not differ to male. Pro-and mesotarsi not dilated. Sternite VIII (Fig 6) with posterior margin emarginate narrowly, a few setae present on marginal region; spiculum ventrale broad, deeply emarginate anteriorly.

Discussion
The coastal genus Lyrosoma includes only two valid species. Lyrosoma pallidum can be distinguished from L. opacum by its smaller body size, absence of epistomal suture and an elytral disc without distinct reticulation (Schawaller 1998). While examining five specimens on slides, we discovered variation in the number of setae on the labrum and ligula of L. pallidum. These features we consider to be intraspecific variation. Schawaller (1998) reported that the genus Lyrosoma has been recorded on the northwestern Pacific coasts, from the western Aleutian Islands to the southernmost parts of northern Honshu, Japan. Our collection revealed that the distributional range of this genus extends to South Korea, representing a new southernmost boundary ( Fig  11). Additionally, although Schawaller (1998) reported records for L. opacum from Kodiak and Afognak islands, Alaska, based on citations of Lafer (1989) and specimens in the Natural History Museum (London), he excluded these records from his map and his summary of the distribution of this species. Along this species' eastern range Schawaller described its distribution as restricted to the western Aleutians and just one of the two Pribilof islands (St. Paul). We have corrected this exclusion and based on our collections (n=6) and literature records not included in Schawaller (1998) (n=17) increased the number of islands on which L. opacum is known from the seven reported in Schawaller (1998) to twenty-three (Fig. 11). The two Lyrosoma species are apparently sympatric on Kamchatka and on the Kurile Islands Ketoi, Cirpoi, and Yanchika.

Key to the known species of Korean Agyrtidae
The key is modified from Newton (1997), Cho et al. (2001), andLafer (2002