Metopelloides paguri, Marin, Ivan & Sinelnikov, Sergey, 2012

Marin, Ivan & Sinelnikov, Sergey, 2012, Metopelloides paguri sp. nov., a new species of symbiotic stenothoid amphipod (Crustacea: Amphipoda: Stenothoidae) associated with sublittoral hermit crabs from the Russian coasts of the Sea of Japan, Zootaxa 3244, pp. 59-67 : 60-61

Metopelloides paguri sp. nov.

Material examined. Holotype ( MIMB), ovigerous female—Southern Kurile Islands, Iturup, Prostor Bay, 45°23’8”N 148°09’4”E, inside gastropod shells occupied by hermit crabs Ellasochirus cavimanus , depth 84 meters, XXth cruise of s/v “Academic Oparin”, 31.08.1997; 5 adult ovigerous females ( MIMB)—Southern Kurile Islands, Iturup, Prostor Bay, 45°23’8”N 148°09’4”E, inside gastropod shells occupied by hermit crabs Ellasochirus cavimanus , depth 84 meters, XXth cruise of s/v “Academic Oparin”, 31.08.1997; 4 ovigerous female (dissected, LEMMI)—Sea of Japan, the Peter the Great Bay, Vostok Bay, about 4 km from the shore in a front of Yuzno-Morskoy village, depth 30–35 meters, inside cavities in sponges occupied by hermit crabs Pagurus pectinatus , coll. I. Marin, 25. 0 6. 2011;

Description. Paratype ovigerous female. Small-sized amphipods with smooth body, tbl. 7.0 mm. Antenna I ( Fig. 2 a) with basal peduncular article oblong, smooth, about twice shorter than head, equal to the second peduncular article and about twice longer that the distal peduncular article, with short naked flagellum slightly longer than peduncle. Antenna II ( Fig. 2 b) with basal peduncular article oblong, covered with small setae, about twice shorter than the second and the third peduncular articles, with short naked flagellum equal to the length of peduncle; accessory flagellum absent. Labrium rounded. Mandible with long distally pointed palp, consisting of 1 article, armed with single apical setae ( Fig. 2 c); with lacinia mobilis and incisor process well developed, serrate; incisor process robust, distally armed with short blunt teeth; lacinia mobilis consists of 8 – 10 fused blunt teeth. Maxilla I ( Fig. 2 d) with inner plate small, with ventral margin armed with thin simple setae and with 5–6 long apical spines; outer plate longer than inner, about twice longer than wide, smooth, armed with 5 short spines distally. Maxilla II normal, without special features, slender; outer and inner plates normal, each distally armed with simple setae. Maxilliped ( Fig. 2 e) normal, characteristic for the genus; inner plates small, partly separated, rounded; outer plate reduced, with 4-articulate palp bearing long simple setae along inner lateral margins of segments, all articles are equal by length, distal, propodal, article ( Fig. 2 f) armed with 5 long simple setae at distolateral inner angle, dactylus distally pointed, sharp, curved, covered with tiny simple setae. Pereon smooth. Gnathopods I subchelate ( Fig. 3 a); coxa elongated; basis subquadrate, about as long as wide; ischium subquadrate, slightly longer than wide; merus elongated with distoventral produced rounded lobe bearing a row of long simple setae; carpus triangular in shape, slightly longer than wide, with ventral margin bearing several rows of long simple setae; propodus rectangular, about 1.5 times longer than wide, with small locking tooth at the middle of the margin, central part of the margin armed with short sharp spines, distal part of palmar margin oblique, slightly convex, serrated, with small submarginal short robust spines; dactylus long, about 6 times longer than wide, reaching the locking tooth on palmar margin of propodus, curved, with smooth inner lateral margin ( Fig. 3 b). Gnathopod II subchelate ( Fig. 3 c), larger than gnathopods I; coxa short, subquadrate; basis elongated, about 4 times longer than wide; ischium subquadrate, about as long as wide, with small rounded distodorsal inner lobe; merus elongated, about twice longer than wide; carpus short, triangular, with well marked distoventral rounded lobe, bearing several plumose setae; propodus rectangular, about twice longer than wide, without small locking teeth; with large rounded projection (tooth) and well marked palmar sinus at central part, distolateral margin oblique, slightly convex, with 3 rounded distal projection; dactylus long, about 3 times longer than wide, pointed distally, reaching palmar sinus of propodus, strongly curved, with smooth inner lateral margin. Pereiopod III normal, characteristic for the genus, without specific morphological features; with smooth segments. Pereiopod IV ( Fig. 4 c) with large oval coxal plate; basis segment elongated, about 5 times longer than wide; ischium subquadrate, about as long as wide; merus elongated, rectangular, about 3 times longer than wide, with several short slender spines along lateral margins, distodorsal angle armed with 2 short slen- der spines; carpus elongated, rectangular, about twice longer than wide, with several short slender spines along ventral margin, distodorsal angle armed with 2 short slender spines; propodus rectangular, about 3.5 times as long as wide, with 3 pairs of short spines along ventral margin, distoventral angle oblique and armed with several short robust spines; dactylus long, about 2,5 times longer than wide, pointed distally, curved, with smooth inner lateral margin, forming with distoventral angle of propodus a similarity of subclaw. Pereiopods V – VII ( Fig. 4 a, b) similar; coxa subquadrate; basis segment elongated, about 4 times longer than wide, with rounded distodorsal angle; ischium subquadrate, about as long as wide; merus elongated, rectangular, about 3 times longer than wide, with several short slender spines along lateral margins, distodorsal and distoventral angles armed with 2 short slender spines; carpus elongated, rectangular, about twice longer than wide, with several short slender spines along ventral margin; propodus rectangular, about 2.5 times as long as wide, with 3 pairs of short spines along ventral margin and 2 short pines on dorsal margin, distoventral angle oblique and armed with several short robust spines; dactylus long, about 3 times longer than wide, pointed distally, curved, with smooth inner lateral margin, forming with distoventral angle of propodus a similarity of subclaw. Urosome smooth. Pleopods biramous ( Fig. 4 f), with peduncles about twice shorter than rami; rami subequal, lined with long simple setae. Uropod I ( Fig. 4 d) longer than uropod II, biramous; peduncle equal to the length of rami; inner ramus longer than outer ramus and armed with 3 small spines along its dorsal margin. Uropod II longer than uropod III, biramous, with peduncle longer than rami; rami subequal armed with 2 spines. Uropod III ( Fig. 4 e) uniramous, with 3 articles; distoventral angle of basal article armed with short bifurcated spine; the second article with 2 medium sharp distoventral spines and 1 spine at ventral margin; distal article smooth. Telson ( Fig. 2 g) tongue-shaped, about twice longer than wide, without submarginal spines or setae, with dorsal margin covered with small blunt tubercles.

Males of the species are unknown.

Remarks. Among observed females any variability of morphological characters are absent.

Measurements. The maximum body length of observed ovigerous female is 7.0 mm.

Differential diagnosis. The genus Metopelloides presently includes 8 valid species known from the northern parts of Pacific and Atlantic oceans (after Gurjanova, 1951). Seven of these species are known from the western part of the northern Pacific as littoral and sublittoral free-living species (see Gurjanova, 1951). The new species is mostly morphologically related to Metopelloides micropalpa (Shoemaker, 1930) , Metopelloides tattersalli Gurjanova, 1938 and M. stephenseni Gurjanova, 1938 possessing a well marked subchela on gnathopods I. From the latter species, probably the most related species within the genus, the new species clearly differs by the absence of spines on telson ( M. stephenseni possesses two well marked lateral submarginal spines on telson; see Fig. 302 in Gurjanova, 1951), the absence of lateral setae on mandibular palp (vs. several lateral setae present in M. stephenseni ) and rounded distolateral internal angles on basal segments of maxilliped (vs. distally produced distolateral internal angles on basal segments of maxilliped in M. stephenseni ; see Fig. 302 in Gurjanova, 1951). From M. micropalpa the new species clearly differs by geographical distribution ( M. micropalpa is known from American coast at the Northern Atlantic), tuberculose dorsal surface of the telson (vs. smooth in M. micropalpa ) and by the structures of distoventral palmar margins of subchela of gnathopods I and II in females (for description of M. micropalpa see Fig. 304 in Gurjanova, 1951; Shoemaker, 1930). From M. tattersalli the new species can be clearly distinguished by elongated mandibular palp with a single apical setae (vs. short mandibular palp armed with several apical setae in M. tattersalli ) and the structures of distoventral palmar margins of subchela of gnathopods I and II in females (for M. tattersalli see Fig. 301 in Gurjanova, 1951).

Coloration. The body coloration generally transparent whitish; sternites and pleurae I and II, distal part of sternite and pleura III and dorsal surface of sternites IV and V are red; eyes pinky colored; appendages are transparent. Similar white-red coloration is also characteristic for other hermit-crab-associated amphipod species like Pagurisaea spp and Liljeborgi a spp (see below).

Etymology. The species is named after its association with the hermit crabs of the family Paguridae (Crustacea: Decapoda ).

Host and ecology. Alive specimens of amphipod were found inside internal cavity of sponges, Suberites sp. (Porifera: Suberitidae ) occupied by large sublittoral hermit crab Pagurus pectinatus (Stimpson, 1858) (Crustacea: Decapoda : Paguridae ) collected at Vostok Bay of the Sea of Japan in front of Yuzno-Morskoy village at the depth of 60–80 meters. Specimens of P. pectinatus were trawled from muddy or muddy sand bottom; the average water temperature is about 1–4 Cº; the average salinity is about 33–34‰. Additional specimens of amphipods were found inside gastropod shells occupied by sublittoral hermit crab Elassochirus cavimanus (Miers, 1879) (Crustacea: Decapoda : Paguridae ) collected from the depth of about 84 meters. Each host was inhabited by several large amphipods; all examined species of amphipods were identified as females.

Distribution. The species is presently known from the Sea of Japan and Southern Kurile Islands only.

Figures

FIGURE 2. Metopelloides paguri sp. nov., ovigerous female, tbl. 7.0 mm, Vostok Bay, Peter the Great Bay, Sea of Japan: аantenna I; b — antenna II; c — mandible; d — maxillula; e — maxilliped; f — same, propodal segment and dactylus; g — telson.

FIGURE 3. Metopelloides paguri sp. nov., ovigerous female, tbl. 7.0 mm, Vostok Bay, Peter the Great Bay, Sea of Japan: a — pereiopod I (gnathopod I); b — same; distal part of propodal segment and dactylus; c — pereiopod II (gnathopods II).

FIGURE 4. Metopelloides paguri sp. nov., ovigerous female, tbl. 7.0 mm, Vostok Bay, Peter the Great Bay, Sea of Japan: a — distal part of propodus and dactylus of pereiopod VII; b — distal segments of pereiopod VII; c — pereiopod IV; d — uropod I; e — uropod II.