Mucrocalliope ryukyuensis, Ariyama, 2021

Ariyama, Hiroyuki, 2021, Two Species of Paracalliopiidae from the Ryukyu Archipelago in Japan, with the Description of a New Species (Crustacea: Amphipoda), Species Diversity 26, pp. 79-91 : 80-87

Mucrocalliope ryukyuensis sp. nov.

[New Japanese name: Ryūkyū-toge-genkotsu-yokoebi] ( Figs 2–9 )

Material examined. Holotype: male (OMNH-Ar-12077), 2.8 mm, mouth of Gesashi River, Higashi Village, Okinawa Island , Okinawa Prefecture ( Fig. 1B ), 26°36′17″N, 128°08′38″E, middle intertidal, sandy mud bottom with mangrove leaves, 2 July 2015, coll. H. Ariyama. Paratypes: 3 males (OMNH-Ar-12179, 12078, 12079), 2.5, 2.5 and 2.4 mm, respectively, and 1 ovigerous female (OMNH- Ar-12080), 2.3 mm, same locality, 26°36′15″N, 128°08′39″E, middle intertidal, sandy mud bottom, 2 July 2015, coll . H . Ariyama ; 1 ovigerous female (OMNH-Ar-12081), 2.3 mm, same locality, 26°36′05″N, 128°08′30″E, lower intertidal, fine sand bottom, 2 July 2015, coll . H . Ariyama ; 1 ovigerous female (OMNH-Ar-12082), 2.3 mm, same locality, 26°36′16″N, 128°08′38″E, middle intertidal, sandy bottom with gravel, 2 July 2015, coll . H . Ariyama; 1 male (OMNH- Ar-12083), 2.1 mm, mouth of Māre River, Funaura , Iriomote Island , Okinawa Prefecture, 24°23′28″N, 123°49′02″E ( Fig. 1D ), uppermost subtidal, mud bottom, 18 July 2015, coll . H . Ariyama; 1 ovigerous female (OMNH-Ar-12084), 2.2 mm, Nominoura, Kakeroma Island , Kagoshima Prefecture, 28°07′01″N, 129°15′36″E ( Fig. 1A ), upper intertidal, sandy mud bottom with gravel, 4 July 2019, coll . H . Ariyama.

Material for comparison. Mucrocalliope shimantoensis . Holotype: male (OMNH-Ar-8689), 2.2 mm, Shimanto estuary, Kochi Prefecture, 32°56′31″N, 132°58′32″E, uppermost subtidal, mud bottom with seagrass, 14 May 2007, coll. K. Azuma and H. Hiraga. Paratypes: 2 males (OMNH- Ar-8690, 8691), 2.4 and 2.3 mm, respectively, and 2 females (OMNH-Ar-8692, 8693), 2.8 and 2.1 mm, respectively, same data as holotype.

Type locality. Mouth of Gesashi River, Higashi Village , Okinawa Island, Okinawa Prefecture .

Etymology. Referring to the collecting sites of the species.

Description of male. Based on holotype (OMNH- Ar-12077, 2.8 mm), paratype (OMNH-Ar-12179, 2.5 mm) only for habitus and paratype (OMNH-Ar-12078, 2.5 mm) for maxilla 1 and pereopod 5.

Body ( Fig. 2 ) relatively slender; pereonites 1–6 narrow, pereonite 7 and pleonites 1–3 wide, pleonites 1 and 2 each with distinct posterodorsal tooth.

Head. Eyes ( Fig. 2 ) large (diameter: 6.4% of BL). Antenna 1 ( Fig. 3A, A 1 ), peduncular articles 1–3 with length ratio of 1.0: 0.65: 0.4, article 1 stout; accessory flagellum 1-articulate, with 2 setae on tip; flagellum with 13 articles, last article minute, articles 1 and 2 in right and articles 1–3 in left each with calceolus medially, articles 9–12 each bearing aesthetasc at distal end. Antenna 2 ( Fig. 3B, B 1 ) slightly longer than antenna 1; peduncular articles 3–5 with length ratio of 1.0: 2.7: 1.7; flagellum with 14 articles, articles 1–5 each with calceolus anteriorly. Upper lip ( Fig. 3C), anterior surface with 2 long thick setae in middle and several long setae sublaterally, ventral margin with many short thin setae. Mandibles ( Fig. 3D, D 1, E, E1 ) with left and right incisors bearing 4 cusps; left lacinia mobilis 4-toothed and right one bifid, left accessory blades 4 in number and right ones 3; article length ratio of palp 1.0: 3.0–3.1: 3.5, articles 1 and 2 bare, article 3 with long proximolateral seta, 2 penicillate setae at mid-length on medial margin, and 3 long and 1 penicillate distal setae, ventral surface pubescent. Lower lip ( Fig. 3F) with short mandibular process, apical part of outer lobe setose, apical part of inner lobe with sparse setae. Maxilla 1 ( Fig. 3G, G 1 ) with ovoid inner plate bearing single long plumose seta; outer plate bearing 11 dentate robust setae apically; tip of palp article 2 with 1 thick and several slender setae. Maxilla 2 ( Fig. 3H) with both plates setose apically, medial margin of inner plate bearing single seta. Maxilliped ( Fig. 3I) with inner plate bearing several distal setae and many dorsal thin setae; outer plate large, medial to distal margin setose; palp stout, articles 1–3 wide, article 4 narrow, claw-shaped, distal end of article 2 not exceeding outer plate, medial margins of articles 1–3 and distal margin of article 3 setose.

Pereon. Gnathopod 1 ( Fig. 4A ) with coxa expanded distally, bearing 4 setae on ventral margin; basis with 2 anterior and 1 posterior long setae; merus with bifid seta and several thin setae on posterior margin; carpus posterodistal lobe with 3 distal and 1 medial setae, lateral surface covered with thin setae; propodus about 1.4 times as long as carpus, anterodistal corner with several long setae, palm weakly setose, without robust setae, anteromedial surface covered with thin setae; dactylus slender. Gnathopod 2 ( Fig. 4B, B 1 ) with coxa narrowed distally, bearing single ventral seta; basis with posterodistal short seta; carpus with 2 bifid setae and many thin setae on posterior margin; propodus about 2.05 times as long as carpus, palm slightly concave posteromedially, with 5 posteromedial and 4 medial robust setae; dactylus slender, almost reaching proximal-most robust seta. Pereopods 3 and 4 ( Fig. 4C, D ) slender, longer than gnathopod 2; coxae subquadrate, each with 3 ventral setae; bases bearing 1–2 posterior setae; anterodistal corners of meri and carpi setose; dactyli long, about 0.65–0.7 times of propodi. Pereopod 5 ( Fig. 4E, E 1 ), coxa bearing anterior and posterior lobes of same depth, posterior lobe with 1 robust and 1 short setae; basis with many anterior setae, posteromedial surface bearing long plumose seta; merus with 3 anterior and 4 anterodistal setae, posterior margin bearing 2 plumose and 2 simple setae, posterodistal corner with 3 setae; carpus with 2 anterior short robust setae, anterodistal and posterodistal corners setose; propodus with anterodistal robust seta; dactylus long, about 0.6 times of propodus. Pereopod 6 ( Fig. 4F ) longer than pereopod 5; posterior lobe of coxa deeper than anterior lobe, with 1 robust and 1 short setae; basis with 4 anterior and 4 posteromedial long plumose setae; merus with 4 setae on anterior margin, posteri- or margin bearing 4 long plumose setae and 2 simple setae, anterodistal and posterodistal corners setose; carpus with 2 anterior setae, anterodistal and posterodistal corners setose; propodus with 3 anterior short robust setae; dactylus long, about 0.55 times of propodus. Pereopod 7 ( Fig. 4G )>1.35 times as long as pereopod 6; coxa subrectangular, broader than long, with 2 short setae posteroventrally, gill absent; basis wide, anterior margin with 4 short robust setae, posterior margin minutely serrate, with 3 long plumose setae distomedially; ischium with 2 robust setae at anterodistal corner; merus with 1+2 robust setae on anterior margin and 2+1 robust setae on posterior margin, anterodistal and posterodistal corners setose; carpus with 1+2 robust setae on anterior margin and 1+1 robust setae on posterior margin, anterodistal and posterodistal corners setose; propodus with 1+3 robust setae on anterior margin and 1+1 robust setae on posterior margin, anterodistal and posterodistal corners setose; dactylus straight, with 2 posterior short setae, tip lost.

Pleon. Pleonal epimera ( Fig. 5A ), ventral margins of epimera 1 and 2 bearing 1 and 2 robust setae, respectively. Pleopods 1 and 2 ( Fig. 5B, C ) similar in length, pleopod 3 ( Fig. 5D ) shorter; peduncles each with 2 coupling hooks, peduncle of pleopod 1 with 2 lateral and 1 medial plumose setae; outer rami slightly shorter than inner rami, with 10 articles, inner rami bearing 9–10 articles. Uropod 1 ( Fig. 5E ) with peduncle bearing 6 dorsolateral and 2 dorsomedial robust setae; outer and inner rami about 1.05 and 1.3 times as long as peduncle, respectively, each with 2 robust setae. Uropod 2 ( Fig. 5F ) with peduncle bearing robust seta on dorsolateral margin; outer and inner rami about 1.3 and 1.6 times as long as peduncle, respectively, each with 3 robust setae. Uropod 3 ( Fig. 5G ) with peduncle bearing mediodistal robust seta; outer and inner rami about 1.5 and 1.7 times as long as peduncle, with 1 and 2 robust setae, respectively. Telson ( Fig. 5H ) longish oval, with 2 minute setae subdistally.

Description of female [based on paratype (OMNH- Ar-12081, 2.3 mm)]. Body ( Fig. 6 ) more inflated than that of male. Eyes smaller than those of male (diameter: 5.4% of BL). Antenna 1 ( Fig. 7A, A 1 ), peduncular articles 1–3 with length ratio of 1.0: 0.7: 0.5, article 1 stout; accessory flagellum 1-articuate, with 2 setae on tip; flagellum with 9 articles, articles 5 and 7–9 each bearing aesthetasc at distal end. Antenna 2 ( Fig. 7B, B 1 ) slightly shorter than antenna 1; peduncular articles 3–5 with length ratio of 1.0: 2.5: 2.25; flagellum with 10 articles.

Gnathopod 1 ( Fig. 7C ) with ovoid coxa, ventral margin with 4 setae; basis anterior margin and posterodistal corner with 2 long and 1 middle-sized setae, respectively; merus with slender seta and several thin setae on posterior margin; carpus posterodistal lobe with 3 distal and 2 medial setae, lateral surface covered with thin setae; propodus about 1.2 times as long as carpus, palm weakly setose, without robust setae, anterolateral and anteromedial surfaces covered with thin setae. Gnathopod 2 ( Fig. 7D ) slightly larger than gnathopod 1; coxa subrectangular, with 3 setae ventrally, oostegite large, oval; basis with 2 short setae anteriorly, posterior margin and posterodistal corner bearing 1 and 2 setae, respectively; merus with 2 slender and several thin setae on posterior margin; carpus with posterodistal lobe twice as long as broad, posterior margin lined with thin setae, apical margin with several setae; propodus about 1.4 times as long as carpus, lacking robust setae on palm. Oostegites on coxae 3 and 4 ( Fig. 7E, F ) very wide and narrow, respectively. Pereopod 5 ( Fig. 7G ) with coxa bearing narrow oostegite; basis anterior margin with 2 plumose and several simple setae, posteromedial surface without plumose seta (lost?); merus with 2 anterior and 3 anterodistal setae, posterior margin bearing single plumose and 2 simple setae, posterodistal corner with 4 setae; carpus short, propodus long, dactylus curved. Pereopod 7 ( Fig. 7H ) with coxa narrowed ventrally, bearing small gill; basis wide, anterior margin with 4 short robust setae, posterior margin minutely serrate, with 2 medial long plumose setae; ischium–propodus almost same as those of male; dactylus about 1.1 times as long as propodus, straight.

Variation. Small male (OMNH-Ar-12083, 2.1 mm). Gnathopod 2 ( Fig. 7I ) almost same as that of holotype (OMNH- Ar-12077, 2.8 mm), but propodus less dilated, palm with 4 posteromedial and 4 medial robust setae. Females (OMNH- Ar-12078–12080, 2.5, 2.4, 2.3 mm, respectively). Pereopod 5 coxa, posteromedial surface with a plumose seta.

Coloration of specimen shortly after fixation ( Fig. 8 ). Eyes reddish black; posterior margins of pereonites, pleonites and urosomite 1 dark red; other body and appendages pale red with sparse red spots.

Remarks. This new species is very similar to M. shimantoensis . A closer re-examination of the type specimen of M. shimantoensis revealed several new characters not described originally, which indicate similarity as well as difference be- tween the two species. Both species share the upper lip with long setae and the female pereopod 7 with coxal gill. However, M. ryukyuensis sp. nov. has the male antenna 2 with larger length ratio of 5th peduncular article to 4th article ( Fig. 9 ) and the basis of male pereopod 5 with a posteromedial plumose seta, which is lacking in M. shimantoensis . In addition, amphipod fauna in the Ryukyu Archipelago mostly differs from that in the other parts of Japan (e.g., Ariyama 2020) and habitat of the species is different from that of M. shimantoensis (estuary located 1.8 km upstream from river

Two species of paracalliopiid amphipod from Ryukyu 87

mouth); therefore, M. ryukyuensis is assumed to be an independent species in spite of small differences.

Habitat. Intertidal and uppermost subtidal, sandy or mud bottom, brackish.

Distribution. Japan: Kakeroma Island in Kagoshima Prefecture and Okinawa and Iriomote Islands in Okinawa Prefecture (present study).

Figures

Fig. 2. Mucrocalliope ryukyuensis sp. nov., paratype, male (OMNH-Ar-12179), 2.5mm, habitus, left lateral view.

Fig. 1. Map showing collecting sites of examined specimens in the Ryukyu Archipelago.

Fig. 4. Mucrocalliope ryukyuensis sp. nov., A–G, holotype, male (OMNH-Ar-12077), 2.8mm; E1, paratype, male (OMNH-Ar-12078), 2.5mm. A, Right gnathopod 1, lateral view; B, left gnathopod 2, lateral view; B1, palm and dactylus of left gnathopod 2, medial view, slen- der setae omitted; C–G, right pereopods 3–7, lateral views, gills on coxae 5, 6 lost; E1, carpus–dactylus of left pereopod 5 (reversed). Scales: 0.1mm.

Fig. 5. Mucrocalliope ryukyuensis sp. nov., holotype, male (OMNH-Ar-12077), 2.8mm. A, Left epimeral plates 1–3, lateral view; B–D, right pleopods 1–3, anterior views; E, right uropod 1, dorsolateral view; F, right uropod 2, lateral view; G, left uropod 3, medial view; H, telson, dorsal view.Scales: 0.1mm.

Fig. 6. Mucrocalliope ryukyuensis sp. nov., paratype, ovigerous female (OMNH-Ar-12081), 2.3mm, habitus, right lateral view.

Fig. 7. Mucrocalliope ryukyuensis sp. nov., A–H, paratype, ovigerous female (OMNH-Ar-12081), 2.3mm; I, paratype, male (OMNH- Ar-12083), 2.1mm. A, B, Left antennae 1, 2, lateral views; A1, accessory flagellum of left antenna 1, lateral view; B1, peduncular articles 2, 3 of right antenna 2, lateral view (reversed); C, D, left gnathopods 1, 2, lateral views; E, F, oostegites on left coxae 3, 4, lateral views; G, H, left pereopods 5, 7, lateral views; I, propodus and dactylus of left gnathopod 2, lateral view, slender setae omitted. Scales: 0.05mm.

Fig. 8. Mucrocalliope ryukyuensis sp. nov. Photograph of a fixed specimen (male, 7 hours after fixation) collected together with paratype female (OMNH-Ar-12082), 2.3mm, most part of pereopod 7 lost. Scale:0.5mm.

Fig. 9. Mucrocalliope ryukyuensis sp. nov. and M. shimantoensis Ariyama and Azuma, 2011. Length ratio of 4th article to 5th article in male antenna 2 peduncle relative to body length.