A new species of the genus Elasmopus from Miyako Island, Japan (Crustacea: Amphipoda: Maeridae) Author Nakamura, Yasuhiro Author Nakano, Takafumi Author Ota, Yuzo Author Tomikawa, Ko text Zootaxa 2019 2019-01-14 4544 3 395 406 journal article 27665 10.11646/zootaxa.4544.3.5 7ee7849b-b7d8-429f-a8a6-1f3787ce7262 1175-5326 2618405 32DE87D6-1D47-4FB6-A1A7-ABB1A1C9C03C Elasmopus nkjaf sp. nov. [New Japanese name: Miyako-iso-yokoebi] ( Figs 1–6 ) Material examined. Holotype : KUZ Z1862 , mature male ( 15.3 mm ) collected from Takano Fishing Port , Hirara , Miyako Island , Okinawa Pref., Ryukyu Islands , Japan ( 24°47′59″N , 125°20′03″E ), occurring in a commercial seaweed bed of Caulerpa lentillifera on 12 March 2013 , collected by Y. Ota. Paratypes : KUZ Z1863 , female ( 9.7 mm ) ; KUZ Z1864 , male ( 9.5 mm ); NSMT-Cr 25881, male (13.0 mm); NSMT-Cr 25882, female ( 5.8 mm ); NSMT- Cr 25883, male (10.0 mm); NSMT-Cr 25884, ovigerous female ( 6.4 mm ); NSMT-Cr 25885, ovigerous female ( 4.6 mm ). Data same as for the holotype . Description of male ( holotype , KUZ Z1862). Body ( Fig. 1 ) smooth, not carinate. Head ( Fig. 2A ): eyes oval; lateral cephalic lobe broad, weakly concave, anteroventral margin with notch. Epimeral plates 1–3 ( Fig. 4 D–F) with clusters of robust setae on ventral margins, each posterior margin setose; ventral margins of epimeral plates 2 and 3 with slender setae; posterodistal corner of epimeral plates 3 notched with small acute tooth. Antenna 1 ( Fig. 2B ): length 0.6 × body length; peduncular articles 1 to 3 in length ratio of 0.9: 1.0: 0.6; peduncular article 1 with robust seta on posterodistal corner; posterior margin of peduncular article 2 with 3 clusters of setae and single seta; peduncular article 3 with 2 clusters of setae on posterior margin; accessory flagellum 3-articulate, reaching to middle of primary flagellar article 3; primary flagellum 42-articulate. FIGURE 1. Elasmopus nkjaf sp. nov. , holotype, male, 15.3 mm, KUZ Z1862, Takano Fishing Port, Miyako Island, Okinawa Prefecture, Japan. Scale bar: 1.0 mm. Antenna 2 ( Fig. 2C ): length 0.5 × antenna 1; gland cone of peduncular article 2 not reaching to end of peduncular article 3; peduncular article 3 with robust setae on anterior submargin; peduncular article 4 slightly longer than article 5, with 1 cluster and 2 pairs of setae on posterior submargin; peduncular article 5 with 4 clusters of setae and single seta on posterior submargin; flagellum 10-articulate. Mouthparts . Upper lip ( Fig. 2D ) with rounded anterior margin, bearing fine setae. Mandible ( Fig. 2 E–G) with left and right incisors 2- and 4-dentate, respectively; left lacinia mobilis 5-dentate, right lacinia mobilis bifid; accessory setal row consisting of 4 setae on each of left and right mandibles; molar process well developed, triturative; palp well developed, 3-articulate; palp article 1 longer than broad, inner distal part weakly produced; palp article 2 slightly shorter than article 3; palp article 3 strongly falcate, length 2.6 × width. Lower lip ( Fig. 2H ) with outer lobes laterally expanded, bearing apical setae; inner lobes ovate, with apical setae. Maxilla 1 ( Fig. 2I ) with inner plate bearing 2 plumose setae apically; outer plate with 7 robust dentate setae; palp 2-articulate, article 1 marginally bare, article 2 with numerous apical and subapical setae, its outer margin without seta. Maxilla 2 ( Fig. 2J ) with outer and inner plates bearing long apical setae. Maxilliped ( Fig. 3A ) with inner plate bearing plumose setae apically; outer plate obovate, reaching less than half of palp article 2; palp article 2 with setae on inner margin; length of palp article 3 1.8 × length of palp article 2; nail of palp article 4 distinct. Gnathopod 1 ( Fig. 3B ): coxa anteroventral corner weakly produced, anterior margin weakly concave; basis with long setae on posterior margin; carpus length approximately 2 times its width, subequal in length to propodus, with slender setae on anterodistal corner and along posterdistal margin; propodus with 6 clusters of setae on anterior margin, palmar margin almost transverse, along with robust setae. Gnathopod 2 ( Fig. 3C, D ): coxa with setae on ventral margin; basis with long setae on posterior margin; merus with sharp posterodistal tooth bearing robust, and slender setae; carpus compressed, lobate, projecting between merus and propodus; propodus with 10 clusters of setae on anterior margin, rounded distomedial shelf with 4 medial and 6 lateral robust setae on palm, length 2.7 × length of carpus, medial face shallowly hollowed; palmar margin weakly concave, approximate two thirds length of propodus, with 1 lateral and 2 medial subacute teeth; lateral tooth large, associating with 4 medial and 6 lateral robust setae; medial teeth small, foremost medial tooth exceeding palmar margin; dactylus strongly curved, subacute, length 0.5 × length of propodus. Pereopod 3 ( Fig. 3E ): coxa longer than broad, ventral margin with numerous short and a few long setae; posterior margin of basis with long setae; posterior margin of merus with slender setae; posterior margins of carpus and propodus with robust, and slender setae, setae on anterodistal corner of propodus shorter than length of dactylus. Pereopod 4 ( Fig. 3F ): coxa expanded with posterior concavity, ventral margin with numerous short setae; posterior margin of basis with long setae; posterior margin of merus with slender setae; posterior margins of carpus and propodus with robust and slender setae, setae on anterodistal corner of propodus shorter than length of dactylus. Pereopod 5 ( Fig. 4A ): coxa bilobed, anterior lobe with 6 short setae, ventral margin of posterior lobe with 5 robust setae, posterior margin of posterior lobe with 4 small setae; posterior margin of basis straight with numerous short setae and a few slender setae; anterior margins of merus and carpus with robust setae and slender setae; anterior margin of propodus with robust setae, slender setae on posterodistal corner shorter than length of dactylus. Pereopod 6 ( Fig. 4B ): coxa bilobed, anterior lobe without setae, ventral margin of posterior lobe with 5 robust setae, posterior margin of posterior lobe with 4 small setae; posterior margin of basis almost straight with short, and long setae; anterior margins of merus and carpus with robust, and slender setae, posterior margins of merus and carpus with slender setae; anterior margin of propodus with robust setae, slender setae on posterodistal corner shorter than length of dactylus. Pereopod 7 ( Fig. 4C ): coxa rounded, with 7 small setae on posterior margin; basis expanded posteriorly, posterior margin rounded with short, and long setae; anterior margins of merus and carpus with robust, and slender setae, posterior margins of merus and carpus with slender setae; anterior margin of propodus with robust setae, slender setae on posterodistal corner shorter than length of dactylus. Coxal gills present on gnathopod 2 and pereopods 3–6. Pleopods ( Fig. 4 G–J): inner distal corner with 2 retinacula; inner basal margin of inner ramus of pleopods 1–3 with 4, 3 or 4, and 3 bifid plumose setae (clothes-pin setae), respectively. Uropods . Uropod 1 ( Fig. 5A ): peduncle with 1 basofacial seta, length 1.3 × length of outer ramus; outer ramus subequal in length to inner ramus, with 5, and 7 robust setae on outer, and inner margins, respectively; inner ramus with 5, and 4 robust setae on outer, and inner margins, respectively. Uropod 2 ( Fig. 5B ): peduncle length 1.1 × length of outer ramus; outer ramus subequal in length to inner ramus, with 6 robust setae on outer and inner margins, respectively; inner ramus 2, and 4 robust setae on outer, and inner margins, respectively. Uropod 3 ( Fig. 5C ): peduncle length 0.9 × length of outer ramus; rami distally truncated; outer ramus length 1.1 × length of inner ramus, with 3 clusters, and 1 cluster of robust setae on outer, and inner margins, respectively; inner ramus with 2 pairs of robust setae on inner margin. Telson ( Fig. 5D ): length 1.2 × width, cleft for 85% of length; inner apical lobes weakly longer than outer apical cusps, each lobe with 2 minute setae laterally, distal part with 2¯3 robust setae and single small seta subapically. Description of female ( paratype , KUZ Z1863). Epimeral plate 3 ( Fig. 6A ) with ventral margin lacking slender setae. Gnathopod 1 ( Fig. 6B ): basis with long setae on medial surface; propodus with 4 clusters of setae on anterior margin. Gnathopod 2 ( Fig. 6C ): merus with sharp posterodistal tooth bearing slender setae; carpus not compressed, without posterodistal lobe; propodus with 6 clusters of, and 1 pair of setae, plus single seta on anterodistal margin, length 1.6 × length of carpus; palmar margin almost transverse, along with robust setae and 3 defined robust setae; dactylus weakly curved. Uropod 3 ( Fig. 6D ): inner ramus with 2 robust setae on subproximal inner margin, 1 cluster of robust setae on subdistal outer margin. Telson ( Fig. 6E ): length 1.3 × width, cleft for 78 % of length; inner apical lobes developed, elongate, each lobe with 1 minute seta laterally, distal part with 2 long, and 1 short robust setae, plus 1 short seta. FIGURE 2. Elasmopus nkjaf sp. nov. , holotype, male, 15.3 mm, KUZ Z1862, Takano Fishing Port, Miyako Island, Okinawa Prefecture, Japan. A, head, lateral view; B, antenna 1, medial view; C, antenna 2, medial view; D, upper lip, anterior view; E, right mandible, medial view; F, incisor, lacinia mobilis, and accessory setal row of right mandible, medial view; G, incisor, lacinia mobilis, and accessory setal row of left mandible, medial view; H, lower lip, ventral view; I, maxilla 1, dorsal view; J, maxilla 2, dorsal view. Scale bars: 1.0 mm (A–C), 0.1 mm (D–J). FIGURE 3. Elasmopus nkjaf sp. nov. , holotype, male, 15.3 mm, KUZ Z1862, Takano Fishing Port, Miyako Island, Okinawa Prefecture, Japan. A, maxilliped, dorsal view; B, gnathopod 1, medial view; C. gnathopod 2, medial view; D, palmar margin of propodus of gnathopod 2, medial view; E, pereopod 3, medial view; F, pereopod 4, medial view. Scale bars: 0.1 mm (A), 1.0 mm (B, C, E, F), 0.5 mm (D). FIGURE 4. Elasmopus nkjaf sp. nov. , holotype, male, 15.3 mm, KUZ Z1862, Takano Fishing Port, Miyako Island, Okinawa Prefecture, Japan. A, pereopod 5, lateral view; B, pereopod 6, lateral view; C, pereopod 7, lateral view; D, epimeral plate 1, lateral view; E, epimeral plate 2, lateral view; F, epimeral plate 3, lateral view; G, pleopod 1, medial view; H, pleopod 2, medial view; I, pleopod 3, medial view; J, bifid setae (clothes-pin setae) on inner basal margin of inner ramus of pleopod 3, lateral view. Scale bars: 1.0 mm (A–I), 0.5 mm (J). FIGURE 5. Elasmopus nkjaf sp. nov. , holotype, male, 15.3 mm, KUZ Z1862, Takano Fishing Port, Miyako Island, Okinawa Prefecture, Japan. A, uropod 1, dorsal view; B, uropod 2, dorsal view; C, uropod 3, dorsal view; D, telson, dorsal view. Scale bars: 0.5 mm (A–C), 0.1 mm (D). Variation. Epimeral plate 3 , ventral margin with or without slender setae; telson , inner apical lobes weakly or much longer than outer apical cusps, length of apical robust setae short, or long; eggs , 4–8. Etymology. The specific name is from the Miyako word for the seaweed Caulerpa lentillifera , the habitat of the new species; thus not a Latin or Latinized word. Sequences and COI genetic distances. In total eight nucleotide sequences were determined: holotype (KUZ Z1862), four sequences, 28S ( LC215811 ; 1194 bp), H3 ( LC215815 ; 328 bp), COI ( LC215813 ; 658 bp), and 16S ( LC215809 ; 417 bp); and paratype (KUZ Z1864), four sequences, 28S ( LC215810 ; 1194 bp), H3 ( LC215814 ; 328 bp), COI ( LC215812 ; 658 bp), and 16S ( LC215808 ; 417 bp). The COI genetic diversity within the newly obtained two COI sequences ( LC215812 , LC215813 ) was 0.6% (4/658). Based on the 653–658 bp aligned sequences, the COI uncorrected p -distance between E . nkjaf and the Portuguese E . rapax was 16.0–16.7% (mean = 16.2%). Remarks. Elasmopus nkjaf is most similar to E. rapax in having the following characteristics: posteroventral corner of epimeral plate 3 notched; short setae on posterior margins of peduncular articles 1–3 of antenna 1 and peduncular articles 4–5 of antenna 2; propodus of male gnathopod 2 with distomedial shelf bearing robust setae and 3 teeth on palm; posterior margin of basis of pereopod 7 with long setae; and both inner and outer rami of uropod 3 almost isometry. However, E. nkjaf differs from the neotype of E. rapax in the following four morphological features (features of the true E. rapax in parentheses): 1) foremost medial tooth on palm of propodus of male gnathopod 2 exceeding palmar margin (not exceeding); 2) distomedial shelf of propodus of male gnathopod 2 with 4 medial and 6 lateral robust setae (2 medial and 4 lateral); 3) posterodistal setae on propodi of pereopods 5–7 shorter than length of dactyli (longer); and 4) basis of male pereopod 7 more expanded, length 1.3 × width (1.5). Additionally, the mean COI distance between E . nkjaf , and the amphipods identified as E . rapax from Portugal was 16.2%. Therefore, we concluded that the present specimens are not conspecific with E . rapax . FIGURE 6. Elasmopus nkjaf sp. nov. , paratype, female, 9.7 mm, KUZ Z1863, Takano Fishing Port, Miyako Island, Okinawa Prefecture, Japan. A, epimeral plate 3, lateral view; B, gnathopod 1, medial view; C, gnathopod 2, medial view; D, uropod 3, dorsal view; E, telson, dorsal view. Scale bars: 0.5 mm (A–D), 0.1 mm (E). Elasmopus nkjaf could be distinguished from the other rapax -group species, which possess long setae on ventral margin of epimeral plate 3 in male ( Vader & Krapp-Schickel 2012 ; Gouillieux & Sorbe 2015 ), by the following combinations of the characters: gland cone of peduncular article 2 of antenna 2 not reaching to end of peduncular article 3 (exceeding in E . thalyae Gouillieux & Sorbe, 2015 ); propodus of gnathopod 1 facially setose (poorly setose in E . vishakhapatnamensis Kanakadurga et al ., 1981 ); length of propodus of male gnathopod 2 shorter than 3 times as long as length of carpus (longer than 4 times in E . arafura Hughes & Lowry, 2011 , E . hooheno , E . integer Myers, 1989 , E . lecroyae García-Madrigal, 2010 , E . mayo Barnard, 1979 , and E . molokai Barnard, 1970 ); medial face of propodus of male gnathopod 2 shallowly hollowed (deeply hollowed in E . tiburoni Barnard, 1979 ); posterior margin of epimeral plate 3 without denticles (with denticles in E . bampo Barnard, 1979 ). An alien isopod species Paracerceis sculpta ( Holmes, 1904 ) was recorded from a commercial seaweed bed at the type locality of E . nkjaf ( Ota 2014 ) . Elasmopus species, e.g. E . rapax and E . pectenicrus , have often been recorded as an introduced species (e.g. Sezgin et al . 2007 ; Hughes & Lowry 2010 ). Therefore, it is possible that E . nkjaf may be also non-native species in Miyako Island. Further molecular study based on the full-range of the Elasmopus species is necessary to reveal whether E . nkaf is an alien species or not.