Elasmopus nkjaf, Nakamura & Nakano & Ota & Tomikawa, 2019

Nakamura, Yasuhiro, Nakano, Takafumi, Ota, Yuzo & Tomikawa, Ko, 2019, A new species of the genus Elasmopus from Miyako Island, Japan (Crustacea: Amphipoda: Maeridae), Zootaxa 4544 (3), pp. 395-406 : 396-404

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.

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.

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 .

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.

Figures

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.

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).

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).