Elasmopus lumbiniger, Yoshimura & Lee & Tomikawa, 2025

Elasmopus lumbiniger sp. nov.

Figs 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8 , 9 View Figure 9 , 10 View Figure 10 , 11 View Figure 11 , 12 [New Japanese name: Sewata-iso-yokoebi View Figure 12 ]

Type material.

Holotype: • male, 9.8 mm ( NSMT -Cr 33064 ), Kannonzaki Coast , Yokosuka, Kanagawa, Japan ( 35.2592°N, 139.7436°E) (Fig. 1 A View Figure 1 ), shallow subtidal zone, rocky shore, among holdfast of the brown alga Eisenia bicyclis , 4 February 2023, H. Yoshimura coll. GoogleMaps Paratypes: • male, 10.4, 9.9, 8.5 mm ( NSMT -Cr 33065 –33067), ovigerous female, 8.7 mm ( NSMT -Cr 33068 ), same data as for the holotype GoogleMaps ; • male, 9.6, 7.1 mm ( NSMT -Cr 33069 , 33070), female, 5.9 mm ( NSMT -Cr 33071 ), Kannonzaki Coast , Yokosuka, Kanagawa, Japan ( 35.2592°N, 139.7432°E) (Fig. 1 A View Figure 1 ), shallow subtidal zone, rocky shore, among holdfast of the brown alga Sargassum sp. , 22 April 2023, H. Yoshimura coll. GoogleMaps ; • male, 7.0 mm ( NSMT -Cr 33072 ), Arasaki Coast , Yokosuka, Kanagawa, Japan ( 35.1947°N, 139.5996°E) (Fig. 1 B View Figure 1 ), shallow subtidal zone, rocky shore, among the red alga Corallina sp. , 2 September 2023, H. Yoshimura coll. GoogleMaps ; • male, 13.8 mm ( NSMT -Cr 33073 : Fig. 6 A View Figure 6 ), Uchiura Beach , Kamogawa, Chiba, Japan ( 35.1262°N, 140.1893°E) (Fig. 1 C View Figure 1 ), shallow subtidal zone, rocky shore, among the red alga Corallina sp. , 18 June 2022, H. Yoshimura coll. GoogleMaps ; • male, 10.0 mm ( NSMT -Cr 33074 ), Shirahama , Minamiboso, Chiba, Japan ( 34.9031°N, 139.8862°E) (Fig. 1 D View Figure 1 ), intertidial zone, rocky shore, 5 June 2023, H. Ogawa coll. GoogleMaps ; • female, 12.6, 10.3 mm ( NSMT -Cr 33075 : Fig. 6 B View Figure 6 , NSMT -Cr 33076 ), Takurazaki , Wakayama, Wakayama, Japan ( 34.2671°N, 135.0605°E) (Fig. 1 I View Figure 1 ), shallow subtidal zone, rocky shore, under the stone, 10 May 2024, H. Yoshimura coll. GoogleMaps ; • male, 10.0 mm ( NSMT -Cr 33077 ), female, 7.9 mm ( NSMT -Cr 33078 ), Uradome Beach , Iwami, Tottori, Japan ( 35.5921°N, 134.3198°E) (Fig. 1 H View Figure 1 ), shallow subtidal zone, rocky shore, among sporophyll of the brown alga Undaria pinnatifida lying on the sea bottom, 16 June 2024, H. Ogawa, Y. Mukaida, M. Ooga, and H. Yoshimura coll. GoogleMaps

Diagnosis.

Epimeral plate 3 posteroventral corner produced into well-developed acute spine. Antenna 1 peduncles bearing slender setae on lateral and medial margins, with tri-articulate accessory flagellum. Mandibular palp article 3 short. Gnathopod 2 carpus anterodistal corner with slender setae, length of the longest seta reaching 0.8–1.1 and 0.9–1.1 × width of carpus in male and female. Male gnathopod 2 propodus posterior margin and inner surface with dense slender setae, length of the longest seta reaching 0.9 × width of propodus, palmar margin with trapezoidal hump near hinge of dactylus, mid-palmer margin with ridge. Pereopods 5–7 basis posterior margin smooth, without long setae. Telson cleft, border than long; lobe trapezoid, with shallow incision at apex, each lobe bearing one plumose and 4–6 robust setae apically.

Description of male

( holotype, NSMT -Cr 33064 ). Body (Fig. 7 A View Figure 7 ): smooth, not carinate, with a few short setae dorsally on pereon and abdomen. Head: eyes oval; lateral cephalic lobe broad, anteroventral margin with notch; dorsal surface with a few short setae. Epimeral plates 1–3 (Fig. 7 B – D View Figure 7 ): each ventral margin with one cluster and one single robust seta, two clusters and one single robust seta, and two clusters and five robust setae, respectively; each posterior margin with three or four, four and four short setae, respectively; posteroventral corner of epimeral plates 1 and 2 weakly produced, epimeral plate 3 produced into well-developed acute spine.

Antenna 1 (Fig. 8 A View Figure 8 ): length 0.55 × body length; peduncular articles 1–3 in length ratio of 1.1: 1.0: 0.6, with slender setae on lateral and medial margin; peduncular article 1 with three robust setae on posteroproximal margin, robust seta on posterodistal corner; accessory flagellum tri-articulate, accessory flagellar article 3 tiny; primary flagellum 34 - articulate, with slender setae. Antenna 2 (Fig. 8 B View Figure 8 ): length 0.5 × antenna 1; peduncular article 2 with six short spines on anterodistal corner, gland cone of peduncular article 2 exceeding distal margin of peduncular article 3; peduncular article 4 slightly longer than 5, with slender setae on lateral and medial margins; flagellum 13 - articulate, with slender setae.

Mouthparts. As holotype upper lip missing, that of paratype (male, 9.9 mm, NSMT -Cr 33066 ) illustrated. Upper lip (Fig. 8 C View Figure 8 ) with rounded anterior margin, bearing fine setae. Mandible (Fig. 8 D – F View Figure 8 ) with left and right incisors two and four teeth, respectively; left lacinia mobilis five teeth and right lacinia mobilis four teeth; accessory setal row three setae on the left and four setae on the right; molar process well developed, triturative; palp (Fig. 8 F View Figure 8 ) well developed, tri-articulate; palp article 1 without setae, article 2 with ten setae, article 3 falcate, length 3.0 × width. Lower lip (Fig. 8 G View Figure 8 ) with outer lobes laterally expanded, bearing apical setae; inner lobes ovate, apically covered with setae. Maxilla 1 (Fig. 8 H View Figure 8 ) with inner plate bearing two plumose setae apically; outer plate with seven robust dentate setae; palp bi-articulate, article 1 marginally bare, article 2 with numerous apical and subapical setae, outer margin bare. Maxilla 2 (Fig. 8 I View Figure 8 ) with inner plate bearing long apical setae, with setae on outer and inner margins; outer plate bearing long apical setae, with setae on outer margin. Maxilliped (Fig. 8 J View Figure 8 ) with inner plate bearing plumose setae apically; outer plate obovate, with spatula plumose setae on apical and inner margins, reaching more than half of palp article 2; palp article 1 with two setae on inner margin, with seta on outer margin; palp article 2 slender, lined with setae on inner margin, outer margin bare; nail of palp article 4 distinct.

Gnathopod 1 (Fig. 9 A – D View Figure 9 ): subchelate; coxa anteroventral corner weakly produced, anterior margin weakly concave, ventral margin with long and short setae; basis with long setae on posterior margin and medial surface; carpus subequal in length to propodus, with slender setae on anterodistal corner, with dense pinnate sided setulated setae on medial surface and posterior margin; propodus with six clusters of setae on anterior margin, with seven clusters of setae on medial surface; palmar margin (Fig. 9 C, D View Figure 9 ) almost transverse, minutely serrate, with rows of robust setae on medial and lateral palmar submargins, palmar corner with two long robust setae; dactylus with slender seta on anteroproximal margin, with six small setae on lateral margin, with spatulate seta and slender seta laterally at the base of nail. Gnathopod 2 (Fig. 9 E – G View Figure 9 ): subchelate; coxa with long and short setae on ventral margin, of which two long setae retrorse; basis with long setae on posterior margin; merus distoventral corner subquadrate bearing long setae; carpus with slender setae on anterodistal corner, length of these setae 0.9 × width of carpus, with dense setae on posterior margin; propodus with five clusters, two pairs and two single setae on anterolateral submargin, length of these setae 0.4 × width of propodus, anteromedial submargin with eight clusters of setae; lateral palmar margin weakly concave with trapezoidal hump (Fig. 9 G View Figure 9 ) on near insertion of dactylus, with one clusters, three pairs and one single setae on lateral surface, with six and seven robust setae on lateral and medial margins, respectively; mid-palmar margin with ridge; posterior margin with row of plumose setae, the proximal seta longer than the distal seta, length of the longest seta 0.9 × width of propodus; dactylus strongly curved, subacute, length 0.6 × length of propodus, with seta on anteroproximal margin.

Pereopod 3 (Fig. 10 A View Figure 10 ): coxa longer than broad, ventral margin with numerous short and a few long setae, of which long seta retrorse; posterior margins of basis with long slender and robust setae, merus with slender setae, carpus and propodus with robust and slender setae; dactylus with plumose seta on anteroproximal margin, with one robust and two slender setae at the base of nail. Pereopod 4 (Fig. 10 B View Figure 10 ): coxa expanded with posterior concavity, ventral margin arched bearing numerous short and a few long setae, of which long seta retrorse; posterior margins of basis with long slender and robust setae, merus with slender setae, carpus and propodus with robust and slender setae; dactylus with plumose seta on anteroproximal margin, with one robust and two slender setae at the base of nail. Pereopod 5 (Fig. 10 C View Figure 10 ): coxa bilobed, ventral margin of posterior lobe with two robust setae, posterior margin of posterior lobe with five short setae; basis broad, subrectangular, posterior margin smooth, with numerous short setae; anterior and posterior margins of carpus with robust setae; propodus with robust setae on anterior margin, with one cluster setae on posteromedial submargin; dactylus with plumose seta on posteroproximal margin, with one robust and two slender setae at the base of nail. Pereopod 6 (Fig. 10 D View Figure 10 ): coxa bilobed, anterior margin of anterior lobe with slender setae, ventral margin of posterior lobe with three robust setae, posterior margin of posterior lobe with five short setae; basis weakly expanded proximally, tapering distally, posterior margin smooth with numerous short setae; anterior margin of carpus with robust and slender setae, posterior margin with robust setae; anterior margin of propodus with robust setae, with two clusters setae on posteromedial submargin; dactylus with plumose seta on posteroproximal margin, with one robust seta and two slender setae at the base of nail. Pereopod 7 (Fig. 10 E View Figure 10 ): coxa rounded, with slender setae on anterior and short setae on posterior margins; basis expanded, subovate, posterior margin rounded, smooth, with numerous short setae; anterior and posterior margins of carpus with robust and slender setae; anterior margin of propodus with robust and slender setae, with three clusters setae on posteromedial submargin; dactylus with plumose seta on posteroproximal margin, with one robust and two slender setae at the base of nail.

Coxal gills on gnathopod 2 and pereopods 3–6.

Pleopods (Fig. 10 F – K View Figure 10 ): peduncles with long setae, inner distal corner of peduncle with two retinacula (Fig. 10 G, I, K View Figure 10 ), peduncle of pleopod 3 broader than pleopod 1 and 2.

Uropods. Uropod 1 (Fig. 11 A View Figure 11 ): peduncle length 1.2 × length of outer ramus, with six dorsolateral, seven dorsomedial and one basofacial robust setae; outer ramus slightly shorter than inner ramus, medial and lateral margins each with four robust setae, distal part with four robust setae; inner ramus medial and lateral margins each with four robust setae, distal part with five robust setae. Uropod 2 (Fig. 11 B View Figure 11 ): peduncle length 0.9 × length of outer ramus; outer ramus slightly shorter than inner ramus, with three and five robust setae on medial and lateral margins, respectively, distal part with four robust setae; inner ramus five and four robust setae on medial and lateral margins, respectively, distal part with five robust setae. Uropod 3 (Fig. 11 C View Figure 11 ): peduncle length 0.8 × length of outer ramus, with pair of robust setae on outer margin; rami distally truncated; outer ramus length 1.5 × length of inner ramus, with three and one clusters of robust setae on lateral and distal margins, respectively, with robust seta and one pair of robust setae on medial margin and surface, respectively; inner ramus with cluster of robust setae distally and two robust setae on medial margin.

Telson (Fig. 11 D View Figure 11 ): broader than long, cleft for 75 % of length; lobe trapezoid, with shallow incision at apex, each lobe bearing one plumose five robust setae apically, lateral margin of each lobe with one or two plumose setae.

Description of female

( paratype, NSMT -Cr 33068 ), sexually dimorphic characters. Gnathopod 1 (Fig. 11 E, F View Figure 11 ): propodus anterior margin with 1 single and 4 clusters of setae, medial surface with 6 clusters of setae. Gnathopod 2 (Fig. 11 G, H View Figure 11 ): slender setae on carpus anterodistal corner reaching width of carpus; propodus with two clusters, three pairs, and two 2 single setae on anterolateral submargin, length of these setae 0.7 × width of propodus, anteromedial submargin with 13 clusters; palmar margin (Fig. 11 H View Figure 11 ) almost straight, with minutely serrate on the distal 1 / 5 of the palmar margin. Pereopod 3 (Fig. 11 I View Figure 11 ): basis with slender setae on anterior margin, the longest seta 0.8 × width of basis. Oostegites on gnathopod 2 and pereopods 3–5, slender with long setae.

Variations.

Mandible: left and right incisors with two or three and three or four teeth, respectively; lacinia mobilis with four or five teeth. Gnathopod 2: length of setae on carpus anterodistal corner 0.8–1.1 and 0.9–1.1 × width of carpus in male and female, length of setae on propodus anterolateral submargin 0.3–0.7 and 0.6–0.7 × width of propodus in male and female, respectively. Telson: each lobe bearing 4–6 robust setae apically.

Large male> 10 mm bearing slender setae on ventral margins of epimeral plates 2 and 3, and urosomite 1 (Fig. 12 View Figure 12 ).

Coloration in life.

Male: eyes black; antenna 1 peduncular articles brown, flagellum with two patterns, brown proximally and black distally, on a white background; body color varies among individuals ranging from reddish brown to brown or black, with small white dot patterns on head, pereon, abdomen, and coxae, with one dark black band along dorsal midline of pleonite 3 and urosomite 1. Female: body black, without distinct black band on dorsal midline of abdomen.

Distribution.

Japan: Chiba, Kanagawa, Wakayama, and Tottori (present study) (Fig. 1 View Figure 1 ).

Ecological note.

This new species was found among brown and red algae or under stones in rocky shore. E. lumbiniger sp. nov. and E. projectus were collected from the same individual algae holdfasts at two sites: Kannonzaki Coast (Fig. 1 A View Figure 1 ) and Uradome Beach (Fig. 1 H View Figure 1 ).

Etymology.

The specific name lumbiniger , from the Latin lumbus (= loin, lower back) and niger (= black), refers to the dark coloration along the dorsal midline of male pleonite 3 and urosomite 1 in life (Fig. 6 A View Figure 6 ). The Japanese name is derived from this band, which resembles a vein running along the back of a shrimp, known as “ Sewata ”.

Remarks.

Elasmopus lumbiniger sp. nov. is morphologically similar to E. antennatus ( Stout, 1913) , E. balkomanus Thomas & Barnard, 1988 , and E. lemaitrei Ortiz & Lalana, 1994 , in having the following features: 1) epimeral plate 3 posteroventral corner produced into well-developed acute spine; 2) male gnathopod 2 propodus palm with dense slender setae; 3) male gnathopod 2 mid-palmar margin with ridge; 4) male gnathopod 2 propodus with hump on near insertion of dactylus; 5) pereopods 5–7 basis posterior margin smooth, without long setae; and 6) telson broader than long. However, E. lumbiniger sp. nov. can be distinguished from the above three species by length of the longest seta on the anterodistal corner of male gnathopod 2 carpus 0.8–1.1 × width of carpus (less than 0.2 in these three species). From E. antennatus , this new species is distinguishable by the following two characters in addition (features of E. antennatus in parentheses): 1) hump on propodus of male gnathopod 2 trapezoidal, produced (semioval, weekly produced); and 2) the length of setae on anterior margin of pereopods 5–7 merus exceeding half the width of each merus (less than half of the width of each merus). Elasmopus lumbiniger sp. nov. can be further distinguished from E. balkomanus and E. lemaitrei by the following two additional features (features of E. balkomanus and E. lemaitrei in parentheses): 1) ridge on mid-palmar margin of male gnathopod 2 propodus not serrate (serrate); and 2) the length of setae on posterior margin of pereopod 7 carpus almost equal to that on anterior margin (more than twice that on anterior margin).

In this study, we calculated the genetic distances of COI among five Elasmopus species recorded in East Asia and Elasmopus lumbiniger sp. nov. E. lumbiniger sp. nov. differs from the other five Elasmopus species by large genetic distances ( 0.158 –0.205 in p - distance; 0.181 –0.244 in K 2 P), which were larger than the intraspecific distances among the Elasmopus species examined in this study (Tables 3 View Table 3 , 4 View Table 4 ). In addition, E. lumbiniger sp. nov. is morphologically distinguished from its congeners. Therefore, it can be concluded that E. lumbiniger sp. nov. is a distinct new species.