Tropichelura J.L. Barnard

Genus Tropichelura J.L. Barnard View in CoL

(New Japanese name: Nangoku-kikuimodoki-zoku)

Tropichelura barasu Tokumori, Kakui and Tomikawa sp. n. (Japanese name: Nangoku-kikuimodoki)

( Figures 2 View Figure 2 (b), 3–13)

Material examined

Holotype. Female 6.0 mm (NSMT-Cr 33039), JAPAN: Okinawa, off the northern coast of Iriomote depth of 17 m on a muddy slope of Daikupee ( 24.4182°N, 123.8366°E), coll. K. Kakui on 4 July 2014. GoogleMaps

Paratypes. 2 males 6.4 mm (NSMT-Cr 33040), 4.2 mm (NSMT-Cr 33041, G2197), female 3.9 mm (33042, G2198), JAPAN: Okinawa, off the northern coast of Iriomote Island, depth of 12.5m off the Uchipanari ( 24.3445°N, 123.7350°E), coll GoogleMaps . K GoogleMaps . Kakui on 11 August 2016; ovigerous female 5.4 mm (33043), data same as for the holotype GoogleMaps .

Etymology

The species name ‘ barasu ’ is an indeclinable noun derived from ‘coral’ in the dialect of Okinawa Japan. The name refers to the fact that this new species inhabits coral rubble and submerged woods

Diagnosis

Female antenna 1 primary flagellum 2.2–2.3 times as long as peduncular article 3. Gnathopod 1 propodus tooth at middle of palmar margin;dactylus posteroproximal margin smooth.Female pereopod 7 basis slender expanded. Male uropod 2 peduncle 1.9 times as long as wide. Uropod 3 ramus with long setae marginally uropod 3 ramus 2.6 times as long as wide. Female and male telson with 2 and 4 pairs, respectively, of long distally.

Description

Female [ holotype, NSMT-Cr 33039]. Head (Figure 3) slightly longer than pereonites 1 and 2 combined;

not produced; eyes large, round; lateral cephalic lobe rounded; antennal sinus shallow. Pereonites 1–7 (dorsally smooth with fine setae.Pleonites 1 and 2 (Figures 3 and 4(a,b)) dorsally smooth, with many short posterodorsal margins, pleonite 3 (Figures 3 and 4(c)) with 3 dentate tubercles dorsally. Epimeral (Figure 4(d–f)) with marginal setae, posterodistal corners not produced. Urosomites fused.

Antenna 1 (Figure 4(g)) 0.25 times as long as body; length ratio of peduncular articles 1–3 1.0:0.9:0.6 length of peduncular articles 1–3 is 0.5, 0.4, 0.6, respectively; peduncular article 1 with marginal setae;

article 2 with posterior margin bearing long setae; peduncular article 3 setose marginally; accessory uniarticulate with 5 terminal setae;primary flagellum 4-articulate,2.3 times as long as peduncular article 3, Figure 3. Tropichelura barasu holotype female (6.0 mm) (NSMT-Cr 33039). Habitus, lateral view.

flagellum 4-articulate, article 1 long, length 0.8 times as long as peduncular article 5, rectangular, length width, with long setae marginally, articles 2–4 sparsely setose distally.

Upper lip (Figure 5(a)) 1.2 times as long as wide, ventral margin with row of minute setae. Left mandibles (Figure 5(b,c)) with incisors 8- and 4-dentate, respectively; lacinia mobilis indistinct; left accessory setal rows each with 6 plumose setae; molar process large, triturative; palp 3-articulate, article long and 3 short setae, article 2 with 7 setae ventrodistally, article 3 with row of setae on ventral margin with 2 long setae. Lower lip (Figure 5(d)) with broad, rounded outer lobes bearing fine setae;inner lobes Maxilla 1 (Figure 5(e)) inner plate ovate, with 6 plumose setae medially; outer plate with 11 pectinate robust palp 2-articulate, with 5 robust and 1 slender setae apically. Maxilla 2 (Figure 5(f)) inner plate slightly shorter outer plate, with setal row medially; outer plate with setae apically. Maxilliped (Figure 5(g)) inner plate apically, with row of setae medially; outer plate exceeding half of palp article 2, apical margin with row some robust;palp 4-articulate,articles 2 and 3 with medial setae, some plumose,article 4 curved with apical

Gnathopod 1 (Figure 6(a)) subchelate; coxa rounded, with setae on anterior and ventral margins broadened and remaining nearly constant width distally, lateral surface with setae; ischium, merus and with row of setae on posterodistal corner; carpus length 0.7 times width, 0.3 times as long as propodus, setae on anterodistal corner; propodus 1.3 times length of width, projected posterodistally, with setae on and posterior margins, palmar margin weakly toothed with lined setae; dactylus narrow, weakly curved, oproximal margin smooth, lined with short setae on posterior margin.Gnathopod 2 (Figure 6(b,c)) slender chelate; coxa squarish, with roundish distal corner, bearing marginal setae; basis slender,with long plumose on anterodistal margin, laterodistal surface with minute setae; ischium short with posterodistal setae surface with minute setae; merus, carpus and propodus with marginal long setae; merus with minute lateral surface; parts of medial regions with densely short setae on basis, ischium and merus; carpus 3.1 length of width, slightly shorter than propodus, merus and carpus overlapping; propodus 3.4 times

HISTORY

Figure 4. Tropichelura barasu holotype female (6.0 mm) (NSMT-Cr 33039). (a–c) Pleonites 1–3, dorsal views. (d–f) plates 1–3, lateral views. (g) Antenna 1, lateral view. (h) Antenna 2, lateral view.

Figure 5. Tropichelura barasu holotype female (6.0 mm) (NSMT-Cr 33039). (a) Upper lip, anterior view. (b) Left medial view (palp twisted). (c) Incisor and accessory setal row of right mandible, lateral view. (d) Lower lip, dorsal Maxilla 1, dorsal view. (f) Maxilla 2, dorsal view. (g) Maxilliped, dorsal view.

HISTORY with setae; length ratio of merus, carpus, propodus and dactylus 1.0:1.0:1.1:0.1; carpus with robust posterodistal corner; propodus with plumose setae on anterodistal corner.Pereopod 4 (Figure 7(a)) coxa square, with setae on ventral margin; basis slightly expanded anteriorly, with setae; length ratio of merus, propodus and dactylus 1.0:0.6:0.9:0.4; carpus with robust setae on posterodistal corner. Pereopod 5 (Figure coxa bilobed, with setae; basis slightly expanded proximally, with setae; merus expanded, with robust posterodistal corner; carpus 0.46 times length of propodus, with robust setae on anterodistal corner;

with robust setae on posterior margin; dactylus thick. Pereopod 6 (Figure 7(c)) coxa bilobed, with setae, lobe with robust seta;basis straight and slightly expanded anteriorly,length 2.8 times width,anterior and margins with setae; merus expanded with setae; carpus 0.4 times as long as propodus, with robust anterodistal corner; propodus with robust setae on posterior margin; dactylus thick.Pereopod 7 (Figure 7(rounded, with setae on ventral margin; basis straight and slightly expanded anteriorly, length 2.3 times posterior margin with plumose setae; merus expanded, with robust setae on anterodistal corner; carpus drate, 0.4 times as long as propodus, with robust setae on anterodistal corner; propodus with robust posterior margin; dactylus thick. Oostegites (brood plates) (Figure 8(a)) narrow, on gnathopod 2 to with marginal setae. Coxal gills (Figure 8(b–f)) oval, on gnathopod 2 to pereopod 6, gill on pereopod 6 Pleopods (Figure 9) peduncle with 2 coupling hooks associated with plumose seta, laterodistal strongly produced; pleopod 1 (Figure 9(a)) peduncle with short seta on lateroproximal margin, outer rami with 9 and 10 articles, respectively; pleopod 2 (Figure 9(b)) peduncle with setae, some inner and outer rami with 9 and 10 articles, respectively; pleopod 3 (Figure 9(c)) peduncle with short inner and outer rami with 10 and 11 articles, respectively. Uropod 1 (Figure 10(a)) peduncle long with setae on margins, ventral surface with slender setae, some plumose; inner ramus 0.4 times as peduncle, with robust seta on medial margin and robust setae apically; outer ramus 0.9 times as inner ramus, with 2 robust setae on lateral margin and robust setae apically. Uropod 2 (Figure peduncle wide and expanded, lateral margin crenulated, with long setae; rami short, widened and lated, inner ramus 0.3 times as long as peduncle, medial to distal margins setose; outer ramus slightly and narrower than inner, with long setae. Uropod 3 (Figure 10(c)) peduncle length 0.5 times as long as with a robust seta at dorsodistal corner; ramus uniarticulate, ovoid, margin crenulated, densely with long slender setae (longest seta 0.5 times as long as ramus). Telson (Figure 10(d)) triangular, distally, apically serrate, length 1.4 times width, dorsal surface with short setae, lateral margins each plumose setae, distal margin with 2 pairs of long setae, 0.2–0.3 times as long as telson.

Male [ paratype, NSMT-Cr 33040]. Antenna 1 (Figure 11(a)) 0.34 times body length; length peduncular articles 1–3 is 1.0:0.96:0.99; width/length of peduncular articles 1–3 is 0.3, 0.2, 0.3, peduncular article 1 with marginal setae; peduncular article 2 with ventral margin bearing long peduncular article 3 setose marginally; accessory flagellum uniarticulate; primary flagellum 5- sparsely setose distally, articles 1–4 with 2, 3, 1 and 2 aesthetascs, respectively. Antenna 2 ( Figure 1.5 View Figure 1 times as long as antenna 1; peduncular article 3 with long setae on posterior margin; peduncular and 5 slightly widened distally, with long setae on posterior margins, both articles 3 and 4 length 3.5 width; flagellum 2-articulate, article 1 long, rectangular, 0.8 times as long as peduncular article 5 times width, with long setae on margins and surfaces; article 2 short, incompletely fused to article 1

Gnathopod 1 (Figure 11(c)) subchelate; coxa rounded, with setae on anterior margin; basis proximal side, lateral surface with row of short setae; ischium with seta on anterior margin and long posterodistal corner; merus with row of plumose setae; carpus length 0.7 times width, 0.2 times as propodus, with row of setae posterodistally, anterodistal corner with setae; propodus length 1.7 times with setae on posterior margin, sparsely setose on anterior margin, projected posterodistally, palmar with 3 strong teeth and setae; dactylus narrow, weakly curved. Gnathopod 2 (Figure 11(d–e)) slender, subchelate; coxa squarish, with roundish distal corner, bearing marginal setae; basis slender, with long setae on anterodistal margin, laterodistal and mediodistal surfaces with minute setae; ischium short posterodistal setae, lateral and medial surfaces with minute setae; merus, carpus and propodus with long marginally; merus with minute setae on lateral and medial surfaces; carpus 3.3 times length of width,

HISTORY

Figure 7. Tropichelura barasu holotype female (6.0 mm) (NSMT-Cr 33039). (a) Pereopod 4, lateral view. (b) lateral view. (c) Pereopod 6, lateral view. (d) Pereopod 7, medial view.

Figure 8. Tropichelura barasu sp. n., holotype female (6.0 mm) (NSMT-Cr 33039). (a) Oostegite (brood plate) on lateral view. (b–f) Coxal gills on gnathopod 2 and pereopods 3–6, lateral views.

HISTORY

Figure 10. Tropichelura barasu sp. n., holotype female (6.0 mm) (NSMT-Cr 33039). (a) Left uropod 1, dorsal view uropod 2, dorsal view. (c) Left uropod 3, dorsal view. (d) Telson, dorsal view.

Pereopod 3 (Figure 11(f)) basis weakly expanded, with setae on posterior margin. Pereopod 7 (Figure basis expanded posteriorly, with long setae on posterior margin.

Uropod 1 (Figure 12(a)) peduncle long, with robust setae on margins, dorsal surface with row slender setae; inner ramus 0.3 times as long as peduncle, with robust seta on medial margin, apical with robust and slender setae; outer ramus 0.8 times as long as inner ramus, with 2 robust setae on margin, apical margin with robust setae. Uropod 2 (Figure 12(b)) peduncle wide, 1.9 times as long lateral margin crenulated with long setae; rami short, widened, crenulated, inner ramus 0.25 times as peduncle, medial to distal margins setose; outer ramus slightly shorter and narrower than inner, with setae on lateral margin. Uropod 3 (Figure 12(c)) peduncle 0.4 times as long as ramus, with 1 robust dorsodistal corner; ramus uniarticulate, 2.6 times as long as wide, weakly crenulated marginally, with long setae (longest seta 0.4 times ramus length).

Telson (Figure 12(d)) triangular, tapering distally, length 1.5 times width, dorsal surface with short lateral margins each with 2 and 3 plumose setae, distal margin with 4 pairs of long setae.

Variation

Based on smaller paratype (female 5.4 mm, NSMT-Cr 33043). Antenna 1 (Figure 13(a)) primary flagellum times as long as peduncular article 3; antenna 2 (Figure 13(b)) flagellum composed of 1 clavate gnathopod 1 (Figure 13(c)) basis, ischium, and merus with densely minute setae on lateral surfaces; (Figure 13(d)) inner ramus with robust seta on medial margin; uropods 2 and 3 (Figure 13(e,f)) crenulated margins of peduncles and rami; telson less produced distally (Figure 13(g)).

Colour

Translucent light brown in life.

Figure 11. Tropichelura barasu sp. n., paratype male ( 6.4 mm) (NSMT-Cr 33040). (a) Antenna 1, medial view. (b) medial view. (c) Gnathopod 1, medial view. (d) Gnathopod 2, medial view. (e) Palmar margin of propodus and gnathopod 2, medial view. (f) Coxa–ischium of pereopod 3, lateral view. (g) Coxa–ischium of pereopod 7, lateral

HISTORY

Figure 12. Tropichelura barasu sp. n., paratype male ( 6.4 mm) (NSMT-Cr 33040). (a) Left uropod 1, dorsal view. (uropod 2, dorsal view. (c) Left uropod 3, ventral view. (d) Telson, dorsal view.

Nucleotide sequence

One COI sequence of the paratype (NSMT-Cr 33041) was determined. Accession number is LC (658 bp).

Figure 13. Tropichelura barasu paratype female ( 5.4 mm) (NSMT-Cr 33043). (a) Antenna 1, medial view (b) medial view. (c) Gnathopod 1, medial view. (d) Right uropod 1, ventral view. (e) Right uropod 2, dorsal view. (f) Right 3, dorsal view. (g) Telson, dorsal view.

Habitat

This new species was collected from coral rubble and submerged woods. This species burrows

HISTORY

Remarks

Tropichelura barasu differs from T. insulae and T. gomezi by the following features (features of T.

and T. gomezi in parentheses): from T. insulae , (1) female antenna 1 primary flagellum 2.2–2.3

long as peduncular article 3 (1.1 times); (2) female pereopod 7 basis slender, not expanded expanded posteriorly); (3) male uropod 2 peduncle 1.9 times as long as wide (more than twice as wide); (4) female uropod 3 ramus with long setae on its margin, longest seta 0.5–0.7 times as ramus (short, longest seta shorter than 0.1 times ramus length); and (5) male uropod 3 ramus 2.6

as long as wide (3 times as long as wide); from T. gomezi , (1) female gnathopod 1 propodus tooth at middle of palmar margin (present tooth); (2) male uropods 1 and 2 peduncles with long marginally, longest seta of uropods 1 and 2 longer than and as long as width of peduncle,

(much shorter); (3) uropods 1 and 2 rami with long setae, longest seta longer than length of rami shorter); (4) male uropod 3 ramus with long setae densely, longest seta 0.4 times length of ramus shorter, sparse); and (5) telson in female and male with 2 and 4 pairs of long setae on distal respectively (4 pairs of long setae in female and 2 pairs of short setae in male).

In laboratory investigations, individuals of Tropichelura barasu entered burrows within submerged and blocked the entrance with their urosomites and uropods. When forceps were brought near the the amphipods used urosomites and uropods to fend them off ( Kakui 2025), suggesting that this behaviour serves to deter other individuals or potential intruders attempting to enter their shelter. behaviour has been reported in T. gomezi , with the heavily calcified quadrate urosome suggested a potential adaptive trait for the defensive behaviour ( Thomas 1979).