Eusiroides pilopalpus, Jung, Tae Won, Kim, Jong Guk & Yoon, Seong Myeong, 2016

Jung, Tae Won, Kim, Jong Guk & Yoon, Seong Myeong, 2016, Two new species of pontogeneiid amphipods (Crustacea, Senticaudata, Calliopioidea) from Korean waters, ZooKeys 635, pp. 53-79 : 55-59

Eusiroides pilopalpus sp. n. Figs 1, 2, 3, 4, 5, 6

Type locality.

Jeju Island, South Korea, 33°14'23"N 126°34'59"E, sublittoral (average depth 24 m).

Material examined.

Holotype: NIBRIV0000328601, adult female, 8.4 mm, collected from the type locality on 30 Nov 2012 by Prof. H.-Y. Soh.

Etymology.

The composite epithet of the specific name of pilopalpus is a combination of Latin pilosus and palpus meaning 'hairy palp’. This name refers to the character of the mandibular palp article 3: the surface is covered with several rows of minute setae along the distal two-thirds length and with a group of brush-like fine setae at the center of the outer margin. Noun in apposition.

Diagnosis.

Head with short rostrum; eyes reniform, well-developed. Antennae with stout peduncular articles, with calceoli on flagellum; accessory flagellum of antenna 1 uni-articulate, as long as 1st proximal article of flagellum. Upper lip slightly angulate distally. Lower lip outer lobe with 7 bifid setae on surface. Mandibles both with bi-dentate (1 small and 1 enlarged) incisors, with trifid and 6-dentate lacinia mobilis on right and left mandibles, respectively; palp article 3 covered with numerous fine setae laterodistally. Maxilla 1 outer plate with 10 dentate robust setae apically. Maxilla 2 inner plate broader than outer plate. Maxilliped with short inner plate; outer plate elongate; palp articles 1-3 expanded, article 4 falcate. Gnathopods moderately subchelate, similar to each other, with developed anterior lobe on basis and ischium; dactylus falcate, elongate. Pereopods 3-4 ordinary; basis lined with short setae posteriorly; ischium anterior lobe acute distally; merus anterodistal corner produced bearing 1 robust seta. Pereopods 5-7 basis expanded posteriorly; ischium posterior lobe developed; merus produced posterodistally. Pleonal epimera each with submarginal setae ventrally; epimera 2 and 3 with oblique redge on surface; epimeron 3 with serrations posteriorly. Uropod 1 peduncle with largest seta mediodistally; outer ramus with lateral setae only. Uropod 2 shorter than uropod 1, peduncle with 1 distal seta laterally. Uropod 3 rami lancerolate. Telson shallowly cleft (approximately 1/4 on its length).

Description of holotype female.

Head (Fig. 1A): rostrum short; lateral cephalic lobes weakly produced and slightly oblique; antennal sinus not deep; eyes reniform, well-developed, enlarged.

Antenna 1 (Fig. 1B, C): stout, with length ratio of 1.0:0.7:0.3 in peduncular articles 1-3; peduncular article 1 with 1 group of 7 plumose setae on anterior margin proximally and with smooth groove bearing setae on lateral margin subdistally; peduncular article 2 with 1 subdistal and 2 distal setae laterally and 1 pair of distal setae medially on anterior margin, also with small groove bearing setae on distal margin; accessory flagellum uni-articulate, as long as 1st proximal article of flagellum, with 5 setae on apex; flagellum more than 72-articulate and slightly longer than twice as long as peduncular articles 1-3 combined, proximal article longest, with single or paired aesthetascs and calceoli present from 1st to 54th articles discontinuously.

Antenna 2 (Fig. 1D, E): stout, shorter than antenna 1; with length ratio of 1.0:0.7 in peduncular articles 4-5; flagellum more than 36-articulate, slightly shorter than peduncular articles 3-5 combined, proximal article longest, with calceoli present from 1st to 24th articles discontinuously.

Upper lip (Fig. 1F): apex convex, slightly angulate distally, covered with apical and subapical fine setae.

Lower lip (Fig. 1G): inner lobe weak; outer lobe apically round with 7 bifid setae on surface; mandibular processes developed bearing round apices.

Right mandible (Fig. 1I): incisor bi-dentate (1 small and 1 enlarged); lacinia mobilis trifid, each multidentate; accessory setal row with 3 serrate and 3 plumose setae alternatively; molar triturative, columnar; palp 3-articulate; palp article 1 shortest; palp article 2 rectilinear, with 12 setae on expanded medial margin; palp article 3 weakly falcate, with marginal and submarginal serrate setae on distal 3/4 of medial margin, covered with several rows of fine setae on distal 2/3 of surface, densely covered with group of brush-like setae at centre on lateral margin and surface, apex bluntly truncate with 6 serrate setae.

Left mandible (Fig. 1H): incisor bi-dentate (1 small and 1 enlarged); lacinia mobilis 6-dentate; accessory setal row with 1 simple, 3 serrate, and 1 plumose setae; palp similar to that of right mandible.

Maxilla 1 (Fig. 1J): inner plate enlarged, with 2 plumose setae at mediodistal corner; outer plate with 10 dentate robust setae apically; palp long, beyond apical setae of outer plate, palp article 1 with 1 long seta laterodistally, article 2 with 1 row of 9 setae along apical and mediodistal margins, with 1 pair of long setae laterally.

Maxilla 2 (Fig. 1K): inner plate ovoid, broader than outer plate, with 1 row of 8 weakly plumose and 1 long plumose setae on medial margin subdistally, covered with fine setae on apical and subapical margins; outer plate with 16 setae on apical margin, with 2 setae on lateral margin distally.

Maxilliped (Fig. 2A): inner plate short, tongue-shaped, with 3 robust setae apically, with 8 bifid and 2 simple setae arranged from apex to mediodistal margin; outer plate elongate, 2.0 times as long as inner plate, lined with numerous long setae arranged from apex to medial margin, with 3 long weakly plumose setae on lateral margin; palp with expanded articles 1-3; article 1 with 1 group of 4 elongate setae laterodistally; article 2 lined with numerous simple long setae on medial margin, with 2 rows of setae subdistally, with 1 group of 6 unequal setae at laterodistal corner; article 3 0.3 times as long as article 2, with ledge bearing 1 row of long setae on surface, with 7 serrate and 4 simple setae at laterodistal corner, covered with numerous fine setae laterodistally; article 4 falcate, slightly shorter than article 3, with 4 setae along inner margin.

Gnathopod 1 (Fig. 2B, C): moderately subchelate; coxa expanded anterodistally, with 16 minute setae on round ventral margin, with 1 small notch bearing 1 minute seta posteroventrally, with 1 oblique row of 5 long setae on surface posteroventrally; basis lined with short setae and shallowly lobed anterodistally, with 2 groups of 3 submarginal setae proximally and with 2 groups of 9 subdistal and 3 distal setae medially on anterior margin, with 1 pair of elongate setae on posterior margin proximally and with 1 group of 6 setae at posterodistal corner; ischium largely lobed anteriorly, without setae on posterior margin and with 1 group of 11 setae posterodistally; merus forming groove anterodistally, with 1 row of 4 setae medially, with acute protrusion posterodistally, lined with numerous setae on posterior margin; carpus longer than merus, without setae on anterior margin and with 1 row of 5 setae at anterodistal corner, posterior margin broadly lobed laterally, weakly crenulate and with groups of serrate and simple setae and with 3 setae mediodistally; propodus ovoid, shorter than basis, with 1 group of 3 setae and 6 single setae on anterior margin and with 1 group of 9 setae at anterodistal corner, with 1 vertical row of 4 robust defining setae on medial surface near posterior margin, palm approximately 3.0 times as long as posterior margin and minutely pectinate, with 7 robust setae along toothed submargin; dactylus falcate, stout, long, fitting palm.

Gnathopod 2 (Fig. 2E, D): moderately subchelate, similar to gnathopod 1; coxa rectangular, not expanded anterodistally, with 1 oblique row of 4 elongate setae on surface posteroventrally, with 1 robust seta on posterior margin, ventral margin subrounded with 7 minute setae, coxal gill longer than coxa and expanded distally; basis shallowly lobed and lined with 8 setae anterodistally, with 1 group of 5 setae mediodistally on anterior margin, with 2 elongate setae proximally and lined with single or paired minute setae on posterior margin, with 1 group of 7 setae at posterodistal corner; ischium largely lobed and slightly dilated anterodistally, without setae on posterior margin and with 1 pair of subdistal and 1 group of 7 distal setae at posterodistal corner; merus forming groove anterodistally, with 1 row of 13 setae medially, with acute protrusion posterodistally; carpus longer than merus, with 2 setae on anterior margin and 1 group of 4 setae at anterodistal corner, posterior margin broadly lobed, weakly crenulate and with groups of simple setae; propodus triangular, shorter than basis, with 3 single and 2 pairs of setae on anterior margin and with 1 group of 8 setae at anterodistal corner, with 1 vertical row of 3 robust defining setae on medial surface near posterior margin, palm poorly defined, about 3.0 times as long as posterior margin and minutely pectinate, with 7 robust setae along toothed submargin; dactylus falcate, stout, long, fitting palm.

Pereopod 3 (Fig. 3A, B): coxa rectangular, similar to that of gnathopod 2, facial setae absent, with 7 minute setae on ventral margin, with 1 robust seta on posterior margin, coxal gill as long as coxa and expanded distally; basis slightly curved proximally, anterior margin lined with setae, anterodistal lobe weak with several setae, with more than 10 groups of minute setae on posterior margin; ischium short, anterodistally lobed, with 1 group of 3 setae at posterodistal corner; merus 0.7 times as long as basis, expanded anterodistally, with 3 proximal and 2 distal setae on anterior margin, anterodistal corner produced with 1 group of 1 robust and 6 simple setae, with 3 groups of simple setae on posterior margin; carpus not expanded, 0.9 times as long as merus, with 2 setae on anterior margin and with 7 setae on anterodistal corner, with 3 pairs of 1 robust and 1 simple setae on posterior margin, posterodistal corner oblique with 4 lateral and 3 medial setae; propodus 1.1 times as long as carpus, with 5 pairs of setae on anterior margin and with 1 group of 5 setae at anterodistal corner, with 7 groups of robust and simple setae on posterior margin and with 1 group of 1 locking seta and 4 simple setae at posterodistal corner; dactylus falcate, as long as half of propodus.

Pereopod 4 (Fig. 3C, D): coxa acutely produced backwards posteriorly; other articles similar to those of pereopod 3.

Pereopod 5 (Fig. 4 A–C): coxa bilobed, posterior lobe narrower and more ventrally produced than anterior lobe, with 5 minute setae on ventral margin, coxal gill subovoid, smaller than that of pereopod 4; basis ovoid, with 3 elongate setae proximally and lined with 3 single setae and 5 groups of setae on anterior margin, anterodistal corner bluntly lobed with 1 group of 5 setae, posterior margin expanded and with 22 weak serrations bearing 1 minute seta, with 3 setae mediodistally, with 7 setae on medial surface proximally; ischium short, anterodistal corner weakly lobed downwards with 1 group of 6 setae, posterior margin largely expanded and slightly lurched posterodistally on lateral border; merus shorter than basis, with 4 groups of robust and simple setae on anterior margin and with 1 group of 5 robust setae at anterodistal corner, posterior margin expanded with 5 groups of robust and simple setae, posterodistal corner produced with 4 robust setae; propodus 1.4 times as long as merus, with 6 groups of paired setae on anterior margin, with paired locking setae and 3 simple setae at anterodistal corner, posterior margin irregularly setose with robust and simple setae, with 6 short setae at posterodistal corner; dactylus falcate, 0.3 times as long as propodus.

Pereopod 6 (Fig. 4D, E): coxa bilobed, smaller than that of pereopod 5, anterior lobe small, posterior lobe expanded backwards and with 1 notch bearing 1 minute seta posteroventrally, coxal gill circular and slightly smaller than that of pereopod 5; basis ovoid, larger than that of pereopod 5, with 2 minute setae proximally and 7 groups of robust and simple setae on anterior margin, anterodistal corner bluntly lobed with 1 group of paired robust setae and 3 simple setae, posterior margin expanded with 25 weak serrations bearing 1 minute seta, with 23 setae proximally and 5 setae distally on medial border, with 8 setae on medial surface proximally; ischium short, anterodistal corner weakly lobed downwards with 1 group of 1 robust and 5 simple setae, posterior margin largely expanded and slightly lurched posterodistally on lateral border; merus shorter than basis, with 1 robust seta and 3 groups of robust and simple setae on anterior margin, with 1 group of 4 robust setae at anterodistal corner, posterior margin expanded with 2 setae and 3 pairs of robust and simple setae, posterodistal corner produced with 5 robust setae; carpus not linear, slightly shorter than merus, with 3 groups of robust and simple setae on anterior margin and with 1 group of 8 robust setae at anterodistal corner, posterior margin broadly expanded with 3 groups of simple setae, posterodistal corner weakly produced with 1 group of 7 robust setae; propodus 1.3 times as long as merus, with 6 groups of paired robust and simple setae on anterior margin, with paired locking setae and 7 simple setae at anterodistal corner, posterior margin setose irregularly with robust and simple setae, with 8 setae at posterodistal corner; dactylus falcate, 0.5 times as long as propodus.

Pereopod 7 (Fig. 5A, B): as long as pereopod 6; coxa unilobed, ventrally convex, coxal gill present, longish subovoid, smaller than that of pereopod 6; other articles similar to those of pereopod 6 except for flattened posterior margin of basis.

Pleonal epimera (Fig. 6E): epimeron 1 with 1 oblique ledge on surface, with 1 group of 2 robust and 2 simple setae on ventral margin anteriorly, with 3 pairs of robust and simple setae and 1 robust seta submarginally, weakly produced at posteroventral corner; epimeron 2 larger than epimeron 1, also with 1 oblique ledge on surface, convex ventrally and with 4 pairs of robust and simple setae and 1 robust seta submarginally on anterior half of ventral margin, weakly produced at posteroventral corner; epimeron 3 largest, flattened ventrally, with 3 single setae and 1 pair of robust and simple setae on anterior half of ventral margin, posterior margin expanded backwards and with 11 serrations bearing 1 minute seta on distal half.

Uropod 1 (Fig. 5C, D): peduncle with 7 marginal and 1 distal robust setae dorsomedially and 7 marginal robust setae dorsolaterally; inner ramus linear, as long as peduncle, with 4 medial and 5 lateral robust setae dorsally, apex blunt with 1 pair of robust setae subapically and 3 robust setae (1 large and 2 small) apically; outer ramus shorter than inner ramus, with 5 lateral robust setae dorsally; apex blunt with 1 robust seta subapically and 2 robust setae (1 large and 1 small) apically.

Uropod 2 (Fig. 5E, F): peduncle 0.7 times as long as that of uropod 1, with 2 marginal and 1 subdistal robust setae dorsomedially, with 1 distal robust seta dorsolaterally; inner ramus 1.6 times as long as peduncle, with 7 medial and 7 lateral robust setae dorsally; apex blunt with 1 pair of robust setae subapically and 3 robust setae (1 large and 2 small) apically; outer ramus much shorter than inner ramus, with 3 medial and 3 lateral robust setae dorsally; apex blunt with 1 robust seta subapically and 2 robust setae (1 large and 1 small) apically.

Uropod 3 (Fig. 5G): shortest; peduncle 0.8 times as long as that of uropod 2, with 1 medial seta dorsally; rami lancerolate; inner ramus 1.6 times as long as peduncle, with 7 robust and 8 plumose setae medially and 7 robust setae laterally; outer ramus slightly shorter than inner ramus, with 6 robust and 5 plumose setae medially and 5 robust setae laterally.

Telson (Fig. 5H): shallowly cleft (about 1/4 length), with 1 pair of robust setae proximally, with single or paired simple setae on surface; each apex with 1 notch and 1 simple seta subapically.

Oostegites (Fig. 6 A–D): present on gnathopod 2 to pereopod 5, with numerous long setae marginally; that of gnathopod 2 largest; that of pereopod 3 larger than that of pereopod 4, both dilated distally; that of pereopod 5 sublinear, smallest.

Male.

Unknown.

Remarks.

Eusiroides pilopalpus sp. n. is very similar to Eusiroides japonica Hirayama, 1985. It can be readily distinguished from Eusiroides japonica by the following characteristic features: (1) degree of setation of peduncular articles 4 and 5 on antenna 2 is weaker than that of Eusiroides japonica ; (2) anterior and posterior margins of peduncular article 5 on antenna 2 are parallel in Eusiroides pilopalpus sp. n. (vs. margins are gradually diminish distally, and anterodistal and posterodistal corners are produced in Eusiroides japonica ); (3) mandibular palp article 3 has a group of brush-like setae on the lateral surface (vs. several rows of minute setae in Eusiroides japonica ); (4) expanded medial lobe of mandibular palp article 2 is not swollen in Eusiroides pilopalpus sp. n. (vs. swollen medially in Eusiroides japonica ); (5) inner plate on maxilla 2 is not enlarged in Eusiroides pilopalpus sp. n. (vs. distinctly enlarged in Eusiroides japonica ); (6) maxillipedal palp article 3 is covered with fine setae on its distal surface (vs. transverse rows in Eusiroides japonica ); (7) anterior lobe of ischium on gnathopods 1 and 2 is well-developed in Eusiroides pilopalpus sp. n. (vs. moderately developed in Eusiroides japonica ), (8) acute protrusion at the posterodistal corner of merus on gnathopods 1 and 2 is larger than that of Eusiroides japonica ; (9) length of the dactylus on gnathopods 1 and 2 is longer than that of Eusiroides japonica ; (10) posterior lobe of ischium on pereopods 5-7 is acutely produced distally; (11) merus, carpus, and propodus on pereopods 5-7 are more slender than those of Eusiroides japonica ; (12) both pleonal epimera 1 and 2 have oblique ridges on their lateral surfaces (vs. the ridges are not present in Eusiroides japonica ) and posterior margin of pleonal epimeron 3 has 11 serrations (vs. seven in Eusiroides japonica ); (13) the outer ramus on uropod 2 has three dorsal setae medially (vs. dorsal setae are absent in Eusiroides japonica ); and (14) the distal fourth of the telson is cleft in Eusiroides pilopalpus sp. n., (vs. cleft beyond the distal half in Eusiroides japonica ) ( Hirayama 1985).

Eusiroides pilopalpus sp. n. shares several characters with Eusiroides diplonyx Walker, 1909. However, Eusiroides diplonyx can be easily discriminated from its congeners because it has stout and round-ended locking setae on pereopods 3 and 4 ( Walker 1909; Pirlot 1936; Barnard JL 1970; Myers 1985). These are not observed at Eusiroides pilopalpus sp. n. in this study. Furthermore, Eusiroides pilopalpus sp. n. is different from Eusiroides diplonyx in the following ways: (1) inner plate on maxilla 2 is not enlarged in Eusiroides pilopalpus sp. n. (vs. the inner plate of maxilla 2 is larger than the outer plate in Eusiroides diplonyx ); (2) one group of fine setae on the surface of mandibular palp article 3 is present in Eusiroides pilopalpus sp. n. (vs. absent in Eusiroides diplonyx ); (3) posterior lobe of the ischium on pereopods 5-7 of Eusiroides pilopalpus is more acute than that of Eusiroides diplonyx ; and (4) the telson of Eusiroides pilopalpus sp. n. is cleft to one fourth of the length (vs. more than half the length in Eusiroides diplonyx ) ( Walker 1909; Pirlot 1936; Barnard JL 1970; Myers 1985; Ren 2012).