Hourstonius geojeensis, Lee, 2010

Lee, Kyung-Sook, 2010, A new species and new record of the Amphilochidae (Crustacea: Amphipoda) from Korea, Zootaxa 2477, pp. 21-36 : 24-29

publication ID	https://doi.org/ 10.5281/zenodo.893974
DOI	https://doi.org/10.5281/zenodo.5618738
persistent identifier	https://treatment.plazi.org/id/B72787B7-BA09-FFAB-FF35-EEEBFD38F917
treatment provided by	Plazi
scientific name	Hourstonius geojeensis
status	sp. nov.

Treatment

Hourstonius geojeensis View in CoL sp. nov. ( Figures 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

(Korean Name: Geo-je-jjal-eun-kko-ri-yeop-sae-u, new)

Type material.

Holotype: adult ♀ (ovigerous), 4.5 mm, (appendages on one slide), cat no. NIBRIV0000169455, Jangseungpo, Geojedo Is., 34° 51' 56"N, 128° 43' 46"E, 3 July 1998, collected from light trap on bottom, depth 6 m, collector Y.H. Kim. Paratypes: 1 ♀, 2.8 mm, dissected (appendages on one slide), CMNC 2010- 0 0 0 1, Oemaemuldo Is., Goheung-gun, 34° 35' 43" N, 127° 30' 54" E, 23 June 2008, SCUBA collection, depth 3–8 m, collector Y.H. Kim; 1 adult ♀, 4.5 mm and 2 juveniles, 1.5, 1.7 mm (not dissected), cat no. DKU 201002, other data same as holotype.

Additional material examined: 3 ♀, Gajin Port, Goseong-gun, 38° 22' 28"N, 128° 30' 32"E, 20 October 2005, light trap, collector Y.H. Kim; 1 ♀, Gyeokryeolbiyeoldo Is., Taean-gun, 36° 57' 17" N, 126° 33' 48" E, 22 August 2006, SCUBA collection, collector Y.H. Kim; 1 ♀, Sacheon Port, Gangreung-si, 37° 50' 0 1"N, 128° 52' 48"E, 8 May 2008, light trap, collector Y.H. Kim.

Etymology. The species name is derived from the type locality, Geojedo Island located off the south coast of Korea.

Diagnosis. Pereopods 3–7, dactyls with distinct inner marginal tooth at unguis; antenna 1, peduncular article 2 slightly longer than peduncular article 1; gnathopod 2, posterodistal corner of basis with seta, lacking spine; epimeron 1–2, posteroventral corners pointed; mandibular palp, article 3 1.67 x length of article 2; maxilliped palp, lateral margin of palp article 1 setose with 8 strong setae; telson, linguiform, 2.1 x as long as wide, apically narrowly rounded not acute.

Description. Holotype, adult (ovigerous) ♀, 4.5 mm, cat no. NIBRIV0000169455.

Body ( Figs. 2 View FIGURE 2 , 3A View FIGURE 3 ) dorsally smooth; pereonite 1 subequal in width to pereonite 2, narrower than pereonite 3; coxa 1 nearly totally concealed by coxa 2; coxae 2–4 deeper than pereonites 2–4.

Head ( Figs. 2 View FIGURE 2 , 3A View FIGURE 3 ) small, subequal in length to pereonites 1 and 2 combined; eye large, reniform; rostrum reaching distal end of peduncular article 1; lateral cephalic lobe slightly angulated, apically broadly triangular.

Antenna 1 ( Fig. 3B View FIGURE 3 ) short, subequal to antenna 2; peduncular articles rectangular, peduncular articles 1–2 long, length ratio of articles 1–3 = 1.00: 1.07: 0.54; accessory flagellum coniform, 1-articulate, about 0.33 x flagellar article 1, with 3 unequal simple setae distally; primary flagellum 0.56 x length of peduncle, 7- articulate, each article bearing 1 or 2 long aesthetascs.

Antenna 2 ( Fig. 3C View FIGURE 3 ) subequal in length to antenna 1; peduncular articles 1–3 short, article 4 stout, slightly longer than article 5; flagellum 9-articulate, about 0.5 x length of peduncle; proximal article slightly longer than articles 2 and 3 combined.

Upper lip ( Fig. 3J View FIGURE 3 ) asymmetrically bilobed, pubescent marginally (drawn from paratype).

Lower lip ( Fig. 3D View FIGURE 3 ) outer lobes tapering apically and cusped, protruded inward, finely setose on inner and outer distal margins, with 3 or 5 small teeth, respectively; inner lobes small, obscure; mandibular lobes small, rounded.

Mandible ( Figs. 3E, 3I View FIGURE 3 ) incisors strongly toothed, 9-dentate; left lacinia mobilis well developed, 10- dentate (drawn from paratype), right lacinia lacking; accessory setal rows long, with 13–19 denticulate setae; molar process large and columnar, triturative, distal margin serrate; palp 3-articulate, lacking setae, article 1 short, article 3 long and slender, falciform, articles 1–3 in ratio of 1.00: 2.00: 3.21.

Maxilla 1 ( Fig. 3F View FIGURE 3 ) inner plate small, rounded with 1 small, plumose apical seta; outer plate narrow with 7 smooth setal teeth apically and 9 simple setae apicomedially; palp stout, 2-articulate, article 2 1.39 x length of article 1, extending beyond outer plate, tapering distally, with 1 acute cusp and 9 fine setae apically.

Maxilla 2 ( Fig. 3G View FIGURE 3 ) inner plate 0.81 x length of outer plate and 2 x its width; medial and apical margins with 8 simple setae and 4 tiny plumose setae; outer plate narrow, with 4 simple or tiny plumose setae apically.

Maxilliped ( Fig. 3H View FIGURE 3 ) inner plate narrow, subrectangular, apically truncate, reaching greater than 0.5 x length of palp article 1, pubescent, 0.79 x length of outer plate, with 2 mediofacial spines, ventrally with 3 short setae in oblique row; outer plate subovate, broad, extending nearly to 0.4 x palp article 2; distolateral margin finely serrulate, with 1 strong spine and fine setules; palp 4-articulate, article 1 longest, widening distally, distolateral margin with 8 strong setae, article 2 rectangular, subequal to article 3, setose distally, article 3 setose distally, medially and distoventral margin with several blunt protrusions, dactylus falcate, length 0.62 x article 3.

Gnathopod 1 ( Fig. 4A View FIGURE 4 ) coxa small, triangular, tapering distally; basis rectangular, 1.20 x length of carpus and propodus combined, proximal part of anterior margin with simple setae, posterolateral margin with row of 10 small spines; merus 0.78 x length of carpus, anterior margin very short, cryptic, concealed by abutment of carpus, posterior margin longer than anterior one, with 6 simple setae; carpus subtriangular, with short setose lobe, posterodistal end of lobe reaching middle of posterior margin of propodus; propodus widening distally, 0.67 x length of basis, palm oblique, convex, finely serrulate, with row of blunt small setules, palm corner defined by 2 spines distally; dactylus long and falcate, slightly exceeding palm corner, inner margin proximally with about 12 strong serrations gradually increasing in size distally.

Gnathopod 2 ( Fig. 4B View FIGURE 4 ) similar to gnathopod 1, but larger; coxa about as long as basis, subrectangular, ventral margin rounded, posteroventral corner lacking serrations; basis rectangular, proximal part of anterior margin weakly setose, posterolateral margin with row of 15 small spines, posterodistal corner bearing 1 or 2 setae; merus posterodistal lobe with 1 small spine; carpus short, 0.35 x length of propodus, posterior lobe slender, reaching about 0.86 x length of ventral margin of propodus; propodus similar but longer than gnathopod 1, palm strongly oblique and convex, palm corner defined by 2 spines distally; dactylus long and falcate, slightly exceeding palm corner, inner margin proximally with about 12 strong serrations gradually increasing in size distally.

Pereopod 3 ( Fig. 4C View FIGURE 4 ) slender, linear, segments uniform in width; coxa 3 similar to coxa 2, but narrower; basis similar to gnathopod 2 basis with setae on anterior and posterior margins; length ratio of articles 2–7 = 1.00: 0.22: 0.56: 0.43: 0.53: 0.24; dactylus, inner margin with distinct tooth at base of unguis.

Pereopod 4 ( Fig. 4D View FIGURE 4 ) similar to pereopod 3 except coxa broadened, posterior margin excavate. Pereopod 5 ( Fig. 4E View FIGURE 4 ) coxa broad, posterolobate, anterior margin convex; basis broadly rounded, expanded posteriorly, anterior margin with 2 rows of short spines, posterior margin with minute setules, posterodistal corner broadly rounded; ischium about as long as broad, with 3 spines anteriorly; merus 0.75 x length of propodus, with 6 clusters of spines anteriorly, spine formula of posterior margin = 1: 1: 1: 1: 2: 4; posterior margin overhanging and tapering distally; articles 5–7 missing. dactylus same as pereopods 3–4. Pereopod 6 ( Fig. 4F View FIGURE 4 ) similar to pereopod 5 except coxa 6 smaller than coxa 5, with anterior margin straight; articles 5–7 missing.

Pereopod 7 ( Figs. 5A, 5G View FIGURE 5 ) similar to pereopods 5–6 except coxa 7 small, narrowly oval, ventral margin rounded; basis slightly broader and posterodistal corner more broadly rounded; articles 5–7 missing (figure 5G drawn from paratype).

Gills ( Fig. 5H View FIGURE 5 ) found on pereopods 2–6, ovate or subrectangular, largest on pereopod 6 (drawn from paratype).

Brood plates ( Figs. 5I –J View FIGURE 5 ) found on pereopods 2–5, on pereopods 2–3 large with many brood setae, on pereopods 4–5, small narrow with few brood setae (drawn from paratype).

Epimeron 1 ( Fig. 5B View FIGURE 5 ) tapering ventrally, posteroventral corner pointed, with 4 ventral spines.

Epimeron 2 ( Fig. 5B View FIGURE 5 ) rounded anterodistally, posteroventral corner pointed, with 8 ventral spines.

Epimeron 3 ( Fig. 5B View FIGURE 5 ) quadrate, posterior margin slightly convex, posteroventral corner nearly right angled, ventral margin with 2 spines.

Uropod 1 ( Figs. 3A View FIGURE 3 , 5C View FIGURE 5 ) extending beyond peduncle of uropod 3; peduncle much longer than rami, 1.52 x length of outer ramus, with 16 dorsolateral, 3 dorsomedial and 1 apicomedial spine; rami strongly lanceolate, outer ramus 0.80 x length of inner ramus, with 5 dorsolateral and 4 dorsomedial marginal spines; inner ramus with 4 dorsolateral and 5 dorsomedial spines.

Uropod 2 ( Figs. 3A View FIGURE 3 , 5D View FIGURE 5 ) short, 0.65 x length of uropod 1, extending beyond peduncle of uropod 1; peduncle 2 x length of outer ramus, with 9 dorsolateral and 1 apicomedial spine; rami as above except outer ramus 0.56 x length of inner ramus, with 3 dorsolateral and 1 apicomedial spine; inner ramus with 4 dorsolateral and 4 dorsomedial spines.

Uropod 3 ( Figs. 3A View FIGURE 3 , 5E View FIGURE 5 ) long, 0.89 x length of uropod 1; peduncle as long as uropod 1 peduncle, longer than rami, 1.73 x length of outer ramus, with 9 dorsolateral and 4 dorsomedial spines; rami as above except outer ramus 0.93 x length of inner ramus, with 7 dorsolateral and 3 dorsomedial spines; inner ramus with 4 dorsolateral and 6 dorsomedial spines.

Telson ( Fig. 5F View FIGURE 5 ). linguiform, triangular, 2.1 x as long as wide, apically narrowly rounded not acute.

Male. Unknown.

Remarks. The new species is morphologically similar to Hourstonius japonica ( Hirayama, 1983) , H. breviculus ( Hirayama, 1983) , which are distributed in Japanese waters, H. pele ( Barnard, 1970) , Amphilochus menehune Barnard, 1970 , in Hawaiian Islands and H. vilordes ( Barnard, 1962) in southern California and Japanese waters. Hourstonius geojeensis however, is distinguished from its congeners by the inner marginal tooth of the pereopod dactyls as well as characters listed in table 2 and the key (page 11). Hourstonius japonica and H. vilordes differ by having a posterodistal spine and not a seta on the basis of gnathopod 2. As well, H. breviculus has smooth posteroventral corners on epimeron 1–2, while the new species has pointed corners. Hourstonius geojeensis is similar to A. menehune , however, it is easily distinguishable by the larger, reniform shaped eye, strongly oblique gnathopod 2 palm and large, columnar, strongly triturative mandibular molar (vs weakly triturative, conical molar). Our new species differs from H. pele in possessing a tooth on the inner margin of the pereopods 3–7 dactyls and lacking serrations on the posteroventral corner of coxa 1. The new species is very similar to H. baciroa ( Barnard, 1979) , however that species has simple pereopod dactyls, the posteroventral margin of coxa 2 is finely serrated, the posteroventral corner of epimeron 2 is drawn out into an acuminate tooth or cusp and the length to width ratio of the telson is 1.7 (vs 2.1). Gitanopsis subpusilla Rabindranath, 1972 (which probably belongs in the genus Hourstonius ) from Indian waters is similar to H. geojeensis , as it also has the inner marginal tooth on the pereopod dactyls. However, it differs in the much longer carpal lobe of gnathopod 2 which extends past the palm corner and the very short, stout merus of pereopod 3.