Kamaka rostra, Jung, Tae Won & Yoon, Seong Myeong, 2015

Jung, Tae Won & Yoon, Seong Myeong, 2015, A new species and new record of the Kamakidae (Crustacea: Amphipoda) from Korea, Zootaxa 3915 (3), pp. 356-374 : 364-371

Kamaka rostra sp. nov.

(Korean Name: Ppyo-jok-ko-ka-ma-ka-yeop-sae-u, new) ( Figures 5–8 )

Type material. Holotype: 1 male, 4.5 mm (appendages on two slides), cat no. NIBRIV0000268875, Yongjung-ri, Hyeongyeong-myeon, Hampyeong-gun, Jeollanam-do, South Korea (35° 4′ 32″N, 126° 23′ 20″E), 11 Apr. 2012, collected by T.W. Jung. Allotype: immature female 3.3 mm (appendages on one slide), cat no. NIBRIV0000268876, collection details same as holotype. Paratypes: 1 immature male, 3.2 mm (appendages on one slide), cat no. NIBRIV0000268877; 1 male, 4.2 mm (not dissected); collection details of paratypes same as holotype.

Description. Holotype, male. Body ( Fig. 5 A) about 4.5 mm long.

Head ( Fig. 5 A, B) slightly shorter than pereons 1 and 2 combined; rostrum indistinct; anterior cephalic lobe triangular, produced forward; eyes reniform, located near cephalic lobe. Pleonal epimeron 1 round and somewhat dilated posteroventrally, with 3 setae near anterior margin; pleonal epimeron 2 round with 10 setae on ventrolateral surface; pleonal epimeron 3 wider than 1 or 2, posterior margin produced backward and ventral margin flattened ( Figs. 5 A, 7G). Urosomites 1 and 2 coalesced, subequal to pleonal epimeron 3; telson also coalesced to urosomite 3 but marked ventrally by suture, proximal margin reaching coalesced urosomites 1 and 2 ( Figs. 5 A, 7K).

Antenna 1 ( Fig. 5 C) shorter than antenna 2, peduncular articles 1–3 in length ratio of 1.00: 1.00: 0.78; peduncular article 1 stout with 5 pencilate setae on anteriormesial margin, posterior margin with several setae gradually increasing in length, distal margin with 2 groups of 3 and 2 pencilate setae, respectively; peduncular article 2 with 6 groups of 2 long and 1 short setae on posterior margin, near antero- and posterodistal corner with pencilate seta, respectively; peduncular article 3 also with 6 groups of 2 long and 1 short setae, anterodistal corner with pencilate seta; flagellum 8-articulate, 4th and 5th articles with aesthetasc, respectively, last segment reduced with pair of aesthetascs.

Antenna 2 ( Fig. 5 D). Gland cone normal, apex round; peduncular article 3 short with several setae on antero- and posterodistal corners; peduncular article 4, anterior margin slightly convex proximally, antero- and posterodistal margins weakly rugose; peduncular article 5 equal to article 4, anterior and posterior margins also wrinkly, posterior margin lined with 4 protuberances those of proximal and distal ones weaker; flagellum 8- articulate, proximal articles from 1st to 5th weakly crenulate with small triangular protuberances on posterodistal corners becoming gradually weaker distally, last segment reduced with 2 long and 2 short setae.

Upper lip ( Fig. 5 E). Apical margin convex with short setae but not densely pubescent.

Lower lip ( Fig. 5 F). Inner lobe oval with short setae on apical and inner margin; outer lobe, apical margin round with short setae; mandibular process short and round apically.

Right mandible ( Fig. 5 G). Incisor 4-dentate; lacinia mobilis 5-dentate; accessory setal row with 2 dentate setae; molar developed with plumose seta; anterolateral corner near basal part of palp with 5 setae; palp robust, triarticulate, 1st article short, 2nd longer than 3rd with 3 setae on surface and 4 long setae near distal corner, 3rd article slightly swollen distally, apex round with several apical and subapical setae which feebly pectinate, outer margin with 2 long and 4 short setae.

Left mandible ( Fig. 5 H). Incisor 4-dentate; lacinia mobilis 5- dentate; accessory setal row with 3 dentate setae; molar developed with plumose seta.

Maxilla 1 ( Fig. 5 I). Outer plate, apical and subapical margin with 9 dentate spines; palp biarticulate, 1st article short with obliquely truncated apical margin, 2nd article dilated distally, apex flattened with 5 simple setae and 2 stout distal spines.

Maxilla 2 ( Fig. 5 J). Inner plate with numerous apical setae; outer plate dilated distally bearing numerous apical setae.

Maxilliped ( Fig. 5 K). Inner plate with 2 large and 1 small spines on apical margin and near distal corner, respectively, and 6 plumose setae on distal corner; outer plate elongated semicircular, distal half of inner margin lined with 7 spatulate-shaped spines, apical corner with 3 pectinate and 2 elongate spatulate-shaped spines, surface near inner margin lined with many setae bearing round tips; palp 4-articulate, 1st article stout and short, 2nd article extending beyond tip of outer plate, inner margin with numerous setae, 3rd article dilated distally, 4th article shorter than 3rd with elongate apical spine.

Gnathopod 1 ( Fig. 6 A, B). Coxa, anterovental corner produced forward, distal half of anterior and ventral margin weakly crenulate with several long setae, posterior margin with stout mesial spine; basis slender, anterior margin bare, posterior margin with 2 long mesial setae, posterodistal corner with group of 3 setae; ischium with anterior lobe, posterodistal corner with group of 6 long setae; merus, posterior margin subrectangular with numerous setae on distal margin; carpus subequal to basis, posterior margin weakly crenulate, lined with 6 groups of normal and pectinate setae, anterodistal corner with group of several setae, medial and lateral surface with several setae; propodus triangular, posteroproximal corner subangulate, palm pectinate, lined with several setae; dactylus long with small protuberance on inner margin.

Gnathopod 2 ( Fig. 6 C) enlarged and stout; coxa smaller than that of gnathopod 1, anteroventral corner produced forward, ventral margin convex with 4 short setae, posterior margin with 2 stout mesial spines, posteroproximal corner truncated obliquely; coxal gill elongate; basis slightly shorter than propodus, anterior margin bare, posterior margin with only 1 short proximal and 1 distal seta; ischium with anterior lobe with short seta at posterodistal corner; merus subrectangular, posterior margin angulate distally with short seta; carpus triangular, anteroproximal margin swollen, anterodistal corner with seta, posteriodistal corner with pair of short setae; propodus enlarged triangular, anterior margin somewhat convex with several setae, posterior margin with long acute process on posteroproximal corner, posterior margin of process with 5 setae; dactylus falcate, larger than process of propodus, inner margin lined with 12 plumose setae.

Pereopod 3 ( Fig. 6 D). Coxa subquadrate, anteroproximal corner truncated obliquely, posterior margin with stout mesial spine; coxal gill elongate; basis subtrapezoidal, slightly longer than merus and carpus combined, anterior margin straightened with 3 short setae, posterior margin swollen mesiodistally with 1 long mesial and 1 pair of distal setae; ischium with anterior lobe and pair of posterodistal setae; merus, anterior margin with 1 mesial and group of 7 distal setae; carpus shorter than merus, anterior margin convex with group of 4 distal setae; propodus slender, slightly curved, subequal to merus; dactylus falcate, shorter than half of propodus, with feeble plumose seta at anteroproximal margin, apex not acute.

Pereopod 4 ( Fig. 6 E). Coxa similar to that of pereopod 3, but anteroproximal corner not oblique, ventral margin more crenulate, and posterior margin with 2 stout mesial spines; other articles of pereopod 4 similar to those of pereopod 3, except for number or locations of setae.

Pereopod 5 ( Fig. 6 F). Coxa bilobate, anterior lobe subequal to basis in size, ventral margin convex with 2 setae, posterior lobe small with plumose seta at posterior margin; coxal gill wider than that of pereopod 4; basis, anterior margin convex with 9 plumose proximal and 3 mesial simple setae, anterodistal corner with group of 4 setae, posterior margin with 4 normal and 10 plumose setae and proximal corner expanded proximally and roundish- rectangular; ischium with developed posterior lobe and anterodistal seta; merus, anterior margin convex with pair of distal setae, posterodistal corner produced but apex round with thick seta; carpus expanded distally, posterior margin with 2 mesial spines, posterodistal corner more produced and lined with 6 spines; propodus slender, slightly curved, subequal to merus and carpus combined, anterior margin bare, anteriodistal corner with pair of seta, posterior margin with 4 short setae and 1 distal spine; dactylus enlarged with thick plumose seta.

Pereopod 6 ( Fig. 7 A–D) slender; coxa bilobate, subsimilar to that of pereopod 5 in shape but smaller in size, anterodistal corner with thick seta, posterior margin with plumose seta; coxal gill similar to that of pereopod 5; basis, anterior margin convex with 3 simple and 3 plumose setae mesially, posterior margin lined with 10 simple and 18 plumose setae, about 1/4 of distal margin slightly swollen; ischium with posterior lobe and pair of anterodistal setae; other articles slender, length ratio of merus, carpus, and propodus 1.00: 0.81: 1.74; merus, anterior margin with mesial seta and anterodistal corner with seta and small spine, posterior margin with 2 thick mesial and 1 distal spines; carpus, lateral surface with 3 spines, anterodistal corner with 1 short seta and 1 small spine, posterodistal corner lined with 5 spines and seta; propodus, anterior and posterior margins lined with several simple setae; dactylus long, subequal to merus, with proximal plumose seta.

Pereopod 7 ( Fig. 7 E, F) slender; coxa unilobate, anteroventral corner slightly expanded with thick seta, posterior margin with simple seta; basis, distal half of anterior margin lined with 5 plumose setae and distal corner with group of 1 plumose and 2 normal setae, posterior margin lined with 14 simple and 19 plumose setae, distal 1/ 4 weakly notched; ischium and merus similar to those of pereopod 6; carpus, posterior margin with mesial spine, posterodistal corner with row of 4 spines; propodus and dactylus similar to those of pereopod 6.

Pleopod 1 ( Fig. 7 L, O). Peduncular article subrectangular, lateral margin with 7 plumose setae, medioproximal margin pubescent with normal seta, mediodistal corner with pair of retinaculae and group of 6 setae; inner ramus longer than outer; each article of rami with inner and outer plumose setae distally.

Pleopod 2 ( Fig. 7 M). Peduncular article, distal half of lateral margin with 5 plumose setae, anteromedial surface with 3 plumose setae, mediodistal corner with pair of retinaculae and group of 6 setae; inner ramus longer than outer; each article of rami with inner and outer plumose setae distally.

Pleopod 3 ( Fig. 7 N). Peduncular article shorter than that of pleopod 1 and 2, lateral margin with 5 plumose setae, anteromedial surface with normal seta; mediodistal corner with pair of retinaculae and group of 6 setae; inner ramus longer than outer; each article of rami with inner and outer plumose setae distally.

Uropod 1 ( Fig. 7 H). Peduncular article long with short inter-ramal peduncular process ventrally, dorsolateral margin with 5 spines, distal corner of dorsomedial margin with stout spine; outer ramus slightly shorter than inner with 3 lateral spines, apex with 2 apicolateral and 2 unequal apical spines; inner ramus with only 2 apicolateral and 2 unequal apical spines.

Uropod 2 ( Fig. 7 I) shorter than uropod 1, peduncular article with 2 lateral and 1 medial spines; outer ramus with 2 lateral spines, apex with 2 apicolateral and 2 unequal apical spines; inner ramus with mesial spine medially, apex with 2 apicolateral and 2 unequal apical spines.

Uropod 3 ( Fig. 7 J, K) uniramus; peduncular article short; ramus longer than peduncular article and rectangular in shape with 6 thick apical setae and that of longest more stout.

Telson ( Fig. 7 J, K) broad, round apically, dorsal surface hollow, that of each side somewhat protruding with 1 simple and 1 plumose setae, each apical corner with additional acute protuberance.

Allotype, immature female. Body about 3.3 mm long.

Antenna 1 ( Fig. 8 A) similar to that of mature male.

Antenna 2 ( Fig. 8 A) not bearing protuberances of peduncular article 5 and flagellum; flagellum 7-articulate, last one very reduced, each article excluding last with pair of long setae at posterodistal corner.

Gnathopod 1 ( Fig. 8 B), carpus shorter than that of male; other articles similar to those of mature male.

Gnathopod 2 ( Fig. 8 C), basis with 2 long setae at posterior margin and 2 setae on anterior medial surface, posterodistal corner with pair of setae; propodus triangular and not bearing long acute process on posteroproximal corner, posterior margin with 5 long setae and defining spine; palm indistinct, pectinate, a little concave.

Oostegites ( Fig. 8 D–G) somewhat narrow; oostegite of gnathopod 2 reduced, not reaching 1/2 that of pereopod 3 in length; others slender.

Paratype, immature male. Body about 3.2 mm long.

Antennae 1 and 2 ( Fig. 8 H, I) similar to those of immature female.

Gnathopod 2 ( Fig. 8 J, K). Coax 2, posteroproximal corner not truncated obliquely, posterior margin with stout mesial spine; propodus, acute process not well developed; setae of dactylus weakly plumose.

Etymology. The species name was derived from the shape of the anterior cephalic lobe, which was not round but produced as a triangular form like a rostrum.

Remarks. The most significant features of this new species distinguishing it from other congeners are as follows: the anterior cephalic lobe is not rounded and is produced as a triangular shape and uneven protuberances are arranged along the inner-distal margin of the flagellum from peduncular article 5 to fourth proximal segment on antenna 2 in mature male. Both of these characteristics are unique among the described species of Kamaka (Table 1).

As mentioned above, the shape of male gnathopod 2 is known as the main characteristic of Kamaka species ( Ariyama 2007a, b). The new species, K. rostra sp. nov., has a gnathopod 2 closely resembling that of K. morinoi in mature male. However, the dactylus on gnathopod 2 of the new species has several plumose setae, while that of K. morinoi bears simple setae only. In the female, K. rostra sp. nov. is also distinguishable from K. morinoi by the following characteristics: the palm of ganathopod 2 has one or two defining spines in K. rostra sp. nov., while that of K. morinoi has none; the oostegite of gnathopod 2 is larger than that of K. morinoi ; and the inner lobe of the maxilliped in K. rostra sp. nov. has distal spines, while there are no spines in that of K. morinoi . Moreover, K. rostra sp. nov. was found in tidal flats near the coast, while the habitat of K. morinoi is known to be freshwater and brackish water ( Ariyama 2007a; Table 1). Kamaka appendiculata also has a gnathopod 2 similar to that of K. rostra sp. nov., but with no protuberances on antenna 2, and both the plumose setae observed on the dactylus and the distal spines on the inner lobe of the maxilliped are absent in mature males ( Ariyama et al. 2010; Table 1). Kamaka biwae also shows a similar shape of gnathopod 2 as the new species in mature male, but this species has only simple setae on the dactylus, similar to K. morinoi , and just inhabits freshwater environments ( Uéno 1943; Table 1). The shapes of the propodus on male gnathopod 2 of K. kuthae , K. derzhavini , K. littoralis , K. excavata , and K. tonlensis are not triangular but subquadrate, while those of K. taditadi , K. poppi , K. songkhlaensis , K. corophina , and K. foliacea are dilated ventrally or backward ( Dershavin 1923; Gurjanova 1951; Thomas & Barnard 1991; Bamber 2003; Ariyama 2007a, b; Ariyama et al. 2010; Morino 2012; Ren & Sha 2012). Therefore, K. rostra sp. nov. is discriminated from these species by the morphology of the mature male gnathopod 2 (Table 1).

Despite of the poor descriptions and figures concerning the eye morphology presented in many of the previous reports, the shape of the eye seems to be ovate or circular and occupies a large portion of the anterior lobe in most of the reported species of Kamaka , but the new species shows a unique reniform eye morphology. Although the presence of apical spines on the inner lobe of the maxilliped is unclear in several Kamaka species for the same reason, K. rostra sp. nov. especially shows very distinct spines on the inner lobe of the maxilliped. The number of plumose setae on the posterior margin of the basis in pereopod 7 is also obscure in several Kamaka species, and seems to vary according to the species. We could confirm the highest number of plumose setae in this new species. However, the taxonomic meaning is still vague and in need of further study with more exacting comparisons between Kamaka species (Table 1).

Figures

FIGURE 5. Kamaka rostra sp. nov., holotype, male: A, habitus, lateral view; B, head; C, antenna 1; D, antenna 2; E, upper lip; F, lower lip; G, right mandible; H, left mandible; I, maxilla 1; J, maxilla 2; K, maxilliped.

FIGURE 6. Kamaka rostra sp. nov., holotype, male: A, gnathopod 1; B, coxa of gnathopod 1; C, gnathopod 2; D, pereopod 3; E, pereopod 4; F, pereopod 5.

FIGURE 7. Kamaka rostra sp. nov., holotype, male: A, pereopod 6; B, coxa 6; C, gill of pereopod 6; D, distal spines of carpus on pereopod 6; E, pereopod 7; F, distal spines of carpus on pereopod 7; G, pleonal epimera; H – I, uropods 1 – 2; J, uropod 3 and telson, dorsal view; K, uropod 3 and telson, lateral view; L – N, pleopods 1 – 3; O, retinaculae of pleopod 1.

FIGURE 8. Kamaka rostra sp. nov., allotype, immature female (A – G) and paratype, immature male (H – K): A, antennae 1, 2 and head, lateral view; B, ganthopod 1; C, gnathopod 2; D – G, oostegites of gnathopod 2 – pereopod 5; H, antenna 1; I, antenna 2; J, coxa of gnathopod 2; K, propodus and dactylus of ganthopod 2.