Kamaka Dershavin 1923

Genus Kamaka Dershavin, 1923

(Korean Name: Ka-ma-ka-yeop-sae-u-sok, new)

Kamaka excavata Ariyama, 2007 (Figures 1–4)

(Korean Name: Gaet-beol-ka-ma-ka-yeop-sae-u, new)

Kamaka excavata Ariyama, 2007b: p. 256, figs. 1–4; Ren & Sha, 2013: p. 392, fig. 1.

Material examined. 1 male and 1 female, Yongjeong-ri, Hyeongyeong-myeon, Hampyeong-gun, Jeollanam-do, South Korea (35° 4′ 32″N, 126° 23′ 20″E), 20 Apr. 2011, collected by T.W. Jung; 10 males and 15 females, Daegok-ri, Sinji-myeon, Wando-gun, Jeollanam-do, South Korea (32° 20′ 26″N, 126° 49′ 7″E), 23 Jun. 2011, collected by T.W. Jung.

Description. Male. Body (Fig. 1 A) 2.3 mm long.

Head (Fig. 1 A, B) slightly shorter than peraeons 1 and 2 combined; rostrum indistinct; anterior cephalic lobe produced forward, apex round; eyes ovate, occupying most of the cephalic lobe. Pleonal epimeron 1 subquadrate and somewhat dilated posteroventrally, with 2 plumose setae on anteroventral margin; pleonal epimeron 2 larger than epimeron 1 with 4 plumose setae on ventrolateral surface; pleonal epimeron 3 wider than 1 or 2, posteroventral corner with short setule (Fig. 1 L). 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 (Figs. 1 A, 3J).

Antenna 1 (Fig. 1 A, C) slightly longer than half of antenna 2; peduncular articles 1–3 in length ratio of 1.00: 0.59: 0.59; peduncular article 1 stout, anterior margin convex; peduncular articles 2 and 3 slender with several setae distally; flagellum 7-articulate, distal 4 segment with pair of aesthetascs, respectively.

Antenna 2 (Fig. 1 A, D). Peduncular article 3 short and stout; peduncular articles 4 and 5 elongate and slender, peduncular article 5 slightly shorter than article 4; flagellum triarticulate, shorter than peduncular article 5.

Upper lip (Fig. 1 E) subhexagonal, apical margin with short setae.

Lower lip (Fig. 1 F). Inner lobe oval; outer lobe, apical margin round with short setae; mandibular process well developed, apex round.

Right mandible (Fig. 1 I). Incisor 5-dentate; lacinia mobilis 2-dentate; accessory setal row with 4 dentate setae; anterolateral corner near basal part of palp with blunt protuberance bearing group of 3 setae; molar developed with plumose seta; palp robust, triarticulate, 1st article short, 2nd article with 1 mesial and 2 long setae near distal corner, 3rd article subequal to 2nd, apex oblique with 7 long setae.

Left mandible (Fig. 1 J). Incisor 4-dentate; lacinia mobilis 4-dentate; accessory setal row with 4 dentate setae.

Maxilla 1 (Fig. 1 G). Outer plate with 9 toothed spines apically; palp biarticulate, 1st article shorter than 2nd, apex of 2nd article blunt with 2 simple setae and 3 stout spines.

Maxilla 2 (Fig. 1 H). Inner plate with many apical setae; outer plate larger than inner, apex slightly blunt with many apical setae.

Maxilliped (Fig. 1 K). Inner plate, 9 plumose setae arranged from distal corner to inner distal margin, apical spines absent; outer plate elongate and semicircular, inner margin lined with 8 spatulate-shaped spines, apical corner with 3 long spines, surface near inner margin lined with many setae bearing round tips; palp 4-articulate, 1st article stout but short, 2nd article long but not reaching apex of outer plate and inner margin with several setae, 3rd article somewhat dilated, 4th article shorter than 3rd with stout apical spine.

Gnathopod 1 (Fig. 2A, B). Coxa enlarged, anteroventral corner produced forward, anteroventral and ventral margins lined with short and long setae, posterior margin convex with stout spine mesially; basis, anterior lobe weak, anterodistal corner with long seta, posterior margin dilated distally with 1 long mesial and 1 distal setae; ischium with small anterior lobe, posterior margin with 2 pairs of long setae; merus, posterior margin angulate with group of 3 long setae, distal margin with 2 pairs of setae; carpus subequal to basis, anterior margin slightly convex with several setae, posterior margin weakly crenulate with 6 groups of pectinate setae; propodus triangular, posteromesial margin somewhat angulate with 3 setae; palm distinct, pectinate, with 5 minute setae, defining spines absent; dactylus long with small protuberance on inner margin.

Gnathopod 2 (Fig. 2C–E) enlarged and stout; coxa produced anteroventrally, anterior margin convex, ventral margin lined with several short and long setae, posterior margin with stout spine mesially; coxal gill elongate; basis, anterior lobe weak with 3 short setae, posterior margin convex distally with 1 long mesial and 1 short distal setae; ischium, anterior lobe small, posterodistal corner with seta; merus subrectangular, posterodistal corner a little produced with seta; carpus triangular, anterior margin with long subdistal seta, anterodistal corner with pair of setae and large spine; propodus stout, enlarged rectangular, anterior margin straightened with 2 mesial and 2 pairs of long and short setae, posterior margin with long acute process, tip extending beyond distal margin of propodus; palm indistinct, distal margin convex with numerous setae; dactylus long, inner margin convex distally, but apex acute and curved.

Pereopod 3 (Fig. 2F, G). Coxa subquadrate, anteroproximal margin truncated obliquely, posterior margin with stout mesial spine, ventral margin round with 6 short and 5 long setae; coxal gill elongate; basis slightly longer than merus and carpus combined, anterior margin straightened with 2 long subdistal setae, posterior margin swollen mesiodistally with 1 mesial and 2 distal long setae; ischium with small anterior lobe and pair of distal setae; merus gradually increasing in width distally, anterodistal corner weakly produced with 7 long setae; carpus subrectangular, slightly convex mesially, anterodistal corner with group of 4 setae, posterior margin with 3 long and 1 short setae; propodus longer than carpus, more slender distally, anterior margin slightly convex; dactylus falcate.

Pereopod 4 (Fig. 2H, I) similar to pereopod 3 except for non oblique anteroproximal corner of coxa, enlarged coxal gill, and the number or locations of setae on other articles.

Pereopod 5 (Figs. 3 A–C). Coxa bilobate, anterior lobe enlarged and subequal to basis in size, expanded downward, ventral margin round with 5 setae, posterior lobe smaller than anterior, slightly extended backward with short seta; coxal gill wider than that of pereopod 4; basis, anterior margin convex with 3 mesial and group of 4 distal setae, posterior margin expanded proximally with 5 normal and 4 plumose setae; ischium with posterior lobe and group of 3 anterodistal setae; merus, anterior margin slightly dilated distally with 2 mesial and pair of 1 thick and 1 minute setae, posterodistal corner with thick seta; carpus smaller than merus, anterior margin slightly convex, anterodistal corner with pair of 1 thick and 1 minute setae, posterodistal corner with 3 stout spines; propodus slightly longer than carpus, anterior margin bare, anteriodistal corner with several setae, posterior margin with 2 mesial spines and pair of unequal distal spines; dactylus falcate, as long as half of propodus.

Pereopod 6 (Fig. 3 D, E). Coxa bilobate, anterior lobe smaller than that of coxa 5 with thick seta on anteromesial margin, posterior lobe with short plumose seta; coxal gill similar to that of pereopod 5; basis oval, anterior margin convex with 5 setae and group of distal setae, posterior margin with 7 simple and 9 plumose setae; ischium with posterior lobe and group of 2 short and 1 long anterodistal setae; length ratio of merus, carpus, and propodus 1.00: 0.93: 1.67; merus, anterior margin with 2 mesial setae and distal corner with pair of seta and spine, posterodistal corner with thick seta; carpus rectangular, shorter than merus in width, anterior margin with 1 mesial and 1 pair of distal setae, posterodistal corner with group of 5 spines; propodus, anterior margin with 1pair of mesial and 1 group of 6 distal setae, posterior margin with 3 mesial spines and pair of unequal distal spines; dactylus falcate, long.

FIGURE. 2. Kamaka excavata Ariyama, 2007, male: A, gnathopod 1; B, coxa of gnathopod 1; C, gnathopod 2; D, coxa of gnathopod 2; E, gill of gnathopod 2; F, pereopod 3; G, gill of pereopod 3; H, pereopod 4; I, gill of pereopod 4.

Pereopod 7 (Fig. 3 F) slightly longer than pereopod 6; coxa unilobate, anterodistal corner somewhat expanded downward with thick seta, posterior margin with simple seta; basis oval, anterior margin convex, distal 2/3 margin with 4 simple and 5 plumose setae, anterodistal corner with group of 1 long simple and 3 plumose setae; posterior margin with 5 spines and 11 plumose setae; ischium with posterior lobe and pair of anterodistal setae; length ratio of merus, carpus, and propodus 1.00: 0.87: 1.22; merus rectangular, each antero- and posterodistal corner with stout spine; carpus rectangular, each antero- and posterodistal corner with pair of setae and spines, respectively; propodus slender, anterior margin with pair of mesial setae, anterodistal corner with group of 8 setae, posterior margin with 3 mesial and 1 pair of unequal distal spines; dactylus falcate, long.

Pleopod 1 (Fig. 4 A). Peduncular article subrectangular, lateral margin with 5 plumose setae, anteromedial surface with plumose seta, mediodistal corner with pair of retinaculae; inner ramus longer than outer; each article of rami with inner and outer plumose setae distally.

Pleopod 2 (Fig. 4 B). Peduncular article, lateral margin with 3 plumose setae, mediodistal corner with pair of retinaculae; inner ramus longer than outer; each article of rami with inner and outer plumose setae distally.

Pleopod 3 (Fig. 4 C). Peduncular article shorter than that of pleopod 1 or 2, lateral margin lined with 3 plumose setae.

Uropod 1 (Fig. 3 G). Peduncular article with long inter-ramal peduncular process ventrally, outer dorsolateral margin with 2 mesial and 1 distal spines, dorsomedial margin with 1 mesial and 1 distal spines; outer ramus shorter than inner one, outer-lateral margin with 2 spines, apex with 2 apicolateral and 2 unequal apical spines; inner ramus, inner-lateral margin with only 1 spine, apex with 2 apicolateral and 2 unequal apical spines.

Uropod 2 (Fig. 3 H) shorter than uropod 1; peduncular article, dorsal surface with 1 lateral and 1 medial spines distally; outer ramus, lateral margin with 2 mesial spines, apex with 2 apicolateral and 2 unequal apical spines; inner ramus, medial margin with 2 mesial spines, apex with 2 apicolateral and 2 unequal apical spines.

Uropod 3 (Fig. 3 I, J) uniramus; peduncular article short, distal corner of medial margin with small spine; ramus with 6 thick apical and subapical setae.

Telson (Fig. 3 J, K) round apically, dorsal surface hollow and each side somewhat protruding, with 1 simple and 1 plumose setae.

Female. Gnathopod 1 almost identical to that of male.

Gnathopod 2 (Fig. 4 D), coxa smaller than that of male; basis, anterior margin slightly convex with 7 setae, anterodistal margin of medial surface with row of 5 setae, posterior margin more swollen than anterior with 3 long mesial and group of 4 distal setae; merus subrectangular, distal margin with several long setae; carpus triangular, longer than merus, anterior margin convex, distal half with 4 setae, distal corner with group of 5 long setae, posteriodistal corner with group of several setae; propodus normally subchelate and lacking long process, subequal to carpus in length, posterior margin and palm lined with several long and normal setae, defining spine absent; dactylus long, falcate, inner margin with 2 setae and one distal protrusion.

Oostegites of gnathopod 2 small with 5 setae; others slender with several setae (Figs. 4 E-H).

Remarks. The species of Kamaka have the unique feature of coalesced urosomites, but definition of their real structure has been controversial (Morino 2012). According to Barnard and Karaman (1991), urosomites 1 and 2 are coalesced into one urosomite, while urosomite 3 is separated from the coalesced urosomite and fused with the telson; the jointed margin between them is marked only by a suture. Thomas & Barnard (1991) reported a clear suture to separate the telson from urosomite 3 in K. taditadi Thomas & Barnard, 1991. On the other hand, Ariyama (2007a, b) and Ariyama et al. (2010), who reported four new species and redescribed two species including K. kuthae, the monotype species of Kamaka, observed the telson to be clearly separated from urosomite 3 in all six of the species examined (K. kuthae Dershavin, 1923, K. biwae Uéno, 1943, K. excavata Ariyama, 2007, K. morinoi Ariyama, 2007, K. appendiculata Ariyama et al., 2010, and K. songkhlaensis Ariyama et al., 2010). In addition, the status of this character unclear in the majority of other species such as K. derzhavini Gurjanova, 1951, K. palmate Dnag, 1968, K. poppi Bamber 2003, and K. littoralis Ren, 2006, because the precise descriptions or figures were not presented with their original descriptions (Morino 2012). We also try to confirm the separation of the telson from urosomite 3 in the present study. However, it is still obscure whether this is a real separated structure or the simple suture after coalescence. Consequently, the status and related taxonomic meanings are in need of further studies.

Ariyama (2007a, b) suggested the shape of gnathopod 2 in mature males to be a useful specific feature for the identification of Kamaka species. The Korean specimens of K. excavata in the present study agreed well with Ariyama's original description (Ariyama 2007b) of the shape of gnathopod 2, and the other characteristic features also are mostly concurrent with those in Ariyama's report. However, the Korean specimens showed some minor differences as follows: the eyes are somewhat smaller; the incisor of the right mandible is 5-toothed in Korean specimens (the last one was very small), while 4-toothed incisor appears in the Japanese specimens; in Korean specimens, the lacina mobilis of the right and left mandibles are 2 and 4-toothed, respectively, but the Japanese specimens have trifid laciana mobilis on both mandibles; the plumose seta on the anterior margin of the basis on pereopod 6 is absent in the Korean specimens, but Japanese specimens have 3 plumose setae in the original description provided by Ariyama (Ariyama 2007b).