Amakusanthura intermedia, Kim & Yoon, 2021

Kim, Sung Hoon & Yoon, Seong Myeong, 2021, Four new species of isopods (Crustacea, Isopoda) from South Korea, ZooKeys 1010, pp. 133-164 : 133

Amakusanthura intermedia sp. nov. Figures 2 , 3 , 4

Material examined.

Holotype. South Korea • 1 non-ovigerous ♀ (5.4 mm); Jeju-do, Seogwipo-si, Daejeong-eup, Gapa-ri; 33°06'54"N, 126°16'42"E; 71 m; 31 Jan. 2018; Smith-McIntyre grab; NIBRIV0000862806.

Paratypes. 2 ♀♀, same data as for holotype; NIBRIV0000880420.

Etymology.

The specific name, Amakusanthura intermedia , originates from the Latin word intermedius, meaning "that is between". This name refers to the length of maxillipedal endite comparing to the related species.

Description of holotype female.

Body (Fig. 2A, B ) 5.4 mm, 13 × longer than wide, smooth and slender. Cephalon square to globular, 0.8 × as long as pereonite I; rostrum as long as anterolateral lobes; eye very small; color not pigmented, white. Pereonites rectangular; pereonites I-VI similar to each other in length; pereonite VII ~ 0.7 × as long as pereonite VI; coxal plates of pereonites IV-VI visible dorsally. Pleonites 1.2 × longer than pereonite VII; pleonites I-V separated by folds except dorsally between pleonites IV and V; pleonites IV and V visible partial sutures laterally; pleonite VI visible dorsally, with dorsal notch posteriorly.

Antennule (Fig. 2C ) composed of three peduncular and three flagellar articles, sequentially slender distally in width. Peduncular article I rectangular, with one simple and a single penicillate seta distally; article II oblong, 0.6 × as long as article I, with three simple and four penicillate setae distally; article III rectangular, 1.2 × longer than article II, with three simple setae distally. Flagellar article I 0.4 × as long as wide, with one simple and one penicillate seta; article II elongated, ~ 4 × longer than article I, without seta; article III minute, square, with seven simple setae distally.

Antenna (Fig. 2D ) consisting of five peduncular and four flagellar articles. Peduncular article I ~ 0.4 × as long as article II, with two simple setae laterally; article II 1.8 × longer than article I, with one short simple seta laterally and one simple seta distally; article III 0.7 × as long as article II, with three simple setae distally; article IV square, subequal to article III, with six simple setae and one penicillate seta distally; article V elongate, 1.4 × longer than article IV, with 13 simple setae on both lateral margin and one penicillate seta on distal end. Flagellar articles much shorter than peduncular article V, consecutively shortened; article I with four simple setae distally; article II with one simple seta; article III without setae; article IV with seven simple setae; articles III and IV minute.

Mandible (Fig. 2E ), incisor with one prominent cusp and serrated margin; molar process bluntly rounded; palp article II 1.5 × longer than article I, slightly stouter than other articles, with two simple setae distally; article III shortest in length, with four serrated setae and a row of spines laterally, one serrated seta distally.

Maxilla (Fig. 2F ) with five teeth distally and several fine setae laterally.

Maxilliped (Fig. 2G ), endite extending to proximal region of palp article III, with one short simple seta apically; palp articles I and II fused, with one simple seta distally; article III free, with two simple setae laterally and two simple setae distally; articles IV and V fused, oblique, smaller than other articles, with four simple setae laterally.

Pereopod I (Fig. 3A ), basis continuously stouter distally, with three simple setae and three penicillate setae on superior margin; ischium slender than basis, rectangular, with one simple seta on inferodistal end; merus much shorter than ischium, wider than long, with one simple seta on superior and inferior distal end, respectively; carpus triangular, protruding inferodistally, with rough margin inferodistally and eight simple setae along with inferior margin; propodus stepped on palm, with twelve simple setae on inferior margin and three simple setae on distal end; dactylus with five simple setae distally, a row of spines and one simple seta laterally; unguis as long as dactylus, much longer than those of other pereopods, with small accessory unguis. Pereopods II and III (Fig. 3B, C ), basis elongate, oval, with one simple seta on inferodistally; ischium slightly shorter than basis, with two simple setae on both lateral margins; merus ~ 0.5 × as long as ischium, tapering proximally, with several simple setae on superior and inferior margins; carpus triangular, with several simple setae on inferodistal angle and fine setae along inferior margin; propodus elongate and oval, with simple setae on both lateral margins and one stout seta on inferodistal angle; dactylus with simple setae distally; unguis 0.5 × as long as dactylus, with small accessory unguis. Pereopods IV-VI (Fig. 3D-F ), carpus more or less rectangular, with one stout seta on inferodistal angle (absent in pereopod V); propodus with several fine setae along both lateral margins and one stout seta on inferodistal angle. Pereopod VII (Fig. 3G ), carpus and propodus with dentate margin baring simple setae along inferior margin.

Pleopods (Fig. 4A-E ), exopod slightly longer than endopod. Pleopod I (Fig. 4A ), exopod ~ 2 × as long as wide; endopod 0.4 × wider than exopod. Pleopods II-V (Fig. 4B-E ), protopod with one or two simple setae on inner or outer margin.

Uropod (Fig. 4F, G ), protopod rectangular, 2.4 × longer than wide, with plumose setae both lateral margins; exopod oval, almost 2 × longer than wide, surrounded by plumose and simple setae, with pointed apex, sinuous distally; endopod with plumose and simple setae along both lateral margins.

Pleotelson (Fig. 4H ) 2.2 × longer than wide, concave proximally, convex medially, tapering distally, with two statocysts on dorsal surface proximally; apex with five simple setae; distal region with several simple setae on dorsal surface and lateral margins.

Distribution.

Southern coast of Jeju-do in South Korea.

Habitat.

Sublittoral zone of sandy bottom.

Remarks.

Amakusanthura intermedia sp. nov. is most similar to four species, A. magnifica (Menzies & Frankenberg, 1966), A. pimelia (Poore & Lew Ton, 1985), A. paramagnifica Müller, 1992, and A. tengo Müller, 1992, in having the following characteristics: (1) pleonites I-III are visible by folds dorsally and laterally, while pleonites IV and V are visible laterally; (2) the uropodal exopod has sinuous and acute distal region; (3) the pleotelson is concave laterally and tapering distally; (4) the maxillipedal endite is present; and (5) the propodal palm of pereopod I is stepped ( Schultz 1969; Poore and Lew Ton 1985; Kensley and Schotte 1989; Müller 1992). However, the new species can be distinguished from the latter species by having the maxillipedal endite (vs. lacking in A. tengo ), the carpus of pereopod I protruding inferodistally (vs. not protruding in A. pimelia ), the maxillipedal endite reaching to the distal end of fused articles I and II (vs. over in A. magnifica and not reaching in A. paramagnifica ) ( Schultz 1969; Poore and Lew Ton 1985; Kensley and Schotte 1989; Müller 1992).

Figures

Figure 2. Amakusanthura intermedia sp. nov., holotype, female A habitus, dorsal view B habitus, lateral view C antennule D antenna E mandible F maxilla G maxilliped.

Figure 3. Amakusanthura intermedia sp. nov., holotype, female A pereopod 1 B pereopod 2 C pereopod 3 D pereopod 4 E pereopod 5 F pereopod 6 G pereopod 7.

Figure 4. Amakusanthura intermedia sp. nov., holotype, female A pleopod 1 B pleopod 2 C pleopod 3 D pleopod 4 E pleopod 5 F uropodal exopod G uropodal endopod H pleotelson.