Microcharon tanakai, Kim, Jeongho, Lee, Wonchoel & Karanovic, Ivana, 2017

Kim, Jeongho, Lee, Wonchoel & Karanovic, Ivana, 2017, A new species of Microcharon from marine interstitial waters, Shizuoka, Japan (Isopoda, Lepidocharontidae), ZooKeys 680, pp. 13-31 : 14-20

Microcharon tanakai sp. n. Figures 2, 3, 4, 5, 6, 7, 8, 9, 10

Type locality.

Interstitial water of coarse sand, Miho-Uchihama beach, Shizuoka city, Shizuoka Prefecture, Japan, 35°01'83"N, 138°51'71"E (Fig. 1).

Material examined.

Holotype: adult female, (NIBRIV0000787789) completely dissected and mounted in lactophenol on four slides; paratype 1 female (NIBRIV0000787790) dissected on three slides, paratype 2 female (NIBRIV0000787791) dissected on one slide; adult male pleotelson dissected on three slides; 2 females and 1 male used for SEM.

Diagnosis.

Antennular article 6 smallest, with one aesthetasc, one penicillate, three simple setae distally; article 1 of mandibular palp with one distal simple seta; lateral lobe of maxillula with eleven robust setae; distal apex of male pleopod 1 convex, round, with three apical, four subapical setae; protopod of male pleopod 2.9 times longer than wide; protopod of uropod 3.1 times longer than wide, with fifteen setae.

Description of the female holotype.

Body (Fig. 2A): elongate, slender in whole appearance, total length, 1.95 mm, measured from anteromedial point of cephalon to posteromedial point of pleotelson, body approximately 8.5 times longer than wide, maximum body width in pereonite 3, 0.92 times of maximum width of pleotelson; color of preserved specimens transparent, whole surface of body with many ornamentation looking like lines.

Cephalon (Fig. 2B): 1.12 times longer than wide and 0.12 times of whole body; anterior margin with weak rostrum; lateral margins straight, with four pairs of simple setae, three pairs of simple setae along dorsomedial surface.

Pereon (Fig. 2A, C): 0.68 times of whole body length, medial margin of tergite convex, pereonites with lateral margin, straight, pereonite 1, 0.62 times longer than wide, four simple setae along lateral margin, two setae on dorsal surface; pereonite 2, 1.12 times longer than wide, with four pairs of setae along lateral margin, two setae on anteromedial edge; pereonite 3, 1.06 times longer than wide, with four pairs of setae along lateral margin, two pairs of setae along dorsal surface; pereonite 4, 1.02 times longer than wide, with nine setae on both lateral and dorsal surface; pereonite 5, 0.99 times longer than wide, with six setae on both lateral and dorsal margin; pereonite 6, 1.13 times longer than wide, with eight simple setae on dorsal margin; pereonite 7, 1.02 times longer than wide, with two setae on both anterolateral corner and three pairs of setae along dorsal surface.

Pleonite 1 (Fig. 2A): as wide as pereonite 7, 0.38 times longer than wide, with two simple setae on dorsomedial margin.

Pleotelson (Fig. 2D): 1.33 times longer than wide, wider than preceding pereonites, with several setae, becoming slightly narrow from basal part to distal end, weak cleft on middle of posterior rim.

Antennula (Fig. 2E): 6 articles; article 1 robust, 1.5 times longer than wide, with three setae: two distomedial simple, one penicillate short setae distolaterally; article 2, smaller than 1, distoventral projection, 1.8 times longer than wide, with two simple, three penicillate setae, one of them elongate, stout, reaching distal tip of antennula; article 3, naked, 1.5 times longer than wide; article 4 with one proximolateral simple seta, two penicillate setae distolaterally; article 5, 1.2 times longer than wide with one simple seta, one aesthetasc distomedially; article 6, smallest 0.6 times of article 5, with one aesthetasc, one penicillate, three simple setae on distal end.

Antenna (Fig. 3A, B): six podomeres, twelve flagellar articles; article 1 globular in dorsal view, with one lateral simple seta; article 2 semicircular, naked; article 3, 1.8 times longer than wide, with one distomedial simple seta, scale thick, robust, with two simple setae laterally (Fig. 8A); article 4, as long as wide, with two simple setae distolaterally; article 5, 3.02 times longer than wide, with three distoventral simple setae, one simple, one penicillate setae distodorsally; article 6, longest, 5.3 times longer than wide, with two simple, five penicillate setae on lateral margin, seven simple setae on distal margin; flagellar articles from 2 to 8 subequal in length, armature of each articles as follows: article 1 with two simple setae distally, article 2 with four simple setae distally, article 3 with three simple setae distally, article 4 with three simple setae distally, article 5 with four simple setae distally, article 6 with six simple setae distally, article 7 with three simple setae distally, article 8 with four simple setae distally, article 9 with four simple setae distally, article 10 with four simple setae distally, article 11 with three simple setae distally, article 12 with four simple setae distally

Mandible (Figs 3 E–G, 8B): body robust, curved inwardly; pars incisiva of both mandibles with four cusps; right mandible (Fig. 3F), lacinia mobilis, with five cusps, tapering proximally three pinnate, three simple setae located below lacinia mobilis; pars molaris of both mandibles with one simple, one pinnate distal setae, slightly longer than pars molaris, almost same length as seta on palp; left mandible (Fig. 3E), pars incisiva with four cusps, lacinia mobilis missing, with three pinnate and one naked robust setae located below pars incisiva; palp (Fig. 3G) with three articles, inserted on cuticular projection; article 1 with one simple seta distally (Fig. 8B), article 2 longest, with two pinnate and several hair-like setae on distal margin, article 3 curved outwardly, with five pinnate and with several hair-like setae on lateral margin.

Paragnaths (Fig. 3D): deeply incised, with two lobes, each distal part of lobes covered with numerous setae.

Maxillula (Fig. 4D): lateral lobe with eleven strong robust setae on distal edge, some denticulate, some setulose, two spinular rows along outer margin; mesial lobe nearly half as long and wide as outer endite, with three short simple and several hair-like setae on distal end.

Maxilla (Fig. 4C): lateral rami slightly shorter than median one, with four pectinate setae on distal end respectively; mesial ramus coalescent with basis, much thicker than others with eight strong setae distally and one of them pectinate.

Maxilliped (Fig. 3C): epipodite wide, apically pointed, distal tip reaching distal part of first palp article; basis 2.1 times longer than wide; palp with 5 articles; article 1, 0.5 times longer than wide, with two simple setae on both distal corners; article 2, 1.7 times longer than article 1, with two simple setae on distomedial corner; article 3 tapering distally, with three simple setae along medial margin, one seta on distolateral corner; article 4 curved inwardly, with four simple setae distally; article 5 with five simple setae, 2 claws distally; endite 2.4 times longer than wide, with five apical pinnate setae, numerous spinules on distomedial corner.

Pereopods 1-4 (Figs 4A, B, 5A, B): inserted on pereon anterolaterally (Fig. 8C); coxal plate minute, hardly discernible (Fig. 8D); anteromedial margin of basis protruded, with one small seta on distal corner, pereopod 1 and 4 with two penicillate, one simple setae (vs pereopod 2, with one penicillate, one simple setae; pereopod 3 with one penicillate, two simple setae); ischium, pereopod 1 and 2 with two simple setae on both anteroposterior margin (vs pereopod 3 with two simple, one penicillate setae; pereopod 4 with three simple setae); merus, shortest article, broaden distally, distinctly shorter than ischium, pereopod 2-4 with four simple setae on both side of distal corner (vs pereopod 1 with five simple setae); carpus, longer than ischium, pereopods 2 -4 with one bifid, two simple, one penicillate setae (Fig. 8E, F), (vs pereopod 1 with two simple setae); propodus, slightly shorter than carpus, pereopod 1 with four simple setae (vs pereopod 2 with two bifid, two simple, one penicillate setae; pereopod 3 with two bifid, three simple, one penicillate setae; pereopod 4 with one bifid, four simple setae); pereopod 4 with distal sclerite covering proximal part of dactylus, dactylus with two claws (Fig. 8E), two pairs of setae on both dorsal and ventral margin (vs pereopod 1 with three simple, two simple setae on both dorsoventral margin respectively).

Pereopods 5-7 (Figs 5C, 6A, B): inserted on pereon posterolaterally, subequal in whole appearance with preceding ones, with small differences in chaetotaxy; coxal plate minute, hardly discernable; basis, with one small seta on distal corner, pereopod 5 with one simple, one penicillate, setae on anteromedial margin (vs pereopod 7 with two simple, one penicillate setae); ischium, with two simple setae on both anteroposterior margin; merus, with four simple setae on both side of distal corner; carpus, with one bifid, two simple, one penicillate setae (vs pereopod 7 with one bifid, one simple, one penicillate setae); propodus, pereopod 5 with two bifid, two simple, one penicillate setae (vs pereopod 6 with two bifid, thre simple, one penicillate setae; pereopod 7 with two bifid, two simple setae), with sclerite on distal margin, covering proximal part of dactylus (Fig. 8F); dactylus with two claws, two pairs of setae on both dorsal, ventral margins.

Female operculum (Fig. 6C): 1.2 times longer than wide, with no ornamentation on dorsal surface, with four setae on distal margin.

Uropods (Fig. 7E): protopod robust, slightly longer than pleotelson, length 3.1 times longer than wide, with thirteen simple and two robust setae proximomedially; endopod 0.5 times longer than protopod, 1.7 times longer than exopod, with nine simple and four penicillate setae; exopod 0.6 times longer than endopod, with four simple setae distally.

Description of male.

Penial papillae (Fig. 9G, H): located at posteromedial margin of pereonite 7 in ventral view, coalescent, proximal margin round, tapering distally, but distal margin straight, with proximomedial opening channel.

Pleopod 1 (Figs 7A, 9 I–L, 10M): elongate, total length almost reaching posterior margin of pleotelson, composed of two coalescent halves, proximal part enlarged, gradually tapering at its distal part, approximately 1.9 times longer than maximum wide (measured at widest section of proximal part); separated in half by medial sperm tube running from triangular opening on proximal part of medial groove, distolateral edge of hyaline lamella straight, without ornamentations; parallel to lateral margin of pleopod, in lateral view distal end of lobes convex, rounded at distal apex, each with three simple setae distally, four subapical setae on ventral margin.

Pleopod 2 (Figs 7B, 10N): protopod elongate, robust, 2.9 times longer than wide; appendix masculina, curved, tapering distally, tip nearly reaching to protopod apex, with no armature; exopod rounded apically, broad.

Pleopod 3 (Figs 7C, 10O, P): no sexual dimorphism, endopod two-articulated, second article suboval, with ornamentation like turtle shell shape, and with one apical, one mesial, one lateral plumose setae; exopod two-articulated, clearly longer than endopod, reaching far beyond tip of endopod, with one simple seta distally.

Pleopod 4 (Fig. 7D): rudimentary, uniramous, no ornamentation, distal margin rounded.

Etymology.

The species is named in honor of the collector, Dr. Hayato Tanaka, to express our appreciation for his support in this study.