Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005

Ariyama, Hiroyuki, 2016, Five species of the family Cyproideidae (Crustacea: Amphipoda) from Japan, with the description of a new genus and two new species, Zootaxa 4097 (3), pp. 301-331 : 320-324

Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005

[Japanese name: Chibimaru-hoteiyokoebi, new] ( Figs 17–20 )

Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005: 171 , figs 1–3 (type locality: Manazuru, Kanagawa Prefecture, Japan).

Material examined. One female, 1 ovigerous female and 1 male? (OMNH-Ar-9961–9963), 3.1, 3.5, 1.8 mm, Tagurazaki coast, Wakayama City, Wakayama Prefecture, 34°16'02"N, 135°03'38"E, uppermost subtidal zone, under small rock, 12 April 2009, coll. H. Ariyama; 1 ovigerous female and 1 male? (OMNH-Ar-9964, 9965), 2.2, 1.3 mm, Kodomari, Takahama Town, Fukui Prefecture, 35°32'10"N, 135°30'56"E, 10 m in depth, among bush of a brown alga Sargassum macrocarpum , using SCUBA, 29 August 1980, coll. H. Ariyama and H. Nakahara.

Description. Female [based on 3.1 mm (OMNH-Ar-9961), and 3.5 mm (OMNH-Ar-9962) for mandibles, lower lip and uropod 1]. Body ( Fig. 17 ) roundish triangular; head longer than pereonite 1, eyes medium-sized; pereonites and pleonites smooth, with pereonites 3–5 enlarged; coxa 5 not reaching posteroventral corner of pereonite 6; pleonites without lateral ridge, pleonal epimeron 1 projected and epimera 2–3 rounded each on posteroventral corner, all ventral margins bare; urosomite 1 long, dorsal margin with roundish keel, urosomites 2–3 very short.

Antenna 1 ( Fig. 18 A) short, with ratio of lengths of peduncular articles 1–3 1:0.5:0.4; accessory flagellum small, 1-articulated, attached on posterodistal corner of peduncular article 3; primary flagellum with 4 articles (articles 2–3 very short), with many aesthetascs. Antenna 2 ( Fig. 18 B) short; peduncular article 3 short and articles 4–5 relatively long; flagellum with 3 articles, tip bearing long setae.

Upper lip ( Fig. 18 C) incised, lateral margin with short setae. Mandible ( Fig. 18 D, D1, E, E1), incisor bearing 8 cusps in left, left lacinia mobilis fan-shaped, distal margin minutely serrated, right lacinia mobilis cylindrical, number of accessory blades 3 in left (probably lost partly) and 8 in right; molar developed; palp article length ratio 1:1.0: 1.6 in right, all articles without setae. Lower lip ( Fig. 18 F), inner lobes indistinct; outer lobes projected anteriorly, covered with fine setae, mandibular processes present. Maxilla 1 ( Fig. 18 G, G1), inner plate long, distal end with 1 short seta; outer plate pointed distally, with 3 minutely-serrated robust setae; distal end of palp bearing 8 robust setae. Maxilla 2 ( Fig. 18 H) slender; inner plate shorter than outer, terminal ends of inner and outer plates with 5 and 3 thick setae, respectively. Maxilliped ( Fig. 18 I, I1), inner plate truncate, dorsodistal part bearing 4 small robust setae; outer plate small, distal margin with 2 robust setae, mediodistal margin setose; palp consisting of 4 articles, mediodistal corner of article 2 projected, with 6 belt-shaped setae, article 3 with large apicodistal process, mediodistal corner with 2 belt-shaped setae, article 4 narrow.

Gnathopod 1 ( Fig. 19 A), coxa small, oval; basis widened distally, anterior margin with several setae; merus short; carpus long, posterior margin with 2 setae, posterodistal projection bearing several distal setae; propodus almost same length as carpus, with 1 anterior and 2 posterodistal setae; posterior margin of dactylus with 1 denticle and several minute setae. Gnathopod 2 ( Fig. 19 B) a little larger than gnathopod 1; coxa small, longish trapezoidal, anterodistal corner with 1 long seta; basis widened distally, anterior margin with several setae; merus short, distal end setose; carpus long, posterior margin bare, posterodistal corner slightly projected, bearing several distal setae; propodus shorter than carpus, slightly widened distally, posterodistal corner projected, with 2 setae; dactylus short, posterior margin with 1 denticle and several minute setae.

Pereopod 3 ( Fig. 19 C), coxa wide, semicircular, anterior margin rounded, posterior margin slightly concave, posteroproximal corner with small projection; basis long, anterior margin setose. Pereopod 4 ( Fig. 19 D), coxa extremely wide, middle–ventral part swollen posteriorly, anterior margin almost straight, anteromedial surface with 4 hollows in middle and 3 creases on ventral corner; basis long, anterior margin setose. Pereopod 5 ( Fig. 19 E), coxa relatively large, swollen posterodistally; basis narrow, anterior and posterior margins bearing sparse short setae; posterodistal corner of merus projected. Pereopod 6 ( Fig. 19 F) shorter than pereopod 5; coxa semiquadrate, produced posteroventrally; basis swollen posteriorly, anterior margin with a few setae; posterodistal corner of merus projected. Pereopod 7 ( Fig. 19 G) shorter than pereopod 6; coxa roundish triangular; basis wide, posteroproximal and posterodistal corners swollen, posterodistal corner angular; merus projected posterodistally.

Pleopods ( Fig. 20 A–C) almost same length; peduncles without setae; inner rami with 7 articles, outer rami with 9, 8, 8 articles in pleopods 1 – 3, respectively. Uropods ( Fig. 20 D–F) slender, peduncle and both rami without robust setae, but bearing minute denticles; peduncle of uropod 1 long, both rami almost same length as peduncle; uropod 2 about 0.8 times as long as uropod 1, inner ramus longer than outer, about 1.4 times length of peduncle, outer ramus almost same length as peduncle; uropod 3 short, 55% as long as uropod 1, peduncle short, inner ramus longer than outer, inner and outer rami about 1.6 and 0.9 times length of peduncle, respectively. Telson ( Fig. 20 G) roundish triangular, breadth about half of length, dorsal surface bearing a few minute setae, margins without setae.

Small individuals (male?) [based on 1.8 mm (OMNH-Ar-9963) and 1.3 mm (OMNH-Ar-9965)]. Gnathopods almost similar to female except for oostegite on coxa 2.

Coloration in fixed specimen. Whole body orange, eyes red.

Remarks. Morphological characters of these specimens almost agree with the original description and figures of Kobayashi & Ishimaru (2005). However, there are two differences (the original description in parentheses): 3- articulated flagellum of the antenna 2 (4-articulated), and indistinct inner lobes of the lower lip (distinct, [other organ attached?]).

Distribution. Japan: Wakayama City in Wakayama Prefecture, Takahama Town in Fukui Prefecture (present study, Fig. 1 ); Manazuru in Kanagawa Prefecture ( Kobayashi & Ishimaru 2005). This species was also collected from Aichi, Mie and Yamaguchi Prefectures (my private collection).

Habitat. Under small rocks or among seaweeds, 0–10 m in depth.

Figures

FIGURE 1. Map showing collecting sites of the examined specimens.

FIGURE 17. Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005. Female (OMNH-Ar- 9961), 3.1 mm. Habitus, lateral view.

FIGURE 18. Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005. A – C, G – I, G 1, I 1, female (OMNH-Ar- 9961), 3.1 mm; D – F, D 1, E 1, female (OMNH-Ar- 9962), 3.5 mm. A, left antenna 1, lateral view; B, left antenna 2, lateral view; C, upper lip, anterior view; D, right mandible, ventral view; D 1, incisor, lacinia mobilis and accessory blades of right mandible, ventral view; E, left mandible, dorsal view, palp lost; E 1, incisor, lacinia mobilis and accessory blades of left mandible, dorsal view; F, lower lip, ventral view; G, right maxilla 1, dorsolateral view; G 1, distal part of right maxilla 1, dorsolateral view, normal setae omitted; H, left maxilla 2, dorsal view; I, right maxilliped, ventral view; I 1, distal part of outer and inner plates of right maxilliped, ventral view, normal setae omitted. Scale: A – B, 0.2 mm; C – I, 0.14 mm; D 1, E 1, G 1, I 1, 0.07 mm.

FIGURE 19. Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005. Female (OMNH-Ar- 9961), 3.1 mm. A – B, left gnathopods 1 – 2, lateral views; C – F, left pereopods 3 – 6, lateral views; G, right pereopod 7, lateral view. Scale: 0.25 mm.

FIGURE 20. Moolapheonoides acutifalcatus Kobayashi & Ishimaru, 2005. All but D, female (OMNH-Ar- 9961), 3.1 mm; D, female (OMNH-Ar- 9962), 3.5 mm. A – B, left pleopods 1 – 2, posterior views; C, left pleopod 3, posteromedial view; D, right uropod 1, lateral view; E, left uropod 2, dorsomedial view; F, left uropod 3, dorsal view; G, telson, dorsal view. Scale: A – C, 0.25 mm; D – G, 0.14 mm.