Dulichia biarticulata Hirayama and Takeuchi, 1993

Ariyama, Hiroyuki, 2019, Four Species of Dulichiidae (Crustacea: Amphipoda) from Japan, with the Description of a New Genus and Two New Species, Species Diversity 24 (1), pp. 29-48 : 31-32

Dulichia biarticulata Hirayama and Takeuchi, 1993 ( Figs 2–5)

[Japanese name: Kishi-shakutoridoronomi, new]

Dulichia biarticulata Hirayama and Takeuchi, 1993: 160 , figs 15, 16.

Material examined. Two males (OMNH-Ar-10798, 10799), 3.1 and 2.4 mm, and female (OMNH-Ar-10800), 2.7 mm, Kitsunezaki-hama, Ishinomaki City , Miyagi Prefecture, 38°21′21"N, 141°25′23"E ( Fig. 1A), 3 m depth, rocky reef, using SCUBA, 3 October 2017, coll . M . Aoki; male (OMNH-Ar-10801), 3.1 mm, Akinohama Beach, Izu Oshima Island ( Oshima Town ), Tokyo Prefecture, 34°47′13"N, 139°24′31"E ( Fig. 1F), 8 m depth, rocky reef, using SCUBA, 4 May 2017, coll . O . Hoshino ; male (OMNH-Ar-10802), 4.8 mm, same place, 6 May 2017, coll . O . Hoshino ; male (OMNH-Ar-10803), 2.9 mm, and 2 ovigerous females (OMNH-Ar-10804, 10805), 4.8 and 3.5 mm, same place, 9 May 2017, coll . O . Hoshino; male (OMNH-Ar-10806), 3.5 mm, Moroiso, Miura City , Kanagawa Prefecture ( Fig. 1D), 3 m depth, rocky reef, using SCUBA, 25 December 2014, coll . H . Kohtsuka; 2 males (OMNH-Ar-10807, 10808), 3.8 and 2.1 mm, and female (OMNH-Ar-10809), 2.7 mm, Kodomari, Takahama Town , Fukui Prefecture, 35°32′10"N, 135°30′56"E ( Fig. 1G), 10 m depth, among a brown alga Sargassum macrocarpum , using SCUBA, 29 February 1980, coll . H . Ariyama and H . Nakahara ; male (OMNH-Ar-10810), 2.8 mm, same place, 25 April 1980, coll . H . Ariyama and H . Nakahara; male (OMNH-Ar-10811), 2.8 mm, Tanigawa, Misaki Town , Osaka Prefecture, 34°19′25"N, 135°07′10"E ( Fig. 1H), 5 m depth, on a tunicate Halocynthia ritteri (Oka, 1906) , using SCUBA, 29 May 1996, coll . H . Ariyama.

Diagnosis. Eyes large, round. Accessory flagellum 2-articulate. Maxilla 1 outer plate bearing 9 terminal robust setae. Maxilla 2 inner plate with mediofacial row of setae. Male gnathopod 2, basis relatively wide, propodus large, posterior margin weakly setose, bearing proximal and distal projections changeable with growth. Pereopod 4 basis expanded. Pereopod 7 carpus about 1.4 times as long as propodus. Uropod 2 outer ramus about 0.8 times length of inner ramus.

Description of male [based on male (OMNH-Ar-10801), 3.1 mm]. Body ( Fig. 2), dorsal margins of pereonites and pleonites smooth, urosomite 1 about 1.35 times as long as pleonites 2+3. Eyes round, about 0.3 times length of head. Antenna 1 ( Figs 2, 3A) about 0.8 times as long as body, accessory flagellum 2-articulate. Antenna 2 ( Fig. 2) about 0.7 times length of antenna 1.

Gnathopod 1 ( Fig. 3B), basis with ridge on anterolateral surface; merus setose posterodistally; carpus with many setae on posterior margin; propodus with many setae posteriorly, medial surface also setose; dactylus curved posteriorly. Gnathopod 2 ( Fig. 3C), coxa wide, larger than coxa 1, subtrapezoidal, ventral margin slightly excavated; basis relatively wide, anterodistal corner a little lobate; carpus triangular, posterodistal corner setose; propodus large, about 0.7 times as long as head, about 2.1 times length of carpus, posterior margin weakly setose, bearing distally-oriented proximal projection and distal projection each with minute setae; dactylus stout, posterior margin produced proximally.

Pereopod 3 ( Fig. 3D, E), basis weakly expanded, about 2.2 times as long as width, with glands in most part; merus short. Pereopod 4 ( Fig. 3D, F) longer than pereopod 3; basis strongly expanded, about 1.6 times as long as width, with glands in central part; merus longer than that of pereopod 3. Pereopod 5 ( Fig. 3G, G 1), basis slender, merus short, carpus about 0.85 times as long as propodus. Pereopod 6 ( Fig. 3H) about 1.1 times length of pereopod 5; basis slightly expand- ed, merus short, carpus about 0.9 times as long as propodus. Pereopod 7 ( Fig. 3H, I) about 1.3 times length of pereopod 6; basis slightly expanded, merus long, carpus about 1.4 times as long as propodus.

Description of female [based on female (OMNH- Ar-10805), 3.5 mm]. Gnathopod 1 ( Fig. 4A) similar to that of male. Gnathopod 2 ( Fig. 4B, B 1), coxa narrower than male coxa 2, trapezoidal; basis straight, anterodistal corner not lobate; carpus pear-shaped, posterior margin heavily setose; propodus about 1.25 times as long as carpus, palm with single robust seta, posterior margin and medial surface setose; dactylus slender. Pereopods 3, 4 ( Fig. 4C, D) almost same as those of male, bases weakly expanded, about 2.3 and 1.9 times as long as width respectively.

Variation. Gnathopod 2: propodi and dactyli in very large male (OMNH-Ar-10802, 4.8 mm; Fig. 4E) and large male (OMNH-Ar-10807, 3.8 mm; Fig. 4F) longer than those of male (OMNH-Ar-10801, 3.1 mm; Fig. 3C), proximal projections of propodi also long and situated more proximally, right-angled to palm in very large male and at about 45° angle to palm in large male; propodi and dactyli in male (OMNH-Ar-10803, 2.9 mm; Fig. 4G) and small male (OMNH-Ar-10808, 2.1 mm; Fig. 4H) almost same as those of male (OMNH-Ar-10801, 3.1 mm; Fig. 3C). Pereopod 3: bases in very large male (OMNH-Ar-10802, 4.8 mm) and large male (OMNH-Ar-10807, 3.8 mm) slender, about 4.1 and 3.45 times as long as width respectively. Pereopod 4: bases in those males weakly expanded, about 2.6 and 2.35 times as long as width respectively.

Coloration in life ( Fig. 5). Eyes dark red; dorsal part of body pale brown, ventrolateral part of body beige, scattered with small brown pigments; distal part of peduncular article 3 and proximal part of flagellar article 1 of male antenna 1 white. Whole body except for eyes orange in some large females.

Remarks. The morphological characters of the specimens are very similar to those of the original descriptions and figures of Dulichia biarticulata . Although Hirayama and Takeuchi (1993) stated “in pereopods 5 and 7, propodi clearly longer than carpi”, the fig. 16P (lower) in their paper is not the left pereopod 7 and the fig. 16O (upper and lower) is also not the left pereopod 6. The figs 16P (lower) and 16O are probably the left pereopod 6 and the right pereopod 7, respectively; therefore, the propodus of the pereopod 7 is shorter than the carpus like my specimens. Hirayama and Takeuchi (1993) described this species based on the male specimen. Morphological characters of the female were firstly described in the present paper.

Habitat. Found on the self-constructed mast on rocky reef ( Fig. 5), on tunicates or among algae, 3–10 m depth.

Distribution. Japan: coasts of Miyagi, Fukushima, Tokyo, Kanagawa, Fukui and Osaka Prefectures ( Hirayama and Takeuchi 1993, present study).