Neocaridina ikiensis, Mendivil & Cardoso, 2022

Shih, Hsi-Te, Cai, Yixiong, Niwa, Nobuaki & Nakahara, Yasuhiko, 2017, A New Species of Land-locked Freshwater Shrimp of the Genus Neocaridina (Decapoda: Caridea: Atyidae) from Iki Island, Kyushu, Japan, Zoological Studies 56 (30), pp. 1-14 : 4-10

Neocaridina ikiensis n. sp.

( Figs. 2-5 ) urn:lsid:zoobank.org:act:128F614E-5F75-4C74-ADEB-F4BB7719C875

Material examined: Holotype: male, cl 4.7 mm, NSMT-Cr 25616; small stream at Kugiyama-hure, Gonoura Town, Iki City , Nagasaki Prefecture (= P r e f.), N3 3°4 3'5 1.5" E1 2 9°4 3'5 2.2", 2 3 November 2015, coll. Yasuhiko Nakahara. Paratypes: 2 males, both cl 3.8 mm, 2 females, cl 4.1-4.6 mm, NSMT-Cr 25617, same collection data as for holotype; 1 male, cl 4.7 mm, 2 females, cl 3.9-4.8 mm, RMNH.CRUS.D.57249, same collection data as for holotype; 1 male, cl 3.9 mm, 2 females, cl 3.3-4.4 mm, OUMNH.ZC.2017- 01-069, same collection data as for holotype; 1 male, cl 4.6 mm, ZRC 2017.0960, 1 female, cl 5.1 mm, ZRC 2017.0961, 8 males, cl 3.0- 5.4 mm, 8 females, cl 2.9-5.1 mm, ZRC 2017.0962, same collection data as for holotype; 15 males, cl 2.9- 6.0 mm, NCHUZOOL 14932, 16 females, cl 3.0- 5.5 mm, NCHUZOOL 14933, same collection data as for holotype.

Others: 14 males, cl 3.0- 4.9 mm, 15 females, cl 3.3-5.3 mm, ZRC 2017.0963, small stream at Ashibe Town, Iki City, Iki island, Nagasaki Pref., N33°50'36.0" E129°45'08.7", 22 November 2015, coll. Y. Nakahara; 9 males, cl 3.6-5.5 mm, 7 females, cl 3.8-5.8 mm, ZRC 2017.0964, small stream at Katsumoto Town, Iki City, Nagasaki Pref., N33°50'18.0" E129°41'40.2", 23 November 2015, coll. Y. Nakahara; 17 males, cl 3.1-5.2 mm, NCHUZOOL 14934, 15 females, cl 3.0- 5.8 mm, NCHUZOOL 14935, small stream at Ashibe Town, Iki City, Nagasaki Pref., N33°50'36.0" E129°45'08.7", 22 November 2015, coll. Y. Nakahara; 9 males, cl 3.9-6.2 mm, NCHUZOOL 14936, 8 females, cl 3.4-6.0 mm, NCHUZOOL 14937, small stream at Katsumoto Town, Iki City, Nagasaki Pref., N33°50'18.0" E129°41'40.2", 23 November 2015, coll. Y. Nakahara. 2 ovig. females, both cl 5.3 mm, NCHUZOOL 14938- 14939, Kugiyama-hure, Gonoura Town, Iki City, Nagasaki Pref., 14 July 2017, coll. Y. Nakahara.

Comparative material: Neocaridina denticulata : 1 male, cl 5.0 mm, 1 female, cl 5.5 mm, ZRC, Yoshii-gawa River, basin, Okayama Pref., western Honshu, Japan, 12 November 1971; 1 female, cl 7.0 mm, no data; 3 males, cl 4.5-4.6 mm, 22 females, cl 3.4-5.3 mm, ZRC, Sendai River, Kagoshima, Japan, coll. H. Suzuki, 22 October 1990.

Description: Rostrum moderately short, straight, slightly sloping down from a crest above postorbital margin, reaching slightly short of, to distinctly beyond end of second segment of antennular peduncle, rarely reaching to end of antennular peduncle; armed dorsally with 11- 17 teeth, including 2-4 (mode 3-4) on carapace, ventrally with 2-6 teeth (mode 2-4). Antennal spine fused with inferior orbital angle. Pterygostomial margin sub-rectangular, armed with a small spine.

Sixth abdominal somite in male 0.43 times of carapace, 1.7 times as long as fifth somite, slightly shorter than telson; sixth abdominal somite in female 0.55 times of carapace, 1.42 time as long as fifth somite, slightly shorter than telson. Telson 2.8 times as long as wide, with 4 pairs of dorsal spinules and one pair of dorsolateral spinules; posterior margin rounded, lined with 5-6 pairs of spines, lateral pair distinctly longer than intermediates of spines. Pre-anal carina high, lacking spine.

Eyes well developed, anterior end reaching to 0.6 times length of basal segment of antennular peduncle. Antennular peduncle 0.7 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment length, anterolateral angle reaching 0.3 length of the second segment, second segment distinctly longer than third segment. Stylocerite reaching 0.7-0.8 length of basal segment of antennular peduncle. Scaphocerite 3.2 times as long as wide.

Incisor process of mandible ending in irregular teeth, molar process truncated. Lower lacinia of maxillule broadly rounded, upper lacinia elongate, with a number of distinct teeth on inner margin, palp short. Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly with some long, curved setae at posterior end. Palp of first maxilliped stout. Second maxilliped typical of genus. Third maxilliped reaching to end of antennular peduncle, with ultimate segment slightly longer than penultimate segment.

Epipods on first four pereiopods. First pereiopod reaching to distal end of basal segment of antennular peduncle; merus 2.5-2.7 times as long as broad, as long as carpus; carpus excavated anteriorly, shorter than chela, 1.5-1.6 times as long as high; chela 2.0-2.1 time as long as broad; fingers slightly longer than palm. Second pereiopod reaching to end of second segment of antennular peduncle; merus shorter than carpus, 4.2-5.0 times as long as broad; carpus 1.2-1.3 times as long as chela, 4.2-4.6 times as long as high; chela 2.3-2.5 times as long as broad; fingers 1.3-1.5 times as long as palm. Third pereiopod reaching end of antennular peduncle, propodus 6-8 times as long as broad, 3.0-3.2 times as long as dactylus; dactylus stout, 2.2 times as long as wide (spines included) in males; dactylus slender, 3.2 times as long as wide (spines included) in females, terminating in one claw, with 6-7 accessory spines on its flexor margin. Fifth pereiopod reaching to end of second segment of antennular peduncle, propodus 8-10 times as long as broad, 2.7-2.8 times as long as dactylus, dactylus 3.0-3.8 times as long as wide (spinules included), terminating in one claw, with 46-72 spinules on its flexor margin.

Endopod of male first pleopod extending to 0.6 times of exopod length, inflated at distal 3/4 into pear-shaped structure, 1.7 times as long as wide, with tiny spinules on distal margin of dorsal surface, appendix interna at base of inflated part, short; outer margin lined with about 10 short setae. Appendix masculina of male second pleopod cylindrical, reaching to about half length of endopod, inner and distal surface densely lined with long, stout spines, appendix interna reaching to 0.8 length of appendix masculina.

Uropodal diaeresis with 13-17 movable spinules.

Eggs 1.13-1.14 x 0.73- 0.68 mm in diameter.

Color: Body color varied from translucent, light blue, brown, to black. Some large individuals with a pale longitudinal stripe on mid-dorsal surface ( Fig. 5A ).

Etymology: The species is named after the type locality, Iki Island, Nagasaki Pref., western Japan.

Ecological notes: Habitat ( Fig. 5B ) of the species is small streams, about 2 m wide, with slow flowing water. Stream banks were heavily vegetated. Collection sites were about 100 m to 1 km away from the coast. In one of the streams, a rice paddy is found adjacent to its upper reach, where substrate was muddy and with various sized rocks submerged in the water. The freshwater crab Geothelphusa dehaani (White, 1847) and the catadromous atyid shrimp Caridina typus H. Milne Edwards, 1837 were found sympatric with the new species.

Distribution: Presently known only from several streams in Iki Island, western Japan.

Remarks: Taking into account the form of endopod of the male first pleopod, the male appendix masculine in the second pleopod, as well as the propodus and dactylus of the third pereiopods, of which, no obvious sexual dimorphisms were observed, the new species could be assigned to N. denticulata species group (cf. Cai 1996; Liang 2004; Shih and Cai 2007).

Neocaridina ikiensis n. sp. differs from Japanese populations of N. denticulata by the relatively short rostrum, which mostly reaches to or slightly beyond end of second segment of antennular peduncle (vs. mostly reaches to or beyond end of antennular peduncle in N. denticulata ); number of post-orbital rostral teeth 2-4 (mode 3-4) in N. ikiensis vs. 1-3 (mode 2) in N. denticulata ; male first pleopod slender, 1.7 times as long as broad (vs. 1.2 to 1.4 times in N. denticulata ); appendix interna of male second pleopod relatively long, reaching to 0.8 length of appendix masculine (vs. 0.7 times in N. denticulata ); and telson ending in a rounded margin (vs. ends with a posterior projection in N. denticulata ).

Liang (2004) described N. denticulata in details based on specimens from China, of which, some of the characters are slightly different from specimens that we have examined from Japan. Neocaridina ikiensis can be separated from Chinese population of N. denticulata (cf. Liang 2004) by the relatively short rostrum, which mostly reaches to or slightly beyond end of second segment of antennular peduncle vs. mostly reaches beyond antennular peduncle in N. denticulata ; larger number of poster orbital rostral teeth 2-4 (mode 3-4) vs. 1-2 in N. denticulata ; male first pleopod slender, 1.7 times as long as broad vs. 1.2 to 1.5 times in N. denticulata ; male first pleopod 0.6 times length of endopod (vs. only slightly shorter in N. denticulata ( Liang 2004: 78, fig. 40t); male second pleopod appendix masculina half-length of endopod vs. ca. 0.7 times in N. denticulata ( Liang 2004: 78, fig. 40u); Telson ending in a rounded margin (vs. ending in a posterior projection in N. denticulata ); dactylus of third pereiopod with 6-7 accessory spines on its flexor margin (vs. 8-10 in N. denticulata ).

With the slender endopod of the male first pleopod, the new species is similar to N. koreana Kubo, 1938 . It can be separated by the relatively shorter rostrum, which mostly reaches to or slightly beyond end of second segment of antennular peduncle vs. almost reaches to or slightly beyond antennular peduncle in N. koreana (cf. Kubo 1938); and the lower number of ventral rostral teeth (2-6 teeth, mode 2-4 vs. 4-6, average 5.6 in N. koreana (cf. Kubo 1938)).

Neocaridina ikiensis is morphologically similar to another Korean species N. keunbaei ( Kim, 1976) described from Jeju island. It can be differentiated from N. keunbaei by the rostrum, which is relatively long, mostly reaches to or slightly beyond end of second segment of antennular peduncle vs. reaches to end of basal segment or near to end of second segment of antennular peduncle in N. keunbaei (cf. Kim 1976); and the endopod of male first pleopod, which of N. keunbaei is “much larger than in the case of Caridina denticulata koreana ” ( Kim 1976: 160) . As mentioned earlier, the new species shares similar slender male first pleopod endopod with N. koreana .

With a relatively short rostrum, Neocaridina ikiensis n. sp. morphologically resembles two Taiwanese species N. saccam Shih & Cai, 2007 and N. ketagalan Shih & Cai, 2007 . It however can be easily separated from N. saccam (cf. Shih and Cai 2007) by having more postorbital rostral teeth, with 2-4 (mode 3-4) vs. 1- 3 (mode 2) in N. saccam ; carpus of first pereiopod slender (1.5- 1.6 times as long as high vs. 1.3-1.4 times in N. saccam ); male first pleopod slender, (1.7 times as long as broad vs. 1.4 times in N. saccam ); male first pleopod 0.6 times length of endopod (vs. 0.9 times in N. saccam ); male second pleopod appendix masculina half-length of endopod (vs. ca. 0.7 times in N. saccam ); and appendix interna of male second pleopod relatively longer (reaches to 0.8 length of appendix masculina vs. 0.6 times in N. saccam ). It differs from N. ketagalan (cf. Shih and Cai 2007) by male first pleopod slender, 1.7 times as long as broad (vs. 1.4 times in N. ketagalan ); male second pleopod appendix masculina half-length of endopod (vs. ca. 0.7 times in N. ketagalan ); and the appendix interna of male second pleopod relatively longer, reaching to 0.8 times length of appendix masculine (vs. 0.6 times in N. ketagalan ).

Figures

Fig. 2. Neocaridina ikiensis n. sp. (A) Cephalothorax and cephalic appendages, lateral view; (B) telson; (C) distal portion of telson; (D) preanal carina; (E) scaphocerite; (F) mandible; (G) maxillula; (H) maxilla; (I) 1st maxilliped; (J) 2nd maxilliped; (K) 3rd maxilliped. Scale bars: A-C = 2 mm; F-K = 0.3 mm; D = 1.5 mm; E = 4 mm (male, cl 4.6 mm, paratype, ZRC 2017.0960).

Fig. 3. Neocaridina ikiensis n. sp. (A) 1st pereiopod; (B) 2nd pereiopod; (C) 3rd pereiopod; (D) the same, dactylus; (E) 5th pereiopod; (F) the same, dactylus; (G, H) male 1st pleopod; (I, J) male 2nd pleopod; (K) uropodal diaeresis. Scale bars: A, B, C, E, G, I = 0.3 mm; D, F, H, J, K = 0.15 mm (male, cl 4.6 mm, paratype, ZRC 2017.0960).

Fig. 4. Neocaridina ikiensis n. sp. (A) Cephalothorax and cephalic appendages, lateral view; (B) 1st pereiopod; (C) 2nd pereiopod; (D) 3rd pereiopod; (E) the same, dactylus; (F) 5th pereiopod; (G) the same, dactylus. Scale bars: A = 2 mm; B-D, F = 0.3 mm; E, G = 0.15 mm (female, cl 5.1 mm, paratype, ZRC 2017.0961).

Fig. 5. Live coloration of Neocaridina ikiensis n. sp. (A) and its habitat in Iki Island (B).