Semicytherura mukaishimensis, Yamada, Shinnosuke & Tanaka, Hayato, 2013

Yamada, Shinnosuke & Tanaka, Hayato, 2013, Two interstitial species of the genus Semicytherura (Crustacea: Ostracoda) from Japan, with notes on their microhabitats, Zootaxa 3745 (4), pp. 435-448 : 444-447

Semicytherura mukaishimensis Okubo, 1980

( Figs 9−11 )

1980 Semicytherura mukaishimensis sp. nov. – Okubo: 24-26, figs. 3h −k, 10.

1982 Semicytherura elongata Ikeya & Hanai : 51, pl. 5, figs. 4, 5.

1985 Semicytherura elongata Ikeya & Hanai : Ikeya et al., 27, pl. 6, figs. 7, 10. 1988 Semicytherura miurensis (Hanai, 1957) : Yajima, 1076-1077, pl. 1, fig. 11. 1992 Semicytherura enshuensis Ikeya & Hanai, 1982 : Ikeya and Suzuki, 134-135, pl. 8, fig. 9. 1998 Semicytherura miurensis (Hanai, 1957) : Yamane, 56-57, pl. 11, fig. 3.

Type series. Holotype: adult male (MO-561), left valve length 0.44 mm, height 0.18 mm, right valve length 0.44 mm, height 0.18 mm. Allotype: adult female (MO-869), left valve length 0.42 mm, height 0.18 mm, right valve length 0.42 mm, height 0.19 mm. Paratype: adult male (MO-564) left valve length 0.42 mm, height 0.18 mm, right valve length 0.42 mm, height 0.18 mm. One adult male (MO-562) and three adult females (MO-563, 571, 573) also examined in Okubo (1980). Light microscopic photographs and illustrations of type specimens (valves and appendages) shown in figures 3 and 10 of Okubo (1980).

Additional specimens, six adult males (SUM-CO-2125, 2126, 2129, 2131, 2133, 2134) and four adult females (SUM-CO-2127, 2128, 2130, 2132).

Type locality. Sand banks near Mukaishima Marine Biological Station, Hiroshima Prefecture (34°21'07"N, 133°13'02"E).

Occurrence. All specimens analysed in this study were collected from Araihama, Kanagawa Prefecture (35°15'85"N, 139°61'10"E) on July 7th 2012. Adult specimens were found abundantly with juvenile specimens from interstitial pore water of marine sediments.

Dimensions. See Table 3 .

Length (µm) Height (µm) Width (µm) Diagnosis. Carapace oblong or sub-trapezoidal in lateral view. Short blunt caudal process situated at lower part of carapace. Carapace surface covered with fine reticulations and small puncta. Prominent ridge running from middle part of anterior margin, descending in posterior direction, and forming rounded ala in posteroventral part.

Sixty-one pore systems per valve. Inside valve, lamella of prismatic layer (LPL) well developed in both male and female. Male copulatory organ bearing oval basal capsule and thick oblong distal lobe. One long clasping apparatus with blunt top. Copulatory duct long, coiled.

Description. Carapace outline and ornamentations ( Figs 9 , 10 ). Carapace small and thin, oblong or subtrapezoidal in lateral view ( Fig. 9 A, B, E, F). Carapace oval in dorsal and ventral views ( Fig. 10 A, B, C, D). Male carapace more elongate than female. Dorsal margin nearly straight and running in parallel to ventral margin. Short blunt caudal process situated at lower part of carapace. Fine reticulations and small puncta developed on carapace surface. Prominent ridge running from middle part of anterior margin, descending in posterior direction, and forming rounded ala in posteroventral part. Eye tubercle absent.

Hingement ( Fig. 10 G, H). Almost straight. Terminal sockets and smooth bar in left valve. Terminal teeth and groove in right valve.

Muscle scars ( Fig. 10 F). Vertical row of four adductor scars in ventromedian area. Upper three scars elongated, lowest scar sub-triangular. Two frontal scars and sub-tetragonal fulcral point situated in front of adductor muscle scars. Two unclear mandibular scars on LPL.

Lamella of prismatic layer ( Fig. 9 C, D, G, H). Broad in both anterior and posterior portions; slightly narrower in female.

Pore systems ( Fig. 11 ). Sixty-one pore systems per valve ( Fig. 11 ). Long marginal pore canals running in both anterior and posterior portions (see fig. 10 in Okubo, 1980).

Appendages. See Okubo (1980). Morphological characters of appendages in agreement with the type series and the specimens of this paper. Male copulatory organ used for identification ( Fig. 10 E).

Remarks. Semicytherura mukaishimensis Okubo, 1980 lives interstitially in the infralittoral zone of the marine beach with other interstitial ostracods ( Table 2). Carapace outline and ornamentations of this species resemble those of S. miurensis (Hanai, 1957) , but a prominent ala is noticeable in S. mukaishimensis . In addition, a caudal process is situated at the lower part of the carapace in S. mukaishimensis , while in S. miurensis it is present at the middle.

Figures

FIGURE 9. SEM photographs of Semicytherura mukaishimensis Okubo, 1980. A, external view of male left valve; B, external view of male right valve; C, internal view of male left valve; D, internal view of male right valve; E, external view of female left valve; F, external view of female right valve; G, internal view of female left valve; H, internal view of female right valve. A and B, SUM-CO- 2125; C and D, SUM-CO- 2126; E and F, SUM-CO- 2127; G and H, SUM-CO- 2128.

FIGURE 10. SEM photographs of Semicytherura mukaishimensis Okubo, 1980. A, dorsal view of male carapace; B, dorsal view of female carapace; C, ventral view of male carapace; D, ventral view of female carapace; E, male copulatory organ; F, muscle scars of male right valve; G, hingement of male left valve; H, hingement of male right valve. A, SUM-CO- 2129; B, SUM-CO- 2130; C, SUM-CO- 2131; D, SUM-CO- 2132; E, SUM-CO- 2133; F, G and H, SUM-CO- 2134. Arrowheads indicate mandibular scars. White and black arrows show the frontal scars and the fulcral point, respectively.

FIGURE 11. Distribution of pore systems in Semicytherura mukaishimensis Okubo, 1980. A, external view of male left valve; B, ventral view of male left valve. Solid circles indicate the positions of pore systems and open circles indicate overlapping pore systems from the lateral view. Grey ovals show the sites of muscle scars internally.

Tables

TABLE 3. Dimensions of Semicytherura mukaishimensis Okubo, 1980 from Araihama.

	Mean Observed range N	Mean Observed range N	Mean	Observed range N
Male	Right valve 0.44 0.43–0.45 5 Left valve 0.43 0.42–0.44 5	0.18 0.18–0.19 5 0.18 0.17–0.18 5	0.20 –	0.20 2 – –
Female	Right valve 0.40 0.40–0.41 2 Left valve 0.40 0.40 2	0.18 0.18–0.19 2 0.18 0.18 2	0.21 –	0.21–0.22 2 – –