Semicytherura kazahana Yamada, Tsukagoshi & Ikeya, 2005

Joest, Anna B., Kim, Taihun, Yang, Hyun-Sung, Kang, Do-Hyung & Karanovic, Ivana, 2022, Revision of the Semicytherura henryhowei group (Crustacea, Ostracoda) with the new records from Korea, Fossil Record 25 (2), pp. 307-330 : 307

Semicytherura kazahana Yamada, Tsukagoshi & Ikeya, 2005

Fig. 7

Note.

First published record of the species from Korean waters. NIBR deposition number: DSEVIV0000003720.

Synonymy.

( Semicytherura henryhowei sensu Yajima 1988: pg. 1076, pl. 1, fig. 12); (This specimen is either S. kazahana or S. sasameyuki , see Discussion). Semicytherura quadrata sensu Ishizaki 1968: pg. 20, pl. 4, figs 11, 12. Semicytherura sp. B sensu Lee 1990 (unpublished): pl. 27, figs 12, 13. Semicytherura sp. 1 sensu Yasuhara and Irizuki 2001: pg. 93, pl. 11, fig. 8. Semicytherura kazahana Yamada, Tsukagoshi & Ikeya, 2005: pgs 247, 253, 254, figs 2C, 6, 7.

Diagnosis.

Juvenile. Sub-rectangular to sub-trapezoid lateral outline, as typical for species of the S. henryhowei group. Anteroventral margin here without crenulations [there are records of specimens showing four or five anteroventral marginal denticles; see Yamada et al. (2005)]. Carapace surface finely pitted. Dorsal margin weakly descending toward posterior. Acute caudal process at mid-height. Ventral margin weakly descending toward anterior. Thick, prominent ridges on carapace, as typical for the S. henryhowei group.

Anterior longitudinal ridge short, slightly ascending in straight line until posterior end of anterior one-third of valve length. Prominent, continuous ventral ridge running horizontally in antero-posterior direction, curving at posterior third of valve length. Two elliptical fossae in anterior half; sub-trapezoid fossa in posterior half.

Material.

Juvenile, right valve # 70, from ARMS sediment (i.e., surface and sedimentation-derived sediments).

Locality and age.

Seongsan (성산), Jeju Island, ROK (33°27'13"N, 126°56'45"E) (Fig. 2 ), 19 m water depth. Extant (collection date 2019; surface and sedimentation-derived sediments, valve only, no soft body).

Description.

Heavily calcified, thick valve, sub-rectangular in lateral view. Maximum height at anterior third. Dorsal margin is weakly ascending towards posterior. Ventral margin is weakly descending towards posterior. Anterodorsal margin is smooth, obliquely rounded; anteroventral margin without visible marginal denticles, but partially broken; posterior margin is slightly curved above the caudal process. Acute posterior caudal process at mid-carapace.

The carapace surface is covered in fine pits and pores with sensory hairs. Valve with thick ridges; ventral ridge prominent; slightly ascending toward posterior third; then describing a steep drop toward the edge of the ventral margin and ascending again in a straight line toward the posterior margin, resembling the lower loop of a large S-shape; the upper loop of the S-shape is the thick posterior end of the dorsal ridge at the posterodorsal corner; interconnection between posterodorsal and posteroventral loops by a thin descending posterior subvertical ridge, completing the S-shape; anterior longitudinal ridge short; starting at mid-height from anterior margin, slightly ascending until terminating at posterior end of anterior third of valve length; dorsal half of anterior subvertical ridge steeply running upward and bending backward to anterodorsal corner, forming elliptical, anterodorsal fossa; ventral half of anterior subvertical ridge less prominent, zig-zag course, connecting to ventral ridge at mid-length of carapace, forming elliptical, anteroventral fossa.

Reticulation. Surface finely pitted (Fig. 7D, E ) with prominent, species-specific ridge system.

Pores. Some simple pores with sensory hairs (Fig. 7D ).

Hingement. Merodont hinge with a socket at each end of a ridge structure in the right valve (Fig. 7C ) [not collected, but complementary negative structures in the left valve (tooth at each end of a groove)]. Typical for genus. Hingeline arched.

Adductor muscle scars. Not observed.

Recurved inner. Absent in juveniles [see e.g., S. subundata in Ozawa and Kamiya (2008), pg. 143, fig. 4; S. kiosti Jöst & Karanovic sp. nov., Fig. 12 herein].

Dimensions.

Carapace dimensions: length: 0.3064 mm, height: 0.166 mm.

Occurrence.

Extant sediments, Korea (this study; surface and sedimentation-derived sediments collected 2019), and Japan ( Yamada et al. 2005; living specimens, surface sediment collection: 1977-2000); Pleistocene sediments, Korea (Lee, 1990; unpublished); (potentially) Miocene sediments, Japan ( Yajima 1988) (after species re-assignment, this study; uncertain whether S. kazahana or S. sasameyuki , see Discussion).

Remarks.

Our specimen greatly resembles the juvenile specimen of Semicytherura sp. 1 sensu Yasuhara and Irizuki 2001 (pg. 93, pl. 11, fig. 8), which was assigned to S. kazahana herein. The specimen of Yasuhara and Irizuki displays small, rounded anterior marginal denticals, which are absent in our specimen. However, S. kazahana has shown to display differing numbers of crenulations along its anterior margin ( Yamada et al. 2005).

Figures

Figure 2. Map of sampling location. A. Overview of Korea including adjacent countries and seas; B. Overview of Jeju Island with sampling location in yellow. Yellow star denotes the deployment site of the ARMS; red location pin icon points at the location of the Korea Institute of Ocean Science and Technology (KIOST) on Jeju Island; grey shades denote land masses, blue denotes seas. Coordinates given in decimal degrees.

Figure 7. Semicytherura kazahana external and internal lateral views. A-E. Specimen 70 A- 1 RV; A-B, D-E. Lateral external view; D. Details of pore with sensory hair and pitted carapace surface; E. Details d anterior subvertical ridge; C. Lateral internal view. Scale bars: 50 µm.

Figure 12. Semicytherura kiosti sp. nov. Joest & Karanovic internal view details, recurved inner lamella. A. Male adult right valve ( 109 _ 2) depicting strongly recurved inner lamella (white arrow); B. Female juvenile right valve ( 239) lacking recurved inner lamella; C. Female adult right valve ( 240) lacking recurved inner lamella.