Semicytherura kiosti Joest & Karanovic, 2022

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 kiosti Joest & Karanovic sp. nov.

Figs 8 , 9 , 10 , 11 , 12

Note.

NIBR deposition number: DSEVIV0000003716.

Synonymy.

Hemicytherura sp. 3 sensu Ikeya and Itoh 1991: pg. 138, fig. 17A.

Etymology.

After the collaborating institution, Korea Institute of Ocean Science and Technology (KIOST), who provided the samples and funding for the MarineGEO project in Korea.

Diagnosis.

Sub-rectangular lateral outline (especially LV), as typical for species of the S. henryhowei group. Anteroventral margin with three crenulations (denticles). Carapace surface roughly pitted with finer, smaller pits at marginal areas. Dorsal margin straight, horizontal. Broadly acute caudal process above mid-height. Ventral margin straight, horizontal, but posterior half obscured by ventral ridge. Thick, prominent ridges on carapace, as typical for the Semicytherura henryhowei group. Prominent posterior subvertical ridge forming large, subtriangular fossa in posterior half of valve. Prominent, horizontal, straight anterior longitudinal ridge forming large, subtrapezoid fossa with dorsal half of anterior subvertical ridge.

Holotypes.

Two valves: adult male left valve, # 109_1 (lost, only SEM) and right valve, # 109_2 from ARMS sediment (i.e., surface and sedimentation-derived sediments).

Paratypes.

Five valves: # 68 (female ARV) and # 108 (male ARV) from ARMS sediment (i.e., surface and sedimentation-derived sediments), and # 177 (female A-1RV), # 239 (female A-2RV), # 240 (female ARV) from scoop sediment (i.e., surface sediment).

Type deposition.

Specimens are deposited at the National Institute of Biological Studies (NIBR, Incheon, South Korea) under the deposition number DSEVIV0000003716.

Type 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; valves only, no soft bodies).

Description.

Heavily calcified, thick valve, sub-rectangular (LV) to ovoid (RV) in lateral view. Right valve larger than left valve (see Fig. 8 , length/height plot, # 109_1 and # 109_2). Maximum height at anterodorsal corner. Dorsal margin is horizontal, straight, parallel to ventral margin. Ventral margin is obscured by overhanging ventral ridge at posterior half. Anterodorsal margin is smooth, obliquely rounded; antero-ventral margin with three small, acute marginal denticles; posterior margin is ascending in a straight line above the caudal process. Broadly acute posterior caudal process above mid-carapace.

The carapace surface is covered in rough pits, and pores with sensory hairs. Finer, smaller pits at marginal areas. Valve with thick ridges; anterior sublongitudinal ridge short, horizontal, straight line, terminating at anterior third of valve length; prominent posterior subvertical ridge connecting posterodorsal corner with ventral ridge at mid-length of valve; posterior ridge branching off posterodorsal corner and running in a straight, vertical manner to posterior corner; posterior subvertical ridge, posterior ridge and posterior half of ventral ridge form large, subtriangular fossa; anterior longitudinal ridge, dorsal half of anterior subvertical ridge, and anterodorsal margin form large, subtrapezoid fossa. Right valves slightly higher and longer than left valves. Females longer and slightly higher than males (see length/height plot, Fig. 8 ).

Reticulation. Surface covered in large pits with prominent, species-specific ridge system.

Pores. Some simple pores with sensory hairs.

Hingement. Merodont hinge with a socket at each end of a ridge structure in the right valve (Figs 9A, C , 10B, F, I ). Complementary negative structures in the left valve (tooth at each end of a groove) (no SEM). Typical for genus. Hingeline arched.

Adductor muscle scars. Vertical row of 4 adductor scars in ventro-median area (Fig. 9 ). Uppermost and lowermost scar less elongate in comparison with the middle two scars. At least 8 dorsal scars in upper half of valve (Fig. 11B ). 2 mandibular scars slightly below, in front of adductor scars (Fig. 11F , blue arrows). 2 frontal scars in front of two uppermost adductor scars (Fig. 11F , white arrows).

Recurved inner. Strongly recurved in male adult (#109_2); absent in female adult (#240); not developed at juvenile stages (# 239) yet (Fig. 12 ).

Dimensions.

Carapace dimensions of holotype: female ARV (# 240): length: 0.330 mm, height: 0.197 mm. Carapace dimensions of paratypes: female ARV: (# 68): length: 0.329 mm, height: posterior margin obscured by glue, ~ 0.196? mm; male ALV (# 109_1): length: 0.306 mm, height: 0.162 mm; male ARV (# 109_2): length: 0.308, height: 0.182 mm; male ARV (# 108): length: 0.310 mm, height: 0.185 mm; female A-2RV (# 239): length: 0.262 mm, height: 0.153 mm; female A-1RV (#177): length: 0.291 mm, height: 0.175 mm (Fig. 8 ).

Occurrence.

Extant sediments, Korea (Jeju Island; surface and sedimentation-derived sediments collected 2019) and Japan (Sendai Bay, Matsushima Bay, Pacific Ocean; surface sediments collected 1985, 1986, 1988).

Remarks.

The present species is characterized by a short, straight, horizontal anterior longitudinal ridge (Fig. 4B , AA). Of all known members of the Semicytherura henryhowei group, Semicytherura kiosti shares this trait only with S. leptosubundata (Fig. 4G ) and S. neosubundata (Fig. 4Y ). Morphological distinction between the three species based on prominent ridge patterns is straightforward. Semicytherura kiosti has an obvious anterior subvertical ridge, which is lacking in the other two species. Hemicytherura sp. 3 sensu Ikeya and Itoh 1991 is identical to our specimens of S. kiosti (fig. 17A in Ikeya and Itoh 1991). Hemicytherura Elofson, 1941 can easily be differentiated from the other members of the Semicytherura henryhowei group by the carapace surface features. Species of Hemicytherura , do exhibit something like ridges, but these do not resemble the characteristic ridge system of thick carinae of the S. henryhowei group. Rather, Hemicytherura is categorized by the characteristic fossa reticulation units that form around pores ( Tanaka et al. 2011). Species of the S. henryhowei complex also show a less coarsely pitted surface ornamentation when compared to the Hemicytherura species.

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 4. Illustrated guide of major ridge systems of the Semicytherura henryhowei species complex. A. Semicytherura kiosti sp. nov. Joest and Karanovic male ARV; based on 109 _ 2 herein; B. Semicytherura kiosti sp. nov. Joest and Karanovic male ALV; based on 109 _ 1 herein; C. Semicytherura robustundata Ozawa & Kamiya, 2008 ARV; based on Ozawa and Kamiya 2008; D. Semicytherura slipperi Yamada, Tsukagoshi & Ikeya, 2005 ALV; based on Yamada et al. 2005; E. Semicytherura subslipperi Ozawa & Kamiya, 2008 ARV; based on Ozawa and Kamiya 2008; F. Semicytherura henryhowei Hanai, 1977 ALV; based on Yamada et al. 2005; G. Semicytherura leptosubundata Ozawa & Kamiya ARV; based on Ozawa and Kamiya 2008; H. Semicytherura kazahana Yamada, Tsukagoshi & Ikeya, 2005 ALV; based on Yamada et al. 2005; I. Semicytherura subundata (Hanai, 1957) ARV; based on Ozawa and Kamiya 2008; J. Semicytherura sasameyuki Yamada, Tsukagoshi & Ikeya, 2005 ALV; based on Yamada et al. 2005; K. Semicytherura tanimurai Ozawa & Kamiya, 2008 ALV; based on Ozawa and Kamiya 2008; L. Semicytherura undata (Sars, 1865) ARV; based on Cronin and Ikeya 1987; M. Semicytherura maxima Yamada & Tsukagoshi, 2010 ARV; based on Yamada and Tsukagoshi 2010; N. Semicytherura ikeyai Yamada & Tsukagoshi, 2010 ARV; based on Yamada and Tsukagoshi 2010; O. Semicytherura sp. nov. sensu Irizuki 1994 (S. sp. 4) ALV; based on Irizuki 1994; P. Semicytherura balrogi Brouwers, 1994 ARV; based on Brouwers 1994; Q. Semicytherura sp. nov. sensu Irizuki 1994 (S. sp. 5) ALV; based on Irizuki, 1994; R. Semicytherura sp. nov. sensu Cronin and Ikeya 1987 (S. sp. A) ARV; based on Cronin and Ikeya 1987; S. Semicytherura sp. nov. sensu Cronin 1989 (S. sp. cf. Semicytherura henryhowei) ALV; based on Cronin 1989; T. Semicytherura sp. nov. sensu Irizuki 1994 (S. sp. 2) ARV; based on Irizuki 1994; U. Semicytherura simplex (Brady & Norman, 1889) ALV; based on Hu 1978; V. Semicytherura sp. nov. sensu Ozawa et al. 2008 (S. sp. 1) ARV; based on Ozawa et al. 2008; W. Semicytherura pseudoundata Irizuki & Yamada, 2004 ALV; based on Irizuki et al. 2004; X. Semicytherura sp. nov. sensu Ozawa et al. 2008 (S. sp. 2) ARV; based on Ozawa et al. 2008; Y. Semicytherura neosubundata (Ishizaki, 1966) ALV; based on Ishizaki 1966; Z. Semicytherura sp. nov. sensu Irizuki 1994 (S. sp. aff. Semicytherura henryhowei) ARV; based on Irizuki 1994; AA. Semicytherura kaburagawensis Tanaka, 2013 RV; based on Tanaka and Hasegawa 2013; AB. Semicytherura sp. nov. sensu Irizuki 1994 (S. sp. 1) ALV; based on Irizuki 1994; AC. Semicytherura usuigawensis Tanaka, 2013 RV; based on Tanaka and Hasegawa 2013; AD. Semicytherura quadraplana Allison & Holden, 1971 ALV; based on the original drawing in Allison and Holden 1971. Red arrows indicate whether anterior sublongitudinal ridge is horizontal or sloped; red numbers indicate the anteroventral marginal denticles.

Figure 8. Length / height plot of Semicytherura kiosti sp. nov. Joest & Karanovic. Circles indicate female, squares indicate males. Adult valves depicted in red, juveniles in blue: light blue: A- 1 stage, dark blue: A- 2 stage; LV indicates left valve, RV indicates right valve.

Figure 9. Line drawings of Semicytherura kiosti sp. nov. Joest & Karanovic internal view with details on muscle imprints. A, B. Specimen 239 juvenile (A- 2, female) RV lateral internal view; C, D. Specimen 240 female ARV lateral internal view. A. Lateral internal view of RV; B. Adductor muscle scar cluster in bold, one of two mandibular muscle scars depicted as dotted line; C. Lateral internal view of RV; D. Adductor muscle scar cluster in bold, two mandibular muscle scars depicted as dotted line. Dotted line indicates frontal, mandibular, and dorsal muscle scars; bold line indicates adductor muscle scars; females lacking strongly recurved inner lamella as observed in adult male. Arrow indicates anterior direction. Grey shaded shapes indicate dirt covering muscle scars. Scale bars: 50 µm.

Figure 10. Semicytherura kiosti sp. nov. Joest & Karanovic external and internal lateral views. A-C. Specimen 109 adult male; A, B. 109 _ 2 RV; A. lateral external view; B. lateral internal view; C. 109 _ 1 LV, lateral external view; D. Specimen 108 male ARV, lateral external view; E, F. Specimen 239 female A- 2 RV; E. lateral external view; F. lateral internal view; G. Specimen 68 female ARV, lateral external view; H. Specimen 240 female ARV, lateral external view; I. Specimen 177 female A- 1 RV, lateral external view. Scale bar: 100 µm.

Figure 11. Semicytherura kiosti sp. nov. Joest & Karanovic muscle scar details. A-C. Specimen 239 female A- 2 RV lateral internal view; D-F. Specimen 240 female ARV lateral internal view. Red arrows indicate adductor muscle scars; yellow arrows indicate dorsal muscle scars; blue arrows indicate mandibular muscle scars; white arrows indicate frontal muscle scars. Not all muscle scars simultaneously visible in both specimens. 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.