IODP Proceedings    Volume contents     Search

doi:10.2204/iodp.proc.346.201.2017

Taxonomic notes

Class OSTRACODA Latreille, 1802

Subclass PODOCOPA Sars, 1866

Order PODOCOPIDA Sars, 1866

Suborder CYPRIDOCOPINA Jones, 1901

Superfamily PONTOCYPRIDOIDEA Müller, 1894

Family PONTOCYPRIDIDAE Müller, 1894

Genus ARGILLOECIA Sars, 1866

Argilloecia lunata Frydl, 1982

(Pl. P1, fig. 1)

Argilloecia lunata Frydl, 1982, p. 127, pl. 8, fig. 3–7; Paik and Lee, 1988, pl. 1, fig. 3; Ikeya and Suzuki, 1992, pl. 1, fig. 9; Tanaka, 2008, fig. 2, e; Ozawa, 2009, fig. 3, 3.

Remarks: This species occurs from the modern seafloor sediments in the Sea of Japan (e.g., Ikeya and Suzuki, 1992; Tsukawaki et al., 2000; Tanaka, 2008). Seven specimens are found at Site U1426.

Argilloecia toyamaensis Ishizaki and Irizuki, 1990

(Pl. P1, fig. 2)

Argilloecia toyamaensis Ishizaki and Irizuki, 1990, p. 63, pl. 1, fig. 1–6; Ozawa, 2003, fig. 7, 12; Ozawa, 2004, pl. 1–7; Ozawa et al., 2004, pl. 1, 2; Irizuki et al., 2007, fig. 5, 1; Ozawa and Tsukawaki, 2008, pl. 1, 2; Ozawa, 2010, pl. 1, 2; Alvarez Zarikian, 2016, pl. 1, 11a, 11b.

Remarks: This species is reported from the bottom sediments in water depth between 370 and 1153 m in the Toyama Bay (Ishizaki and Irizuki, 1990). The two specimens differ from the type-specimen in having a slightly less arched dorsal margin. This species is diagnostic for the Japan Sea Intermediate-Proper Water. It is found abundantly in the lower half of the water column (Ozawa, 2003).

Argilloecia sp.

(Pl. P1, fig. 3)

Remarks: The specimen has an oblong lateral shape and a moderate-rounded posterior margin. It resembles Argilloecia toyamaensis but differs from the latter species in having a more triangular lateral outline. Only one carapace was found.

Genus PROPONTOCYPRIS Sylvester-Bradley, 1946

Propontocypris uranipponica Ishizaki and Irizuki, 1990

(Pl. P1, fig. 4)

Propontocypris uranipponica Ishizaki and Irizuki, 1990, p. 62, pl. 1, fig. 7–12.

Remarks: This species is found in bottom sediments at water depths between 470 and 1265 m in the Toyama Bay (Ishizaki and Irizuki, 1990). It is an indicator of the lower half of the Japan Sea Intermediate-Proper Water mass (Ozawa, 2003). Six specimens were found at Site U1426.

Suborder CYTHEROCOPINA Sars, 1866

Superfamily CYTHEROIDEA Baird, 1850

Family CYTHERURIDAE Müller, 1894

Genus CYTHEROPTERON Sars, 1866

Cytheropteron cf. carolae Brouwers, 1994

(Pl. P1, fig. 5)

cf. Cytheropteron carolae Brouwers, 1994, p. 17, pl. 9, fig. 3, 4, pl. 10, fig. 12–14.

Cytheropteron carolae Brouwers, 1994; Irizuki et al., 2007, fig. 5, 11; Goto et al., 2014a, fig. 5, 8.

Cytheropteron sp., Ishizaki and Matoba, 1985, pl. 3, fig. 9, 10.

Cytheropteron sp. 3, Tabuki, 1986, p. 102, pl. 17, fig. 11, 12.

Cytheropteron sp. 2, Ozawa, 2010, pl. 1, 18.

Remarks: This species was originally described from the Gulf of Alaska (Brouwers, 1994) and reported from the Pliocene and Pleistocene strata exposed in the Sea of Japan coast (e.g., Tabuki, 1986; Irizuki et al., 2007; Ozawa, 2010). The specimens from Site U1426 sediments are slightly different from the type-specimen of C. carolae by having larger ovoid pits on the valve surface. The difference in the pit size might be caused by the thick calcified valve of the specimens.

Cytheropteron eremitum Hanai, 1959

(Pl. P1, fig. 6)

Cytheropteron rarum [sic] Hanai, 1959, p. 28, pl. 4, fig. 3.

Cytheropteron eremitum Hanai, 1959; Ishizaki and Matoba, 1985, pl. 3, fig. 5, 6.

Cytheropteron sp. D Alvarez Zarikian, 2016, pl. 1, fig. 5.

Remarks: This species was reported from the Pleistocene Sawane Formation in Sado Island, the eastern part of the Sea of Japan (Hanai, 1959), and the Wakimoto Formation in the Oga Peninsula, the northeastern part of the Japan Sea coast (Ishizaki and Matoba, 1985). Only juvenile specimens were found at Site U1426.

Cytheropteron cf. perlaria Hao in Ruan and Hao, 1988

(Pl. P1, fig. 7)

For comprehensive synonymy see Swanson and Ayress (1999), Stepanova (2006), and Yasuhara et al. (2009, 2014).

cf. Cytheropteron perlaria Hao in Ruan and Hao, 1988, p. 280, pl. 47, fig. 4–9.

Cytheropteron aff. perlaria Ruan and Hao, 1988; Swanson and Ayress, 1999, p. 155, pl. 7, fig. 1–6.

Cytheropteron carolae Brouwers, 1994; Ozawa and Kamiya, 2005, pl. 1, 6.

Cytheropteron testudo Sars, 1869; Zhao et al., 2000, p. 266, pl. 1, fig. 23, 24.

Remarks: The specimens are similar to Cytheropteron perlaria Ruan and Hao, 1988, in having a more triangular lateral outline and weaker alae. However, they have larger punctae than the types of C. perlaria. Swanson and Ayress (1999) recognized the intraspecific variations in size and number of punctation on the valve surface in Cytheropteron sarsi Swanson and Ayress (1999). Hence we consider that this characteristic difference in the surface ornamentation is an intraspecific variation.

Genus KOBAYASHIINA Hanai, 1957

Kobayashiina hyalinosa Hanai, 1957

(Pl. P1, fig. 8)

Kobayashiina hyalinosa Hanai, 1957, p. 30, pl. 4, fig. 5a, 5b; Ishizaki and Matoba, 1985, pl. 4, fig. 13; Irizuki et al., 2007, fig. 5, 12; Ozawa, 2010, pl. 3, 4.

Remarks: This species was originally described from the Pleistocene Sawane Formation, Sado Island in the Sea of Japan (Hanai, 1957). Only fragments of three specimens were found at Site U1426.

Family KRITHIDAE Mandelstam in Bubikyan, 1958

Genus KRITHE Brady, Crosskey, and Robertson, 1874

Krithe antisawanensis Ishizaki, 1966

(Pl. P1, fig. 9; Pl. P2, fig. 1)

Krithe antisawanense [sic] Ishizaki, 1966, p. 137, pl. 18, fig. 17, 24, 25; Zhou and Ikeya, 1992, p. 1111, fig. 9, 4, 5, fig. 10, 4; Irizuki et al., 2007, fig. 5, 2; Tanaka, 2009, p. 37, pl. 3, fig. 1, 2; Tanaka et al., 2012, p. 16, pl. 2, 3; Tanaka, 2016, p. 33, fig. 2A–2N.

Remarks: In the internal view (Pl. P2, fig. 1), the specimens exhibit elongate pore canals in the third of the anterior marginal pore canals and pocket-shaped anterior vestibula. These characteristics are in agreement with K. antisawanensis (Tanaka, 2016). This species was originally described from the Miocene Hatatate Formation, northeastern Japan (Ishizaki, 1966). It is found in the Pliocene–Pleistocene strata such as the Kuwae Formation (Irizuki et al., 2007). This species lives in the Sea of Japan, Suruga Bay (Zhou and Ikeya, 1992), and Toyama Bay (Ishizaki and Irizuki, 1990) around the Japanese Islands.

Krithe dolichodeira Van Den Bold, 1946

(Pl. P1, fig. 10; Pl. P2, fig. 2)

Krithe dolichodeira Van Den Bold, 1946, p. 75, pl. 4, fig. 14a, 14b; Coles et al., 1994, p. 81, pl. 1, fig. 13–18; Ayress et al., 1999, p. 6, fig. 3, G, H.

Parakrithe hemideclivata Ruan in Ruan and Hao, 1988, p. 272, pl. 45, fig. 12–15.

Krithe hemideclivata (Ruan and Hao, 1988), Whatley and Zhao, 1993, fig. 3, 9; Zhao and Whatley, 1997, fig. 5, 4; Irizuki et al., 2007, fig. 5, 3.

Remarks: According to Coles et al. (1994), this species has a large valve, the right valve is overlapped by the left valve, an elongate pore canal in the second of the antero-dorsal radial pore canals (type 2B in Coles et al., 1994), and a mushroom shaped anterior vestibulum (Zhao and Whatley, 1997). It was described from bottom sediments in the Okinawa Trough as Parakrithe hemideclivata (Ruan and Hao, 1988). Today this species occurs together with Krithe antisawanensis as dominant taxa in muddy substrate under water temperatures between 6° and 20°C in the East China Sea (Zhao and Whatley, 1997). In the Pliocene Kuwae Formation, both the species occur abundantly, indicating temperate intermediate water existence during the Pliocene (Irizuki et al., 2007).

Krithe reversa Van Den Bold, 1958

(Pl. P1, fig. 11, Pl. P2, fig. 3)

Krithe reversa Van Den Bold, 1958, p. 404, pl. 1, fig. 3–7; Coles et al., 1994, p. 77, pl. 1, fig. 1–6;

Krithe sawanensis Hanai, 1959, p. 301, pl. 18, fig. 3–7; Zhou and Ikeya, 1992, p. 1108, fig. 9, 1–3, fig. 10, 1–3; Ayress et al., 1999, p. 8, fig. 2F, 3O, 8M; Tanaka et al., 2012, p. 16, pl. 2, fig. 2.

Remarks: This species has an elongate pore canal in the third antero-dorsal radial pore canal and a pocket-shaped anterior vestibulum (Zhao et al., 2000). Further, it is characterized by the left valve overlapped by the right valve, that is the reversed valve overlap (Coles et al., 1994) to the other Krithe species. This species is characteristic of the lower half of the Japan Sea Intermediate-Proper Water mass (Ozawa, 2003). The specimens found have a slightly larger anterior vestibulum than K. reversa of Zhao et al. (2000).

Family LOXOCONCHIDAE Sars, 1925

Genus LOXOCONCHIDEA Bonaduce, Ciampo, and Masoli, 1975

Loxoconchidea dolgoiensis Brouwers, 1993

(Pl. P1, fig. 12)

Basslerites ? sp. Ishizaki and Matoba, 1985, pl. 2, fig. 2.

Loxoconchidea sp. Ishizaki and Irizuki, 1990, p. 64, pl. 1, fig. 14.

Loxoconchidea dolgoiensis Brouwers, 1993, p. 32, pl. 15, fig. 4–16; Irizuki et al., 2007, fig. 5, 13.

Remarks: This species occurs from the Gulf of Alaska (Brouwers, 1993), the Pliocene–Pleistocene strata in the Sea of Japan coast (e.g., Ishizaki and Matoba, 1985), and the modern sediments from the Toyama Bay (Ishizaki and Irizuki, 1990). Only juvenile specimens were obtained.

Genus PALMOCONCHA Swain and Gilby, 1974

Palmoconcha saboyamensis (Ishizaki, 1966)

(Pl. P1, fig. 13)

Loxoconcha saboyamensis, Ishizaki, 1966, p. 149, pl. 18, fig. 17, 24, 25.

Palmoconcha saboyamensis (Ishizaki, 1966); Irizuki et al., 2007, fig. 5, 14; Tanaka, 2009, p. 36, pl. 3, fig. 5, 6; Tanaka and Nomura, 2009, fig. 3, F.

Not Palmoconcha saboyamensis (Ishizaki, 1966); Ishizaki and Matoba, 1985, pl. 5, fig. 15.

Remarks: This species is found at water depth of 80–130 m in the Toyama Bay (Ishizaki and Irizuki, 1990). This species is an indicator of the lower half of the Japan Sea Intermediate-Proper Water mass (Ozawa, 2003). Only four specimens were obtained.

Palmoconcha sp.

(Pl. P1, fig. 14)

Palmoconcha saboyamensis (Ishizaki, 1966); Ishizaki and Matoba, 1985, pl. 5, fig. 15.

Remarks: This species resembles Palmoconcha saboyamensis in the lateral outline but differs from the latter in having smaller punctae and lacking blunt horizontal muri in the postero-central area. Only three specimens were obtained.

Family PECTOCYTHERIDAE Hanai, 1957

Genus MUNSEYELLA Van Den Bold, 1957

Munseyella oborozukiyo Yajima, 1982

(Pl. P1, fig. 15)

Munseyella oborozukiyo Yajima, 1982, p. 188, pl. 10, fig. 9, 12; Paik and Lee, 1988, pl. 1, fig. 8; Ikeya and Suzuki, 1992, pl. 6, fig. 8; Tanaka, 2008, fig. 2, f; Tanaka et al., 2012, p. 14, pl. 1, 12.

Remarks: This species was originally described from the Kioroshi Formation, in Boso Peninsula, the Pacific Ocean side of the central Japan (Yajima, 1982). It occurs from the modern bottom sediments in the Sea of Japan (Ikeya and Suzuki, 1992) and the Suruga Bay (Tanaka et al., 2012) as well as the Boso Peninsula.

Family TRACYLEBERIDIDAE Sylvester-Bradley, 1948

Genus ACANTHOCYTHEREIS Howe, 1963

Acanthocythereis dunelmensis (Norman, 1865)

(Pl. P1, fig. 16)

For comprehensive pre-2002 synonymy see Tanaka et al. (2002).

Acanthocythereis dunelmensis (Norman, 1865); Ozawa, 2003, fig. 7, 11; Irizuki et al., 2007, fig. 5, 6; Tanaka and Nomura, 2009, fig. 3, J; Ozawa and Domitsu, 2010, fig. 3, 1.

Remarks: This species is commonly found in continental shelf sediments in mid to high latitudes of the Northern Hemisphere such as the Bering Sea and Arctic Ocean (Gemery et al., 2015) as well as the Sea of Japan (Ozawa, 2003). The fossil specimens occur from the outcrops of the Pliocene and Pleistocene strata along the coast of the Japanese Island (e.g., Irizuki et al., 2007). This species occurs abundantly under the Japan Sea Intermediate-Proper Water (Ozawa, 2003).

Acanthocythereis tsurugasakensis Tabuki, 1986

(Pl. P1, fig. 17)

Acanthocythereis tsurugasakensis Tabuki, 1986, p. 85, pl. 11, fig. 2–10; Ozawa, 1996, pl. 1, 3; Tanaka et al., 2002, p. 13, fig. 8.5; Irizuki et al., 2007, fig. 5, 7; Tanaka and Nomura, 2009, fig. 3G; Ozawa and Domitsu, 2010, fig. 3.2.

Remarks: This species occurs from the Pliocene and Pleistocene sediments exposed in the Japan Sea coast. Most of the specimens are juveniles.

Acanthocythereis sp.

(Pl. P1, fig. 18)

Acanthocythereis? sp. 1 Ikeya and Suzuki, 1992, pl. 1, fig. 4.

Remarks: This species resembles Acanthocythereis dunelmensis but differs from the latter species in having a smaller valve, a more rounded posterior margin, more spines, and more developed reticulation on the valve surface. It occurs from the bottom sediments off Shimane in the Sea of Japan (Ikeya and Suzuki, 1992).

Genus FALSOBUNTONIA Malz, 1982

Falsobuntonia taiwanica Malz, 1982

(Pl. P1, fig. 19)

Ambocythere sp., Hu, 1978, p. 146, pl. 3, fig. 25.

Falsobuntonia taiwanica Malz, 1982, p. 392, pl. 8, fig. 51–56; Ishizaki and Matoba, 1985, pl. 3, fig. 11, 12; Huh and Paik, 1992b, pl. 2, fig. 15; Huh and Paik, 1992a, pl. 2, fig. 15; Ikeya and Suzuki, 1992, pl. 4, fig. 8, 9; Kamiya et al., 1996, pl. 3, fig. 1; Ozawa, 1996, pl. 4, 7; Irizuki et al., 1998, fig. 6, 9; Kamiya et al., 2001, fig. 15, 10; Irizuki et al., 2001, fig. 7, 16; Tanaka et al., 2002, p. 18, fig. 9, 5; Hu and Tao, 2008, p. 329, pl. 28, fig. 12; Tanaka et al., 2012, p. 17, pl. 3, 13.

Remarks: This species was first reported from the Pliocene and Pleistocene strata in the southwest Taiwan (Malz, 1982). It was widely reported from the strata around the Japanese Islands (e.g., Tanaka et al., 2002; Irizuki et al., 2007) and southwest Taiwan (Hu, 1978; Hu and Tao, 2008). It abounds at water depth of >150 m off Shimane, southwestern Japan (Ikeya and Suzuki, 1992).

Genus HIRSUTOCYTHERE Howe, 1951

Hirsutocythere? hanaii Ishizaki, 1981

(Pl. P1, fig. 20)

Hirsutocythere ? hanaii Ishizaki, 1981, p. 46, pl. 9, fig. 4a, 4b, 5a, 5b, 6a, 6b, 7; Ozawa, 1996, pl. 5, 6; Irizuki et al., 1998, fig. 6, 7; Irizuki et al., 2001, fig. 7, 15; Nakao et al., 2001, fig. 11, 13; Ozawa, 2003, fig. 7, 9; Tanaka, 2008, fig. 2r; Ozawa, 2009, fig. 4, 1.

Hirsutocythere hanaii Ishizaki, 1981; Paik and Lee, 1988, pl. 2, fig. 17; Kamiya et al., 1996, pl. 4, fig. 9; Tanaka and Seto, 2010, p. 12, pl. 3, fig. 3; Tanaka et al., 2012, p. 29, pl. 3, 11.

Remarks: This species was first described from modern seafloor sediments in the East China Sea (Ishizaki, 1981). It is widely distributed in Miocene, Pliocene, and Pleistocene strata in Japan within the Naganuma Formation (Ozawa, 2009), Omma Formation (Ozawa, 1996), and Kobana Formation (Irizuki et al., 1998). This species is included in the assemblages that live in the Tsushima Warm Current Core water (Ozawa, 2003). It is also dominant at water depths of ~135 m in the outer sublittoral zone in the southwest part of the Sea of Japan (Tanaka, 2008). From the samples at Site U1426, eight juvenile valves were obtained.

Genus ROBERTSONITES Swain, 1963

Robertsonites hanaii Tabuki, 1986

(Pl. P1, fig. 21)

Robertsonites hanaii Tabuki, 1986, p. 90, pl. 13, fig. 1–12; Cronin and Ikeya, 1987, p. 84, pl. 2, fig. 11; Irizuki, 1994, pl. 2, fig. 7; Ozawa, 1996, pl. 8, 5; Yamada, 2003, p. 171, pl. 1, fig. 1, 2; Ozawa, 2004, pl. 1, 4; Ozawa et al., 2004, pl. 2, 20.; Tanaka et al., 2012, p. 18, pl. 3, fig. 17.

Remarks: This species was originally described from the Pleistocene Daishaka Formation, northeastern Japan (Tabuki, 1986) and is found abundantly in the Pliocene and Pleistocene strata along the Sea of Japan coast of the Japanese Islands. It is also reported from the modern bottom sediments under the upper half of the Japan Sea Intermediate-Proper Water (Ozawa, 2003). Only juvenile valves were identified.

Robertsonites tabukii Yamada, 2003

(Pl. P1, fig. 22)

Buntonia ? sp., Ishizaki and Matoba, 1985, pl. 2, fig. 6.

Robertsonites reticuliforma Ishizaki, 1966: Tabuki, 1986, p. 91, pl. 14, fig. 1–12; Cronin and Ikeya, 1987, p. 84, pl. 2, fig. 15; Irizuki, 1994, fig. 5–6; Irizuki, 1996, fig. 7, 3, 4.

Robertsonites tabukii, Yamada, 2003, p. 176, pl. 2, fig. 3–19; Irizuki et al., 2007, fig. 5, 10; Ishida et al., 2012, fig. 3, 16; Goto et al., 2014a, fig. 5, 18.

Remarks: Previously, the specimens of this species from the Pliocene and Pleistocene strata in the Sea of Japan were misidentified as Robertsonites reticuliformus, that was described from the Miocene strata in the northern part of Japan (Ishizaki, 1966). However, this species differs significantly from R. reticuliformus by its distinct murus below the eye tubercle extending into the ventral ridge at the anterior quarter of valve length. Tanaka (2009) displays scanning electron microscope (SEM) images of the types of R. reticuliformus, allowing us to distinguish these two species clearly. This species is one of the dominant species in the upper Pliocene Kuwae Formation (Yamada et al., 2005; Irizuki et al., 2007).