SETHOPERIDAE Haeckel, 1882

Family SETHOPERIDAE Haeckel, 1882 sensu Suzuki emend. herein

Sethoperida Haeckel, 1882: 433 [as a tribe]; 1887: 1192, 1194, 1232 [as a subfamily].

Archicorida Haeckel, 1882: 427 [nomen dubium, as a tribe]; 1887: 1133, 1179, 1180 [as a subfamily]. — Wisniowski 1889: 687.

Callimitrida Haeckel, 1882: 431 [below tribe].

Sethophatnida Haeckel, 1882: 433 [as a tribe].

Sethophaenida – Haeckel 1887: 1192, 1242, 1285 [nomen dubium, as a subfamily].

Tripocyrtida Haeckel, 1887: 1192-1194 [as a family]. — Bütschli 1889: 1986 [as a family]. — nec Rüst 1892: 181 [as a family]. — nec Cayeux 1894: 212.

Tripocyrtidae – Haecker 1908: 448. — Popofsky 1908: 274; 1913: 333. — Schröder 1914: 100. — Wailes 1937: 13. — Clark & Camp- bell 1942: 65; 1945: 37. — Campbell & Clark 1944a: 41; 1944b: 23. — Chediya 1959: 199. — Tan & Tchang 1976: 274. — Tan & Su 1982: 169; 2003: 113. — Chen & Tan 1996: 153. — Tan & Chen 1999: 296. — Chen et al. 2017: 182.

Sethoperinae – Haecker 1908: 448-451. — Campbell 1954: D124. — Chediya 1959: 203. — Petrushevskaya 1971a: 76-80; 1971b: 989-990 (sensu emend.); 1981: 295. — Tan & Tchang 1976: 279. — Afanasieva et al. 2005: S293. — Afanasieva & Amon 2006: 140. — Chen et al. 2017: 198.

Archicorinae – Clark & Campbell 1942: 65 [nomen dubium]; 1945: 35. — Campbell & Clark 1944a: 40; 1944b: 22. — Chediya 1959: 196.

Sethoperidae – Petrushevskaya & Kozlova 1972: 535 (sensu emend.); Petrushevskaya 1975: 589; 1981: 291-295. — Dumitrica 1979: 30. — Takahashi 1991: 98. — De Wever et al. 2001: 236, 238. — Afanasieva et al. 2005: S293. — Afanasieva & Amon 2006: 140.

Tripocyrtididae – Poche 1913: 220.

Sethophatninae – Campbell 1954: D128 [nomen dubium].

Sethophaeninae – Chediya 1959: 208 [nomen dubium].

Sethophatnidae – Loeblich & Tappan 1961: 228 [nomen dubium].

TYPE GENUS. — Sethopera Haeckel, 1882: 433 [type species by subsequent designation (Campbell 1954: D124): Sethopera tricostata Haeckel, 1887: 1232] = junior subjective synonym of Clathrocanium Ehrenberg, 1861b: 829 [type species by subsequent designation (Campbell 1954: D122): Clathrocanium squarrosum Ehrenberg, 1873a: 303].

INCLUDED GENERA. — Callimitra Haeckel, 1882: 431 (= Arachnothauma n. syn.). — Clathrocanium Ehrenberg, 1861b: 829 (= Clathrocanidium with the same type species; Arachnopilium, Clathrocorona, Clathrolychnus synonymized byPetrushevskaya 1971a: 80; Tripocyrtis synonymized by Petrushevskaya 1981: 300; Sethopera n. syn.). — Clathrocorys Haeckel, 1882: 431. — Dictyocodoma Haeckel, 1887: 1335. — Dictyocodon Haeckel, 1882: 435 (= Dictyocodella with the same type species). — Pteropilium Haeckel, 1882: 435 (= Clathropilium with the same type species).

INVALID NAME. — Sethophaena.

NOMINA DUBIA. — Archibursa, Archicorys, Sethophatna.

DIAGNOSIS. — Sethoperidae consist of a one- to two- segmented, rounded pyramidal shell with one long apical horn and three long feet (or wings). The cephalis is latticed. A wired screen develops between the apical horn and each of the feet, (or wings) and/or between the feet (or wings) and thorax. The thorax varies from a three-sided, rounded pyramid to a basket-like from. The cephalic initial spicular system consists of MB, A-, V-, D-, and the double-L rods. Double l-rod absent. The basal ring is directly connected to the D- and double L-rods forming three collar pores. Several arches develop freely in the cephalic cavity, or are attached on the inner side of the cephalic wall. However, but these do not form sutures on the cephalic wall. The combination and connecting ends of the arches such as AD-arch, ap -arch (one of AL-arch), ac -arch (one of AD-arch) and pj -arch (one of VL-arch) are variable. A straight double a -spinule extends laterally as a part of the ap -arch, a second double arch named the m -(ap) arch, may develop between the m -position on the A-rod and the ap -arch. A further second double arch may be present between the g -position of the A-rod and the m -(ap) arch. The V-rod is present but never protrudes through the cephalic wall. In its place, a very small ventral tube exists.

The protoplasm is observed in Callimitra and Clathrocanium. The endoplasm with multi-nuclei or a single nucleus is very small, transparent, and located in the cephalic cavity. Several algal symbionts are located inside and/or just below the cephalis.

STRATIGRAPHIC OCCURRENCE. — Late Eocene-Living.

REMARKS

The taxonomic position of the Sethoperidae at the superfamily and lineage levels, as well as the taxonomic differences between the Phaenocalpididae and Sethoperidae require additional studies. Tripocyrtis appear to be a synonym of Periplecta (Phaenocalpididae) while Dictyocodoma and Clathropilium appear to be members of the Stichopiliidae and Ceratocyrtidae, respectively. In most cases, the Sethoperidae are distinguished from the Phaenocalpididae by the presence of a wired screen in the cephalis and thorax. However, in some critical cases, a detailed examination of the cephalic initial spicular system is necessary (Tripocyrtis vs Periplecta). The cephalic initial spicular system of the Phaenocalpididae is broadly similar to that of the Sethoperidae. The differences between the Sethoperidae and the Phaenocalpididae are: 1) the development a second arch along D- and double L-rods outside of the basal ring in Sethoperidae; 2) the lack of developed sutures on the cephalis with cephalic arches in Sethoperidae; and 3) the presence of a straight a-spinule and arches that are related to m- and g-positions on the A-rod forming a “segmented” appearance inside the cephalis from dorsal or ventral view in Sethoperidae. The type-illustration of Dictyocodoma is probably obtained from the dorsal or ventral view of Stichopiliidae. This view allows the user to find a single apical horn if the supporting image is indeed correct. However, this observation is structurally impossible as the view with the three wings should be also associated with the identification of both apical and ventral horns. A Pteropilium species was previously identified as a member of Lipmanella (Nishimura & Yamauchi 1984: pl. 34, fig. 7). However, if the cephalic initial spicular system defined by Funakawa (2000) is considered, Pteropilium is completely different from Lipmanella.

The cephalic initial spicular system has been well illustrated for Callimitra (Nishimura 1990: figs 22.3, 22.4; Takahashi 1991: pl. 27, fig. 3), Clathrocanium (Poluzzi 1982: pl. 29, figs 1-3; Takahashi 1991: pl. 26, figs 12; Sugiyama et al. 1992: pl. 15, fig. 4), Clathrocorys (Nishimura 1990: figs 21.3, 22.1, 22.2, 23.5; Sugiyama 1994: pl. 2, figs 1, 2), Pteropilium (Nishimura & Yamauchi 1984: pl. 34, fig. 7), and Tripocyrtis (Nishimura 1990: figs 23.1, 23.2, 23.4). These genera have small size and they are frequently overlooked in many plankton studies. Nonetheless, some living images were illustrated for Callimitra (Anderson 1983: fig. 1.2.G; Matsuoka 1999: pl. 1, fig.1; 2017: fig.20; Zhang et al. 2018: 9, fig. 33; pl. 10, figs 31, 46, 47) and Clathrocanium (Suzuki et al. 2009b: figs 2O, 2P; Zhang et al. 2018: 10, fig. 4, p. 13, fig. 21).

VALIDITY OF GENERA

Callimitra

The precise anatomical description of Callimitra was written by Petrushevskaya (1981: 301) and revised by Goll (1979:

386) as follows: “[...] characterized by 3 large lattice panels extending laterally from the tip of the apical apophysis to the tips of each of the frontal and primary lateral apophyses.” Arachnothauma was described as follows: “ Shell cupola- or helm-shaped with three delicate convex appendages downwardly curved. From them originate pairs of divergent small lateral apophyses [...] From the top of the cephalis originates a similar appendage [...] with also lateral apophyses. Between them are distributed extremely thin threads that are linked again to other oblique threads. This structure gives the impression that a very small spider web has covered a very elegant beam structure ” (translation from Zacharias 1906: 566-567). This description of Arachnothauma and the type-illustration (Zacharias 1906: fig. 19) match those of Callimitra. Zacharias (1906) did not compare Arachnothauma to Callimitra. They are indeed clearly synonyms. The name Callimitra is older than Arachnothauma.

Clathrocanium

Clathrocanidium has the same type species as Clathrocanium. Clathrocanium, Clathrocorona, Arachnopilium, Clathrolychnus, Sethopera, and Tripocyrtis are defined in terms of their ontogenetic growth stages. Clathrocanium (Suzuki et al. 2009c: pl. 54, figs 5a-d), Sethopera (Haeckel 1887: pl. 97, fig. 11), and Tripocyrtis (Haeckel 1887: pl. 60, fig. 10) represent the youngest stage, without a perforated apical horn. Clathrocorona (Haeckel 1887: pl. 64, fig. 2), with perforated apical horn and three perforated basal feet, represents the next growth stage, and is illustrated in the Atlas as a supporting image for Clathrocanidium. The next growth stages are Clathrolychnus (Haeckel 1887: pl. 64, fig. 5), with a perforation connecting the apical horn and basal feet, followed by Arachnopilium (Haeckel 1887: pl. 64, fig. 7), with the development of a perforated thin cover around the three gates between the basal feet. Arachnopilium is illustrated as a supporting image for Clathrocorona and Clathrolychnus in the Atlas.