EUCYRTIDIIDAE Ehrenberg, 1846
Creators: name: Suzuki, Noritoshi
name: Caulet, Jean-Pierre
name: Dumitrica, Paulian
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy

description: Family EUCYRTIDIIDAE Ehrenberg, 1846
sensu Suzuki emend. herein
Eucyrtidina Ehrenberg, 1846: 385 [as a family]; 1847: 54 [as a family]; 1876: 156. — Schomburgk 1847: 124, 125 [as a family].
Stichocyrtida Haeckel, 1862: 238, 280, 312 [nomen dubium, as a tribe]; 1882: 438 [as a subfamily];1887: 1434 [a section between suborder and family]. — Zittel 1876-1880: 121 [rank unknown]. — Mivart 1878: 178 [as a subdivision of subsection Cyrtida]. — Stöhr 1880: 101 [as a family].— Bütschli 1889: 1993 [as a suborder].— Rüst 1892: 186 [as a suborder]. — Poche 1913: 221 [as super-superfamily]. — Popofsky 1913: 401 [as a section between suborder and family]. — Schröder 1914: 91, 132 [as a group between suborder and family]. — Chediya 1959: 225 [as a group between superfamily and family].
Artocapsida Haeckel, 1882: 438 [as a tribe].
Artophormida Haeckel, 1882: 438 [as a tribe].
Artophatnida Haeckel, 1882: 439 [nomen dubium, as a tribe].
Stichocorida Haeckel, 1882: 438 [as a tribe]; 1887: 1435, 1468 [as a subfamily]. — Wisniowski 1889: 690.
Stichophatnida Haeckel, 1882: 439 [as a tribe].
Stichoperida Haeckel, 1882: 439 [nomen dubium, as a tribe]; 1887: 1435, 1436, 1447 [as a subfamily].
Stichophormida Haeckel, 1882: 439 [as a tribe]; 1887: 1435, 1454 [as a subfamily].
Podocampida Haeckel, 1887: 1435, 1436 [nomen dubium, as a family]. — Bütschli 1889: 1993 [as a family]. — nec Rüst 1892: 186.
Stichophaenida Haeckel, 1887: 1435, 1454, 1463 [as a subfamily].
Lithocampida Haeckel, 1887: 1435, 1467-1468 [as a family]. — Wisniowski 1889: 689. — Bütschli 1889: 1994 [as a family]. — nec Rüst 1892: 187 [as a family].
Podocampidae – Popofsky 1908: 290 [nomen dubium]; 1913: 401. — Schröder 1914: 132. — Campbell & Clark 1944b: 36. — Chediya 1959: 225. — Tan & Tchang 1976: 290. — Tan & Su 1982: 179. — Chen & Tan 1996: 154. — Tan & Su 2003: 113, 206. — Chen et al. 2017: 219.
Lithocampidae – Haecker 1908: 460. — Popofsky 1908: 292; 1913: 406. — Schröder 1914: 133. — Clark & Campbell 1942: 91; 1945: 49. — Campbell & Clark 1944a: 51; 1944b: 38. — Chediya 1959: 230. — Chen & Tan 1996: 154. — Tan & Su 2003: 113, 216. — Chen et al. 2017: 222.
Stichocorinae [sic] – Clark & Campbell 1942: 91 (= Stichocorythinae); 1945: 49. — Campbell & Clark 1944a: 51; 1944b: 38. — Ichikawa 1950: 308-309. — Frizzell & Middour 1951: 32. — Chediya 1959: 230.
Stichophorminae [sic] – Campbell & Clark 1944b: 37 (= Stichophormidinae). — Clark & Campbell 1945: 38. — Chediya 1959: 228.
Stichocoridae [sic] – Frizzell & Middour 1951: 32 (= Stichocorythidae).
Stichoperinae – Campbell 1954: D136. — Chediya 1959: 227.
Artophormididae – Campbell 1954: D138.
Arthophormidinae – Campbell 1954: D138-139.
Stichocorythidae – Campbell 1954: D140. — Dieci 1964: 188.
Stichocorythinae – Campbell 1954: D140. — Dieci 1964: 188.
Lithocampinae – Orlev 1959: 458.
Stichoperidae – Loeblich & Tappan 1961: 229 [nomen dubium].
Eucyrtidiidae – Petrushevskaya 1971a: 169-171 (sensu emend.); 1971b: 985 (sensu emend.); 1975: 578; 1981: 200-202. — Petrushevskaya & Kozlova 1972: 545. — Dumitrica 1979: 30-31; 2017a: 47. — De Wever 1982b: 293. — Steiger 1992: 68-70. — Hollis 1997: 73-74. — Cordey 1998: 106. — Kozlova 1999: 152. — De Wever et al. 2001: 278, 280. — Afanasieva et al. 2005: S298. — Afanasieva & Amon 2006: 146. — Matsuzaki et al. 2015: 57.
Eucyrtidiinae – Petrushevskaya 1971a: 215 (sensu emend.); 1971b: 985 (sensu emend.); 1975: 580; 1981: 202. — Takahashi 1991: 114. — Afanasieva et al. 2005: S298. — Afanasieva & Amon 2006: 146-147.
Eucyrtididae [sic] – Amon 2000: 62-63 (= Eucyrtidiidae).
Eucyrtidinae [sic] – Amon 2000: 63 (= Eucyrtidiinae).
TYPE GENUS. — Eucyrtidium Ehrenberg, 1846: 385 [type species by subsequent designation (Frizzell & Middour 1951: 33): Lithocampe acuminata Ehrenberg, 1844a: 84].
INCLUDED GENERA. — Artocapsa Haeckel, 1882: 438 (=? Acanthocyrtis n. syn.). — Cymaetron Caulet, 1991: 536. — Cyrtocapsella Haeckel, 1887: 1512 (= Syringium synonymized byRiedel & Sanfilippo 1970: 530). — Eucyrtidium Ehrenberg, 1846: 385. — Glomaria Sanfilippo & Riedel, 1970: 455. — Lithocampe Ehrenberg, 1839: 128 (= Lithocampula with the same type species; Ariadnella n. syn., Cyrtopenta, synonymized by Haeckel 1862: 316, Lithomitrissa n. syn.). — Lithopera Ehrenberg, 1846: 385. — Stichocorys Haeckel, 1882: 438 (= Artophormis n. syn., Cyrtharia n. syn.,? Cyrtocapsoma n. syn., Cyrtophormiscus synonymized by Petrushevskaya & Kozlova 1972: 547; Cyrtophormium n. syn.,? Eusyringoma n. syn.; Cyrtophormis, Stichophaenoma, synonymized byPetrushevskaya 1981: 213). — Stichophatna Haeckel, 1882: 439 (= Stichophaenidium with the same type species; Cyrtolagena, Stichophormium synonymized byPetrushevskaya 1981: 175; Sticholagena synonymized by Petrushevskaya 1975: 582; Stichophormiscus synonymized by Nishimura & Yamauchi 1984: 55). — Stichopterygium Haeckel, 1882: 439 (= Artocyrtis n. syn., n. syn. Conostrobus, Stichopodium n. syn.; Spirocyrtoma synonymized by Petrushevskaya 1981: 205). — Theocoronium Haeckel, 1887: 1415 (= Theocapsetta n. syn., Theocapsomma n. syn.). — Tricolocamptra Haeckel, 1887: 1413. — Udan Renz, 1976: 127.
INVALID NAMES. — Artophaena, Stichophaena.
NOMINA DUBIA. — Artophatna, Diabolocampe, Podocampe, Pylosphaera, Spirocampe, Stichocyrtis, Stichopera, Stichoperina.
DIAGNOSIS. — Eucyrtidiidae with two to six segmented shell with an aperture. The segments are divided by distinctive inner-ring dividers. Feet are not observed. The cephalis is spherical to globular in shape, with a thick wall and relict or true fine pores. The wall of the cephalis is discernible in such a way that the collar suture between the cephalis and the thorax appears distinctive. Even if covered by silica, the cephalic boundary with the thorax remains recognizable under a light microscope. The cephalis is attached to the cephalic base by a base ring or to a thickened wall. The sutural pores are developed to separate the cephalis and thorax in some species or genera. The pores are randomly scattered or horizontally aligned. The cephalic initial spicular system is characterized by MB, A-, V-, D-, and double L-rods. When present the ax-rod has a dot-like shape. The double l-rod is absent, except in Lithocampe. The A-rod is embedded inside the cephalic wall or is freely oriented upright in the cephalic cavity. In some members, an indistinct tubular structure is visible near the end of the V-rod. Basal ring is directly connected with the A-rod side end of MB, V- and double L-rods to form four collar pores. A basal ring is bended along the line with the double L-rod such that double pores related to the LV-arch are raised towards the ventral side. The D- and double L-rods are visible on the thoracic and subsequent segmental wall in some members.
The size of the endoplasm is variable, but never occupies the complete shell. A very long pseudopodium (axial projection) extends from the aperture of the shell and is used as a tool to capture food. Algal symbionts are observed in some species of Eucyrtidium.
STRATIGRAPHIC OCCURRENCE. — Early Paleocene-Living.
REMARKS
The cephalic initial spicular system have been illustrated for: Cyrtocapsella (Nishimura H. 1987: figs 6.A, 6.B; pl. 1, figs 2, 3 5; pl. 2, figs 1, 2; 1990: figs 4, figs 40.1, 40.2), Stichophatna (Sugiyama 1998: pl.4, fig. 2b), Eucyrtidium (Cachon & Cachon 1972a: figs 4.a-4.c, fig. 5.a; Nishimura & Yamauchi 1984: pl. 39, figs 5, 11; Takemura & Nakaseko 1986: figs 5.4-5.5, 5.8-5.9; Nishimura 1990: fig. 41.2; Sugiyama et al. 1992: pl. 23, fig. 7?), Lithocampe (Sugiyama et al. 1992: pl. 22, figs 2-8), Lithopera (Nishimura & Yamauchi 1984: pl. 33, fig.6; Nishimura H. 1987: pl. 1, fig. 4) and Stichocorys (Takemura & Nakaseko 1986: figs 5.10-5.11; Nishimura H. 1987: pl. 1, fig.1; 1990: fig. 41. 4; O’Connor 1997a: pl. 9, figs 13-16; pl. 11, figs 4, 8). The basal ring with four collar pores is a common feature among the genera Lithocampe due to the lack of a double l-rod. Nishimura (1986) thought that the l-rods are covered through a thickening process of the cephalic wall; however, this is unlikely for most of the genera because the edge of the double arch between MB and L-rod occupies the place where that the l-rod occupies. The generic assignment is uncertain for Cyrtocapsa osculum O’Connor because the cephalic structure remains unknown (O’Connor 1997a: pl. 1, figs 15-17; pl. 2, figs 1, 2; pl. 8, figs 3-10), Eucyrtidium inflatum (Takemura & Nakaseko 1986: figs 5.6-5.7) and Eucyrtidium calvertense (Sugiyama et al. 1992: pl. 23, fig. 3), Eucyrtidium ventricosum O’Connor, 1999 (O’Connor 1999: pl. 3, figs 17-21b; pl. 6, figs 28-31). Eucyrtidium inflatum and E. calvertense have double l-rods that form very small double pores with the double Dl-arch as in Lithocampe.
Over the last century, the taxonomy of the Eucyrtidiidae has been problematic because few keys were available to determine the evolutionary lineages. This was partly due to the polyphyletic character denoted in many groups of the Eucyrtidiidae (De Wever et al. 2001). Based on the consistency with molecular phylogeny, five Cenozoic genera (Buryella, Calocyclas, Calocycloma and Phormocyrtis) are excluded from the family. Instead, seven Cenozoic genera (Stichophatna, Lithocampe, Stichopterygium, Theocoronium, Tricolocamptra and Udan) are newly included as their cephalic similarity with Eucyrtidium was considered. Many genera of Eucyrtidiidae were historically included in “theoperids” but this name is inappropriate for a taxonomic position as the Eucyrtidiidae have no morphological characters in common with the genus Theopera (see also De Wever et al. 2001: 278).
The evolutionary hypotheses in some linages of Eucyrtidiidae were well documented (Sanfilippo & Riedel 1970; Sanfilippo et al. 1985: figs 16, 23). The “ Eucyrtidium ” spp. in the sense of Sanfilippo & Riedel (1970) is considered a direct ancestor of Cyrtocapsella and Stichocorys; Lithopera originated from Stichocorys diploconus in Sanfilippo & Riedel 1970, and Glomaria diverged from Lithopera (Riedel & Sanfilippo 1981: fig. 12.9). Little is known about the evolutionary phylogenies of other genera. The specific divergent process between Eucyrtidium calvertense and Eucyrtidium matuyamai was also noted. This was quantitively evaluated with high-resolution models as a typical gradual evolution phenomenon (Hays 1970; Kellogg 1976). Morphological changes in the Lithocampe peregrina (originally Stichocorys peregrina) lineage associated to different geographic areas were also quantitatively documented (Kamikuri 2012). The paleobiogeographic morphotypes of Lithocampe (originally Stichocorys, Casey et al. 1983) were well studied in time-series distribution changes in the North Pacific (Lombari 1985; Oseki & Suzuki 2009).
The protoplasm and living specimen images were illustrated for Eucyrtidium (Matsuoka 1993a: fig. 2:7;2007: fig. 4a;2017: figs 24, 25; Sugiyama & Anderson 1997b: pl. 1, figs 1, 2; Sashida & Kurihara 1999: figs 11.6, 11.9, 11.11; Sugiyama et al. 2008: figs 2-6; Suzuki & Aita 2011: fig. 5.P; Suzuki & Not 2015: figs 8.4.3, 8.11.18, 8.11.19; Matsuoka et al. 2017: Appendix B), Lithopera (Gowing 1989: figs 2.D-2.F; 1993: fig. 6.i; Zhang et al. 2018: 21, fig. 8.11) and Stichopterygium (Sashida & Uematsu 1994: fig. 3.1). Cytological ultrafine structure was also observed in Eucyrtidium (Sugiyama & Anderson 1997b: pls 2, 3). Growth lines of pore frame are well documented in Cyrtocapsella (Nishimura H. 1987: pl. 1, figs 5b, 5c; pl. 2; 1990: figs 4, 40), Eucyrtidium (Nishimura 1990: figs 41.2b), Lithopera (Nishimura H. 1987: pl. 1, fig. 4b) and Lithocampe (Nishimura H. 1987: pl. 1, fig. 1b; Nishimura 1990: figs 41.4b). Live silicification sites on the shell were localized for Eucyrtidium with an epi-fluorescence microscopy PDMPO dyeing method (Ogane et al. 2010: figs 1.11-1.12, 2.11-2.12, 3, 4.3).
VALIDITY OF GENERA
Artocapsa
Artocapsa is defined by a pointed, conical, terminal segment with a basal spine and an apical horn (Campbell 1954: D143) and Acanthocyrtis is defined by a solid apical horn, variable heights of segments, a spiny surface, and an open aperture (Campbell 1954: D140). As the remarkable characteristics for these genera are different in each other except for the presence of an apical horn and the distal terminal structure, it is impossible to discuss about their synonymy based on the definition. The topotypic specimen of Eucyrtidium tricinctum from the H.M.S. Challenger Station 225 is a little bit different from the description in Campbell (1954) by the similar height of the segments (supporting image for Acanthocyrtis). This difference is well explained by intra-species variations. The topotypic specimen has a thorny appearance but it is not significant compared to the type-illustration for Artocapsa. The genus Artocapsa has a closed final segment whereas Acanthocyrtis has a fenestrated aperture. This is insufficient to separate them at generic level. Both these genera were simultaneously published in Haeckel (1887: 437 for Acanthocyrtis and 438 for Artocapsa). As the species with a basal spine at the end of the final segment is rare in other genera, Artocapsa is selected as a valid name.
Stichophatna
The synonymy of Cyrtolagena, Sticholagena, Stichophaenidium, Stichophatna, Stichophormium, Stichophormiscus has been well established by previous studies (Petrushevskaya 1975; De Wever et al. 2001; Nishimura & Yamauchi 1984). Cyrtolagena published in Haeckel (1887: 1449) has been used a long time as the valid name but the oldest available name is Stichophatna published in Haeckel (1882: 439).
Lithocampe
Lithocampanula has the same type species as Lithocampe. Tochilina (1989a, 2008) erected two genera Ariadnella and Cyrtopenta associated with Stichocorys under the Lithocampidae in her sense. The translated diagnosis from the original Russian for Cyrtopenta follows. “ Fundamental part of the shell constituted by five segments relatively of same height, progressively enlarging from the first one to the fourth, but the fifth narrower. From two to five additional segments. Shell of conical shape. Pores distributed symmetrically ”. The topotype of Lithocampe radicula (Suzuki et al. 2009c: pl. 12, figs 8a, 8b), type species of Lithocampe, exactly matches the definition of Cyrtopenta. It is noted that “ Stichocorys delmontensis ” and “ Stichocorys peregrina ” were placed in Cyrtopenta in Tochilina (1989a). This also means that both these species belong to Lithocampe but not to Stichocorys.
Ariadnella is defined by “ six to seven main segments and one to two additional ones with a nearly conical-cylindrical shape, and by a terminal tube with a mesh structure ” (translation from Tochilina 2008: 62-63). Tochilina (2008) commented that Ariadnella differs from Lithocampe and Stichocorys by its general shape and the much greater number of segments. When compared, Lithocampe radicula and Lithocampe subligata, respectively type species of Lithocampe and Ariadnella, the former has six segments and the latter eight segments. However, all other characters including the general shape are nearly identical. The difference pointed out by Tochilina (2008) is not applicable as genus criteria. Tochilina (1989a: 63) includes Lithomitra infundibulum as a member of this Ariadnella. As L. infundibulum is the type species of Lithomitrissa, Tochilina (2008) herself agrees with the synonymy relationship between Ariadnella and Lithomitrissa. The oldest available name is Lithocampe among them.
Stichocorys
The practical usage of Stichocorys was once extremely broaden by Sanfilippo & Riedel (1970) in order to include “ Stichocorys peregrina ” and “ Stichocorys delmontensis.” Stichocorys differs from Lithocampe by the fact that the proportions between the segments are less variable and that external constrictions are well-differentiated (translation from Petrushevskaya 1981: 212). Stichocorys in the sense of Sanfilippo & Riedel (1970) was mixed with Lithocampe under the modern sense. Tochilina (1989a: 56) revised the definition to separate Lithocampe (Cyrtopenta in original) from Stichocorys on the basis of “ a three-segmented conical shell, thin-walled fourth and fifth segments (when present), the third segment with a maximum width, and the occurrence of regular pores on the second and third segments differently from the irregular pores located on the fourth and fifth segments ” (translation from Tochilina 1989a by J. P. Caulet). Except pore patterns, these distinguishing points are well fit with our concept of Stichocorys.
The same type species is designated for Cyrtophormis, Cyrtophormium and Cyrtophormiscus. Referred to Campbell (1954), the main difference at family level in the sense of Campbell (1954: D139-143) is the number of radial apophyses around the test (four to nine or more radial apophyses for Artophormis, Cyrtophormis, Stichophaenoma; presence of radial apophyses for Cyrtocapsoma and Eusyringoma). Obviously, the state of development of the radial apophyses illustrated in the type specimens are intraspecies variations but cannot be a criterion for genus level. The next distinguishing character of lower value at the subfamily level in the sense of Campbell (1954) is the fenestrated basal end of the test (Cyrtocapsoma and Stichophaenoma), or the opened basal end (Artophormis, Cyrtophormis and Eusyringoma). The difference between “fenestrated” and “open” is easily recognizable in the type-illustrations, but such kind of variation is commonly encountered in each of the samples. If this difference is accepted for subfamily classification, tens or hundreds of subfamilies will be created with only a few samples. Due to these reason, the difference under the definition written is as follows: oval or spindle-shaped shell, radial ribs prolonged into feet for Artophormis (Campbell 1954: D139); oval or spindle-shaped shell, absence of lateral ribs, and six to five feet for Cyrtophormis (Campbell 1954: D139); pointed final segment with basal spines for Stichophaenoma (Campbell 1954: D140); long narrow appendage as the last segment and 4 or more segments for Eusyringoma (Campbell 1954: D140); and presence of apical horn and four or more ring-like strictures for Cyrtocapsoma (Campbell 1954: D143). The type-illustration for Artophormis shows very indistinguishable radial ribs, sufficient characteristic to be separated from Cyrtophormis. “Feet” for both Artophormis and Cyrtophormis depend on specimens but not even at species level nor genus level. There are no reasons to separate Artophormis and Cyrtophormis. As both these genera, the characteristic of a pointed final segment with basal spines can be included in a variation between “ Artophormis / Cyrtophormis ”, thus Stichophaenoma is also a synonym of these two genera at genus level. The definition of Eusyringoma written in Campbell (1954) does not match the illustrated type specimen (Stöhr 1880: pl. 4, fig. 8). More clearly, the type specimen is exactly the same as that of Stichocorys in the sense of Tochilina (2008). The presence of an apical horn is noted only for Cyrtocapsoma among the genera discussed here, but the apical horn of the type specimen (Stöhr 1880: pl. 4, fig. 9) is so tiny as not to be differentiate in other genera. In conclusion all characteristics pointed by Campbell (1954) have no value for generic differences. Excluded these characteristics, the synonymy is simply evaluated following the similitude with Stichocorys in the sense of Tochilina (2008). It is a little bit unclear for Stichophaenoma but all other genera are fallen in her concept. Artophormis and Stichocorys were simultaneously published in Haeckel (1882: 438 for both genera). Stichocorys is the best valid genus for taxonomic stability.
Stichopterygium
The five genera listed here were used to be classified into the “Tricartinae” (Campbell 1954: D136 for Stichopodium and Stichopterygium) and “Stichocorythinae” (Campbell 1954: D140 for Artocyrtis, D141 for Conostrobus, and D142 for Spirocyrtoma) in the sense of Campbell (1954). They are synonymized herein with a significant apical horn, an open aperture, and four or more segments. The presence of a significant apical horn in Stichopterygium makes the difference with Eucyrtidium and Lithocampe. The following discussion is largely commented after Campbell (1954): All these five genera have “radial apophyses” but these structures are not recognizable in any type-illustrations; Stichopodium is characterized by three latticed basal feet but real specimens (supporting image for Stichopodium) are exactly similar with Conostrobus except for the basal feet (supporting image for Conostrobus). Conostrobus is defined by a conical shell with a straight axis and similar strictures between segments (Campbell 1954: D141) and these characters do exactly fit with the type species of Stichopodium. Spirocyrtoma is marked by an ovate to spindle-shaped shell and spirally disposed strictures (Campbell 1954: D142). The ovate to spindle appearance can be classed into intraspecies variations and spirally disposed strictures occur in any species of bizarre forms. As these characteristics are not considered as valuable at genus level, “ Spirocyrtoma ” can be classified into Conostrobus or Spirocyrtoma. Artocyrtis is characterized by joints of dissimilar lengths and a smooth surface, according to Campbell (1954: D140). Referred to the lectotype of Artocyrtis (Suzuki et al. 2009c: pl. 55, figs 5a-c), “joints of dissimilar length” is interpreted as a larger thorax (2nd segment). This larger thorax and a smooth surface are also characteristics in common with the type-illustration of Stichopterygium. Except for the larger thorax, Artocyrtis can be interpreted as a cylindrical form typical of Conostrobus and Spirocyrtoma.
This synonymy, however, should be re-examined by the shape of the evolutionary lineages. The first, latticed lateral ribs, or wings, is the only character in Stichopterygium (Campbell 1954: D136). As the type species of Artocyrtis, Conostrobus, Stichopodium and Stichopterygium are living species, as the occurrence of latticed lateral ribs or wings is impossible to be explained by intraspecific variations, this characteristic must be considered to be as differences at species or genus level. This point has not yet been evidenced. The second characteristic, the importance of the larger thorax, has not yet been evaluated. If this character is important, these five genera would be divided into two groups. For the lack of lattice lateral ribs or wings, Artocyrtis is the only genus which can be synonymized with Stichopterygium. The third characteristic (presence of a significant apical horn) is regarded as a major character to differentiate Stichopterygium from Eucyrtidium and Lithocampe. No papers prove it can be considered as a phylogenetic marker based on evolutionary phylogeny. For example, Artocyrtis is exactly similar to “ Cyrtopenta ” except for the apical horn as referred to the lectotypes of these two type species in Suzuki et al. (2009c: pl. 15, fig. 7b for Cyrtopenta and pl. 55, figs 5a-c for Artocyrtis). These three points must be evaluated in future studies.
Theocoronium
As Theocoronium was placed in the “Theocorythinae” (Campbell 1954: D134) while Theocapsetta and Theocapsomma were placed in the “Theocapsinae” (Campbell 1954: D136) sensu Campbell (1954), the difference at subfamily level is relied on whether the distal end of the last segment is open or fenestrated. As commonly discussed for the Eucyrtidiidae, this difference is within intra-or infra variations. According to Campbell (1954), these three genera have in common similar thoracic and abdominal pores. ForCampbell (1954) Theocoronium is marked by a swollen ovate abdomen and a single apical horn, Theocapsetta has thorax and abdomen of nearly the same size, and Theocapsomma has a thorax much smaller than the abdomen. Referred to the lectotype of Theocoronium (Suzuki et al. 2009c: pl. 55, figs 11a, 11b) and type-illustrations in Haeckel (1887: pl. 66, fig. 6 for Theocapsetta and pl. 66, fig. 13 for Theocapsomma), all these three genera have a single apical horn. The shape of the abdomen is only noted for Theocoronium but the difference in the abdomen among the three type species is commonly observable as a difference in the ontogenetic growth. The characteristic difference between Theocapsetta and Theocapsomma is the size ratio between the thorax and the abdomen. As already commented, the difference of abdomen is a difference in the ontogenetic growth stages. These three genera were simultaneously published in Haeckel (1887: 1415 for Theocoronium, 1426 for Theocapsetta and 1428 for Theocapsomma). Theocoronium is validated among them because the real type specimen is found in the Ehrenberg collection.
description: Published as part of Suzuki, Noritoshi, Caulet, Jean-Pierre & Dumitrica, Paulian, 2021, A new integrated morpho- and molecular systematic classification of Cenozoic radiolarians (Class Polycystinea) - suprageneric taxonomy and logical nomenclatorial acts, pp. 405-573 in Geodiversitas 43 (15) on pages 470-474, DOI: 10.5252/geodiversitas2021v43a15, http://zenodo.org/record/5101757