EUCHITONIIDAE Stöhr, 1880

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, Geodiversitas 43 (15), pp. 405-573 : 426-428

Family EUCHITONIIDAE Stöhr, 1880

sensu Suzuki emend. herein

Euchitonida Stöhr, 1880: 86 [as a subfamily]. — Haeckel 1882: 460 [as a tribe]; Haeckel 1887: 484, 516 [as a subfamily]. — Wisniowski 1889: 685 [as a subfamily]. — Schröder 1909: 43 [as a subfamily].

Ommacampida Haeckel, 1887: 392 [as a subfamily].

Euchitoninae [sic] – Clark & Campbell 1942: 46 (= Euchitoniinae); Campbell & Clark 1944b: 17. — Chediya 1959: 136. — Tan & Tchang 1976: 246-248. — Tan 1998: 219. — Tan & Chen 1999: 217. — Amon 2000: 49.

Ommatocampinae Campbell, 1954: D76. — Chediya, 1959: 119.

Monaxoniinae Campbell, 1954: D76.

Euchitoniidae – Campbell 1954: D86. — Nakaseko & Sugano 1976: 125. — Kozur & Mostler 1978: 134-135 ( sensu emend. ). — Petrushevskaya 1979: 112-113 ( sensu emend. ). — Matsuzaki et al. 2015: 18-19.

Euchitoniinae – Campbell 1954: D86. — Kozur & Mostler 1978: 135-136. — Petrushevskaya 1979: 113 ( sensu emend. ).

Myelastrinae Riedel, 1971: 654. — Kozur & Mostler 1978: 153.

Chitonastrinae Kozur & Mostler, 1978: 136 [nomen dubium].

Myelastridae – Takahashi 1991: 87. — De Wever et al. 2001: 160-161. — Afanasieva et al. 2005: S284. — Afanasieva & Amon 2006: 127.

Euchitonidae [sic] – Amon 2000: 48-49 (= Euchitoniidae ).

TYPE GENUS. — Euchitonia Ehrenberg, 1861b: 831 [type species by subsequent monotypy: Euchitonia furcata Ehrenberg, 1873a: 308 ] = junior subjective synonym of Dictyocoryne Ehrenberg, 1861b: 830 [type species by subsequent designation ( Haeckel 1887: 591): Dictyocoryne profunda Ehrenberg, 1873a: 307 ].

INCLUDED GENERA. — Amphicraspedum Haeckel, 1882: 460 (= Amphicraspedon with the same type species; Amphirrhopella n. syn.). — Dictyocoryne Ehrenberg, 1861b: 830 (= Dictyocorynula with the same type species; Dictyastrum synonymized by Matsuzaki et al. 2015: 19, Dictyastrella , Euchitonia ,? Hymenastromma , Rhopalodictya, Rhopalodictyum synonymized by Ogane et al. 2009a: 89), Styla synonymized by Matsuzaki et al. 2015: 19; Pteractis. — Hexinastrum Haeckel, 1882: 461 (= Hexalastromma n. syn., Pentalastromma n. syn., Pentinastrum n. syn.). — Ommatocampe Haeckel, 1861b: 832 (= Ommatocampium with the same type species; Amphymenium synonymized by Petrushevskaya & Kozlova 1972: 527). — Tessarastrum Haeckel, 1887: 547 (= Tessarastrella with the same type species; Hagiastromma n. syn., Tessarostromma n. syn.). — Tricranastrum Haeckel, 1879: 705 (= Dicranaster n. syn., Dicranastrum n. syn., Myelastrella n. syn., Myelastrum n. syn., Spongomyelastrum n. syn., Myelastromma n. syn., Pentophiastromma n. syn., Spongodi- cranastrum n. syn., Spongohagiastrum n. syn., Spongopentophiastrum n. syn., Spongostaurina n. syn., Tetracranastrum n. syn., Triastrum , n. syn.). — Trigonastrum Haeckel, 1887: 538 (= Trigonastrella with the same type species; Rhopalastromma synonymized by Kozur & Mostler 1978: 128; Chitonastromma synonymized byKozur & Mostler 1978: 136; Amphicraspedina n. syn., Amphirrhopoma n. syn., Dictyastromma n. syn., Monaxonium n. syn., Trigonastromma n. syn.).

INVALID NAME. — Tessarastromma.

NOMINA DUBIA. — Amphirhopalum , Amphirrhopalium , Chitonastrella , Chitonastrum , Hexalastrum , Pentalastrella , Pentalastrum , Pentophiastrum , Rhopalastrella , Rhopalastrum .

JUNIOR HOMONYMS. — Spongostaurus Swanberg, Anderson & Bennett, 1985 (= Spongostaurina ) nec Haeckel, 1882; Stylactis Ehrenberg, 1873 ( Ehrenberg 1873a = Styla Stechow, 1921) nec Allman, 1864.

DIAGNOSIS. — Flat shaped Polycystinea with circular center and arms. The central part is a convex lens-shaped structure (named “margarita”) which includes a spinose microsphere and two to three concentric convex lens-shaped crusts. The exterior structure of the margarita with a variable number of arms: two to four, rarely eight. Arm is constituted by a very highly dense concentric structure which resembles a spongy, a segmented structure with dividers, or superimposed cupolas. Patagium developed in some members but were differentiated from the border of the arm. Both polar sides of the margarita crop out or are occasionally seen covered with fine appendages.

The protoplasm can be divided in Dictyocoryne - and Tricranastrum - types. Typically, the spongy shell in Dictyocoryne is filled with a light brown endoplasm. A robust, long axoflagellum emerges from a non-walled pylome on one-side of the test. Pseudopodia radiate throughout the shell. The margarita portion is more transparent than the other skeletal parts. It should be noted that Dictyocoryne truncata (Ehrenberg) and Dictyocoryne profunda Ehrenberg exclusively possess cyanobacteria as symbionts, on the surface of the endoplasm. Dictyocoryne muelleri harbors algal symbionts outside the shell, as opposed to cyanobacteria. In Tricranastrum , the shell is occupied by a light brown endoplasm. A probable ectoplasmic membrane wraps around all skeletons including by-spines.

STRATIGRAPHIC OCCURRENCE. — early Middle Miocene-Living.

REMARKS

The central part of the Euchitoniidae is named by the special word: “margarita” ( Matsuoka 1992c: pl. 2, figs 1, 5; 1993b: pl. 1, figs 4, 5; Zheng 1994: pl. 40, figs 4-7, 9). This is confirmed in the Amphicraspedina -form of Trigonastrum ( Takayanagi et al. 1979: pl. 1, figs 11, 12; Poluzzi 1982: pl. 20, figs 2, 3; Wang & Yang 1992: pl. 2, figs 26-29; Zheng 1994: pl. 40, figs 5, 9; van de Paverd 1995: pl. 51, fig. 3), the Dictyastromma -form of Trigonastrum ( Poluzzi 1982: pl. 20, fig. 5), Dictyocoryne ( Poluzzi 1982: pl.20, fig. 4), the Euchitonia -form of Dictyocoryne ( Poluzzi 1982: pl. 20, fig. 8; Anderson & Bennett 1985: pl. 1, figs 1, 2, 3), Tricranastrum (Matsuoka 2017: figs 12.1, 12.3, 12.5- 12.7), Ommatocampe ( Poluzzi 1982: pl. 20, fig. 1) and the Pteractis -form of Dictyocoryne (Matsuoka 2017: figs 15.4- 15.7; Zheng 1994: pl. 40, figs 4, 6, 7). The margarita is not covered by a patagium in the Amphicraspedina -form of Trigonastrum ( Cheng & Yeh 1989: pl. 1, figs 7, 10), Dictyocoryne ( Onodera et al. 2011: pl. 6, fig. 8), the Pteractis - and Euchitonia -forms of Dictyocoryne ( Yamauchi 1986: pl. 4, figs 10, 12), Trigonastrum ( Dumitrica 1973a: pl. 10, figs 1-4). Typically, Dictyocoryne tends to thicken in its central part ( Cheng & Yeh 1989: pl. 2, fig. 12) whereas the Pteractis -form of Dictyocoryne remains very flat ( Cheng & Yeh 1989: pl. 2, figs 8, 14). Internal skeletal structure was illustrated for the Hymenastromma -form of Dictyocoryne ( Sugano, 1976: pl. 6, fig. 3), but Hymenastromma appears to be similar to the Phorticiidae .

Molecular studies sometimes noted trouble separating Dictyocoryne and Euchitonia . This issue has been already solved from the morphological classification’s point of view ( Ogane et al. 2009a; Matsuzaki et al. 2015). The genus name Euchitonia must not no longer be applied. The existence of Amphicraspedum and Hexinastrum has been considered doubtful because no specimens identified as such have been reported. These genera are kept as valid until future confirmation of their existence.

Dictyocoryne is one of the most examined and studied living radiolarians in ecological observations ( Matsuoka 1992 a, 1992c, 1993 a, 1993b, 2017; Sugiyama & Anderson 1997a), ecological experimental studies ( Matsuoka & Anderson 1992; Sugiyama & Anderson 1997a), cytological ultrafine structures, symbionts, symbiosis ( Matsuoka 1992c), and cytomechanics ( Anderson et al. 1987). Images of living forms were repeatedly illustrated for Dictyocoryne ( Matsuoka 1992a: pls 1, 3; 1992c: pls 1, 3; 1992b, figs 1A, 1B, 2A, 2B; 1993a: pl. 2, figs 1, 2; 1993b: pl. 3, figs 1-4; 1994: fig. 2A; 2017: figs 13.1, 13.2; 14.1, 14.2; Sugiyama & Anderson 1997a: pl. 2, figs 2, 4; Matsuoka et al. 2001: pl. 1, fig. 1; Takahashi et al. 2004: figs 1, 2; Yuasa et al. 2005: fig. 1a; Ichinohe et al. 2019: fig. 2), the Euchitonia -form of Dictyocoryne ( Matsuoka 1993b: pl. 4, figs 1, 2), Tricranastrum ( Yuasa et al. 2005: figs 1b, 1c; Matsuoka 2007: fig. 12; 2017: figs 12.1, 12.2), the Pteractis -form of Dictyocoryne ( Matsuoka 1992b: figs 2C, 2D; 1993a: fig. 2.4; 1993b: pl. 4, figs 3, 4; 1994: fig. 2D; 2017: figs 15.1, 15.2) and the Spongostaurus -form of Tricranastrum ( Caron & Swanberg 1990: fig. 3.B). Protoplasm and algal symbionts were documented by epi-fluorescent observation with DAPI dyeing and other dyeing methods for Dictyocoryne ( Ogane et al. 2010: figs 1.14-1.15; 2.14- 2.15; Zhang et al. 2018: 11, figs 1, 6, 7, p. 14, figs 4, 5; p. 16, figs 2, 3), the Euchitonia -form of Dictyocoryne ( Ogane et al. 2010: figs 1.13, 2.13), and Tricranastrum ( Zhang et al. 2018: 16, fig. 4). An image fixed using dye method was published for Tricranastrum ( Aita et al. 2009: pl. 27, fig. 1; pl. 29, fig. 1). A cytological ultrafine-structure was observed in Tricranastrum (Swanberg et al. 1985: pl. 2).

Algal symbionts of Dictyocoryne elegans were identified as Gymnoxanthella radiolariae by Yuasa et al. (2016), the same dinoflagellate species as those of Acanthodesmia ( Acanthodesmiidae , Nassellaria ) and Dictyopodium (originally Pterocanium , Lithochytrididae , Nassellaria ).

VALIDITY OF GENERA

Amphicraspedum

Amphirrhopella is characterized by terminal spines but this character is induced by intraspecies or intraspecies variation.

Dictyocoryne

The combinations Dictyocoryne and Dictyocorynula , Dictyastrum and Dictyastrella , and Rhopalodictyum and Rhopalodictya have respectively the same type species. Since Rhopalodictyum has already been synonymized with Dictyocoryne ( Ogane et al. 2009a: 89) and Dictyastrum also synonymized with Dictyocoryne ( Matsuzaki et al. 2015: 19) , Rhopalodictya and Dictyastrella are both automatically synonyms of Dictyocoryne . “ Styla ” is also synonymized with Dictyocoryne as the name of Stylactis by Matsuzaki et al. (2015:19). In this context, our paper newly synonymized Hymenastromma with Dictyocoryne . As shown in the supporting image of the Atlas for Hymenastromma , the central structure is different from Dictyocoryne . Both these genera may be independent from each other.

The oldest available names are listed as Dictyocoryne , Dictyastrum , Euchitonia and Rhopalodictyum fromEhrenberg (1861b). The formal publication and years of publication for these genera have been confused due to a nomen nudum in Ehrenberg (1861a) and the mismatch of volume number as “1860” and the published year for Ehrenberg (1861a; 1861b) ( Lazarus & Suzuki 2009: 31 ). The names Dictyocoryne and Rhopalodictyum are commonly used in references but the condition of preservation and the completeness of the shell are better for the lectotype of Dictyocoryne than for Rhopalodictyum.

Hexinastrum

As far as we know, real specimens identifiable as Hexinastrum , Hexalastromma , Pentalastromma and Pentinastrum have never been so far illustrated. Here we simply put together these suspected genera. Six-armed genera might be conjoined specimens like in the Jurassic Tritrabs worzeli illustrated by Dumitrica (2013b: fig. 4.1). The oldest available names are Hexinastrum and Pentinastrum in Haeckel (1882: 450 for Hexinastrum and 460 for Pentinastrum ). If their morphology results from a conjoined phenomenon, six-armed specimens like Hexinastrum are predicted to be found rather than starlike five-armed specimens like Pentinastrum .

Tricranastrum

Tricranastrum corresponds to the current usage of Myelastrum . The following genera have the same type species, respectively: Myelastrum , Myelastrella and Spongomyelastrum ; Dicranastrum , Dicranaster and Spongodicranastrum; Pentophiastromma and Spongopentophiastrum. The ontogenetic changes at intraspecies or species level are well illustrated in Tan & Tchang (1976: 246-250). The authors seemed to consider these variations at a genus level but their illustrated morphological variations are obviously continuous among specimens. The number of arms at least is variable at intraspecific level because if it is used as a genus criterion, many genera would be “created” by monotypy. The oldest available name is Tricranastrum Haeckel (1879: 705) . As this name was once used as valid in van de Paverd (1995: 175), it is unable to keep the name Myelastrum .

Tessarastrum

The difference between Tessarastrum and Ommatocampe is in the number of arms but two of the four arms of Tessarastrum are developed in secondary growth mode in the sense of Ogane et al. (2010) (the supporting image for Tessarastrella in the Atlas ). Hagiastromma is characterized by a patagium and dissimilar longitudinal arms ( Campbell 1954: D86) whereas Tessarostromma by a bilateral symmetry along the long axis, the presence of a patagium and dissimilar arms ( Campbell 1954: D88 as Tessarastromma, the invalid name at present). The shorter arms illustrated in the type images of Hagiastromma and Tessarostromma are explained by a different ontogenetic growth in Tessarastrum . The patagium changes during ontogenetic growth in the Euchitoniidae . The bilateral symmetry change is related to intraspecies variation. All of these available genera were simultaneously published inHaeckel (1887: 543 for Hagiastromma ; 547 for Tessarastrum and Tessarastrella ; 548 for Tessarostromma ). Of these, Tessarastrum is the only name established with a generic-rank.

Trigonastrum

This genus is different from Dictyocoryne due to the significant diversity of each arm. The illustrated type specimen of Dictyastromma shows a significant diversity but the probable same species of Dictyastrum trispinosum looks to be a Dictyocoryne (the supporting image for Dictyastromma in the Atlas ). The stratigraphically important species “ Amphirhopalum ypsilon ” is classified into this genus, although this species itself is a nomen dubium due to an un-illustrated type. Monaxonium initially belong to the Panartidae (= Zygartidae originally) ( Popofsky 1912: 125-126) and it was later moved to the Spongodiscidae sensu Riedel (1971: 653) . The distinguishing features of the listed genera are the occurrence of terminal spines ( Campbell 1954: D86 for Amphicraspedina and Dictyastromma ) or spinules on arms ( Campbell 1954: D89 for Rhopalastromma ), the occurrence of a patagium ( Amphicraspedina , Rhopalastromma ; Campbell 1954: D86 for Chitonastromma , D88 for Trigonastromma ), the occurrence of two to three forked arms ( Amphicraspedina , Chitonastromma , Trigonastromma ) or undivided arms ( Dictyastromma ). As repeatedly responsible of the validity of genera in Euchitoniidae , terminal spines and spinules on arms as well as patagium are intraspecies variations. The condition of forked arms is so variable that it is considered as an intraspecies or species variation. All available synonym genera except for Monaxonium were simultaneously published in Haeckel (1887: 523 for Amphicraspedina and Amphirrhopoma ; 525 for Dictyastromma ; 528 for Rhopalastromma ; 537 for Chitonastromma ; 538 for Trigonastrum ; 539 for Trigonastrella , Trigonastromma ). As the forked arms are one of the characters of this morphotype, Trigonastrum is selected as the valid name.