HEXACROMYIDAE Haeckel, 1882

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 : 415-417

Family HEXACROMYIDAE Haeckel, 1882 n. stat.

Hexacromyida Haeckel, 1882: 453 [as a tribe]; 1887: 170, 201 [as a subfamily]. — Schröder 1909: 9 [as a subfamily].

Hexalonchida Haeckel, 1882: 451 [nomen dubium, as a tribe];1887: 170, 179 [as a subfamily]. — Schröder 1909: 8 [as a subfamily].

Staurocontida Haeckel, 1882: 452 [nomen dubium, as a tribe];1887: 152, 163 [as a subfamily].

Hexacontida Haeckel, 1882: 452 [nomen dubium, as a tribe]; 1887: 170, 191 [as a subfamily]. — Schröder 1909: 9 [as a subfamily].

Staurocromyida Haeckel, 1882: 453 [nomen dubium, as a tribe]; 1887: 152, 166 [as a subfamily].

Hexadorida Haeckel, 1882: 455 [nomen dubium, as a tribe]; 1887: 170, 204 [as a subfamily]. — Schröder 1909: 9 [as a subfamily].

Cubosphaerida Haeckel, 1887: 55, 169-170 [as a family]. — Bütschli 1889: 1952 [as a family]. — nec Rüst 1892: 146. — Schröder 1909: 2 [as a family]. — Anderson 1983: 23.

Cubosphäriden [sic] – Haecker 1907: 118 [as a family].

Cubosphaeridae – Haecker 1908: 437. — Popofsky 1908: 209; 1912: 77, 84-87. — Enriques 1932: 982. — Clark & Campbell 1942: 31; 1945: 15. — Campbell & Clark 1944a: 14; 1944b: 5. — Deflandre 1953: 417. — Campbell 1954: D58. — Orlev 1959: 436. — Chediya 1959: 90. — Hollande & Enjumet 1960: 71-72. — Dieci 1964: 185. — Nakaseko & Sugano 1976: 122. — Tan & Su 1982: 142. — Tan 1998: 126. — Tan & Chen 1999: 146.

Hexalonchinae – Clark & Campbell 1942: 31 [nomen dubium]; 1945: 15. — Campbell 1954: D58. — Chediya 1959: 91. — Kozur & Mostler 1979: 20 ( sensu emend. ).

Hexacontinae – Campbell & Clark 1944a: 14 [nomen dubium]. — Campbell 1954: D60. — Chediya 1959: 92.

Hexadorinae – Campbell & Clark 1944b: 5 [nomen dubium]. — Chediya 1959: 94. — Petrushevskaya 1979: 107-108 ( sensu emend. ).

Staurocromyinae – Campbell 1954: D58 [nomen dubium]. — Chediya 1959: 88.

Staurocontiinae – Campbell 1954: D58 [nomen dubium].

Hexadoradinae – Campbell 1954: D60 [nomen dubium].

Cubosphaerinae – Campbell 1954: D58.

Stauracontinae [sic] – Chediya 1959: 87 (= Stauracontiinae) [nomen dubium].

Hexacromyinae – Campbell 1954: D60. — Chediya 1959: 93.

Hexadoridae – Dumitrica 1979: 21 [nomen dubium].

Nanininae Kozur & Mostler, 1982: 409.

Hexalonchidae – Dumitrica 1984: 94 [nomen dubium]; 1985: 186. — De Wever et al. 2001: 210, 212. — Afanasieva et al. 2005: S272-273. — Afanasieva & Amon 2006: 109.

Stauracontidae – Cachon & Cachon 1985: 279 [nomen dubium].

TYPE GENUS. — Hexacromyum Haeckel, 1882: 453 [type species by subsequent designation ( Campbell 1954: D60): Hexacromyum elegans Haeckel, 1887: 201 ].

INCLUDED GENERA. —? Carpocanthum Chen & Tan, 1989: 1. — Hexacromyum Haeckel, 1882: 453 (= Cubosphaera n. syn., Hexacontura n. syn.). — Hexalonchilla Haeckel, 1887: 184 (= Hexalonchusa synonymized by Petrushevskaya 1975: 569; Staurolonchantha n. syn.). — Nanina Kozur & Mostler, 1982: 409 (= Pentactinosphaera with the same type species).

NOMINA DUBIA. — Cromyostaurus , Cubaxonium , Hexacontanna , Hexacontarium , Hexacontosa , Hexacontium , Hexadoras , Hexalonchara , Hexaloncharium , Hexalonche, Hexalonchidium, Spongiuspinus , Staurancistra , Stauracontarium , Stauracontellium, Stauracontidium , Stauracontium, Stauracontonium , Staurocromyum , Staurolonchella , Staurolonchissa , Staurolonchura .

DIAGNOSIS. — Bladed six primary radial spines or bladed six radial beams are directly arising from a tetrapetaloid microsphere or a heteropolar microsphere with tetrapetaloid apical structures. Two or three latticed spherical shells are present (except for Nanina ).

Protoplasmic characters seem to be different between shallow and deep-water species. As for shallow water Hexacromyum and Hexalonchilla , the spherical endoplasm, reddish brown in color, fills the medullary shell and is outside of it. Capsular wall always situated within the cortical shell. A robust, straight, thick axoflagellum appears in Hexacromyum at least. Algal symbionts may be present or absent. Algal symbionts, if present, surround the endoplasm or are scattered within the cortical shell. No algal symbionts are outside of the cortical shell. As for the mesopelagic taxa of Hexacromyum , the endoplasm is a dark gray in color and fills the medullary shell. It is also found outside of it.

The Axopodial system is of centroaxoplastid-type: Axoplast is placed in the center of the endoplasm and is encrypted with a spherical nucleus. Bundles of axoneme penetrate through the one side of nucleus and form one thick bundle of axoneme in the endoplasmic reticulum zone of the intracapsular zone. This bundle probably forms a straight, thick and robust axoflagellum. A clear zone with radiated thin bundles of axoneme surrounds the nucleus. The axoplast is situated in the microsphere (the inner medullary shells) and the nucleus is placed in the outer medullary shell. A clear zone also appears inside the outer medullary shell. An endoplasmic reticulum occupies the space between the outer medullary shell and the cortical shell.

STRATIGRAPHIC OCCURRENCE. — Late Paleocene-Living.

REMARKS

This family was originally called Hexalonchidae , but this family name is a nomen dubium. Yuasa et al. (2009) first proved that Hexacromyum (originally Hexacontium ) is a member of Spumellaria . Several widely used taxon genus names such as Hexacontium and Hexalonche should be omitted in taxonomic works as they have been established on the basis of an un-illustrated type species. Internal skeletal structure, including growth line, was illustrated for Hexacromyum ( Nishimura 1986: fig. 7.1; Sugiyama et al. 1992: pl. 14, figs 5, 6, 8; van de Paverd 1995: pl. 33, fig. 7; pl. 34, fig. 5), Hexalonchilla ( Nishimura 1986: fig. 7.2; Suzuki 1998b : pl. 6, figs 2, 5-9) and Nanina (Nakaseko et al. 1982: pl. 1, figs 1-3; Sugiyama 1992a; pl. 1, fig. 1). A living image was given for Hexacromyum ( Yuasa et al. 2009: fig. 1a; Suzuki & Not 2015: fig. 8.8.8; Matsuoka 2017: figs 7.1, 7.2, 8.1, 8.2) and Hexalonchilla ( Suzuki & Not 2015: fig. 8.10.12). Protoplasm and algal symbionts were documented by epi-fluorescent observation via DAPI dyeing or other dyeing methods in Hexacromyum ( Ogane et al. 2010: figs 1.9-1.10, 2.9-2.10; Zhang et al. 2018: 11, figs 14, 15; p. 14, fig. 10; pl. 17, fig. 9) and Hexalonchilla ( Zhang et al. 2018: 11, fig. 16). Protoplasm was also illustrated for fixed specimens of Hexacromyum ( Aita et al. 2009: pl. 9, figs 1, 2; KrabberØd et al. 2011: figs 1.G-1.L). Fine protoplasmic structure was illustrated in Hexacromyum ( Hollande & Enjumet 1960: pl. 33, fig. 4; pl. 35, fig. 4). Hexacromyum can be infected by Marine Alveolata of Group II ( Ikenoue et al. 2016), but real images of these symbionts have not been captured as of yet.

Classic Hexalonche is largely transferred to Hexalonchilla . It is also mixed with Hexalonchetta (Hexacaryidae) , Hexancistra (Hexacaryidae) , Hexarhizacontium ( Rhizosphaeridae ), the sixradial spine-form of Centrolonche (Centrolonchidae) , and the six-radial spine-form of Stylosphaera (Stylosphaeridae) .They are carefully identified by an examination of their internal structure. Two shelled spherical radiolarians with six radial spines are generally classified into Hexalonchilla . However, types of bladed or non-bladed radial beams, types of bladed or non-bladed radial spines, and types of spherical and tetrapetaloid microspheres are still overlooked. For instance, the supporting image of Hexalonchilla in the catalogue has non-bladed radial beams, non-bladed radial spines and a tetrapetaloid microsphere, whereas the typeillustration for the representative genus shows non-bladed radial beams, bladed radial beam and a spherical microsphere.

Classic Hexacontium is largely transferred to Hexacromyum . It is also mixed with the six-radial spine-form of Axoprunum (Axoprunidae) , the six-radial spine-form of Haliomma (Haliommidae) and Hexacontella (Haliommidae) . Like in the case of Hexalonchilla , they were carefully identified by an examination of their internal structure. The morphological status of the radial spines, the radial beams and the microsphere were also poorly discriminated. Some three shelled morphospecies with six radial spines, likewise, have many radial beams between the outer double medullary shell and the cortical shell. Furthermore, some morphospecies, recovered from plankton samples, developed many fragile concentric shells between the outer double medullary shell and the cortical shell, which sometime is missing due to dissolution.

VALIDITY OF GENERA

Hexacromyum

Hexacromyum itself was used as a valid genus inPetrushevskaya (1975: 569).The usage of this genus in our paper is corresponded to the widely accustomed usage of Hexacontium . The definition of Hexacromyum mentioned the four concentric shells ( Campbell 1954: D60) but the “4th” shell of the neotype is additionally formed following the secondary growth mode of Ogane et al. (2009c) (See the supporting image for Cubosphaera in the Atlas part). Cubosphaera has “five or more concentric shells” ( Campbell 1954: D58) and Hexacontura has three concentric shells with irregular pores of dissimilar sizes ( Campbell 1954: D60). The subsequent “4th” or “5th” concentric shell illustrated in the type species of Cubosphaera is also the shell formed following the secondary growth mode of Ogane et al. (2009c). Pore size and shape continuously changed from regular pores with similar size, so this difference is related to species or within species variations, if we refer to the numerous photos in publications. Aita et al. (2009) observed Hexacromyum elegans in the plankton slide from the H.M.S. Challenger Station 271 which was examined by Haeckel himself.The type material for this species is from a “Central Pacific, Station, surface” ( Haeckel 1887: 201). The valid name is the oldest synonym among them (1882 for Hexacromyum ; 1887 for both Cubosphaera and Hexacontura ). However, one concern is the taxonomic status of Haliphormis . The specimen corresponding to the type-illustration of Haliphormis hexacanhtus in the Ehrenberg collection have a single cortical shell, whereas other specimens in the same collection have three concentric shell (see support image for Haliphormis in the Atlas ). If these specimens are conspecific, Haliphormis would not belong to the Hexacaryidae , and hence it would not be a senior synonym of Hexastylanthus , Hexastylettus , Hexastylissus and Hexastylurus . This means that Haliphormis is the oldest synonym among Hexacromyum , although the genus name Haliphormis has not been used for recent 50 years so the valid genus remains unchanged as Hexacromyum .

Hexalonchilla

Hexalonchilla partly corresponds to Hexalonche based on both concentric shells but is limited for those that have a heteropolar microsphere with un-bladed six radial beams. Hexalonchusa is characterized by irregular pores of dissimilar sizes and the spiny surface of the cortical shell ( Campbell 1954: D60) but these differences are related to infra- or intra-specific variations. The spiny surface is also induced by the preservation effect. Staurolonchantha was considered to have four equidistant main radial spines ( Campbell 1954: D56) but the lectotype has a typical structure with six radial spines ( Suzuki et al. 2009c: pl. 36, figs 2a-d). The lectotype of “ Haliomma hexagonum ” has an unclear innermost shell but has presumably three concentric shells. All these four “genera” were initially established with a subgenus rank in the same publication ( Haeckel 1887: 170 for Hexalonchilla , 186 for Hexalonchusa and 158 for Staurolonchantha ). In consideration of uncertainty for the type specimen of Staurolonchantha , the genus which is published first is selected as the valid name.

Nanina

Regarding the proposal of Nanina byKozur & Mostler (1982), the genus name was established as follows. The new taxon status for Nanina was first published as a tentative genus name: Pentactinosphaera Nakaseko et al. (1982) with the mention of “ We assigned it to Pentactinosphaera hokurikuensis (Nakaseko) as a tentative name ” (Nakaseko et al. 1982: 423). The available description for Pentactinosphaera was formally described by Nakaseko et al. (1983) with the same type species for Nanina by Kozur & Mostler (1982) published in December 1982. Under the description of Nanina, Kozur & Mostler (1982) cited Nakaseko et al. (1982) with the comment: “ described the internal structure of this genus for the first time ”, but they never cited the nomen nudum name “ Pentactinosphaera ” in the synonym list included in the English abstract or within the figure explanation ofNakaseko et al. (1982). At this time, the Code (ICZN 1964) included on page 93 a “code of ethics” which stated that: “ A zoologist should not establish himself a new taxon if he has reason to believe that another zoologist has already recognized the same taxon [...] He should communicate with the other zoologists [...] consider himself free to establish the new taxon only if the other zoologists [...] fail to do so in a reasonable period (not less than a year). ” As Kozur & Mostler (1982) recognized Nakaseko et al. (1982) as the first describer of the internal structure on page 409, there is no doubt they knew that Nakaseko would prepare a new taxonomic paper for “ Nanina ”. Despite the prescribed code of ethics, Kozur & Mostler (1982) established a new taxon without communicating with Nakaseko (Kozur, personal comm.; Nishimura, personal comm. to NS) and after a very short waiting period (less than a year). The problem is not to identify the first discoverer; instead, the problem lies in understanding why Kozur & Mostler (1982) did not respect the “code of ethics” which could have avoided future trouble regarding the author priority of the taxon, even though this is not a scientific requirement.