PLAGIACANTHIDAE Hertwig, 1879

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 : 505-507

Family PLAGIACANTHIDAE Hertwig, 1879

sensu Dumitrica (2004)

Plagiacanthiden [sic] Hertwig, 1879: 200-202 (= Plagiacanthidae ) [as a family].

Triplagida Haeckel, 1882: 423 [as a tribe];1887: 908 [as a subfamily].

Plagonida Haeckel, 1882: 423 [nomen dubium, as a subfamily]; 1887: 906-908 [as a family]. — Bütschli 1889: 1975 [as a family]. — Anderson 1983: 29 [as a family].

Tetraplagida Haeckel, 1882: 423 [nomen dubium, as a tribe]:1887: 908, 911 [as a subfamily].

Plectanida Haeckel, 1882: 424 [as a subfamily];1887: 906, 919-921 [as a family]. — Anderson 1983: 29 [as a family].

Polyplagida Haeckel, 1882: 424 [nomen dubium, as a tribe]; 1887: 908, 917 [as a subfamily].

Polyplectida Haeckel, 1882: 424 [as a tribe]; 1887: 921, 929 [as a subfamily].

Tetraplectida Haeckel, 1882: 424 [nomen dubium, as a tribe];1887: 921, 923 [as a subfamily].

Triplectida Haeckel, 1882: 424 [nomen dubium, as a tribe]; 1887: 921 [as a subfamily].

Cystidina [sic] – Haeckel 1884: 30 (= Cystidiidae) [as a family].

Nassellida Haeckel, 1887: 896 [nomen dubium, as a family]. — Anderson 1983: 29 [as a family].

Hexaplagida Haeckel, 1887: 908, 915 [nomen dubium, as a subfamily].

Hexaplectida Haeckel, 1887: 921, 927 [nomen dubium, as a subfamily].

Nasselida [sic] – Bütschli 1889: 1975 (= Nassellidae ) [as a family].

Plectanidae – Popofsky 1908: 262; 1913: 277. — Schröder 1914: 72. — Wailes 1937: 12. — Chediya 1959: 166. — Tan & Tchang 1976: 269. — Tan & Chen 1999: 268. — Tan & Su 2003: 81.

Plagoniidae – Poche 1913: 219 [nomen dubium]. — Campbell 1954: D103. — Riedel 1967b: 295 ( sensu emend. ); 1971: 655- 656. — Sanfilippo & Riedel 1973: 529. — Nakaseko et al. 1975: 173. — Nakaseko & Sugano 1976: 129. — Riedel & Sanfilippo 1977: 869-870. — Petrushevskaya 1981: 97. — Anderson 1983: 40. — Boltovskoy 1998: 33. — Anderson et al. 2002: 1005. — Afanasieva et al. 2005: S293. — Afanasieva & Amon 2006: 140.

Plagonidae [sic] – Popofsky 1908: 262 [nomen dubium] (= Plagoniidae ). — Schröder 1914: 72. — Chediya 1959: 164. — Cachon & Cachon 1985: 291 ( sensu emend. ).

Nassellidae – Poche 1913: 219 [nomen dubium]. — Chediya 1959: 163.

Plagoniinae – Campbell 1954: D103 [nomen dubium].

Cystidiidae – Campbell 1954: D103. — Petrushevskaya 1981: 98. — Afanasieva et al. 2005: S293. — Afanasieva & Amon 2006: 140.

Triplagiinae – Campbell 1954: D104.

Plectaniidae – Campbell 1954: D104. — Chen & Tan 1996: 152. — Chen et al. 2017: 164.

Plectaniinae – Campbell 1954: D104. — Petrushevskaya 1981: 72. — Afanasieva et al. 2005: S292. — Afanasieva & Amon 2006: 139.

Tetraplagiinae – Campbell 1954: D104 [nomen dubium].

Tetraplectinae – Campbell 1954: D104 [nomen dubium]. — Chediya 1959: 166. — Petrushevskaya 1981: 304-305. — Afanasieva et al. 2005: S293. — Afanasieva & Amon 2006: 140.

Triplectinae – Campbell 1954: D104 [nomen dubium]. — Chediya 1959: 166. — Tan & Tchang 1976: 269.

Enneaplegmatinae Campbell, 1954: D105.

Triplaginae – Chediya 1959: 164.

Hexaplaginae – Chediya 1959: 165 [nomen dubium].

Polyplaginae [sic] – Chediya 1959: 165 [nomen dubium] (= Polyplagiidae).

Polyplectinae – Chediya 1959: 167.

Hexaplectinae – Chediya 1959: 167 [nomen dubium].

Plagiacanthidae – Petrushevskaya 1971a: 69 ( sensu emend. );1971b: 988-989 ( sensu emend. ); 1981: 73-74; 1986: 132. — Dumitrica 1979: 28, 30; 2004: 198-199 ( sensu emend. ). — Goll 1979: 383 ( sensu emend. ). — Takahashi 1991: 92. — Hollis 1997: 55. — Sugiyama 1998: 233. — Kozlova 1999: 104. — De Wever et al. 2001: 219. — Afanasieva et al. 2005: S268 ( sensu emend. ). — Afanasieva & Amon 2006: 100.

Plagiacanthinae – Petrushevskaya 1971a: 147-149; 1971b: 990; 1981: 91-92. — Takahashi 1991: 92. — De Wever et al. 2001: 219, 221. — Dumitrica 2004: 216. — Afanasieva et al. 2005: S269. — Afanasieva & Amon 2006: 102.

Plagiacanthida [sic] – Nishimura 1990: 81 (= Plagiacanthidae ) ( sensu emend. ).

TYPE GENUS. — Plagiacantha Claparède in Müller, 1856: 500 [type species by monotypy: Acanthometra arachnoides Claparède, 1855: 675 ].

INCLUDED GENERA. — Arachnocalpis Haeckel, 1882: 427 . — Cystidium Hertwig, 1879: 214 (= Paracystidium n. syn.). — Dumetum Popofsky, 1908: 264 (= Pentaplagia synonymized by Dumitrica 2004: 216). — Enneaplegma Haeckel, 1882: 424 (= Polyplecta with the same type species). — Jeanpierria Dumitrica, 2004: 217 . — Neosemantis Popofsky, 1913: 298 (= Deflandrella synonymized by Dumitrica 1978: 240). — Plagiacantha Claparède in Müller, 1856: 500 (= Plagoniscus n. syn.; Triplagia synonymized by Dumitrica 2004: 199; Triplagiacantha synonymized by Petrushevskaya 1981: 96). — Plectagonidium Cachon & Cachon, 1969: 236 . — Plectanium Haeckel, 1882: 424 (= Plectaniscus n. syn.). — Pseudocubus Haeckel, 1887: 1010 (=? Drepotadium n. syn.; Rhizoplecta synonymized by Dumitrica 1973a: 836; Talariscus synonymized by Petrushevskaya 1971a: 149).

INVALID NAME. — Hexaplecta.

NOMINA DUBIA. — Hexaplagia , Hexaplegma , Nassella , Plagonidium , Plagonium, Plectophorina , Polyplagia , Tetraplagia , Tetraplecta , Triplecta .

JUNIOR HOMONYMS. — Campylacantha JØrgensen, 1905 (= Neosemantis ) nec Scudder, 1897; Obeliscus Popofsky, 1913 (= Talariscus) nec Beck, 1837; Plectophora Haeckel, 1882: 424 (= Plectophorina) nec Gray 1834: captions for pl. 42, fig. 2.

DIAGNOSIS. — The skeleton is exclusively made of bladed, initial spicules. No arch develops between A- and V-rods (e.g., AV-arch) Sagittal ring is absent, unlike other genera of Acanthodesmioidea . Protoplasm was observed in Cystidium, Neosemantis, Plagiacantha and Pseudocubus . The yellowish to brown endoplasm is located within the spicules’ area. In fully grown specimens, the endoplasm extends beyond this area. Except for Cystidium, no algal symbionts are observed in any known genera. Fine pseudopodia radiate around the endoplasm in Cystidium and Neosemantis . The terminal cone is visible from the base of the Pseudocubus’ cephalic part. No axial projection is observed.

STRATIGRAPHIC OCCURRENCE. — late Middle Eocene-Living.

REMARKS

This taxon is rarely illustrated in references. However, the spicular system of the following genera is examinable in references:? Dumetum ( Sugiyama 1992a: pl. 1, fig. 5), Neosemantis ( Nishimura & Yamauchi 1984: pl. 22, figs 7, 10; Nishimura 1990: fig. 13.1, 13.2, 12.4, 12.6; Takahashi 1991: pl. 27, fig. 12; Sugiyama et al. 1992: pl. 20, fig. 2), Plagiacantha ( Nishimura 1990: fig. 13.3?), and Pseudocubus (Sugiyama et al. 1992: pl. 18, figs 1-3; Sugiyama 1993: figs 7.1-7.3, 8.1; Funakawa 1995a: pl. 4, figs 1-3, pl. 5, figs 1-3). The shell is too small and too transparent to observe in seawater, as such Plagiacanthidae can only be identified at higher magnifications (40x or 60x objective lens) with a phase-contrast microscope or a Nomarski differential interference contrast microscope. Under such constraints, “living images” were illustrated for Cystidium ( Anderson 1977: pl. 1, figs 1, 2; Probert et al. 2014: S1, SES 28), Neosemantis (Matsuoka 2017: fig. 17), Plagiacantha ( Sashida & Kurihara 1999: fig. 11.18; Suzuki et al. 2009b: figs 3A, 3B; Zhang et al. 2018: 13, fig. 25), and Pseudocubus ( Sashida & Uematsu 1994: figs 3.8, 3.9; Sashida & Kurihara 1999: fig. 12.12; Matsuoka 2007: fig. 4d; Suzuki & Not 2015: fig. 8.11.11; Zhang et al. 2018: 15, fig. 19). Algal symbionts of Cystidium were identified as Brandtodinium nutricula by Probert et al. (2014). Ultrafine cellular structure was documented for Cystidium ( Anderson 1977).

VALIDITY OF GENERA

Cystidium

The original French description for Paracystidium is translated as follows: “ Paracystidium has all the characteristics of Cystidium, except for the occurrence of a very small spicule, free in the protoplasm surrounding the central capsule and located at its aboral pole. ” Cystidium is a type of naked Nassellaria ; the differences specified in its description are minor and could indicate either different ontogenetic stages or different species. The name Cystidium is older than Paracystidium .

Plagiacantha

According to the type-illustrations, Plagiacantha ( Claparède & Lachmann 1858: pl. 22, fig.9), Triplagia ( Haeckel 1887: pl. 91, fig.2), and Triplagiacantha ( Hertwig 1879: pl. 7, fig. 6) appear to have only three robust rods, but as the supporting image for Plagiacantha ( Dumitrica 1973b: pl. 22, figs 2, 4) shows, the main rods are identified as A-, D-, and double L-rods; thus, these genera have four rods in principle. It is likely that a short D-rod was overlooked in these type-illustrations. Triplagia and Triplagiacantha have been synonymized with Plagiacantha in previous studies. The architecture of Plagoniscus is identical to that of Plagiacantha , except for a long D-rod that has variable length among species. Plagiacantha is the oldest available name among these genera.

Plectanium

Plectanium has six radial spines that arise in two opposite groups from poles of the common central rod ( Campbell 1954: D104). Plectaniscus has four radial spines that arise from the common central point, and its apical spine differs from three basal spines ( Campbell 1954: D104-105). Specimens identifiable as Plectanium (the supporting image for Plectanium in the Atlas ) possess four bladed rods, not six. It is unnecessary to differentiate these groups at the genus level. If the type-illustration ( Haeckel 1887: pl. 91, fig. 11) is accurate, then the two opposite groups arising from poles of the common central rod illustrated in Haeckel (1887) appear similar to the initial spicular system of the conjoined individuals shown in Dumitrica (2013b: fig. 2.2). The name Plectanium is older than Plectaniscus .