Arachnocorallium calvata ( Haeckel, 1887 ) Petrushevskaya, 1971

Trubovitz, Sarah, Renaudie, Johan, Lazarus, David & Noble, Paula, 2022, Late Neogene Lophophaenidae (Nassellaria, Radiolaria) from the eastern equatorial Pacific, Zootaxa 5160 (1), pp. 1-158 : 17

Arachnocorallium calvata ( Haeckel, 1887) Petrushevskaya, 1971

Plate 3, Figs. 1A – 3B .

Arachnocorys circumtexta (juv.?), Hertwig, 1879, p. 79, pl. 8, fig. 2a.

Arachnocorys hexaptera n. sp., Haeckel, 1887, sp. 1271.

? Lychnodictyum scaphopodium n. sp., Haeckel, 1887, pl. 56, fig. 4.

Psilomelissa calvata n. sp., Haeckel, 1887, p. 1212, pl. 56, fig. 3.

Peridium spinipes Haeckel, Popofsky, 1913 , text-figs. 33–34 (non text-figs. 31–32).

Arachnocorallium calvata Haeckel , emend., Petrushevskaya, 1971, pl. 70, figs. 1–8.

Arachnocorallium calvata Haeckel group, Boltovskoy and Riedel, 1987, pl. 3, fig. 24.

Arachnocorallium calvata Haeckel, Itaki et al., 2008b , pl. 4, fig. 27 (? fig. 26).

Arachnocorallium calvata Petrushevskaya, Bjørklund et al., 2012 , pl. 4, figs. 8–9.

Arachnocorallium calvata Petrushevskaya group, Matsuzaki et al., 2019, pl. 2, figs. 6–9.

Arachnocorallium calvata Haeckel, Matsuzaki et al., 2020 , pl. 6, fig. 7, 9–10 (?figs. 6, 8).

Arachnocorallium calvata Haeckel, Trubovitz et al., 2020 , supplementary data 7.

? Arachnocorallium cf. calvata Haeckel, Trubovitz et al., 2020 , supplementary data 7.

Remarks. This species appears to be often confused with species of Archiperidium (formerly Peridium ), another lophophaenid that lacks a thoracic segment, in the literature. Here we follow Petrushevskaya’s (1971) concepts of Arachnocorallium and Archiperidium . Archiperidium differs from the former in that the apical spine is more clearly expressed, usually with a set of relatively large, paired pores on the cephalis running along the apical spine. However, even ignoring the confusion regarding Archiperidium and Arachnocorallium , Arachnocorallium calvata (Haeckel) Petrushevskaya, 1971 , seems to have highly variable development and/or preservation of cephalic horns and the thoracic segment. In the material we observed, some Arachnocorallium specimens had short spines on the cephalis, or none at all, which we identified as Arachnocorallium calvata sensu Petrushevskaya (1971) , pl. 70, figs. 1–6, 8 (Pl. 3, Figs. 1A–B in this manuscript). Other specimens we observed resembled Arachnocorallium calvata in most characteristics, except that these specimens exhibited three long, thin cephalic horns, that extended upward by approximately the same length as the cephalis (Pl. 3, Figs. 2A–B ). Petrushevskaya (1971) mentioned observing an alternate form of Arachnocorallium calvata with three horns on the cephalis. She illustrated one such specimen on pl. 70, fig. 7, but this individual differs from our specimens in that its spines are shorter and relatively weaker. In Trubovitz et al. (2020) these 3-horned specimens were considered Arachnocorallium cf. calvata ; however, it is possible that spine development could constitute intraspecific variation or be a preservational artifact. Future work involving well-preserved specimens and genetic diversity within this genus is needed to determine whether specimens showing different types of cephalic spines, and different levels of thorax development should be considered multiple species.

Range. Arachnocorallium calvata was present from the early Late Miocene—Recent in the EEP. The form of this species exhibiting three equally-prominent spines on the cephalis was observed only from the Early Pleistocene– Recent in the EEP. See Table 1 .

Figures

FIGURE 1. Diagram illustrating the general skeletal morphology of Lophophaenidae, and terminology used in this manuscript. Dashed lines indicate spines that are not visible from the angle shown, as they extend into the skeleton. An example specimen of Lophophaena casperi n. sp. is included for comparison to the diagrams.

FIGURE 2. Relative abundance of specimens and taxa belonging to Plagiacanthoidea and Lophophaenidae per sample, from IODP Site U1337 in the EEP over the last ~10 Ma. The relative percentages of total taxa are represented by the blue lines and the red lines represent the percentages of total specimens (triangles = Plagiacanthoidea; circles = Lophophaenidae). The Plagiacanthoidea was among the most abundant and speciose of radiolarian groups encountered in Trubovitz et al. (2020), with at least 10% of the specimens and 20% of the taxonomic richness in every sample. Within the Plagiacanthoidea, lophophaenids consistently made up the majority of specimens (~67%) and taxa (~61%). Data are from Trubovitz et al. (2020).

FIGURE 3. Locality map of IODP Site U1337, where all samples for this study were collected. Map from Google EarthTM.