Arachnocorys pentacantha wanii, Trubovitz, Sarah, Renaudie, Johan, Lazarus, David & Noble, Paula, 2022

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 : 21-22

Arachnocorys pentacantha wanii n. subsp.

Plate 5, Figs. 1A – 7B .

urn:lsid:zoobank.org:act:7E6BF77B-06FF-4793-8326-6554CC6B0823

Arachnocorys cf. pentacantha Petrushevskaya, 1971 , pl. 65, figs. 10–11.

Arachnocorys cf. pentacantha sp. 3 Trubovitz et al., 2020, supplementary data 7.

Diagnosis. Subspecies of Arachnocorys pentacantha that has a relatively larger and wider cephalis than the typical form, and a thorax that attaches relatively lower toward the base of the cephalis.

Description. This subspecies of Arachnocorys pentacantha has consistently larger measurements and a larger cephalis:thorax ratio. It also has the thorax attachment relatively lower on the cephalis than typical in A. pentacantha pentacantha . While A. p. pentacantha often has arches of the thorax reaching the upper third of cephalis, this subspecies has arches reaching only the lower third of the cephalis. In the material used for this study, we observed an average cephalis height of 59 microns for A. p. wanii, whereas typical A. p. pentacantha specimens had a cephalis height of approximately 45 microns.

Remarks. This form was first recognized by Petrushevskaya (1971) as Arachnocorys cf. pentacantha . She illustrated it beside Arachnocorys pentacantha to show its relatively larger size. In her emendation of Arachnocorys pentacantha , she determined that the cephalis height of this species is between 35–45 microns. By contrast, the Arachnocorys cf. pentacantha form she identified has a cephalis height of approximately 60 microns. She did not mention observing any specimens with intermediate dimensions, suggesting that they could be different taxa. Petrushevskaya (1971) also noted that Arachnocorys cf. pentacantha differs in that it has smaller gaps between the cephalis and thorax, and the pores on the anterior side of the cephalis are proportionally smaller. In our material, many specimens similar to Petrushevskaya’s Arachnocorys cf. pentacantha were observed. The cephalis height of these specimens averaged 59 microns, ranging between 54–67 microns, making it approximately the same size as Petrushevskaya’s specimens. Some specimens had relatively smaller pores on the anterior side of the cephalis whereas others did not, suggesting that this may be a developmental feature and should not be used to strictly distinguish this subspecies from classic A. p. pentacantha . Another difference between A. p. pentacantha and this new subspecies, is that the apical horn protrudes near the cephalis maximum height in A. p. pentacantha , whereas in A. p. wanii n. subsp., the apical horn tends to depart from the wall of the cephalis before it reaches its maximum height. A few specimens were observed that did not neatly fit into the classic concept of A. p. pentacantha nor the new subspecies wanii; they exhibited a cephalis height between ~45 and 55 microns. Because of these somewhat intermediate forms, we are establishing a subspecies rather than a new species until the range of variability can be confidently determined.

Material examined. 64 specimens from samples 321-1337A-6H-3, 29–32cm (Late Pliocene), 321-1337A-5H-5, 11–14cm (Late Pliocene), 321-1337A-4H-6, 115–118cm (Early Pleistocene), 321-1337A-4H-2, 16–19cm (Middle Pleistocene), 321-1337A-3H- 2, 103–106cm (Middle Pleistocene), 321-1337A-2H-3, 76–79cm (Late Pleistocene), 321-1337D-1H-1, 0–3cm (Recent).

Holotype. Pl. 5, Figs. 1A–C ; sample 321-1337A-4H-2 , 16–19cm; ECO-127; P21-1 .

Paratypes. (1) Pl. 5, figs. 3A–B; sample 321-1337A-3H- 2, 103–106cm; ECO-126; G2-2. (2) Pl. 5, figs. 6A–B; sample 321-1337A-3H- 2, 103–106cm; ECO-126; J42-3. (3) Pl. 5, figs. 7A-B; sample 321-1337A-3H- 2, 103–106cm; ECO-126; Y4-3. (4) Pl. 5, fig. 5; sample 321-1337A-4H-2, 16–19cm; ECO-127; P19-3. (5) Pl. 5, figs. 2A-B; sample 321-1337A-3H- 2, 103–106cm; ECO-126; D37-3.

Measurements. Height of cephalis 64–67 (59)μm; maximum width of cephalis 42–50 (47)μm; width of thorax at emergence of primary spines, approximately the maximum width 53–63 (59)μm. Based on 13 specimens.

Etymology. Named for the Japanese sea monster yokai, Wani.

Range. Late Pliocene—Recent in the EEP ( 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 7. Internal skeletal structure of Arachnocorys umbellifera (Haeckel, 1862) Petrushevskaya, 1971.