Lithomelissa sirin, 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 : 45-46

Lithomelissa sirin n. sp.

Plate 17, Figs. 1 –11B.

urn:lsid:zoobank.org:act:E7AD61E4-915D-4C1A-B114-F5BEE876639A

cf. Lithomelissa sp. B aff. L. mitra Bütschli, Chen, 1975 , pl. 8, figs. 4–5.

Lithomelissa sp. aff. L. mitra Bütschli, Weaver and Dinkelman, 1978 , pl. 1, fig. 11.

cf. Lithomelissa cf. mitra Bütschli, O’Connor, 1999 , pl. 9, fig. 25.

unknown plagonid group C sp 26, Trubovitz et al., 2020, supplementary data 7.

Diagnosis. Lithomelissa with few or small and irregular pores on the cephalis, a strong and distinct apical spine, and a thorax of approximately the same width as the cephalis.

Description. The cephalis of this species ranges from broadly hemispherical in outline (i.e., figs, 2 and 4) to somewhat more elongated and kidney-shaped (i.e., figs. 1 and 3). However, having few and/or small pores irregularly distributed on the cephalis is a consistent characteristic of this species. Some species may even have a nearlyhyaline cephalis (i.e., figs. 4 and 6). The apical horn is the only spine present on the otherwise-smooth cephalis. This spine usually has a small rounded bulb of silica at its tip, and the base of the spine can be bladed where it exits the cephalis. This species has a strong ventral spine, and the dorsal and lateral spines protrude from the thorax about as far as the apical spine does from the cephalis. The thorax is cylindrical in shape, and exhibits larger and more numerous pores than the cephalis. When fully preserved, the thorax terminates with several small teeth (i.e., figs. 2, 7, 8, 9, and 10).

Remarks. Compared to Lithomelissa mitra (Pl. 15, Figs. 4A – 6 ), this species has more irregular pores, particularly on the cephalis (which can be completely hyaline). It also has a less distinct constriction at the neck than L. mitra , with the cephalis appearing to sink slightly into the thorax rather than developing the clear neck area present in L. mitra . The shape of the cephalis is less spherical than L. mitra , and can be slightly elongated in some specimens. The apical spine of this species often presents a little rounded bulb of silica at the tip, which is not a character we observed in L. mitra or L. alkonost (Pl. 16, Figs. 1A – 7B ). This species also differs from L. alkonost in that it lacks the bulge at the base of the dorsal side of the cephalis. Both L. sirin and L. dybbuki (Pl. 19, Figs. 1–7 ) have a single spine on the cephalis that often has a distinct rounded tip; however, L. sirin differs from L. dybbuki in its overall larger size, proportionally larger cephalis compared to the thorax, and tendency to have very small or few pores on the cephalis.

This species was figured by Weaver and Dinkelman (1978) as Lithomelissa sp. aff. L. mitra Bütschli. A similar form was illustrated by Chen (1975) as Lithomelissa sp. B aff. L. mitra Bütschli , but those specimens differed in being much more heavily silicified than the individuals observed in the present study. Otherwise, however, they are extremely similar in segment proportions and irregularity of pores, particularly on the cephalis. Chen (1975) ’s specimens are from the Oligocene, so it’s possible that this species was the ancestor of Lithomelissa sirin n. sp. O’Connor (1999) also figured a specimen identified as Lithomelissa cf. mitra Bütschli , which was described as having a poreless cephalis. This specimen has a very similar cephalis to our new species, but differs in its thorax, which has strong downward-curving winglike appendages. L. sirin has much weaker spines that extend sub-horizontal from the thorax.

Material examined. More than 400 specimens observed from samples 321-1337D-23H- 6, 134–137cm (Late Miocene), 321-1337A-18H-6, 77–80cm (Late Miocene), 321-1337A-16H- 6, 121–124cm (Late Miocene), 321- 1337A-14H-7, 39–42cm (Late Miocene), 321-1337A-12H-5, 23–26cm (Late Miocene), 321-1337A-10H-2, 91– 94cm (Early Pliocene), 321-1337A-7H- 6, 104–107cm (Early Pliocene), 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), and 321-1337A-3H- 2, 103–106cm (Middle Pleistocene).

Holotype. Pl. 17, Fig. 1 ; sample 321-1337A-16H- 6, 121– 124cm ; ECO-141; X39 -2 .

Paratypes. (1) Pl. 17, fig. 2; sample 321-1337A-16H- 6, 121–124cm ; ECO-142; M3-3. (2) Pl. 17, figs. 4A–B; sample 321-1337A-16H- 6, 121–124cm ; ECO-143; Y10-4. (3) Pl. 17, fig. 7; sample 321-1337A-16H- 6, 121–124cm ; ECO-143; O8-3. (4) Pl. 17, figs. 3A–B; sample 321-1337A-14H-7 , 39–42cm; ECO-138; P17-2. (5) Pl. 17, figs. 11A-B; sample 321-1337A-14H-7 , 39–42cm; ECO-140; M17-2. (6) Pl. 17, figs. 8A–B; sample 321-1337A-14H-7 , 39–42cm; ECO-140; R37-4 .

Measurements. Height of cephalis 39–45 (42)μm; width of cephalis 35–42 (38)μm; width at neck 31–36 (34)μm; width of thorax at shoulders 41–53 (44)μm. Based on 15 specimens.

Etymology. Named for the mythological creature of Slavic folklore, the Sirin, which has the head of a woman and the body of a bird and sings captivating songs.

Range. Late Miocene—Middle Pleistocene, 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 4. Examples of specimen measurements discussed in the Systematic Paleontology section of this study.

FIGURE 6. Internal skeletal structure of Arachnocorallium calvata (Haeckel, 1887) Petrushevskaya, 1971.

FIGURE 7. Internal skeletal structure of Arachnocorys umbellifera (Haeckel, 1862) Petrushevskaya, 1971.