Lithomelissa alkonost, 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 : 41-42

Lithomelissa alkonost n. sp.

Plate 16, Figs. 1A – 7B .

urn:lsid:zoobank.org:act:2904452E-3B02-47D6-9F23-0E37211ED8F2

? Lithomelissa sp. A , Kamikuri, 2019, pl. 6, fig. 5.

unknown plagonid group C sp 3, Trubovitz et al., 2020, supplementary data 7.

Diagnosis. Lithomelissa with an elongated, irregular-shaped cephalis that has small pores and a distinctive bulge on the dorsal side of the neck area.

Description. This species is identifiable for its long, irregular-shaped cephalis, which typically has pores smaller in size than those on the thorax. The cephalis can be widest near the top third of the segment (i.e., figs. 3, 4, 6, and 7), or approximately the same width throughout (i.e., figs. 1, 2, and 5). The apical spine runs through the interior of the cephalis, clearly placing this species in Lithomelissa . The neck area is distinct for being approximately the same width as the rest of the shell, and having a large bulge on the bottom third of the cephalis on the dorsal side, where the AD and AL arches run along the wall of the cephalis. This forms an outward bulge on the dorsal side of the cephalis. The thorax is about the same width as the cephalis, but can be slightly narrower. Both the thorax and cephalis tend to have pores distributed irregularly, occasionally leaving hyaline areas on the shell. Appendages on the thorax derived from the dorsal and lateral spines are short and/or poorly-developed. At the junctions of the median bar with the lateral and dorsal spines, there are short, thornlike, downward hanging skeletal elements that do not connect to the thorax. The base of the thorax can fully enclose at the base with short feet, if the skeleton is fully developed and well preserved. However, such specimens were rare in our material.

Remarks. This species is similar in overall structure to Lithomelissa sirin n. sp. (Pl. 17, Figs. 1 –11B), but differs in that the cephalis is larger, more irregular, and elongated, and is always at least as wide as thorax. This relatively wide cephalis and large bulge at the neck differentiates this species from both Lithomelissa mitra (Pl. 15, Figs. 4A – 6 ) and Lithomelissa sirin n. sp. The thin, sometimes nearly hyaline nature of the cephalis wall and irregular pores throughout the shell differentiate this species from Lithomelissa ehrenbergi (Pl. 15, Figs. 7A–C ), L. cheni (Pl. 15, Figs. 3A–B ), and L. celsagula (Pl. 15, Figs. 1A – 2B ). This species shows significant variation in overall size, but the proportions remain consistent. The apical horn tends to be thin and short, compared to the other Lithomelissa species we observed. This species resembles a specimen figured by Kamikuri (2019) (pl. 6, fig. 5), but is on average is slightly smaller in size and has fewer, more irregular pores throughout the skeleton. However, once we have a better understanding of the variability within L. alkonost , it may be determined that they are conspecific.

Material examined. 76 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-4H- 6, 115–118cm (Early Pleistocene), and 321-1337A-3H- 2, 103–106cm (Middle Pleistocene).

Holotype. Pl. 16, Figs. 1A–B ; sample 321-1337A-14H-7 , 39–42cm; ECO-138; U15-3.

Paratypes. (1) Pl. 16, figs. 3A–B; sample 321-1337A-16H- 6, 121–124cm; ECO-141; Q26-3. (2) Pl. 16, figs. 4A-B; sample 321-1337A-16H- 6, 121–124cm; ECO-143; P14-2. (3) Pl. 16, fig. 5; sample 321-1337A-16H- 6, 121– 124cm; ECO-143; M3-2. (4) Pl. 16, fig. 6; sample 321-1337A-16H- 6, 121–124cm; ECO-143; C17-2. (5) Pl. 16, figs. 7A-B; sample 321-1337A-16H- 6, 121–124cm; ECO-141; K17-2. (6) Pl. 16, figs. 2A-B; sample 321-1337A-16H- 6, 121–124cm; ECO-143; Q5-2. (7) [not figured] sample 321-1337A-16H- 6, 121–124cm; ECO-142; X34-3.

Measurements. Height of cephalis 39–56 (48)μm; width of cephalis 36–48 (42)μm; width of thorax at shoulder area 34–44 (39)μm; ratio of cephalis width:thorax width 0.9–1.2 (1.1). Measurements based on 24 specimens.

Etymology. Named for the woman-headed bird, Alkonost, the counterpart to Sirin in Slavic mythology.

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 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.

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.