Lithomitra lineata, from

Belongs within: Nassellaria.
Contains: Eucyrtidiinae, Theocotylinae, Pterocoryinae.

The Eucyrtidioidea are a group of radiolarians with a multi-segmented, spindle-shaped skeleton known from the Triassic to the present (Afanasieva et al. 2005).

Characters (from Afanasieva et al. 2005): Multi-segmented spindle-shaped skeleton, composed of two to six, rarely more segments (up to 20). Cephalis small, variously constructed, clearly delineated from thorax. Segmentation of postcephalic test clear. Cephalis and thorax sometimes forming stable cephalothorax. Second to fourth or fifth to eighth segments largest in volume, in many genera one segment hyperbolised. External apophyses corresponding to spines A, D, and L developed rarely and present only in oligo-segmented taxa. Walls thin, with longitudinal arrangement of pores. Rows of pores may be separated by longitudinal costae. Pores may also be arranged in transverse rows or ortho-hexagonally.

Silicon rockets
Published 22 November 2020

In a previous post, I spoke of the radiolarians, marine protists renowned for their intricate skeletons, and the major radiolarian group known as the Spumellaria. Standing in contrast to the spumellarians is another major group, the Nassellaria. Like spumellarians, nassellarians have a skeleton of silica but whereas the basic shape of spumellarian skeleton is a sphere, that of nassellarians is a cone, bell or some similar shape, arranged along a longitudinal axis. The origination point of the skeleton is at or near the top of the cone and is known as the cephalis (from the Greek for ‘head’). There may be an apical spine rising above the cephalis. Below it, the skeleton is commonly divided into recognisable sections referred to as the thorax, abdomen and post-abdominal segments (if present). The nucleus of the cell is more or less associated with the cephalis, contained within it at least during the juvenile stage of development though it may shift below the cephalis as the cell matures (Suzuki et al. 2009).

Skeleton of a Eucyrtidium sp., copyright Picturepest.

As is commonly the case with unicellular organisms, radiolarian taxonomy has been influenced by disagreements about which features should be regarded as more significant. Some would arrange taxa based on the overal formation of the skeleton. Others would focus on the development of the initial embryonic spicule around which the cephalis develops. A recent phylogenetic analysis of living nassellarians by Sandin et al. (2019), based on both morphological and molecular data, found that overall skeleton morphology was a much better indication of relationships than the internal structure. One well supported subgroup of the Nassellaria is the superfamily Eucyrtidioidea.

Eucyrtidioids have a fossil record going back to the Triassic (Afanasieva et al. 2005). The cephalis is spherical and clearly distinguished from the following segments by a constricted basal aperture. The test is usually multi-segmented; members of the subfamily Theocotylinae may have just two segments but other members of Eucyrtidiidae have up to ten segments. Fossil families assigned to Eucyrtidioidea by Afanasieva et al. (2005) may have up to twenty (but as Afanasieva et al.‘s concept of Eucyrtidioidea was not found to be monophyletic by Sandin et al., the affinities of these fossil families perhaps warrant re-investigation). Segments are commonly divided by distinct inner rings. The skeleton lacks feet, the term used for protruding spines around the basal aperture of the skeleton found in many other nassellarians.

The phylogeny of nassellarians indicated by Sandin et al. (2019) places the Eucyrtidiidae as the sister taxon to other living nassellarians. Other living families included in the Eucyrtidioidea by Afanasieva et al. (2005) were placed in more nested positions. The implication is that the multi-segmented condition may be ancestral for crown Nassellaria. Segments are added progressively during the life of the radiolarian, leading the organism to look quite different at different ages. Indeed, this metamorphosis is pronounced enough that one of the earliest influential researchers on radiolarians, Ernst Haeckel (he of Kunstformen der Natur fame), made the mistake of classifying different ages as different species, genera and even families. Our understanding may be better than in Haeckel’s time but there may still be a lot to learn about these intricate organisms.

Systematics of Eucyrtidioidea
<==Eucyrtidioidea [Sethophaenida, Sethophatnida, Sethophatninae]AA05
    |  i. s.: Sethophaena Haeckel 1881AA05
    |--Eucyrtidiellum Baumgartner 1984 [Eucyrtidiellidae]AA05
    |    |--Ladinocampe Kozur 1984AA05
    |    |--Planispinocyrtis Kozur & Mostler 1981AA05
    |    `--Spinotriassocampe Kozur 1984 [incl. Bikinella Tikhomirova 1986]AA05
    |    |--Birkenmajeria Widz & De Wever 1993AA05
    |    |--Obeliscoites O’Dogherty 1994AA05
    |    `--Olanda Hull 1997AA05
    |    |--EucyrtidiinaeAA05
    |    |--TheocotylinaeAA05
    |    `--CalocyclinaeAA05
    |         |--Theocapsomma Haeckel 1887AA05
    |         |--Theocoronoium Haeckel 1887AA05
    |         `--Calocyclas Ehrenberg 1847AA05
    |              `--C. monumentumH04
    |    |--Aphetocyrtis Sanfilippo & Caulet 1998AA05
    |    |--Apoplanius Sanfilippo & Caulet 1998AA05
    |    |--Clinorhabdus Sanfilippo & Caulet 1998AA05
    |    |--Cyclampterium Haeckel 1887AA05
    |    |--Lophocyrtis Haeckel 1887AA05
    |    |--Paralampterium Sanfilippo 1990AA05
    |    `--Sciadiopeplus Sanfilippo 1990AA05
    |    |--Corum Blome 1984AA05
    |    |--Latium Blome 1984AA05
    |    |--Loopus Yang 1993AA05
    |    |--Pachus Blome 1984AA05
    |    |--Shana Wu & Pessagno 1993AA05
    |    `--Pseudodictyomitra Pessagno 1977AA05
    |         |--P. paronai (Aliev 1965)BW04
    |         `--P. pseudomacrocephala (Squinabol 1903)BW04
    |    |--Annulotriassocampe Kozur 1994AA05
    |    |--Nevanellus Kozur & Mostler 1981AA05
    |    |--Paratriassocampe Kozur & Mostler 1994AA05
    |    |--Pseudotriassocampe Kozur & Mostler 1994AA05
    |    |--Ruesticyrtium Kozur & Mostler 1979AA05
    |    |--Striatotriassocampe Kozur & Mostler 1994AA05
    |    |--Triassocampe Dumitrica, Kozur & Mostler 1980AA05
    |    |--Xiphotheca De Wever 1979AA05
    |    `--Yehamia Nakaseko & Nishimura 1979AA05
    |    |--Clavaxitus Dumitrica 1997AA05
    |    |--Foremanina Empson-Morin 1981AA05
    |    |--Neorelumbra Kiessling 1994AA05
    |    |--Novixitus Pessagno 1977AA05
    |    |--Praexitus Dumitrica 1997AA05
    |    |--Pseudoxitus Wu & Pessagno 1993AA05
    |    |--Tugurium O’Dogherty 1994AA05
    |    |--Crolanium Pessagno 1977AA05
    |    |    `--C. cuneatum (Smirnova & Aliev in Aliev & Smirnova 1969)BW04
    |    `--Xitus Pessagno 1977AA05
    |         |--X. elegans (Squinabol 1903)BW04
    |         `--X. mclaughlini (Pessagno 1977)BW04
    |--Pterocoryidae [Pterocorythidae]AA05
    |    |--PterocoryinaeAA05
    |    |--PodocyrtiinaeAA05
    |    |    |--Anthocyrtonium Haeckel 1887AA05
    |    |    |--Calocycletta Haeckel 1887AA05
    |    |    |--Phormocyrtis Haeckel 1887AA05
    |    |    |--Podocyrtis Ehrenberg 1847AA05
    |    |    `--Theocyrtis Haeckel 1887AA05
    |    `--SethocoryinaeAA05
    |         |--Antocyrtissa Haeckel 1887AA05
    |         |--Antocyrtura Haeckel 1887AA05
    |         |--Conarachnium Haeckel 1881AA05
    |         |--Phormocampe Haeckel 1887AA05
    |         |--Sethocorys Haeckel 1881AA05
    |         `--Sethocyrtis Haeckel 1887AA05
    |    |--Complexapora Kiessling 1992AA05
    |    |--Sethamphora Haeckel 1887LT61 [=Cryptocephalus Haeckel 1881 non Geoffroy 1762AA05]
    |    |--Excentropylomma Dumitrica 1970AA05
    |    |--Kozurium Pessagno 1977AA05
    |    |--Williriedellum Dumitrica 1970AA05
    |    |--Zhamoidellum Dumitrica 1970AA05
    |    |--Hemicryptocapsa Tan Sin Hok 1927AA05
    |    |    `--H. regularisBL79
    |    |--Holocryptocapsa Tan Sin Hok 1927AA05
    |    |    `--H. hindeiBL79
    |    |--Cryptamphorella Dumitrica 1970AA05
    |    |    |--C. conara (Foreman 1968)BW04
    |    |    `--C. sphaericaBL79
    |    `--Holocryptocanium Dumitrica 1970AA05
    |         |--H. barbui Dumitrica 1970BW04
    |         `--H. hinderBL79
    |    |--Asecta Popofsky 1913AA05
    |    |--Carpocanistrum Haeckel 1887AA05
    |    |--Carpocanium Ehrenberg 1847AA05
    |    |--Carpocanobium Haeckel 1887AA05
    |    |--Carpocanopsis Riedel & Sanfilippo 1971AA05
    |    |--Carpocryptocapsa Petrushevskaya 1981AA05
    |    |--Cystophormis Haeckel 1887AA05
    |    |--Myllocercion Foreman 1968AA05
    |    |--Sethamphorus Burma 1959AA05
    |    |--Tricolocapsa Haeckel 1881AA05
    |    |--Carpocanarium Haeckel 1887AA05
    |    |    `--C. papillosum (Ehrenberg 1872)BC98
    |    |--Diacanthocapsa Squinabol 1903 [Diacanthocapsidae]AA05
    |    |    `--D. ovoidea Dumitrica 1970BW04
    |    `--Cyrtocalpis Haeckel 1860 [incl. Cyrtolepis Rüst 1885]AA05
    |         |--C. operosaBL79
    |         `--C. ovalisBL79
         |--Artostrobium Haeckel 1887AA05
         |--Buryella Foreman 1973AA05
         |--Lithomitrella Haeckel 1887AA05
         |--Lithamphora Popofsky 1908AA05
         |--Lophocorys Haeckel 1881AA05
         |--Phormosctichoartus Campbell 1951AA05
         |--Poroamphora Popofsky 1904AA05
         |--Siphocampula Haeckel 1887AA05
         |--Siphostichartus Nigrini 1977AA05
         |--Spirocyrtis Haeckel 1881AA05
         |--Theocamptra Haeckel 1887AA05
         |--Tricolocampium Haeckel 1887AA05
         |--Botryostrobus Haeckel 1887AA05
         |    `--B. tumidulus (Bailey 1856)BC98
         |--Dictyoprora Haeckel 1881AA05
         |    `--*D. hexapleura (Haeckel 1887) [=Sethamphora hexapleura, Cryptocephalus (*Dictyoprora) hexapleurus]LT61
         |--Siphocampe Haeckel 1887AA05
         |    `--S. arachneaAA05
         `--Lithomitra Buetschli 1882AA05
              |--L. arachneaBC98
              `--L. lineata (Ehrenberg 1839)BC98

*Type species of generic name indicated


[AA05] Afanasieva, M. S., E. O. Amon, Y. V. Agarkov & D. S. Boltovskoy. 2005. Radiolarians in the geological record. Paleontological Journal 39 (Suppl. 3): S135–S392.

[BW04] Babazadeh, S. A., & P. de Wever. 2004. Early Cretaceous radiolarian assemblages from radiolarites in the Sistan Suture (eastern Iran). Geodiversitas 26 (2): 185–206.

[BL79] Basov, V. A., B. G. Lopatin, I. S. Gramberg, A. I. Danjushevskaya, V. Ya. Kaban’kov, V. M. Lazurkin & D. K. Patrunov. 1979. Lower Cretaceous lithostratigraphy near Galicia Bank. Initial Reports of the Deep Sea Drilling Project 47: 683–717.

[BC98] Bjørklund, K. R., G. Cortese, N. Swanberg & H. J. Schrader. 1998. Radiolarian faunal provinces in surface sediments of the Greenland, Iceland and Norwegian (GIN) Seas. Marine Micropalaeontology 35: 105–140.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

[LT61] Loeblich, A. R., Jr & H. Tappan. 1961. Remarks on the systematics of the Sarkodina (Protozoa), renamed homonyms and new and validated genera. Proceedings of the Biological Society of Washington 74: 213–234.

Sandin, M. M., L. Pillet, T. Biard, C. Poirier, E. Bigeard, S. Romac, N. Suzuki & F. Not. 2019. Time calibrated morpho-molecular classification of Nassellaria (Radiolaria). Protist 170: 187–208.

Suzuki, N., K. Ogane, Y. Aita, M. Kato, S. Sakai, T. Kurihara, A. Matsuoka, S. Ohtsuka, A. Go, K. Nakaguchi, S. Yamaguchi, T. Takahashi & A. Tuji. 2009. Distribution patterns of the radiolarian nuclei and symbionts using DAPI-fluorescence. Bulletin of the National Museum of Nature and Science, Series B 35 (4): 169–182.

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