CATALOG OF ORIGINAL DESCRIPTIONS: Actinomma medianum Nigrini 1967

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Higher levels: rads_cat -> A -> Actinomma -> Actinomma medianum
Other pages this level: << < A. golownini, A. haysi, A. henningsmoeni, A. heptacanthum, A. hexactis, A. hexagonium, A. hirsutum, A. holtedahli, A. imperfecta, A. intermedium, A. japonicum, A. kerguelenensis, A. leptodermum longispina, A. livae, A. magnifenestra, A. medianum, A. mediterranensis, A. miocenicum, A. mirabile, A. multispinula, A. nigriniae, A. octoacanthium, A. okurai, A. pachycapsa, A. pachyderma, A. pellucidata, A. plasticum, A. polyceris, A. regulare, A. rotula, A. saccoi> >>

Actinomma medianum

Citation: Actinomma medianum Nigrini 1967
Rank: species
Type specimens: pl.2, fig.2
Type repository: Holotype: LSDA 124G, A-P25/0; Sedgwick Museum No.856.5. U.K.
Described on page(s) : p.27
Family (traditional): Actinommidae
Family (modern): Rhizosphaeridae

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Current identification/main database link: Actinomma medianum Nigrini 1967

Original Description
Cortical shell a somewhat irregular sphere, thin-walled, with 9-12 subcircular to subangular pores on a half-equator. Medullary meshwork irregular, more delicate than, but otherwise similar to, that of Actinomma antarcticum (p.26), with an internal shell having 2.5-3 subcircular pores on a half-equator (cf. pl. 2, fig. 2b).
Numerous radial beams extend from the outer surface of the medullary meshwork to the cortical shell and sometimes extend externally. Additional, more delicate spines, originating on the cortical surface, are present in some specimens. Occasionally, these spines support a delicate extracortical shell.

Diameter of cortical shell 164-227µm; of medullary shell 81-100µm. Inner medullary capsule approximately one-third the diameter of the medullary meshwork. Distinguishing characters (rw): This species was first described by Nakaseko (1959) as A. capillaceum. However, the specific name chosen by Nakaseko is preoccupied by Actinomma (Actinommura) capillaceum. Therefore, according to Article 57(a) of the International Code of Zoological Nomenclature, the specific name capillaceum is unavailable and cannot be used in the genus Actinomma. Although this was brought to the attention of Dr. Nakaseko several months prior to publication, he has not proposed another name. The species must, therefore, be described as new herein. The specific name medianum has been selected because the species exhibits characters intermediate between A. antarcticum (p.26) and A. arcadophorum (p.29) - It may be distinguished from the former by its simply latticed cortical shell and more delicate medullary meshwork, and from the latter by its larger cortical pores and heavier medullary meshwork. Distribution of A. medianum in the Indian Ocean is also intermediate between that of A. antarcticum and A. arcadophorum. A. antarcticum is found in cold (Antarctic) water, A. medianum in cool (middle latitude) water, and A. arcadophorum in warm (low latitude) water.

Editors' Notes
Occurrence previously recorded.- Nakaseko (1959) - Second Japanese Antarctic Research Expedition Station 9 (68°31’ S., 37°12’ E., 570 m).
Indian Ocean occurrences (fig. 11) - A. medianum is almost completely absent from low latitudes, but forms 6 percent to 12 percent of the described population in middle latitude samples. The species is present in high latitudes, but is far outnumbered by A. antarcticum (p.26). A. medianum appears to be a reliable and potentially useful member of the middle latitude assemblage. Holotype: LSDA 124G, A-P25/0; Sedgwick Museum No.856.5.


Nigrini, C. A. (1967). Radiolaria in pelagic sediments from the Indian and Atlantic Oceans. Bulletin of the Scripps Institution of Oceanography. 11: 1-125. gs


Actinomma medianum compiled by the radiolaria@mikrotax project team viewed: 20-4-2021

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