Set number: 255

  • Aculithus rioi 30092 1
  • Aculithus rioi 30095 2
  • Aculithus rioi 30099 3
  • Aculithus rioi 30079 4
  • Aculithus rioi 30093 5
  • Aculithus rioi 30094 6
  • Aculithus rioi 30098 7
  • Pennalithus rioi 30074 8
  • Aculithus rioi 30106 9
  • Aculithus rioi 30060 10
  • Aculithus rioi 30070 11
  • Aculithus rioi 30090 12
  • Aculithus rioi 30110 13
  • Aculithus rioi 30059 14
  • Aculithus rioi 30069 15
  • Aculithus rioi 30084 16
  • Aculithus rioi 30091 17
  • Aculithus rioi 30089 18
  • Aculithus rioi 30088 19
  • Aculithus rioi 30087 20
  • Aculithus rioi 30086 21
  • Aculithus rioi 30081 22
  • Aculithus rioi 30077 23
  • Aculithus rioi 30080 24
    10µm
Velonalithus , Middle Miocene, ODP Leg 154, Site 925C, Ceara Rise, Equatorial Atlantic Ocean

in mobile mount

Set number: 256

  • Aculithus rioi 30323 1
  • Aculithus rioi 30326 2
  • Aculithus rioi 30327 3
  • Aculithus rioi 30316 4
  • Aculithus rioi 30324 5
  • Aculithus rioi 30325 6
  • Aculithus rioi 30328 7
  • Aculithus rioi 30322 8
  • Aculithus rioi 30336 9
  • Aculithus rioi 30340 10
  • Aculithus rioi 30338 11
  • Aculithus rioi 30320 12
  • Aculithus rioi 30335 13
  • Aculithus rioi 30341 14
  • Aculithus rioi 30337 15
  • Aculithus rioi 30321 16
    10µm
Velonalithus rioi, Middle Miocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

in mobile

Final Epithet
Pennalithus rioi (Olafson, 1989) varol, 2025
Basionym

Triquetrorhabdulus rioensis Olafsson, 1989

Synonyms

1998 Triquetrorhabdulus rioi Olafsson – Young in Bown, Pl. 9, Fig. 18, 19 non-Pl. 9, Fig. 17, 20.

Remarks

Narrower species of Pennalithus exhibit two blades of slightly unequal width and a median ridge, often straight. This species naturally settles in the plan or side views.

Optical Properties: In the side view, Pennalithus rioi displays high birefringence (Plate 18, Figs. 9-11, 13-15 in Varol, 2025). The blade shows first-order yellow interference colours, while the ridge exhibits second-order red and blue colours. Pennalithus rioi produces parallel extinction, with an extinction angle of 0° (Plate 18, Figs. 10, 14 in Varol, 2025). It exhibits length-slow (+) elongation in this orientation. In the plan view, when the ridge faces observers, Pennalithus rioi experiences constant extinction; the optic axis is perpendicular relative to the microscope stage in this orientation (Plate 18, Figs. 17-19, 21-23 in Varol, 2025).

References

Olafsson, G., 1989. Quantitative calcareous nannofossil biostratigraphy of upper Oligocene to middle Miocene sediment from ODP Hole 667A and middle Miocene sediment from DSDP Site 574. Proceedings of the Ocean Drilling Program, Scientific Results 108, 9-22.

Varol, O. 2025. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication, 29, 222 pp.

Young, J. R. 1998. Neogene. In, Bown, P. R. (Ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 225-265.