Helcionopsis radiatum
Encyclopedia
Helcionopsis radiatum is an extinct species of paleozoic monoplacophora
n in the family Tryblidiidae
.
This species was first named as Tryblidium radiatum and described from Silurian in crystalline limestone of Wialmsudd near Fårösund
in Sweden by Gustaf Lindström
in 1884. Lindsröm found only one specimen.
is oval and much elevatedly conical. The greatest height is lying near the middle of the longitudinal axis. The apex
is in anterior end, truncated, curved as to lean forwards over the anterior margin of the aperture. The shell between the apex and the margin is consequently much concave. The apertural border is straight and horizontal. The surface is covered by fine, closely packed, radiating striae and a few concentric lines of growth. The shell has been thick, as may be seen by a few fragments which are left along the borders.
The length of the shell is 24 mm, width 20 mm and the height of the shell is 15 mm. Length of the aperture is 23 mm.
Monoplacophora
Monoplacophora, meaning "bearing one plate", is a polyphyletic class of mollusks with a cap-like shell, living on the bottom of deep sea. Extant representatives were unknown until 1952; previously they were known only from the fossil record.- Definition :...
n in the family Tryblidiidae
Tryblidiidae
Pilina is an extinct family of paleozoic monoplacophorans in the superfamily Tryblidioidea.- Genera :Genera in the family Tryblidiidae include:* Tryblidium Lindström, 1880...
.
This species was first named as Tryblidium radiatum and described from Silurian in crystalline limestone of Wialmsudd near Fårösund
Fårösund
Fårösund is a locality situated in Gotland Municipality, Gotland County, Sweden with 862 inhabitants in 2005. The village can be reached by car from Visby. The little island of Fårö can be reached by ferry from Fårösund....
in Sweden by Gustaf Lindström
Gustaf Lindström
Gustaf Lindström was a Swedish paleontologist.He was born in Visby on Gotland. In 1848 he entered Uppsala University, and in 1854 he took his doctor's degree...
in 1884. Lindsröm found only one specimen.
Shell description
The shellMollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
is oval and much elevatedly conical. The greatest height is lying near the middle of the longitudinal axis. The apex
Apex (mollusc)
Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...
is in anterior end, truncated, curved as to lean forwards over the anterior margin of the aperture. The shell between the apex and the margin is consequently much concave. The apertural border is straight and horizontal. The surface is covered by fine, closely packed, radiating striae and a few concentric lines of growth. The shell has been thick, as may be seen by a few fragments which are left along the borders.
The length of the shell is 24 mm, width 20 mm and the height of the shell is 15 mm. Length of the aperture is 23 mm.