Hexasterophora
Encyclopedia
Hexasterophora are sponges, a subclass
in the class Hexactinellida. The Hexasterophora first appeared in the Ordovician and is separated into five recent orders, including the Lyssacinosa
, the Hexactinosa, and the Lychniscosa, all of which have living representatives in the seas today.
Hexasterophorans have skeletons composed of overlapping six-rayed spicule
s. The sponge is commonly firmly attached by its base to a hard substratum
; less often rooted by the anchoring spicules and rarely inserted directly into the loose bottom sediments. The three groups are differentiated by the extent of fusion of adjacent spicules.
The Lyssacinosa, Hexactinosa, and Lychniscosa appear sequentially in the fossil record. The least fused group, the Lyssacinosa, appears in the Ordovician
, while the intermediate group, the Hexactinosa is known from the Devonian
. Finally, the Lychniscosa, with the most tightly interlocking spicules is first found in rocks of Triassic
age.
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
in the class Hexactinellida. The Hexasterophora first appeared in the Ordovician and is separated into five recent orders, including the Lyssacinosa
Lyssacinosa
Lyssacinosa is an order of glass sponges belonging to the subclass Hexasterophora. These sponges can be recognized by the parenchymal spicules usually being unconnected, unlike in other sponges in the subclass where the spicules form a more or less tightly connected skeleton.-References:*...
, the Hexactinosa, and the Lychniscosa, all of which have living representatives in the seas today.
Hexasterophorans have skeletons composed of overlapping six-rayed spicule
Spicule
Spicules are tiny spike-like structures of diverse origin and function found in many organisms, such as the copulatory spicules of certain nematodes or the grains on the skin of some frogs.In sponges, spicules perform a structural function....
s. The sponge is commonly firmly attached by its base to a hard substratum
Substratum
In linguistics, a stratum or strate is a language that influences, or is influenced by another through contact. A substratum is a language which has lower power or prestige than another, while a superstratum is the language that has higher power or prestige. Both substratum and superstratum...
; less often rooted by the anchoring spicules and rarely inserted directly into the loose bottom sediments. The three groups are differentiated by the extent of fusion of adjacent spicules.
The Lyssacinosa, Hexactinosa, and Lychniscosa appear sequentially in the fossil record. The least fused group, the Lyssacinosa, appears in the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
, while the intermediate group, the Hexactinosa is known from the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
. Finally, the Lychniscosa, with the most tightly interlocking spicules is first found in rocks of Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
age.