Holonema

Holonema Temporal range: Givetian to Frasnian
H. westolli
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Family:	†Holonematidae
Genus:	†Holonema Newberry, 1889
Type species
Pterichthys rugosum Claypole, 1883
Species
H. rugosum (Claypole, 1883) H. arcticum Marik-Kurik, 1975 H. bruehni Markus, 1998 H. harmae Mark, 1953 H. farrowi Stevens, 1964 H. obrutshevi Mark, 1953 H. ornatum Traquair, 1903 H. haiti Denison, 1968 H. radiatum Obruchev, 1932 H. westolli Miles, 1971
Synonyms
Pterichthys rugosus Claypole, 1883  ?Glyptaspis eastmanni Swartz, 1913 Holonema horridum Cope, 1892 Holonema rohoni nomen nudum Obruchev 1931

Holonema is an extinct genus of relatively large, barrel-shaped arthrodire placoderms that were found in oceans throughout the world from the Mid to Late Devonian, when the last species perished in the Frasnian-Fammian extinction event. Most species of the genus are known from fragments of the armor, but the Gogo Reef species, H. westolli, is known from whole, articulated specimens. According to these specimens, species of Holonema lived by grazing on stony, horn-shaped, stromatolite-like algae called oncholite, apparently by snipping off the points with a specialized snout.

H. rugosum is the type species. It was originally described as a species of the antiarch genus, Pterichthys. Fossils are found in Frasnian strata of New York and Pennsylvania, and Givetian strata of Wisconsin and Michigan. It is a fairly large species, though the type specimen is of an 18 centimeter long median dorsal plate belonging to a small individual. Fossils of H. horridum and Glyptaspis eastmani may be this species. Fossils from Frasnian Iran (H. cf. rugosum) may also belong to this species.

A large species from Givetian-aged strata in Novaya Zemlya, Russia, known only from two plates from one individual's trunk shield.

H. bruehni is a recently discovered species from the Middle Eifelian-aged Brandenberg stratum of Sauerland, Northwestern Germany. Juveniles had a dermal ornamentation of irregularly spaced tubercles, while the dermal surface of adults' armor were smooth.

Known from fragments from the Givetian-aged "Traverse Group" stratum in Michigan. The median dorsal plates range up to 20 cm in length. The median dorsal plate is fairly broad at the posterior end, but narrows as one approaches the anterior end.

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