Metacanthina

Order:  PHACOPIDA  Salter, 1864

Suborder: PHACOPINA  Struve, 1959

Superfamily: ACASTOIDEA  Reijers, 1972

Family: ACASTIDAE  Delo, 1935

Subfamily: ASTEROPYGINAE  Delo, 1935

Genus METACANTHINA  Pillet, 1954

 

Occurence

Metacanthina is found in the Pragian (Lower Devonian).

 

Recognizing Metacanthina species

Metacanthina issoumoursensis

Morzadec 2001 (Pragian)

Cephalon: Metacanthina has a pointed cephalon with a tongue in front. The genal spines are rather short and the glabellar furrows are deep. It also has an occipital spine. The eyes have 24 rows of maximum 8 lenses.

The thorax has 11 segments.

The pygidium is triangular in shape. The median spine of the pygidium is broad at the base and is barely longer than the fifth pair of lateral pygidial spines. The narrow and raised pygidial axis has 11 axial rings.

The whole carpace is covert with a strong granulation.

Metacanthina maderensis

Morzadec 2001 (Pragian)

This species has a cephalon that is twice as large as long. It has a strong occipital spine. The eyes have 29 rows of maximum 10 lenses.

The thorax has 11 segments. There is a large thorny tubercle on each of the 5 posterior axial rings of the thorax.

The pygidium has a median spine that is very broad at the base and then acute at its extremity. The pygidial axis has 12 rings without tubercle.

Metacanthina wallacei

G. & H. Termier, 1950 (Pragian)

The cephalon is large with a small point in front. The glabella is decorated with fine granulation. The genal spines of this species have not been described. The eyes have 28 rows with a maximum of 11 lenses. (Gandl, 1972 speaks about 30 rows). It does not have the strong occipital spine like M. maderensis.

The thorax has 11 segments. M. wallacei does not have  the tubercles on each of the 5 posterior axial rings like M. maderensis.

The pygidium has an axis that is wider than the pleural lobes. It has 13 rings without median tubercle. The 5 pairs of laterial pygidial spines are flat and curved towards the back. The median spine is very broad and ends in a very short point. It has the same length as the 5th pair of laterial spines.

 

References

Morzadec, P., 2001. Les trilobites Asteropyginae du Dévonien de l’Anti-Atlas (Maroc). Palaeontographica Abteilung A 262, 53–85.