Helcionelloida

Pelagiella atlantoides

• Helcionellida
• Yochelcionellida
• Jinonicellida

The only known fossil Helcionelliden ( Helcionelloida ) are a class of molluscs ( Mollusca ), become a master of the shell molluscs ( Conchifera ) expected. You have endogastrisch to curved, cup- to planispiral rolled housing. On the housing rear end is a sine or a point at which the edge of the shell is more or less strongly curved upwards; in derived forms can this be sinus closed down and form a snorkel. The stratigraphic range is from Lower to Middle Cambrian. They were spread throughout the world.

Construction

The Helcionelliden get the basic blueprint of the shell molluscs ( Conchifera ) still very close. The body was probably (as in Urschalenweichtier ) in the head, foot and visceral hump divided. The foot was probably trained in most forms as crawling foot. The Helcionelliden be oriented so that the a snorkel or of marginal sinus is behind. The housing and the visceral sac was thus rolled endogastrisch. The gills were thus with some probability in the posterior part of the mantle cavity. The water flow could have occurred in front and was able to leave the mantle cavity through the snorkel or the posterior sinus again. Thus, the Helcionelloida are oriented the other way around as the Einplatter ( Monoplacophora ) whose cases are exogastrisch curled or curved. That was also the reason for the elimination of these fossils from the Einplattern ( Monoplacophora ) to which they were originally placed.

Way of life

The Helcionelliden probably lived in shallow marine areas of the sea front during the Lower to Middle Cambrian. Presumably they advanced in the areas of riffnahen Archaeocyaths reefs in the Cambrian up.