Conostichoceras is an exogastric, breviconic oncocerid

Oncocerida

The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...

 included in the family Nothoceratidae

Nothoceratidae

Nothoceratidae is a family of nautiloid cephalopods in the orthoceratoid order Oncocerida in which shells are exogastrically or endogastrically breviconic, planospiral, or torticonic; often with a constricted or visored aperture; and a siphuncle commonly composed of concave segments and occupied by...

, known from the Middle Devonian of central Europe and Upper Devonian of Australia. It probably lived on and swum above the sea floor.

Morphology

Conostichoceras, named by Foeste, 1926, produced a depressed exogastric breviconic shell with short, wide chambers and large living chamber, similar to Blakeoceras

Blakeoceras

Blakeoceras is a nautiloid cephalopod from the Oncocerida family Nothoceratidae with a curved shell that lived in shallow seas from the Silurian to the middle Devonian in what has become Europe....

and Turnoceras

Turnoceras

Turnoceras is Devonian cephalopod belonging to the oncocerid family Nothoceratidae. Its shell is a broadly expanding exogastric cyrtocone with a flattened dorsum -on the inner concave side, unconstricted aperture, no hyponimic sinus, and ventral siphuncle -on the outer, convex side- composed of...

but differing details especially of the siphuncle. The siphuncle is ventral; nummuloidal in the adapical half of the phragmocone

Phragmocone

The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae.In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a siphuncle which determines buoyancy by means of gas...

 but with concave profiles in the adoral half, and is actinosiphonate. The sides of the living chamber in the adult converge slightly on the aperture.

Taxonomy

In its broader taxonomy Conostichoceras belongs to a group of nautiloid cephalopods known as the Nautilitoidea

Nautilitoidea

The Nautilitoidea is a superoder within the subclass Nautiloidea, comprizing the phylogenetically related Nautilida, Oncocerida, and Tarphycerida....

, a superorder that includes the orders Oncocerida

Oncocerida

The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...

, Tarphycerida

Tarphycerida

The Tarphycerida were the first of the coiled cephalopods. They are found in marine sediments from the Lower Ordovician to the Middle Devonian. Some like Aphetoceras and Estonioceras are loosely coiled, gyroconic, others like Campbelloceras, Tarphyceras, and Trocholites are tightly coiled, but...

, and Nautilida

Nautilida

The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species...

. The family Nothoceratidae

Nothoceratidae

Nothoceratidae is a family of nautiloid cephalopods in the orthoceratoid order Oncocerida in which shells are exogastrically or endogastrically breviconic, planospiral, or torticonic; often with a constricted or visored aperture; and a siphuncle commonly composed of concave segments and occupied by...

to which it belongs is one of 16 included in the Oncocerida.