Are endocerids all that different.

Some cephalopod classifications have the Order Endocerida separated from the Nautiloidea and put instead in the Subclass Endoceroidea (or Endoceratoidea), following the scheme of Curt Teichert in the Treatise on Invertebrate Paleontology. The question is, are they all that different so as to warrant their exclusion from the Nautiloidea and inclusion in another subclass. Teichert thought so, as he did for the Actinocerida, placing them in the Actinoceratoidea (or Actinoceroidea). Russeau Flower thought not, on both accounts, for which I'm in full agreement.

First of all, in brief, what are endocerids. They are cephalopods with straight or downwardly curved shells, close spaced septa, chaambers free of organic deposits, and large ventral siphuncles containing conical deposits concentrated toward the rear known as endocones. The septa are dish-shaped, concave from the front. Septal necks, protrusions of the septa that make up part of the siphuncle point to the rear. Both are characters of the Nautiloidea. These don't necessarily limit the Endocerida to the Nautiloideaas their could be other things calling for their separation. So let's take a quick look at Teichert's reasoning.

The addition of the Subclass Endoceroidea is based on the comination of the Endocerida with the Intejocerida, which turms out to be a group of unrelated cephalopods (according to Flower) whose common charater happens to be the presence of radial lamenllae in the siphuncle. In other characters such as siphuncle location they are quite different. I'll try and touch on the Intejocerida later on. Meanwhile there doesn't seem to be any reason to exclude the Endocerida from the Nautiloidea.

They aren't all that different