First interpreted by L. von Buch as the spines of the brachiopod Leptaena lata in 1831. Over the past century tentaculitids have been referred to several phyla, but no convincing evidence wich settles the systematic position of the group has been presented. They have been affiliated to annelids, lophophorates and molluscs. Particularly the phylum Mollusca has attracted many authors as a possibility, when pteropods and cephalopods have mainly been suggested as closely related groups (Larsson 1979). However, the ultrastructural similarities with lophophorates does not support the latter theory. As in Cornulites, tentaculitids have the growth lamellae oriented subparallel to the shell wall, pseudopuncta, subdivision of juvenile shell cavity by septa, and a similarly shaped and sized embryonic shell (Larsson, 1979b). However, their shell has a cross-bladed lamellar structure (Towe, 1978) instead of the regularly foliated lamellar structure as in Cornulites.
Larsson, K. 1979b. Silurian tentaculitids from Gotland and Scania. Fossil and Strata, 11:1-180.
Towe, K. M. 1978. Tentaculites: Evidence for brachiopod affinity? Science, 201:626-628.