Grooves
There is more than one phylum represented by tube-like structures with perpendicular grooves or lines. One is a tube-like mollusk in the class cephalopoda. Modern cephalopods are the nautilus. Some cephalopods have a straight body shape, unlike the spiral of the nautilus and related organisms. These straight nautiloids have a cone-shaped outer shell that is progressively larger from the end. You may see a circular structure in the center of your sample.
Another possibility is that your fossil is a stem from the Phylum Echinodermata. These stems are columns that attach a more complex crown to the seafloor. The stem only gradually increases in size and is likely not noticeable from the sample in your kit.
Another possibility is that your fossil is a stem from the Phylum Echinodermata. These stems are columns that attach a more complex crown to the seafloor. The stem only gradually increases in size and is likely not noticeable from the sample in your kit.