Six general types of funnel locking-apparatuses exist within the "teuthoid" decapodiforms and several others within the "sepioid" decapodiforms.
1. Lazy-T shape. The groove in the cartilage has roughly the shape of the capital letter "T" laying on its side. This type is found only in the family Thysanoteuthidae. |  |
2. Inverted-T shape. The groove in the cartilage has roughly the shape of the capital letter "T" upside down. This type is found only in the family Ommastrephidae. |  |
3. Straight shape. The groove in the cartilage is more or less straight. This is a common shape and is found in the following families: Ancistrocheiridae, Batoteuthidae, Bathyteuthidae, Chtenopterygidae, Enoploteuthidae, Gonatidae, Histioteuthidae, Lepidoteuthidae, Loliginidae, Lycoteuthidae, Neoteuthidae, Octopoteuthidae, Onychoteuthidae, Pholidoteuthidae, Pyroteuthidae. In some squids the groove is narrow and very straight while in others the groove is rather broad and may curve slightly. |  |
4. Triangular shape. The groove in the cartilage has roughly the shape of a triangle. This shape is found only in the family Cycloteuthidae. |  |
5. Oval with tragus and /or antitragus. The groove in the cartilage has roughly an oval shape with lateral (tragus) and/or posterior (antitragus) bumps impinging on the depression. This shape is found in most members of the Chiroteuthidae and Mastigoteuthidae. Various modifications of the size, shape and position of the tragus and antitragus can greatly effect the appearance of the cartilage. For example, in some Mastigoteuthis the tragus and antitragus impinge on the oval depression anteriorly yielding a flask-shaped depression. |  |
6. Oval shape. The groove in the cartilage has roughly an oval shape. This shape is found in the Joubiniteuthidae, Magnapinnidae, Promachoteuthidae. |  |
7. Boomerang shape. The groove in the cartilage varies between slightly curved to a strong boomerang shape. This shape is found in the Sepiidae. |  |
8. Keyhole shape. The groove consists of two distinct portions: an anterior deep, oval depression and a posterior, elongate groove with a more shallow depression. This shape is found in Sepioloidea. |  |
Illustrations are modified from: Roper, C. F. E., R. E. Young and G. L. Voss (1969). An illustrated key to the families of the order Teuthoidea. Smiths. contr. zool., 13:1-32.
