1. Arms
1. Arms IV longest, thickest and with expanded lateral membranes which form tentacular sheaths which can envelope entire contracted tentacles.
   
   
2. Tentacles
1. Tentacular clubs elongate, virtually cylindrical; with suckers in many irregular series (30 or more in some species).
   
   
3. Head.
   1. Beaks. An overview of the beaks of mastigoteuthid species can be seen here.
      
      
4. Funnel
1. Funnel locking-apparatus oval, usually with knobs (tragus, antitragus) affecting the shape of the depression in the funnel component that often varies between species.
   
   
5. Fins
1. Fins large (ca. 50% of ML) to very large (ca. 90% of ML).
2. Fins with terminal position.
   
   
6. Tail
1. Short tail present (often absent due to damage during capture).
2. Tail supported by secondary conus.
   
   
7. Photophores
1. Photophores present on eyeball or eyelid and/or integument or absent.

Comments

Species and species groups in the Mastigoteuthidae

1. M. agassizii group: M. agassizii (Atlantic), M. dentata (IndoPacific), M. psychrophila (Antarctic and adjacent waters).
   
   
2. M. cordiformis (West Pacific).
   
   
3. M. glaukopis group: M. atlantica (Atlantic), M. famelica (N. E. Pacific), M. glaukopis (Indian).
   
   
4. M. hjorti (circumglobal).
   
   
5. M. magna group: M. magna (Atlantic), M. microlucens (tropical Pacific), Mastigoteuthis type beta (subantarctic Pacific).
   
   
6. M. pyrodes (North Pacific).
   
   
7. M. danae (Atlantic, Indian) M. tyroi (Indian): These are known only from paralarvae that probably represent the young of known species.

The following table compares species/species-groups.

	Funnel pocket*	Funnel locking- apparatus*	Integumental photophores*	Eyeball photo- phores	Eyelid photo- phores*	Chromato- phores**	Tubercules in subadults
M. agassizii group	Yes	Ear shaped	Yes	No	Tiny	Scattered	No
M. cordiformis	No	Ear shaped	No	No	No	Abundant	Yes
M. glaukopis group	Yes	Ear shaped	No	No	Large	Abundant	No
M. hjorti	No	Oval	No	Yes	No	Abundant	Yes
M. magna group	No	Flask shaped	No / microscopic	No	No	Abundant/absent?	No
M. pyrodes	Yes	Ear shaped	Yes	No	Medium	Abundant	No

*Funnel pocket (arrow) extends between funnel bridles deep into the head to the cephalic vein. Presence of the pocket can be recognized in the paralarval stage onward (at least in M. famelica).

*Funnel locking-apparatuses have three major forms.

*Integumental photophores are of three types. Those of the M. agassizii-group (below left) and M. pyrodes (below middle) look superficially the same. Those of M. microlucens (below right, a member of the M. magna-group) are much smaller and very difficult to see (in the photograph they are apparent since most of the covering chromatophore-bearing skin has been lost during capture.

*Eyelid photophores (arrows) occur in three sizes. Compare Small and Medium sizes with the size of the nearby integumental photophores. Species with Large eyelid photophores lack integumental photophores.

**Chromatophores. See photographs of integumental photophores above. Count the number of chromatophores between photophores in M. agassizii and in M. pyrodes to see the difference between "scattered" and "abundant" chromatophores. See the M. agassizii-group page to compare the integument of these two species.