1. Arms and web
   1. Suckers in males not greatly enlarged, not in two fields.
   2. Sucker aperatures without tooth-like structures (see Luteuthis for tooth-like structures).
   3. Cirrus length comparable to 2.5 times largest sucker diameter.
   4. Single web nodules present (arrow).
   

   Figure. Oral view of arm of Grimpoteuthis bathynectes showing single web nodule. Drawing modified from Voss and Pearcy, 1990.

2. Head
   
   1. Eyes: Large, diameter typically 1/3 of head width.
   2. Beaks: Descriptions of some species can be found here: Lower beak; upper beak.
      
      
3. Pigmentation
   1. No areolar spots
      
      
4. Fins
   1. Length approximately equals mantle width.
      
      
5. Gills
   1. Semi-sepioid (in G. innominata) or half-orange appearance.
      
      
6. Digestive system
   1. Intestine approximately equal to esophagus (including crop) in length.
   2. Digestive tract arranged in simple U-shape.
   3. Digestive gland unilobular.
   4. Radula present or absent.
   

   Figure. Side view of digestive tract of Grimpoteuthis bathynectes (?). Drawing modified from Voss and Pearcy, 1990.

7. Optic lobe and optic nerve bundles
   1. Optic lobe circular (rather than kidney-shaped) in cross-section.
   2. Single nerve bundle from optic lobe penetrates white body.
   

   Figure. Optic lobe, optic nerve bundles and white body of Grimpoteuthis abyssicola. Drawing from O'Shea, 1999.

8. Shell
   1. U-shaped, lateral walls of wings usually parallel to one another. Mid-saddle often with outer and inner surfaces convex but outer surface flat or concave in some species (eg, G. meangensis).
   2. Shoulders with or without shoulder blades.
   

   Figure. Dorsal view of shell of Grimpoteuthis bathynectes. Drawing modified from Voss and Pearcy, 1990.

Comments

The male reproductive tract shows considerable variation between species and is frequently described for new species. However the amount of variation within a species is unknown and therefore the specific value of the structures of the tract is uncertain. In addition there is some confusion regarding the identification of the various parts. Ebersbach (1915) made a careful dissection of the digestive tract of a Grimpoteuthis that he believed was G. umbellata. His illustration, relabeled, is shown on the right. The proximal glands on the sperm duct are often called "seminal vesicles." However, as Ebersbach pointed out, they are spermatophore-forming glands and should be called "spermatophore glands." A small gland (labeled "?") lies between the spermatophore and accessory glands that Ebersbach called the accessory spermatophore gland but may be Needham's sac.

Species comparisons

Species	No. arm suckers	Sucker no. at Arm I nodule	First cirrus between suckers	Length: cirrus/sucker; Male, female	Salivary glands	Gill lamellae	Eye size	Shell shoulder blades	Shell wings expanded	Shell saddle shape: Outer surface	Ocean
G. abyssicola	77	32-34	4-6	2.5x	None	8	Large	No	Yes	Convex	South Pacific
G. bathynectes	47-58	26	3-4	1.1x, 1.3x	Posterior	7-9	Large	No	No	Convex?	North Pacific
G. boylei	55-58	31	4-7	1.9x, 2.2x	Ant., Post.	7-8	1/3 HW	Weak	No	Depressed	North Atlantic
G. challengeri	63-72	34	4-7	2.5x, 3.5x	Anterior	7-8	1/3 HW	Yes	No	Convex	North Atlantic
G. discoveryi	56-61	31	3-5	1.2x, 1.6x	Anterior	6-8	1/3 HW	Weak	No	Convex	North Atlantic
G. hippocrepium	50,	25	4-5	?	?	?	?	No	No	Flat?	E. tropical Pacific
G. innominata	50-60	22-24	4-6	1x	None	7	large	Yes	Yes	Median ridge	South Pacific
G. meangensis	60-70	?	4-7	?	?	?	?	Yes	?	Flat	W. tropical Pacific
G. megaptera	?	?	?	2x	?	?	1/3 HW	?	?	?	North Atlantic
G. pacifica	52	?	6-8	2x	?	?	Large	?	?	?	W. tropical Pacific
G. plena	55	?	?	1.2-1.6	?	?	small	?	?	?	North Atlantic
G. tuftsi	63-75	?	5-7	1.5-3.5	None	7-8	Large	Yes	No?	Transverse groove	North Pacific
G. umbellata	65-68	?	4-5	1.2x	?	8	?	?	?	?	North Atlantic
G. wuelkeri	60-70	28	4-7	2.5x, 1.2x	Ant., post.	6-7	1/3 HW	Yes	No	Convex with ridge	North Atlantic