Unlike Cranchiinae, the other subfamily within Cranchiidae, Taoniinae all lackcartilaginous strips which extend back from the funnel-mantle point of fusion. Their funnels are free laterally, and they have one to three photophores on the eyes. The largest photophore is crescent-shaped for most genera, but it's triangular in Helicocranchia, a semicircle in Bathothauma, and circular in Sandalops. This is in contrast to glass squids in the subfamily Cranchiinae, which have at least four small photophores which are round or oval in shape. In addition, males lack hectocotyli; these are arms which have evolved to specialize in storage and transfer of spermatophores to females. Taoniinae are also often larger than Cranchiinae and have darker beaks. Another characteristic is that a Taoniinae's caecum, is smaller than its stomach; in Cranchiinae, the caecum is larger than the stomach.
Taxonomic history and synonyms
When Georg Johann Pfeffer circumscribed this subfamily in 1912, he grouped its genera into three tribes:
Synonyms of Taoniinae include Galiteuthinae and Teuthoweniinae. S. Stillman Berry's 1912 circumscription of the subfamily Galiteuthinae only consisted of its type genusGaliteuthis. Like Pfeffer's Taoniinae, this was a subfamily within the family Cranchiidae. This was in contrast to Louis Joubin's classification, which placed Galiteuthis in a new, distinct family: Cranchionychiae. Georg Grimpe's 1922 circumscription of Teuthoweniinae included its type genus Teuthowenia as well as Hensenioteuthis, Helicocranchia, and Sandalops. He placed the genus Bathothauma into a new family, Bathothaumatidae, now just treated as a junior synonym of Cranchiidae. Subsequent research did not pay much heed to Grimpe's taxonomy.
Phylogeny
Below is Nancy A. Voss and Robert S. Voss's 1983 proposal for a phylogeny of the Taoniinae subfamily.
Genera and species
, the World Register of Marine Species classifies the Taoniinae as containing ten genera; they classify Belonella as a synonym of Taonius following Nancy A. Voss. However, Patrizia Jereb and Clyde F. E. Roper recognize Belonella as a distinct genus from Taonius, although they also note they are a frequently synonymized. Jereb and Roper also note Kir Nazimovich Nesis and Takashi Okutani as teuthologists who rejected Voss's synonymization of Belonella. Nesis's classification had Taoniusconsisting of only the single species T. pavo, and had Belonella consisting of B. belone, B. borealis and an undescribed species from the Antarctic.
