Liocranchia

These moderate-sized squids reach a maximum size of 250 mm (Nesis, 1982). They are cosmopolitan in tropical and subtropical waters although Young (1995) suggested that L. reinhardti may be a mesopelagic boundary species (i.e., associated with land masses). In Hawaiian waters L. reinhardti is a vertical migrator while L. valdiviae is a deep-living non-migrator (Young, 1978). Brief diagnosis: A cranchiin with two strips of diverging cartilaginous tubercules (together forming  a V shape--see image below) originating at each funnel-mantle fusion.
From Voss (1980):
  • Tentacles: Suckers and pads in two series on distal 2/3 of tentacle stalk
  • Head: Eyes sessile in paralarvae
  • Funnel: With funnel valve; funnel organ with very large ventral pads
  • Mantle: With distinct V-shaped series of cartilaginous strips on ventral mantle, originating at mantle-funnel fusion sites and diverging posteriorly (visible on live animal at 0:33 here)
  • Fins: United posterior to gladius (nearly circular in combined outline)
  • Photophores: Number of oval photophores on each eye varies with species (4 or 14; see table below); mature or nearly mature females develop photophores on tips of Arms III
Cartilaginous tubercles present along dorsal midline of mantle Number of photophores on eyeball
L. reinhardti Yes 14
L. valdiviae No 4
Live animal Video footage of Liocranchia has been collected on several recent Schmidt Ocean Institute dives. Here (timestamp 2:57:40) Dhugal Lindsay explains some of the squid's features during an observation in Australian waters (a great example of the transparency that inspired the common name 'glass squids').  Here a much more opaque (probably older) individual is observed in the Galapagos hydrothermal vent field.
  • Nesis, K.N. 1982/1987. Abridged key to the cephalopod mollusks of the world’s oceans. Light and Food Industry Publishing House, Moscow, 358pp. [In Russian]. Cephalopods of the World; Squids, Cuttlefishes, Octopuses, and Allies. T.F.H. Publications, Inc., Neptune City, NJ, USA, 351 pp.
  • Voss, N. A. 1980. A generic revision of the Cranchiidae (Cephalopoda; Oegopsida). Bull Mar Sci 30: 365-412.
  • Young, R. E. 1978. Vertical distribution and photosensitive vesicles of pelagic cephalopods from Hawaiian waters. Fish Bull 76: 583-615.
  • Young, R. E. 1995. Aspects of the natural history of pelagic cephalopods of the Hawaiian mesopelagic-boundary region. Pac Sci 49: 143-155.