FAMILY THYSANOTEUTHIDAE KEFERSTEIN, 1866

(ONE SPECIES)

Diagnosis: Large adult-sized muscular Cranchioidea with mantle locking apparatus having a modified (‘lazy’) ‘T’ shape; anal photophore in juveniles; buccal connectives attached to the ventral borders of ventral arms; nuchal-locking apparatus with two hook-like knobs on mantle component and opposing nuchal knobs and pits; tentacles with carpal locking apparatus; large and wide muscular rhomboidal fins inserted in the dorsolateral surface of the mantle; gladius with vanes projecting anteriorly; with multiple seminal receptacles in the buccal membrane; large, long, cylindrical, gelatinous egg masses; embryos and paralarvae covered by dense chromatophores.