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GALLERY



 
Hydatina physis
(Linnaeus, 1758)
 
Hydatina physis
Maximum size:  92 mm (extrapolated from shell length of Leeward Is. animals); main island animals probably seldom exceed 54 mm.

Identification:  This species has a translucent brown body shading to iridescent blue-white marginally. The shell is faun marked with fine spiral brown lines. (Note 1)

Natural history:  Hydatina physis is a rarely seen nocturnal species that buries itself in sand during the day. It is found in tide pools and mixed habitats to depths of 1-2 m (3-6 ft) at moderately exposed sites. It feeds on polychaete worms (Rudman, 1972) and its egg mass is similar to that of Hydatina amplustre (though usually more elongate). (Kay, 1979)

Distribution:  Big Island, Maui, Molokai, Oahu, Kauai, Niihau, Pearl & Hermes Reef and Midway: circumtropical.

Taxonomic notes:  It's referred to as the "paper bubble shell" in Hoover, 1998 & 2006 and may have been first reported from Hawaii in Pilsbry, 1921 (as Hydatina physis staminea).

Photo:  Mike Severns: found by CP in Napili Bay tide pool; Sept. 8, 1995.

Observations and comments:

Note 1:  Shells of this species show strong red fluorescence under ultraviolet light (395 nM).
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