Feeding and some trophic interactions of Glaucus atlanticus

August 2, 2006
From: Irina Roginskaya

Dear Bill,
I want to add to my previous messages (Roginskaya, 2006, 2006a) some more field observations of Dr.A.I.Savilov (1956,1971), concerning the feeding behaviour of Glaucus atlanticus. And to show two pictures from the set of my recent SEM photos of details of buccal apparatus of early juveniles of Glaucus from the material , collected by A.I. Savilov in 1961 in Tropical Western Pacific.
A.I. Savilov writes: " The hungry Glaucus, holding on to Velella by the ends of tentaculiform papillae, starts to tear off and engulf the rather big pieces of the floating disc of the siphonophore . Sometimes Glaucus, bending its body, captures the edge of the disc, gnawing a whole section of the colony of polyps". (see Upper right drawing: - Glaucus eating Velella - the original illustration of A.I.Savilov in Priroda ).

The buccal armature of Glaucus includes stout chitinous jaws with rather well developed long serrulated chitinous masticatory borders with a single row of multiple curved pointed denticles (fairly even in size) along the cutting edge.(I counted more than 45 denticles on the masticatory process of a juvenile Glaucus 1.5 mm long in spirit).[see Photo B: SEM photo , x600]. When the mouth of Glaucus is closed, and the odontophore is retracted, the matched rows of denticles along the cutting edge, create a strong construction, which reminds me of a real zip fastener [see Photo C: SEM photo of the part of  "zipper". x2000 of the juvenile Glaucus 1.2 mm long in spirit].

Locality: Open Ocean, surface of water, Tropical Western Pacific, 18 September 1961, pleuston. Length: 1.2 -1.5 mm. Photographer: Irina Roginskay, Viktor Karlov.

Both specimens are from the material of A.I.Savilov, collected during the cruise no.34 of R/V "Vityaz" in the Tropical Western Pacific; Sta.5086 (3 2'N, 140 8'W), 18.Sept.1961). May be these denticles help juvenile Glaucus to grasp portions of the prey and keep attached in mobile surroundings. The worn and even completely broken denticles I discovered on the masticatory borders of some minute juveniles of Glaucus, suggests that the process of feeding sometimes demands considerable efforts by juveniles and that the denticles on the cutting edge have an important role in the primary feeding.

There are very contradictory opinions by different authors concerning the predator prey interactions betweem Glaucus and Janthina. Perhaps the perfectly equipped buccal mechanism permits specimens of Glaucus from South Africa to attack and feed on the pelagic shelled gastropods Janthina.   Barnard (1927) indicates Janthina as the main food item of his specimens of Glaucus. Though this seems rather unusual and puzzling for a cnidarian-feeding nudibranchs.  A.I.Savilov (1971) stated on the contrary that Janthina janthina, collected during the cruise of R/V "Akademic Kurchatov" in the region of the Peru Current and kept in the aquarium with juvenile Glaucus from the same catch, successfully attacked them. Savilov even suggested that the almost complete absence in September 1968 of juveniles of Glaucus in the middle parts of Peru current, where the mass development of the population of J. janthina had been observed, could be linked not only with advancement along the Peru Current of different generations of Glaucus, but with the eating of juvenile Glaucus by Janthina.

In the observations by R. Bieri (1966) Janthina were absolutely indifferent to Glaucus: " Several times I placed active Glaucus close to Janthina prolongata, but they were never attacked and never elicited the feeding response in Janthina."

I came across another quite amazing statement of R. Buchsbaum and L.I. Milne (1962): "In warmer seas far from land the deep-violet blue nudibranch Glaucus eucharis creeps along on the underside of the surface film scavenging for minute plants and animals". Perhaps the authors mean that Glaucus eats the sutface-dwelling larval stages of Velella - Rataria?

  • Barnard K.H. 1927. South African Nudibranch Mollusca with description of new species and a note on some specimens from Tristan d'Acunha. Annals of the South African Museum, vol.XXV, no.1, pp171-215, pls.19-20.
  • Bieri R. 1966. Feeding preferences and rates of the snail Janthina prolongata, the barnacle Lepas anserifera, the nudibranch Glaucus atlanticus and Fiona pinnata and the food web in the marine pleiston. Publications Seto Marine Biological Laboratory, vol.XIV, no.2,pp.161-170, Plates III-IV.
  • Buchsbaum R. and L.J. Milne.1962. The Lower Animals.Living Invertebrates of the World. 303 pp. Published by Doubleday and Co.,Inc. Gordon City, New York.Third printing.
  • Roginskaya I.S. 2006.(May 9). Some notes about Glaucus atlanticus.[Message in] Sea Slug Forum.Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16534
  • Roginskaya I.S. 2006a. (May 25). About egg masses of Glaucus atlanticus. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/ 16663.
  • Savilov A.I. 1956. Floating biocoenosis in the Pacific Ocean based on the material of the Expeditions of the Institute of Oceanology, Academy of Sciences USSR. Priroda, vol.45, no.3, pp.62-68.
  • Savilov A.I. 1971. Pattern of Pleuuston Distribution in the Region of the Peru Current. The Academy of Sciences of the USSR. Transaction of the P.P.Shirshov Institute of Oceanology. vol.89. Oceanologic Investigation in the Peru Current Area, pp.60-76.


Roginskaya I.S/, 2006 (Aug 2) Feeding and some trophic interactions of Glaucus atlanticus. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17264

Thanks Irina,
Bill Rudman

Rudman, W.B., 2006 (Aug 2). Comment on Feeding and some trophic interactions of Glaucus atlanticus by Irina Roginskaya. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17264


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