THE STRUCTURE OF THE OPERCULUM OF THE SPECIES OF ATLANTIDAE (GASTROPODA : Title HETEROPODA) AS A TAXONOMIC CRITERION, WITH RECORDS OF SOME PELAGIC MOLLUSKS IN THE NORTH PACIFIC Author(s) Tokioka, Takasi PUBLICATIONS OF THE SETO MARINE BIOLOGICAL Citation LABORATORY (1961), 9(2): 267-332 Issue Date 1961-12-20 URL http://hdl.handle.net/2433/175291 Right Type Departmental Bulletin Paper Textversion publisher Kyoto University THE STRUCTURE OF THE OPERCULUM OF THE SPECIES OF ATLANTIDAE (GASTROPODA: HETEROPODA) AS A TAXONOMIC CRITERION, WITH RECORDS OF SOME 1 PELAGIC MOLLUSKS IN THE NORTH P ACIFIC ) T AKASI TOKIOKA Seto Marine Biological Laboratory, Sirahama With 42 Text-figures and 22 Tables CONTENTS Page Introduction ............................................................................................. 268 I. General structure of the operculum in Atlantidae ................................. 269 II. Descriptions of opercula of the species that can be identified easily and distinctly by shell characters ............................................................... 271 1. Oxygyrus keraudreni ..................................................................... 271 2. Atlanta turriculata ........................................................................ 271 3. Atlanta fusca .............................................................................. 274 4. Atlanta lesueuri ........................................................................... 277 5. Atlanta inclinata .....•..................................................................... 280 III. Description of the operculum, by which the species can be identified distinctly ........................................................................................... 285 6. Atlanta injlata .............................................................................. 285 IV. Descriptions of opercula of the species, shells of which resemble one another rather closely......................................................................... 289 7. Atlanta gaudichaudi ........................................................................ 289 8. Atlanta Peroni .............................................................................. 303 9. Atlanta helicinoides ........................................................................ 312 10. ? Protatlanta souleyeti ...................................................................... 318 V. Records of other Heteropods, with some brief notes. .......................... 320 11. Carinaria galea ...............................................•........................... 320 12. Carina ria cithara var. procumbens ................................................... 320 13. Carinaria sp................................. 321 14. Cardiapoda Placenta ..................................................................... 321 15. Cardiapoda sp ............................................................................... 322 16. Pterosoma Planum ........................................................................ 322 17. Pterotrachea coronata ..................................................................... 322 18. Pterotrachea spp. .. .. .. 322 19. Firoloida desmaresti ..................................................................... 322 1) Contributions from the Seto Marine Biological Laboratory, No. 371. Publ. Seto Mar. Biol. Lab., IX (2), 1961. (Article 15) 268 T. TOKIOKA VI. Records of some Pteropods, with some brief notes............................... 323 1. Limacina helicina ........................................................................... 323 2. Limacina trochiformis ...................................................- ............... 323 3. Limacina inflata . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 323 4. Limacina lesueuri ........................................................................... 324 5. Limacina bulimoides ..................................................................... 324 6. Euclio pyramidata ........................................................................ 324 7. Euclio cuspidata ........................................................................... 324 8. Euclio balantium ........................................................................... 324 9. Creseis acicula acicula .................................................................. 326 9a. Creseis acicula clava ..................................................................... 326 10. Creseis virgula virgula .................................................................. 326 lOa. Creseis virgula coni ca ..................................................................... 326 11. Creseis sp..................................................................................... 327 12. Styliola subula .............................................................................. 327 13. Hyalocylis striata ........................................................................... 327 14. Diacria trispinosa trispinosa ............................................................ 327 15. Diacria quadridentata quadridentata ................................................ 327 16. Cavolinia tridentata ........................................................................ 328 17. Cavolinia longirostris longirostris ................................................... 328 17a. Cavolinia longirostris angulata ...................................................... 328 17b. Cavolinia longirostris strangulata ................................................... 328 18. Cavolinia gibbosa ........................................................................... 328 19. Cavolinia uncinata ........................................................................ 328 20. Cavolinia globulosa ........................................................................ 328 21. Cavolinia inflexa . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 328 22. Cavolinia spp. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 329 23. Peraclis reticulata ........................................................................ 329 24. Peraclis apicifulva ........................................................................ 329 25. Peraclis spp .................................................................................. 329 26. Cymbulia sibogae ........................................................................... 330 27. Corolla ovata ................................................................................. 330 28. Corolla sp..................................................................................... 330 29. Desmopterus papilio ........................................................................ 330 30. Hydromyles globulosa ..................................................................... 331 31. Thliptodon akatsukai .............................. , ...................................... 331 32. Thliptodon spp ............................................................................... 331 33. ? Pneumodermopsis sp ...................................................................... 331 34. Gymnosomata unidentified............................................................... 331 Introduction The toxonomic criteria for the species of the Family Atlantidae of Heteropoda (Gastropoda) have been based chiefly on structures or features of the shell. Indeed, these criteria are distinct for a few species: Atlanta lesueuri, A. jusca, A. turriculata, A. inclinata, and Oxygylus keraudreni ; but they are so exact for other species, including their jeveniles and those of some of the above-mentioned species, that sometimes the identification is made only provisionally without any confidence. Especially, the juveniles of Atlantidae are mostly left without any -22- Structure of Operculum of Atlantidae 269 definite identification. To improve such a circumstance even a little, I tried to show a part of the morphological characters of the shell by means of numerical representations (1955 a). This is, however, still insufficient, and moreover it cannot be applied for specimens, the shells of which are softened in some in- adequate states of preservation. • While I was examining many plankton samples, especially of the Shellback Expedition, at the Scripps Institution of Oceanography in 1956-1957, I found so many softened shells of Atlantidae in those samples and was urged to find out some way to identify them to record the occurrences of respective species. Examining these softened shells under the binocular, I found that the operculum could be removed rather easily off these specimens and began to study the morphology of the operculum in a hope to get any definite criterion for iden­ tification. Evidently, some species are provided respectively with a quite unique operculum, while the operculum structures in others are related one another rather closely, although they seem to be helpful for identification. It was found that Atlanta injlata can be identified very easily and distinctly by the structure of the operculum. For other species, it is very effective to examine the operculum to ascertain the identification. An effort was made to support the validity of Atlanta pacifica, which I separated from A. gaudichaudi on the basis of the difference found in the whorl formula, by examining closely the operculum, but this was not successful. I am unhappy but have to admit that the validity of my 1· pacifica