• Abstract and Figures
• Public Full-text

27. THE LAND AND FRESHWATER MOLLUSCA OF RENNELL ISLAND, SOLOMON ISLANDS BY WILLIAM J. CLENCH MUSEUM OF COMPARATIVE ZOOLOGY, HARVARD UNIVERSITY CONTENTS Introduction .................................................155 Ellobiidae .........................................................172 Acknowledgements........................................156 Succineidae.........................................................1 Zoogeographical Remarks ........................156 Tomatellinidae..................................................I Station Data......................................................158 Pupillidae .........................................................1 Systematic P a r t ...............................................159 Subulinidae.........................................................1 Neritidae ........................................................159 E ndodontidae..................................................1 Helicinidae........................................................159 Ariophantidae..................................................1 Cyclophoridae.................................................164 Bulimulidae.......................................................180 Pupinidae ........................................................166 P artu lid ae .........................................................ISO Truncatellidae.................................................166 Camaenidae...................................................... 180 Assimineidae..................................................... 167 Rhytididae.........................................................200 Thiaridae............................................................172 References.........................................................202 INTRODUCTION The following report is based upon the material collected by Mr. H arry K nudsen and Dr. T orben W olff, members of the Danish Renneil Expedition 1951 which was part of the “Galathea” Deep-Sea Expedition 1950-52. In addition, I have in­ cluded records and descriptions of new species from material obtained mainly by the “Whitney” Expedition to the Solomon Islands, which was collected by Ernst Mayr and W.J.E yerdam in 1927 and 1930. Certain records are based upon material collected by W. M.M ann during his extended trip to these islands in 1916. Most of these data are new. A few locality records are duplicated. References and some notes are given for all known Solomon Island species in the Family Helicinidae. In the Camaenidae, full citations are given for all Solomon Island species in the subfamily Chloritinae and in the genus Crystallopsis. A general description and maps of Renneil Island, details of the stations of the Danish Expedition, etc. will be found in W olff, 1955 a & b. ACKNOWLEDGEMENTS I am deeply indebted to Dr. T orben W olff for the opportunity to study and report upon the material collected by the “Galathea” Expedition on Rennell and Guadal­ canal Islands. Also my sincere thanks are due to R alph W. M iner, formerly of the American Museum of Natural History for permission to work up the material collected by the Whitney Expedition, and to his successors, W illiam E merson and F rederick W eir for their continued interest in supplying data and material from the Solomon Islands. My thanks are also due to Dr. R. K. D ell of the Dominion Mu­ seum, Wellington, New Zealand, for the loan of specimens collected on Rennell and Bellona Islands, Solomon Islands. ZOOGEOGRAPHICAL REMARKS The existance of the endemic genus Quirosella on Rennell is certainly understandable if we accept the time factor and isolation. The occurrence, however, of three rather well defined species in this genus on this Island is far more difficult to understand. These three endemic species on Rennell Island occupy the same ecological niche, at least in certain stations they were all found together while in others they occurred singly. Rennell Island is small and its relief is low and the general ecology fairly uni­ form. This is in no way a unique example. The Island of Kauai in the Hawaiian Is­ lands possesses several genera in a family of mollusks, the Amastridae, known only from the Hawaiian Islands. The endemic genus Carelia has evolved several species on this island and its small associated island Niihau. Certainly Kauai is very different from Rennell. It is a “high island” of volcanic origin and presents a multitude of physiographic differences not found on a raised coral atoll. Nevertheless, the differ­ ence is probably more apparent than real. Isolation on the higher elevations of this island has probably played its part in segregation. On the other hand, low land areas spread about the island making accessible most of the valleys and the ridges. Carelia is a ground species, living in the leaf litter on the forest floor. Perhaps another answer is suggested. It is possible that Quirosella is a relict genus on Rennell and may at one time have occurred on other islands in the Solomons. It is also possible that it still does exist on one or more of the islands but has so far eluded the collector. It is important to realize that all of these islands of the Solomon Archipelago are still very imperfectly known and many existing anomalies may be erased when the islands have been more thoroughly explored. However, there are two rather important points which are indicated by the land mollusks of the Solomon Islands. These are the relatively high endemicity of mollusks on San Cristobal (at least two subgenera which include several peculiar species) and Choiseul Strait (between Choiseul and Bougainville) marking a very definite barrier in distribution of many groups of land mollusks. The first of these would seem to indicate that San Cristobal has been isolated for a long period of time and that, if it ever was connected with other islands in the Solomon group, it must have been in the remote past. The second problem is far more difficult to understand. Choiseul Strait is not particularly wide (25 miles) and is studded with islands. Two genera, Placostylus and Crystallopsis, common on all of the islands to the south, have failed to reach Bougain­ ville Island. On the other hand, a,few genera and subgenera on Bougainville have failed to reach Choiseul and the islands to the south. Crystallopsis is peculiar to the Solomon Islands but Placostylus (s. 1.) occurs in the Fiji Islands, New Caledonia, Norfolk, Lord Howe and the north island of New Zealand. Why has it failed to cross the relatively narrow Choiseul Strait? These problems are presented here with no idea of solution. The facts are given with the data which are at hand. In the broader considerations of geographical distribution no single group of animals should be selected as a basic pattern of what may have been distributed by former land connections. Certainly it is fairly apparent, as indicated by the land mollusks, that no connection between Bougainville and Choiseul could have existed within recent geographical times, otherwise both Crystallopsis and Placostylus should occur on Bougainville just as certain Bougainville genera, such as Quirosena. should have extended at least into Choiseul. Why, in this particular area did mechanical transport, at least in part, fail these genera, for they were unable to cross this island studded strait? Crystallopsis was able to reach Rennell Island from San Cristobal, a distance of at least 90 miles over open water, yet it has failed to island-hop a comparatively narrow strait. Future studies of other animal or plant groups may shed some light on this problem. The land and freshwater mollusks of Rennell Island are disharmonic and show relationships with several islands in the Solomon group and in one case. Quirosella, with the Admiralty Islands. However, the two species noted below, Af. guppvi and C. rennellensis, indicate a little stronger relationship with San Cristobal than to the remaining islands in the Solomon Archipelago. Melanoides guppyi is known elsewhere only from Lake Waileva, Santa Ana Island, while other species in the Tbiaridae indicate a relationship to several islands in the Solomon group. Crystallopsis ( Cristovala) rennellensis (new) is most closely allied to C. conica Gude from San Cristobal Island. Also Nesopoma galaihea (new) occurs on Rennell, Malaita and San Cristobal. This, however, is a very small land snail and as such means but little in the geographic relationships of these islands at present. It is to be remembered that very few small spccies have beer collected in these islands. Many species now limited to single or only a few islands may eventually be found on most of the larger islands. It is, however, interesting that neither Placostylus (s. 1.) or Papuina (s. I.) reached Rennell, both genera being very common throughout most of the Solomon Islands. STATION DATA of the Danish Rennell Island Expedition October-November 1951 (W olff 1955 b). GUADALCANAL, SOLOMON ISLANDS L 340 Honiara 9.10. Under leaves and stones close to vertical wall of coral rock L 342 - 9.10. In mud and on plant debris in a freshwater pond near the shore L 343 - 9.10. Under stones at above named pond L 345 - 9.10. Under stones at the sea shore L 346 5 km W of Honiara 10.10. In and under dry-rotten wood and under stones RENNELL ISLAND, SOLOMON ISLANDS L 351 Lavanggu 13.10. In coarse grass in coconut grove near the shore L 352 - 13.10.-14.10. Under stones and plant debris in coconut grove near slope of coral rock L 353 - 13.10.-I3.il. Rain forest above the slope L 357 ^ 15.10.-12.il.

Load more

  52

Copy Link