The Liguus Tree Snails of South Florida

Submitted by Steve Wilkinson on Mon, 10/05/2010 23:58
Reference

Henry T. Close 2000, University Press of Florida. 162 pp. ISBN 0-8130-1814-5.

Review source

Originally reviewed by Kevin Brown in 2002.

Published in Journal of Conchology (2002), Vol.37

Few molluscs have shells exhibiting a greater degree of colour polymorphism than the genus Liguus. Although there are only 5 or 6 species no less than 180 colour forms have been named. This book looks at the single species found in Florida, Liguus fasciatus (Muller, 1774), which occurs there in some 59 named colour forms. Although the species is also found in Cuba, where at least 32 additional named colour forms occur, these are not discussed here.

The author has brought together a mass of information covering amongst other things; the animal's life cycle, feeding, habitat preference, predators, Liguus as the inspiration for Seminole Indian costume, sinistral specimens, etymology, and especially distribution. Many of the colour forms originally existed as isolated populations living on the different Florida Keys or on 'hammocks' - slightly elevated wooded areas within swamps or grassland. Over the years this pattern has been obscured as hurricanes or fires or more recently human land development obliterated colonies or through human intervention with the accidental or deliberate transplantation of colour forms to different areas. Today there are many threats to these animals, which are protected under Florida law, and colonies of the different colour forms have been established on hammocks within the Everglades National Park to try to ensure their continued survival.

The core of this book, some 66 pages looks at the identification of Florida Liguus. Each form is discussed commencing with "As much of the original description as you will need to identify the form" together with detailed comments and comparisons with similar forms. Although the quoted original descriptions are indicated by indented paragraphs it would perhaps have been clearer had they been given in quotation marks, many readers will use the identification section without reading the explanatory preamble. To further facilitate identification 8 full colour plates, several of which are double page spreads providing 14 pages of colour in all, illustrate some 266 specimens. Each form is illustrated by several examples showing variation within the form. It is perhaps unfortunate that all bar one specimen is shown in dorsal view, especially since "There are differences in the columellae of certain white shells that make them a little easier to tell apart". The book also contains some 44 black and white photographs and 11 maps. There is a good bibliography, and a useful chronology although it is surprising that several publications mentioned in the chronology are not detailed in the bibliography. The index, however, is totally inadequate, many subjects covered in the text are not indexed or only partially indexed.

This book is best where the author is reporting factual information, however, when it comes to the interpretation of this information the author shows both a lack of under- standing of biological principles and of taxonomic practice. As an example of the former the author spends much space discussing hybrids between different colour forms of Liguus, whereas the glossary incorporated in the International Code of Zoological Nomenclature specifies that a hybrid is "The progeny of two individuals belonging to different species. The progeny of two individuals belonging to different subspecies of the same species are not hybrids". Therefore, by clear implication, the progeny of two different colour forms should not be considered as hybrids. When it comes to taxonomic practice, throughout the book the author refers to the colour forms simply as marmoratus and castaneozonatus etc. rather than Liguus fasciatus form marmoratus or even L.f. form marmoratus. This frequently leads to the situation where these names are confusingly capitalised as in the picture caption "Roseatus and castaneozonatus mating". This is particularly annoying in the principal headings in the identification section, when the genus and specific names are used to show how the original authors treated each form. Osmenti, L.f. (Clench 1942) would be clearer as L.f. form osmenti Clench, 1942.

These beautiful shells have aroused a passionate interest among some collectors, and the author's own enthusiasm clearly comes over through the text. It is this enthusiasm, together with the extreme polymorphism of these shells, which has led to this group being a 'splitters' delight since "As far as Liguus collectors are concerned, once a name has appeared, it will probably never be relinquished, especially by those collectors who happen to have shells exhibiting the subtle distinguishing characteristics involved". Enthusiastic collectors will, no doubt, find this book useful in order to be able to put numerous names to their shells, however the scientific validity of many of these names is somewhat dubious. Henry Pilsbry wrote of Liguus colour forms that "Many of them intergrade freely, being selective stages of dines, and most of them are of a taxonomic grade which would not be worth naming in other genera".