It’s the gaps that fascinate me the most.
I’ve long been drawn to biogeography, that special junction of life and landscape, and more particularly to the dynamics of absence: the romance and intrigue of discontinuities, disjunctions, and relict species rising like half-drowned continents amidst an ocean of hostile upstarts. And so it was when I read Huxley’s Crayfish. To emphasis some quirks of “negative biogeography” as it relates to these creatures, I’ve selected some excerpts from Chapter VI (not necessarily in the same order as in the text):
No crayfishes are known to inhabit the rivers of the northern Asiatic watershed, such as the Obi, Yenisei, and Lena. None are known [note 13] in the sea of Aral, or the great rivers Oxus and Jaxartes, which feed that vast lake; nor any in the lakes of Balkash and Baikal.
Confusingly, “epischura” (Epischura baikalensis), the enormously abundant copepods (Temoridae) whose feeding habits underpin much of Lake Baikal’s famous purity (see here), is sometimes translated as “crayfish.” Though the world’s deepest lake is characterized by an incredible amphipod fauna, it’s bereft of crayfish.
Species of [Cambarus — today split into several different genera, including Procambarus and Cambarus proper] also occur in Cuba, [note 17], but, so far as is at present known, not in any of the other West Indian islands.
This is a reference to Procambarus cubensis.
All the crayfishes of the northern hemisphere belong to the Potamobiidæ [Superfamily Astacoidea: Astacidae and Cambaridae], and no members of this family are known to exist south of the equator.
All southern hemisphere crayfish belong to Superfamily Parastacoidea.
The report from Fiji doesn’t seem to be valid. According to the Transactions and Proceedings of the Royal Society of New Zealand, “The New Zealand fresh-water crayfishes belong to the genus Paranephrops, which is confined to New Zealand, its reported occurrence in Fiji being probably due to an error in the locality labels.”
. . . No crayfish have as yet been found in any of the great rivers, such as the Orinoko; the Amazon, in which they were specially sought for by Agassiz; or in the La Plata, on the eastern side of the Andes.
This, on the other hand, remains true today.
Japan has one species (A. japonicus), perhaps more; but no crayfish has as yet been made known in any part of eastern Asia, south of Amurland. There are certainly none in Hindostan; none are known in Persia, Arabia, or Syria. In Asia Minor the only recorded locality is the Rion. No crayfish has yet been discovered in the whole continent of Africa. [note 15]
As I first read this sentence, I set Huxley’s book down and jumped to my feet. Whole continents make for clunky biogeographic units, but it seemed staggering that from Cairo to Capetown mainland Africa had not a single crayfish to call its own. The absence felt troubling in the midst of an otherwise nicely Gondwanan pattern (southern South America, Australia, New Zealand, and Madagascar). My mind started churning out rationalizations, but the cryptozoologist within me just as quickly began to long for a Mantophasmatodea-type discovery — some isolated pond in the veldt, exquisitely overlooked, with a familiar pair of claws to arc up at my approach.
What’s on deck: Reasons for African absence, Antarctic crayfish, and the Kigoma photograph (was Huxley wrong?), with some intermissions.
Huxley, Thomas Henry. The Crayfish: An Introduction to the Study of Zoology. 1879. Vol. XXVIII. International Scientific Series. New York: D. Appleton and Company, 1880.