The Anatomy of Amphidesma ventricosum (Gray)

Abstract

Amphidesma ventricosum, belonging to the family Amphidesmatidae, was first described by Gray in 1843. The earliest systematic account of New Zealand Mollusca was published by Hutton in 1830. He places A. ventricosum with six other species in the genus Mesodesma, under the family Paphiidae. Suter in his "Manual of N.Z.Mollusca", continues the use of Mesodesma, but changes the family name to Mesodesmatidae. He distinguishes three species, placing each in a separate subgenus. Thus M. ventricosum was placed in the genus Taria (Gray 1853). In 1915, T. Iredale reviewed this group and eliminated the name Mesodesma, preferring Amphidesma. He points out that the generic name Mesodesma was introduced in 1832 by Deshayes as a substitute for the original name Donacille, given to the genus by Lamarck in 1812. In 1818, however, Lamarck had himself submerged the genus Donacille in the genus Amphidesma, rejecting the former because of its inapplicability to all species admitted into the genus. Thus Amphidesma takes precedure over Mesodesma. Iredale also shows that in "Zool. Voy. Coquille", vol ii, 1831, Lesson proposed the new generic name Paphies for this genus, that is, a year before Deshayes introduced Mesodesma. Thus in any case, Mesodesma passes into absolute synonymy. Iredale introduced the family name Amphidesmatidae, and allows to the genus Amphidesma four species and two subgenera. A. ventricosum is placed with two other species, A. gaymardi (Desh), and A. quoyi (Desh), under the subgenus Taria. The species Taria stokesii described by Gray in 1853 is shown by Iredale to be synonymous with A. ventricosum. Findlay in 1927 also reviewed Suter's work and agrees with Iredale’s classification of A. ventricosum adding, however, another species, A. forsteriana n.sp. to the genus of Taria. The species, A. ventricosum, is peculiar to New Zealand and is commonly known under the Maori name of toheroa, apparently meaning "long tongued". In the southern districts of the North Island, however, the Maori name appears to be tohemangu.....mangu meaning bluish or dark. It is interesting to note in this connection that the specimens found on the southern beaches of the North Island are much darker than those found further north, the shells of the former having dark bluish shadings. The Maoris used the toheroa extensively as food, and to-day toheroa soup is considered a great delicacy all over the world. There are two canning factories in the North of New Zealand, one at Waipapa Kauri near Ninety Mile Beach, and the other at Tikinui near Kaipara Beach. Though the output is low at present, due to the economic depression, there is reason to believe that A. ventricosum is of considerable commercial importance. As very little is known of this animal, work extending over a period of several years is necessary, and if carried out, will yield results of interest to the economist as well as to the biologist.