A list of land and fresh-water Mollusca of the Malay Peninsula
F. F. Laidlaw published this second part of his checklist of Malayan land and fresh-water molluscs in 1933, completing a survey first begun with the Operculata in 1928. Working from museum collections and field material gathered across the Peninsula, Laidlaw undertook what he candidly described as a “first attempt” to systematise the Pulmonate fauna—a group he acknowledged remained “very imperfectly known” (p. 211). The article follows Thiele’s 1931 classification and documents the family-level and generic composition of the group, with particular attention to cave-dwelling assemblages and the problem of introduced species.
Summary
Laidlaw’s list spans twelve families of terrestrial pulmonates, from the highly primitive Rathouisiidae (the genus Atopos, which he notes are “probably the most primitive of existing land-mollusca”) through the more familiar Achatinidae, Ariophantidae, and Streptaxidae (pp. 211–234). A recurring theme is the contrast between the Peninsula’s comparatively impoverished pulmonate fauna and that of neighbouring islands: of the 159 terrestrial pulmonate species recorded for Java by van Benthem Jutting, only thirteen are shared with the Peninsula, and all of those are species whose range has been extended by human activity (p. 211). Similarly, the genus Amphidromus—richly represented in Borneo, Sumatra, and Java—yields only a handful of forms in Malaya, including a single immature specimen of the section Syndromus collected by Dr. Annandale at Patalung (p. 229).
The Batu Caves in Selangor emerge as a critical locality, hosting species of Prosopeas, Subulina, Opeas, Kaliella, Microcystis, Indoennea, and Durgella, often in association with bat guano as a nutrient medium (pp. 215–216, 220, 228, 232). Laidlaw also draws attention to the apparently endemic genus Plicaxis, known only from the Peninsula, whose anatomy remains unknown (p. 216). Two new species are described: Sarika planata from the Cameron Highlands, distinguished from its nearest relative S. limbata by radular formula and shell morphology, and Parmarion peilei, a dark slug from the same locality whose spermatophore structure is compared in detail with that of P. malayanus (pp. 218–219, 223–224).
A significant portion of the article is devoted to taxonomic revision and synonymy. Laidlaw follows Hoffmann in collapsing several Atopos species into fewer taxa, reassigns Parmarion doveri back to the type genus on the grounds that the external character used to separate it is not valid, and discusses the uncertain placement of Megaustenia ophiria and Durgella hatchongi (pp. 212, 225, 221). He also flags a transposition error in his earlier 1931 paper on the Dyakiinae, correcting the identity of the species from Pulau Aor (p. 234).
Key Findings
- Only 13 of the 159 terrestrial pulmonate species recorded for Java (van Benthem Jutting, 1929) are shared with the Malay Peninsula, and all thirteen are species whose distribution has been extended by human activity (p. 211).
- Achatina fulica, an African species, became established in Kedah and Province Wellesley after accidental introduction, and is preyed upon by the larva of a glow-worm (p. 215).
- The genus Plicaxis is apparently endemic to the Malay Peninsula; its two known species (P. perakensis and P. mirabilis) are known only from Perak and Kelantan respectively, and the anatomy of the animal is unknown (p. 216).
- Parmarion malayanus Collinge, described from the Cameron Highlands, possesses a spermatophore approximately 6 mm in length (excluding the filiform tail), S-shaped with comb-like chitinous plates along the convex curvature of the upper limb; the radular formula is 98–26–1–26–98 (pp. 223–224).
- The genus Amphidromus is represented in the Peninsula by only a small number of forms compared to Borneo, Sumatra, and Java; the sole representative of the section Syndromus is a single immature specimen of A. fultonia collected by Dr. Annandale at Patalung (p. 229).
- Indoennea ridleyi Peile is recorded as “abundant” in the Batu Caves and Gua Tembus, Selangor, indicating a significant cave-adapted component of the local streptaxid fauna (p. 232).
Conclusion
Laidlaw’s definitive takeaway is that the Pulmonate fauna of the Malay Peninsula is a small, poorly understood assemblage, markedly less diverse than that of the surrounding islands, and heavily influenced by both cave microhabitats and human-mediated introductions. The work establishes a baseline checklist against which future revision—particularly of the Atopos complex, the Parmarion slugs, and the cave-dwelling streptaxids—can proceed, while explicitly flagging the taxonomic uncertainties that remain.
Context
- Primary material drawn from the F.M.S. Museums (including the Raffles Museum collection), the British Museum, and Laidlaw’s own field collections from the Cameron Highlands (1931), Gunong Pulai, Johore, and the Batu Caves, Selangor.
- The article represents a foundational taxonomic synthesis for Malayan pulmonate malacology, bridging the earlier descriptive work of Stoliczka (1873), de Morgan (1885), Collinge (1902–1903), and von Mollendorff (1891, 1902) with the more systematic frameworks of Thiele (1931) and Hoffmann (1924, 1929).