無脊椎動物佔999%以上的動物多樣性； 然而，他們所獲得關注極不相稱，只吸引不成比例少數的研究努力，相對於脊椎動物。(Ponder and Lunney 1999, in Lydeard et al. 2004). 非海洋軟體動物包括一些系統發育同異的品系與種類豐富的集合，佔有軟體動物兩個綱，雙殼綱(蛤與貝)與腹足綱(蝸牛與笠貝)。(Lydeardet al.2004)非海洋軟體動物全球性減少，可能與掠食扁形蟲的引入與傳佈有關，尤其是扁蟲(Platydemus manokwari)。
扁蟲已經被引入許多地方，作為控制非洲大蝸牛(Achatina fulica))的生物控制劑。它是一種有效率的捕食者，引入後嚴重威脅原生蝸牛。脆弱的本土蝸牛族群受到 P. manokwari威脅，包括關島特有的 Partulidae與日本小笠原群島的 Mandarina蝸牛。
估計太平洋島嶼上的原生陸蝸牛約有 4000種(這個數目不包括紐西蘭的 1350種新幾內亞島的 1000種以上)。這些獨特的原生蝸牛群正在迅速消失。Endodontidae, 可能是太平洋島嶼中多樣性最大的科，似乎已經完全滅絕，或者在他們從前居住的每個島上縮小成稀疏的剩餘族群。Moorea(法屬玻里尼西亞)的所有的 Partulidae 已在野外滅絕。在夏威夷，750種陸蝸牛其中高達 90% 已經滅絕。在Rota(馬里亞納群島北方)，43 種陸蝸牛其中68% 已經滅絕或者族群下降，而在薩摩亞群島，幾乎全部族群都在下降，雖然滅絕的比率較小。(Cowie and Robinson 2003). 這些估計整體來說也許顯示出太平洋島嶼 50% 的陸蝸牛動物群，已經在最近消失。專家建議，應該堅決阻止繼續引進外來天敵如 P. manokwari，以保護這種獨特的島嶼蝸牛(Cowie and Robinson 2003).
降低本地生物多樣性: Tree snails of the family Partulidae have declined on Guam since World War II (Hopper & Smith 1992). Hopper and Smith (1992) describe the distribution of various snails endemic to the region. One species, indigenous to the western Pacific, radiolate partula (Partula radiolata), is locally common along streams in southern areas of the island. The Mariana Island endemic tree snail Samoana fragilis is not found in abundance anywhere on Guam. The (fat Guam partula Partula gibba ), another Mariana endemic, is currently known only from one isolated coastal valley along the northwestern coast, and appears to be in a state of decline. The Mount Alifana partula (Partula salifana), endemic to Guam, is believed to be extinct. The single most important factor causing their decline is likely predation by snails that were introduced as biological control agents for the giant African snail (Achatina fulica). The current, most serious threat is probably the introduced flatworm P. manokwari. This flatworm is also the likely cause of extinctions of other native and introduced gastropods on Guam and may be the most important threat to the Mariana Partulidae (Hopper and Smith 1992).
Chichi-jima Is. (Japan)
捕食: There used to be other land planarians (such as Bipalium sp.) and a land nemertean (G. pelaensis) distributed widely on Chichijima Island, but in recent years there are few in areas where P. manokwari has already invaded (Kawakatsu et al. 1999, Ohbayashi 2002, in Ohbayashi et al. 2005). This is in contrast to the abundance of these land planarians and a land nemerteans on Hahajima Island, which has not been invaded by P. manokwari (Kawakatsu et al. 1999, Okochi et al. 2004, in Ohbayashi et al. 2005). Therefore, these land planarians and land nemerteans may have been consumed by P. manokwari on Chichijima Island (Ohbayashi et al. 2005).
生態系統變化: The selective land snail-feeding carabid beetle (Badister sp.) was found only in land snail survival areas (Hasegawa et al. 2009). This indicates that the extinction of land snails might cause the successive extinction of other species, ie: a "cascade" effect (Hasegawa et al. 2009). The population of Badister sp. around the Ogasawara Islands, in areas with and without land snails, needs to be monitored for the conservation of the species (Hasegawa et al. 2009).
競爭: There used to be other land planarians (including snail predators) and land nemertean worms distributed on Chichijima Island (Kawakatsu et al. 1999, in Ohbayashi et al. 2005), but in recent years there are few in areas where P. manokwari has already invaded, suggesting that these land planarians and land nemerteans have been defeated by interspecific competition with P. manokwari (Ohbayashi 2002, in Ohbayashi et al. 2005).
降低本地生物多樣性: Land snails have already become extinct in most areas on Chichijima Island (Tomiyama & Kurozumi 1992, Tomiyama 1994, in Ohbayashi et al. 2005). The most likely cause of the decline of land snails on Chichijima Island is thought to be the invasion of P. manokwari in the 1990s (Tomiyama 2002, in Ohbayashi et al. 2005; Sugiura et al. 2006, Ohbayashi et al. 2007, Chiba 2009, Sugiura & Yamaura 2009, in Sugiura 2009). For example, Mandarina tomiyamai, Boninosuccinea punctulispira and Elasmias kitaiwojimanum were driven to extinction on Chichijima in the 1990s
through flatworm predation (Chiba 2009, in Sugiura 2009).
Ogasawara-Shoto Is. (Japan)
捕食: Mandarina snail species have suffered serious destruction of habitat due to cultivation since 100 years ago (Kurozumi 1988; Tomiyama 1994 in Satoshi 2003). However, the most serious problem is predation by introduced species. For example, the predatory flatworm, P. monokwari, other predatory flatworms and the carnivorous land snail Euglandina rosea (Kawakatsu et al. 1999, Ohkouchi et al. 1999, Tomiyama 2002, in Satoshi 2003). The effect of these introduced predators on native land snail fauna is so serious that they may rapidly cause the extinction of many of the native land snails in the Ogasawaras. A conservation program is needed to avoid the extinction of Mandarina spp.
Okinawa Is. (Japan)
捕食: P. manokwari has been reported as feeding on 17 snail species on Okinawa.
Rota Is. (Northern Mariana Islands)
捕食: Platydemus manokwari threatens endemic snails (Eldredge & Smith 1995).
Saipan Is. (Northern Mariana Islands)
捕食: P. manokwari threatens endemic snail species.
Tinian Is. (Northern Mariana Islands)
捕食: P. manokwari threatens endemic snail species.
降低本地生物多樣性: In 1992-1994 we surveyed the fauna in order to evaluate its status and, by comparison with previous surveys, to detect any trends. Twelve species have declined (eight native, two cryptogenic); 17 (15 native, two cryptogenic) show a ''probable decline'' or ''possible decline''; five (four alien, one native) have increased or possibly increased. Some species showed no clear trend; others could not be evaluated, but some of them may be extinct. The fauna faces threats similar to those faced elsewhere, primarily habitat destruction and alien species impacts. Most notable is the introduction of a predatory flatworm, P. manokwari, in attempts to control the giant African snail, Achatina fulica, which became established in Samoa in the 1990s. The flatworm may or may not be able to control A. fulica but poses a serious threat to the native snail fauna. Further introduction and distribution of alien predators should be strongly discouraged (Cowie and Robinson 2003)