A novel anti-predatory mechanism in Indrella ampulla (Gastropoda: Ariophantidae)

Gastropods depend on their shells and slime for defence but they also have certain other strategies which serve as effective measures to avoid predation. This is an opportunistic observational account of individuals of Indrella ampulla (Ariophantidae) smearing their slime on the surface of their shells when agitated. Such a behaviour is novel to our knowledge and has not been reported earlier. This note will further add to the natural history observations of such animals and decipher the lesser-known facts about the defence strategies. 

ISSN 0974-7907 (Online); ISSN 0974-7893 (Print) In this note we report the smearing behaviour as a novel anti-predatory strategy followed by these large gastropods as an extension of the frothing behaviour reported earlier. Three individuals of Indrella ampulla (two yellow morphs and one orange morph) were observed after agitating them by hand on 25 June 2022 at 12:44 h and 14 July 2022 at 15:41 h. All three individuals were fairly aggressive in terms of their defence mechanism by producing froth along with a slimy secretion to cover their shell. The observations were made in Wayanad in the state of Kerala (11.5144°N and 76.0389°E, 838 m) and in Coorg in the state of Karnataka (12.2283°N and 75.6542°E, 1,088 m) in India. All the observations were made on private properties.
The observations were made while assessing the microhabitat preference of land snails in the Western Ghats. Two of the individuals (yellow morph of Indrella ampulla) were agitated by hand in Lakkidi to observe their behaviour when subjected to stress; these individuals were found on different substrates -one on a rock and the other on a tree trunk. We observed that both individuals secreted foam that was viscous and sticky in nature. Upon detection of physical stress, the individuals stopped their movement and started smearing their slime on their shell with the tail end of their body until the potential threat was over ( Figure 1; see Video 1). Such response was only observed upon overstimulating the animal. The source of the secreted foam was observed to be the surface of the mantle mucus cells (Rollo & Wellington 1979) (Image 1; Video 2). A similar behaviour was also observed in case of the orange individual in Coorg. The agitation experiments were performed by KM in all three cases.
Frothing behaviour was earlier reported as a defence mechanism in the red morph of Indrella ampulla during an observation of a cane turtle feeding on one of the individuals (Deepak & Vasudevan 2009). Here for the first time, we observed similar occurrences in the yellow and the orange morph as well. Foaming as an anti-predatory strategy was also reported earlier in

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several other species of terrestrial gastropods such as Helix pomatia (Pollard, 1975), which when attacked produced a copious amount of froth. Exudation of slime is also studied in many slugs such as Arion fasciatus and Deroceras reticulatum, the sticky slime makes slugs a difficult prey (Pakarinen 1994;Mair & Port 2002). Certain other species of terrestrial snails such as Karaftohelix editha and Karaftohelix gainesi swing their shells in order to get rid of the predators (Morii et al. 2016). Ovachlamys fulgens, also known as the jumping snail, propels (jump) its body when disturbed (Teixeira et al. 2017). Cantareus apertus rocks its shell back and forth to produce sound (Wenger 2014).
In case of Indrella ampulla, smearing the slime over the shell with the tail also serves as a defence mechanism, potentially covering the animal completely with slime to deter predators. It is a large-bodied semislug like animal which requires an effective strategy to avoid predation since it cannot retract its entire body into the shell to protect itself. Similar observation and assessing the nature of the secretion and the trait governing it may also provide important insights to the mechanisms of defence. The Journal of Threatened Taxa (JoTT) is dedicated to building evidence for conservation globally by publishing peer-reviewed articles online every month at a reasonably rapid rate at www.threatenedtaxa.org. All articles published in JoTT are registered under Creative Commons Attribution 4.0 International License unless otherwise mentioned. JoTT allows allows unrestricted use, reproduction, and distribution of articles in any medium by providing adequate credit to the author(s) and the source of publication.