GASTROPOD MOBILITY ON ROCKY SHORES |
INTRODUCTION

Molluscs are invertebrates usually containing one or two shells with a few exceptions. They are soft-bodied bilaterally symmetrical animals with organs present in a fluid-filled cavity hence soft bodied referring to word mollusc (latin). Classification of the Molluscs has major turmoil of instability in the Animal Kingdom. Since, most of the resources and text books use old system of classification, and that is stable, easy to recognize, and complies with Cambridge Zoology Museum, so we are adapting that very system for their identification.
Habitat of Molluscs
Molluscs occupy mostly marine and moist environments that are why some of them have rudiments of amphibians they kept along during the evolutionary attempts. Some of the gastropods however, dwell in the freshwater also. Others occupy the bottoms of lakes depending on their feeding habits. Some of the molluscs reach the terrestrial environments e.g. snails and slugs.
Habitat of the shells typically affect their adaptive structural formation and hence identification. The lines of the shells are dependent upon the tidal emersions. Also, the internal tidal indications of the structure indicate micro-growth line formation in molluscs from sub-tidal areas (Mirzaei et al., 2014).
Classfication of the molluscs has classicaly been associated with the structure of the radula or structure of the shell. Within the phylum Mollusca, there are seven classes (Barnes et al., 1993); viz Aplacophora – solenogastrids and caudofoveates (without shells); Cephalopoda – octopi, squid, cuttlefishes, nautilus; Polyplacophora – chitons or coat-of-mail shells; Scaphopoda – tusk shells; Monoplacophora – neopilinids; Bivalvia – ‘clams’ including cockles, oysters and mussels; and Gastropoda – slugs and snails (both marine and terrestrial).
Gastropods comprise around 50,000 to 100,000 species other than fossils belonging to Cambrian dates. They are the most successful molluscs known to date, and consist most fundamental transformation and translocation adaptations. According to previous classifications, gastropods are classified into three major groups:The Prosobranchia or G1 Prosobranchia are the marine snails and divided into primitive, middle and late snails based upon a progression identified amonst them.
The primitive marine snails; G1a Archaeogastropoda are spanning simple lives. Even they suffered a complication of getting water for respiration into the opening of their shell, gills, and for the excretory system. They were considered as the experimental models adapting water for ingestion under the shell and for excretory route, they developed as chimney like flues for the efflux from solitary hole in the intermediate keyhole limpets (Diadora) or many holes in the abalones (Haliotis) to sort out the ventilation current in limpets (Patella), from front to the back. The shell could be strengthened, thickened, or coiled to make a fortification like in turban snails (Turbo) or top shells (Trochus). Though they are very successful in colder shores like ones in UK, Devon for instance, yet they find problem in the tropics where their own big foot is overheated hence modified by nerites as in Nerita. The Nerites adapt to make more globular shell, smaller mouth, adapted with ridges to act like cooling fins on the rocks. These nerites and tops make together the first snails to make operculum meant for defense and keeping from desiccation on the open shore.
The middle marine snails, G1b Mesogastropoda are a bit advanced in that their gills are attached to one wall contrary to Archaeogastropods. This way, their ventilation current is more efficient than later. Also, the Mesogastropods have one channel in the aperture of the shell contrary to Archeaogastropods. These herbivores include candidates like conches (Strombus), winkles (Littorina), and spider conches (Lambis); in addition to predators such as cowries (Cypraea), tuns (Tonna) and helmets (Cassis, Phalium).
The new snail, G1c Neo-gastropoda, evolved with aeration currents with water flow in both direction. The inflow is through a structure called siphon leading to a siphonal canal in shell that extend upto a V-like notch posteriorly for the exhalation through efferent water. This advanced group includes predators mostly comprising cones (Conus), volutes (Voluta), and whelks (Buccinum).
Fig 1. Division of shores and tidal zones
Evolutionary Trends and adaptation of Marin Molluscs is significantly dependent upon the surface structures or architecture of shells formed on the basis of tidal effects on the structure. The composition of this habitat of animals consist splash zone, upper shore, middle shore, lower shore, and subtidal zone (Fig 1). The marine molluscs habituate and adapt to live their life at lower shore, middle shore and upper shore; with a few exceptions of subtidal zone. Periwinkles, dog whelks and top shells can easily be found on the rocky shores and are excellent subjects for experimental studies present in this habitat. Translocation of these molluscs, their accession and succession is dependent upon adapted features they opted during evolution. Locomotion and translocation of snails
With an enormous attention to study the dynamics of the locomotion of gastropods in applied robotics, this study provides an interesting art to combine the ecology and zoology of gastropods. The terrestrial gastropods move with a periodic muscular contractions call pedal waves and relaxations called interweaves which arise from from their tails to heads. This propagation is the key to a unique movement aided by a mucus screted during this propulsion. The ventral waves interact with that mucus and transmits propulsive forces to the ground (Lai et al., 2010).
The presence of mollucs at the shores is associated with their response and ability to withstand salinity, exposure to air, and sunlight. Translocation of molluscs provides them a push to compete or seek the better ventilation partially and to maintain the salt concentration majorly. The variation of temperature, salinity, amount of sunlight and time of exposure to air gradually increase in strength towards upper shore region contrary to the competition that gradually rises towards lower shore (Fig 1). The driving force of translocation and direction of locomotion of molluscs will be majorly dependent upon their existing optimal adaptations to the ecological succession. Theoretically, the composition and architecture of shells, muscular adaptability of animals, and their salt bearing potential will define the preference of the level of their habitat on shore. The shape and strength in their locomotory organ, internal fluid dynamics and movement sense of the animals is developed as they experience the tides and salinity. On the basis of a unanimous adaptive characters, the similar members live and locomote similarly. Further, the dislocation and segregation of the animals of one adaptation and level of shore will try to move in one direction to get back to their optimal level.
Objectives of study
-Do top shells and others (periwinkles or dog whelks) have a preferred level on the shore?
-If moved would they attempt to return to this level again?
METHOD
Collection of specimen and analysis
Various translocation experiments were performed to figure out the answers to objectives. Samples were collected from mid and up shores of Devon shore, UK as given in Fig. 2.
The upper shore samples (snails) were collected at 11:30am when sea level was pretty high. However, at Devon, the sea level recedes starting afternoon so we planned to get samples from mid shore too while the tides were down.
We painted the shells with different colours including Yellow (Common Periwikles), Blue (Top Shell) and Orange (Rough Periwikle) as given in table 1 for colour codes.

Fig 1A | Fig 1C Fig 1DFig 1A.Geographical Location of Devon ShoreFig 1B. Devon South Shore Dock Fi 1C. Specie Richness Map of Mulluscs, Devon Shore, UKFig 1D. Grid: No. of Species per area (Km).(https://data.nbn.org.uk/Datasets/GA000321) | Fig 1B | |
Figure 2. Site of Sampling and associated characteristics
We then collected other random seashells from the mid shore at 1:00pm, when the tide went shallow. We painted the collected specimen again with different colours but different than ones for upper shore. The mid shore samples were colorured with Green (Common Periwikles), Purple (Top Shell) and Red (Rough Periwikle) pigments.

Table 1. Colour Coding of the collected specimen Upper Shore | Mid Shore | Yellow(Common Periwikles) | Green(Common Periwikles) | Blue(Top Shell) | Purple(Top Shell) | Orange(Rough Periwikle) | Red(Rough Periwikle) |
After painting the tops, we mixed all seashells from the mid and upper shore in two containers EQUALLY.
We took one of the containers that had the seashells to the mid shore and made a mark in a specific area and then took the other container and did the same thing in the upper shore to see how far the seashells traveled in the next 24 hours. We used a measuring tape to measure the distance of the seashells after these hours. The mark that we made was on the sandpit before the stones. In the next morning, the seashells moved their place and were found at top of the stones.
In one container, we had 157 seashells and when we came to check it, we only found 99 animals (Mid shore). For the upper shore container, we had 157 and the next day, we found 117 animals. The translocation of the animals with their particular direction of movement is given in discussion part.

RESULTS
The tabulated data of specimen collected from Up shore and Mid shore are given in the tables 2, and 3. The detailed information of the translocation, climbing the rocks or grouping of the gastropods is narrated with details in given in appendix 1.1.

Table 2. Data from collection of specimen from Up Shore | Red | yellow | orange | purple | green | blue | cave | 1 | 4 | 4 | 8 | 1 | 4 | sea | 2 | 4 | 0 | 0 | 0 | 0 | right | 0 | 12 | 4 | 14 | 6 | 14 | left | 2 | 6 | 15 | 5 | 6 | 5 |

Table 3. Data from collection of specimen from Mid Shore | Red | yellow | orange | purple | green | blue | cave | 3 | 9 | 12 | 6 | 0 | 1 | sea | 1 | 1 | 1 | 9 | 0 | 7 | right | 0 | 4 | 4 | 0 | 0 | 4 | left | 0 | 13 | 2 | 10 | 0 | 11 |

Data Analysis
The results in the Table 1 and 2 are corresponding to various groups of mollusks that are grouped on the basis of their locomotory information, movement sense or direction.
Table 4.1: Up-Shore; ANOVA: Two-Factor Without Replication SUMMARY | Count | Sum | Average | Variance | | | Rows | | | | | | | Cave | 6 | 22 | 3.666667 | 6.666667 | | | Sea | 6 | 6 | 1 | 2.8 | | | Right | 6 | 50 | 8.333333 | 34.26667 | | | Left | 6 | 39 | 6.5 | 19.5 | | | Columns | | | | | | | Red | 4 | 5 | 1.25 | 0.916667 | | | Yellow | 4 | 26 | 6.5 | 14.33333 | | | Orange | 4 | 23 | 5.75 | 41.58333 | | | Purple | 4 | 27 | 6.75 | 34.25 | | | Green | 4 | 13 | 3.25 | 10.25 | | | Blue | 4 | 23 | 5.75 | 34.91667 | | | | | | | | | | | | | | | | | ANOVA | | | | | | | Source of Variation | SS | df | MS | F | P-value | F crit | Rows | 186.4583 | 3 | 62.15278 | 4.194002 | 0.024223 | 3.287382 | Columns | 93.875 | 5 | 18.775 | 1.266917 | 0.328381 | 2.901295 | Error | 222.2917 | 15 | 14.81944 | | | | | | | | | | | Total | 502.625 | 23 | | | | | UP Shore P-Value= Locomotion=0.024223 Types of Snails= 0.328381 Table 4.2: Mid-Shore; ANOVA: Two-Factor Without Replication | SUMMARY | Count | Sum | Average | Variance | | | Rows: | | | | | | | Cave | 6 | 31 | 5.166667 | 22.16667 | | | Sea | 6 | 19 | 3.166667 | 14.56667 | | | Right | 6 | 12 | 2 | 4.8 | | | Left | 6 | 36 | 6 | 35.6 | | | Columns | | | | | | | Red | 4 | 4 | 1 | 2 | | | Yellow | 4 | 27 | 6.75 | 28.25 | | | Orange | 4 | 19 | 4.75 | 24.91667 | | | Purple | 4 | 25 | 6.25 | 20.25 | | | Green | 4 | 0 | 0 | 0 | | | Blue | 4 | 23 | 5.75 | 18.25 | | | | | | | | | | | | | | | | | ANOVA | | | | | | | Source of Variation | SS | df | MS | F | P-value | F crit | Rows | 60.16667 | 3 | 20.05556 | 1.362264 | 0.292251 | 3.287382 | Columns | 164.8333 | 5 | 32.96667 | 2.239245 | 0.10393 | 2.901295 | Error | 220.8333 | 15 | 14.72222 | | | | | | | | | | | Total | 445.8333 | 23 | | | | |

Mid Shore P-Value= Locomotion=0.292251 Types of Snails= 0.10393

DISCUSSION
What is expected pattern of mobility of gastropods especially at rocky shore? What is role of tides on their adaptive mobility? If moved would they attempt to return to their habitat?
The translocation experiment designed here was to assess the pattern of movement of gastropods and their ability to translocate and move back with the sense of direction. The pattern of movement of top shells, their adaptations at up and mid shore, and their ability to translocation once dislocated can be investigated as a model study to understand the mobility among candidates of gastropods.
Depending upon variables, the purple colored animals were found maximum in number and indentified as given in the grid (index 1.1).

Most of the orange (Rough Periwikle) snails moved to cave, i.e they had sense of direction and terrestrial orientation. Most of the yellow (Common Periwikles) tended to move in left and considered to be without any locomotory sense except dampness. Half of the purple (Top Shell) specimen moved to left and sea meaning that they were belonging to subtidal origin and had evolved required sense for that direction. Most of the blue snails (Top Shell) twisted left, mostly towards sea and others right. | Sea | | Left | | Right | | Shore | | Scheme of Directions at Devon Shore |

Out of 157 specimen, only 99 left that means 58 shells had travelled i.e 36% of our population of samples had developed locomotory abilities where as the remaining 64% were sessile. For the upper shore samples, 74% of the collected samples were sessile and the rest of 36% got ability to locomote. The ability of locomotion is a notion that upshore specimen are either less energetic or they do not need to move faster and hence didn’t develop their locomotory organs, evolutionarily; hence belonging to a separate class.
Whereas the ones from mid shore with higher capacity of movement probably have adapted to move faster and energetic to withstand the tidal currents; and represent the different class.
The distance of movement the specimen showed was interesting; blue (top shells moved maximum i.e. 8.3 and 7.7 meters towards sea. Downhill movement is no doubt an easy task, still the movement of the sub-tidal snails seems much more developed evolutionarily and they are most successful of all. Also, the purple, again top shells were successive and consistent in faster locomotion. Both of the groups travelled significantly in terms of number of population and distance.
Out of the pool of snails, the ones who remained sessile, moved left or right more than towards sea were yellow and found belonging to the upshore and may belong to Cephalopoda, Bivalvia, and Scaphopoda; whereas- blue could be from Gastropoda.
Movement of shells to the up of the rocks means that those snails tended to move outwards of the shore site and searching more air and sunlight (anti subtidal movement). Probably, these snails should be having rudiments of evolution similar to amphibians also.
CONCLUSION
So overall, most advanced snails with locomotory point of view are top shells both in mid shore and upshore and considered as the pre-dominant group of marine molluscs. Their adaptive locomotory characteristics are upto date with their habitat and they are successfully leaning towards terrestrial/rocky environment. They must have characteristics to withstand salinity, as well as sunlight and ambient air when outside of the shore.
Gastropods particularly top shells may induce some genes or have already expressed some elements at the level of transcription which may indicate that this group can be successful in terrestrial adaptations in future.
References
1. Mirzaei, M.R., Yasin, Z., Shau Hwai, A.T.S. (2014). Periodicity and shell microgrowth pattern formation in intertidal and subtidal areas using shell cross sections of the blood cockle, Anadara granosa. Egyptian Journal of Aquatic Research 40: 459–468. 2. Chapman, M.G. (1999). Assessment of variability in responses of intertidal periwinkles to experimental transplantations. Journal of Experimental Marine Biology & Ecology 236: 171-190.

3. Ruppert, E.E., Fox, R.S. & Barnes, R.D. (2004). Mollusca. 283-412. In: Invertebrate zoology: a functional approach (seventh edition). Brooks/ Cole – Thompson Learning, Belmont, California.

4. Barnes, R.S.K., Calow, P. & Olive, P.J.W. (1993). The molluscs. 122-137. In: The invertebrates: a new synthesis (second edition). Backwell Science, Osney Mead.

5. De Bruyne, R.H. (2003). The complete encyclopedia of shells. Rebo Publishers, Lisse, Netherlands, 336 pp.

6. Lai, J.H., del Alamo, J.C., Rodriguez, J.R., Lasheras, J.C. (2010). The mechanics of the adhesive locomotion of terrestrial gastropods. J Exp Biol (213): 3920-3933.

7. Location of South Devon Shore Dock SAC/SCI/cSAC. http://jncc.defra.gov.uk/protectedsites/sacselection/sac.asp?EUCode=UK0030060

8. https://data.nbn.org.uk/Datasets/GA000321)

INDICES 1.1. Data of Mid Shore Pooled Samples
Table: Frequency distribution in terms of translocation of specimen along with distance they covered, overnight. Colors | Destines\m | Direction | No. | | Colors | Destines\m | Direction | No. | yellow | 0.5 | Right | 50 | | orange | 0.09 | cave | 1 | purple | 0.4 | Left | 51 | | orange | 0.25 | cave | 2 | purple | 0.8 | Left | 52 | | orange | 0.1 | cave | 3 | purple | 0.7 | left | 53 | | orange | 0.9 | cave | 4 | purple | 1.2 | left | 54 | | orange | 1 | cave | 5 | purple | 0.8 | cave | 55 | | orange | 1 | cave | 6 | purple | 1.4 | left | 56 | | orange | 1.1 | cave | 7 | purple | 1.6 | left | 57 | | orange | 0.8 | right | 8 | purple | 0.6 | left | 58 | | orange | 0.5 | right | 9 | purple | 1.3 | left | 59 | | orange | 0.8 | left | 10 | purple | 1.2 | left | 60 | | orange | 1 | cave | 11 | purple | 1.2 | left | 61 | | orange | 1.1 | cave | 12 | purple | 1.9 | sea | 62 | | orange | 0.4 | sea | 13 | purple | 2.4 | sea | 63 | | orange | 1.2 | right | 14 | purple | 2.6 | sea | 64 | | orange | 1.3 | right | 15 | purple | 2.6 | sea | 65 | | orange | 1 | cave | 16 | purple | 2.6 | sea | 66 | | orange | 1.2 | cave | 17 | purple | 3.9 | sea | 67 | | orange | 0.8 | left | 18 | purple | 2.3 | sea | 68 | | orange | 1.8 | cave | 19 | purple | 4.3 | sea | 69 | | red | 0.25 | cave | 20 | purple | 4.1 | sea | 70 | | red | 0.25 | cave | 21 | purple | 0.8 | cave | 71 | | red | 1.1 | cave | 22 | purple | 3 | cave | 72 | | red | 0.6 | sea | 23 | purple | 3 | cave | 73 | | yellow | 0.2 | cave | 24 | purple | 2.7 | cave | 74 | | yellow | 0.6 | cave | 25 | purple | 1.8 | cave | 75 | | yellow | 1.2 | left | 26 | blue | 0.3 | right | 76 | | yellow | 1.2 | left | 27 | blue | 0.5 | left | 77 | | yellow | 1.2 | left | 28 | blue | 0.5 | left | 78 | | yellow | 1.2 | left | 29 | blue | 0.7 | left | 79 | | yellow | 0.7 | left | 30 | blue | 1 | left | 80 | | yellow | 1.1 | left | 31 | blue | 1.2 | left | 81 | | yellow | 1.3 | cave | 32 | blue | 1.4 | left | 82 | | yellow | 1.1 | cave | 33 | blue | 1.3 | cave | 83 | | yellow | 1.5 | left | 34 | blue | 2.1 | left | 84 | | yellow | 1.5 | left | 35 | blue | 1.6 | left | 85 | | yellow | 1.6 | left | 36 | blue | 1.4 | left | 86 | | yellow | 1.3 | left | 37 | blue | 1.4 | left | 87 | | yellow | 1.2 | left | 38 | blue | 0.9 | sea | 88 | | yellow | 1.2 | left | 39 | blue | 1.4 | right | 89 | | yellow | 1.3 | left | 40 | blue | 1.3 | right | 90 | | yellow | 0.2 | sea | 41 | blue | 1.6 | right | 92 | | yellow | 2 | right | 42 | blue | 2 | sea | 93 | | yellow | 2.3 | right | 43 | blue | 2.4 | sea | 94 | | yellow | 2.1 | right | 44 | blue | 2.6 | sea | 95 | | yellow | 2.8 | cave | 45 | blue | 7.7 | sea | 96 | | yellow | 2.2 | cave | 46 | blue | 8.3 | sea | 97 | | yellow | 4.7 | cave | 47 | blue | 0.7 | left | 98 | | yellow | 3.8 | cave | 48 | blue | 3.9 | sea | 99 | | yellow | 1.1 | Cave | 49 |