| Amphidromus | |
|---|---|
 | |
| The speciesAmphidromus roseolabiatus has dextral shell coiling. | |
 | |
| The speciesAmphidromus fuscolabris has sinistral shell coiling. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Order: | Stylommatophora |
| Superfamily: | Helicoidea |
| Family: | Camaenidae |
| Subfamily: | Camaeninae |
| Genus: | Amphidromus Albers, 1850[1] |
| Type species | |
| Helix perversa | |
| Species | |
See text | |
| Diversity[2][3] | |
| Over 110 species | |
| Synonyms | |
| |
Amphidromus is agenus of tropical air-breathingland snails,terrestrialpulmonategastropodmollusks in the familyCamaenidae. The shells ofAmphidromus are relatively large, from 25 mm (0.98 in) to 75 mm (3.0 in) in maximum dimension, and particularly colorful. During the 18th century, they were among the firstIndonesian land snail shells brought to Europe by travelers and explorers. Since then, the genus has been extensively studied: several comprehensive monographs and catalogs were authored by naturalists and zoologists during the time period from the early 19th to the mid 20th centuries. Modern studies have focused on better understanding theevolutionary relationships within the group, as well as solvingtaxonomic problems.
The genusAmphidromus is unusual in that it includes species that havedextral shell-coiling and species that havesinistral shell-coiling. In addition, some species within this genus are particularly notable because their populations simultaneously include individuals with left-handed and right-handed shell-coiling. This is an extremely rare phenomenon, and very interesting to biologists. Studies focused on the soft anatomy ofAmphidromus are scattered and fragmentary. Information on the internal anatomy is known only from a few species, and no larger, comparative morphological study has ever been carried out.
Species in the genusAmphidromus arearboreal — in other words, they are tree snails. However, more detailed information on their habits is still lacking. The general feeding habits of these snails are unknown, but a few species are known to feed on microscopicfungi,lichens orterrestrial algae.Amphidromus themselves are preyed upon by birds, snakes, and probably also by smaller mammals such as rats.
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Thegeneric name is derived from theancient Greek wordsamphí (ἀμφί), meaning "on both sides", anddrómos (δρόμος), meaning "running", alluding to the differentchiralities of the shells.[5] The shells ofAmphidromus are relatively large, and quite colorful; considerable numbers of them were among the firstIndonesian land snail shells brought back to Europe bytravelers and explorers during the 18th century. Comparatively speaking, malacologists have gathered a much smaller number of specimens.[4]
Several species andforms were described before 1800, most of them with inadequate locality data. At least two names —Amphidromus laevus (Müller, 1774) and the formA. perversus f.aureus Martyn, 1784 – still (as of 2017) have not yet been reported from a precise locality. During the first half of the nineteenth century, many species and varieties were named, again usually with poor locality data. Not until Eduard von Martens (1867) published hismonograph[6] was there an attempt to cover the entire complex of species within this genus. The 1867 monograph contained considerable information both on the variation within the genus, and on the problems of thegeographic distribution of the species. Many concepts that originated with von Martens are still (as of 2017) in use.[4]
In 1896,Hugh Fulton[7] organized 142 specific and varietal names into eighteen species groups containing a total of 64 species. WhenHenry Augustus Pilsbry's 1900 monographManual of Conchology[8] appeared, the number of species in the genusAmphidromus had increased to 81, and these were placed in nineteen groups. Pilsbry's study has remained the only illustrated monograph of the genus, and it is still considered indispensable for any serious study of the genus.[4]
Since 1900, the majortaxonomic studies onAmphidromus have beenfaunistic (a study of the fauna of some territory or area) in scope. The papers of American malacologistPaul Bartsch (1917, 1918, 1919)[9][10][11] on the Philippine species,Bernhard Rensch (1932)[12] on theLesser Sunda Islands forms, andTera van Benthem Jutting (1950, 1959)[13][14] on Javan and Sumatran populations are especially comprehensive. Potentially the most valuable[4] contribution is that ofCurt Haniel (1921),[15] who discussed the variation withinA. contrarius andA. reflexilabris onTimor; the variations in color and form were well illustrated in a series of color plates.
Literature published after 1900 contains many scattered descriptions of new color forms and subspecies. Of the 309 names in the nomenclatural list, 111 (35.9%) were published after Pilsbry (1900).Adolf Michael Zilch (1953)[16] listed type specimens in theSenckenberg Museum, and illustrated many previously unfigured species.Frank Fortescue Laidlaw &Alan Solem (1961) recognized 74 species by name, and considered that material from theBanda Islands probably represented an undescribed species. Eleven of the species recognized by Laidlaw & Solem were described after the appearance of Pilsbry's monograph. However, several species recognized by Pilsbry have subsequently been subordinated to subspecific or varietal status, and a few names have been transferred toincertae sedis, since they are based on hundred-year-old references that have not been substantiated by more recent collectors. In fact, the study by Laidlaw & Solem (1961) forms a supplement to Pilsbry's monograph with his extensive plates, and many of Laidlaw & Solem's conclusions concerning the relationships of color forms described as species were taken not so much from new samples, but from the extent of variation that was outlined by Haniel (1921) in his pioneer study.[4]
Species in the genusAmphidromus usually have smooth, glossy, brightly colored, elongate or conic, dextrally or sinistrally coiledshells. The shells are moderately large, ranging from 25 mm (0.98 in) to 70 mm (2.8 in) in maximum dimension, having from 6 to 8 convexwhorls. Their color pattern is usuallymonochromatic yellowish or greenish, but can be variegated. Theaperture is oblique or ovate in shape, without any teeth or folds, and with the aperture height ranging from two-fifths to one-third of total shell height. The peristome is expanded and/or reflected, and is sometimes thickened. Thecolumella may be straight or recurved, and theparietal callus is weak to well-developed, and theumbilicus may be open or closed. Theradula is spatulate, has cusped teeth arranged in rows, usually with a monocuspid central tooth and bicuspid or tricuspid lateral teeth. Thejaw is thin and weak, with low flat ribs. The pallial region issigmurethrous, with a very long, narrow kidney. Thegenitalia are that of typical camaenids, with a long seminal receptacle, a short penis with low insertion of the retractor muscle, and a short or long epiphallic caecum (flagellum and appendix). Thespermatophores have a pentagonal outline incross-section.Amphidromus are typicallyarboreal animals.[4][17]
Theshells ofAmphidromus are relatively large, from one to three inches high, and colorful.Amphidromus has an elongate-conic or ovate-conic helicoid shell of 5 to 8whorls. The shell may be thin and fragile, or very heavy and solid, with no known correlation of shell structure with distribution or habitats.[4]
In some species within this genus, theshell coils invariably to the right, and in many others just as invariably to the left. However, a significant number of species in this genus are "amphidromine"; this term means that both left- and right-handed shell coiling are found within the same population. One could say they are "polymorphic" for the direction of shell coiling, but because there are only two possible types of shell coiling, they are described as "dimorphic" in coiling. The two types of shell coiling occur in some species in approximately equal numbers, other species have a distinct predominance of one phase. There is as yet no information on the heredity of this character inAmphidromus.[4]
Because almost all other species of amphidromine gastropods, such as ones within the generaPartula andAchatinella, have already become extinct,[18] the genusAmphidromus, containing over 110 species, is uniquely useful for the study of theevolution ofasymmetry in animals,[18] and this is why theconservation of this genus is of essential importance to biologists.
The whorls of the shell of species ofAmphidromus are moderately convex and, with only a few exceptions, are smooth or have a faintsculpture of growth lines. However, a sculpture of moderately heavy oblique radial ribs has appeared at least four separate times in the genus, and can be seen in the following species:Amphidromus costifer Smith fromBinh Dinh Province in Vietnam;A. begini Morlet from Cambodia;A. heccarii Tapparone-Canefri from Celebes; and theA. palaceus-A. winteri complex from Java and Sumatra. Correlated with the ribbing is a light, monochrome coloration, and a thin shell with a largeaperture and a flaring lip. Many solid shells in other species do show a slight roughening of the surface, but this is very different from the ribbed sculpture mentioned above.[4]
The aperture is generally large, varying from about two-fifths to one-third the height of the shell, often within the same population. Usually the lip is at least somewhat expanded, and in forms such asA. reflexilabris Schepman andA. winteri (Pfeiffer) var.inauris Fulton, the lip can only be called flaring. InA. perversus (Linnaeus) and most other thick-shelled species, the lip is internally thickened, forming a "roll" in its expansion, and has a very heavyparietal callus. In thin-shelled species, the lip is usually a simple reflected edge. Theumbilical area can be partially open, nearly closed, or sealed. This feature sometimes provides a useful criterion for specific identification. The angle of the parietal wall varies, but no precise information on this has been compiled.[4]
Generally the whorls of the shell increase rather regularly in size, however, species which are probably closely related, such asA. sinistralis (Reeve) andA. heccarii Tapparone-Canefri, can have quite different degrees of whorl increment. No attempt has been made to express these differences meristically, since most of the available material was inadequate for statistical treatment. Actual dimensions of the shell vary greatly both within and between species. The minimum adult size is about 21 mm high, the observed maximum about 75 mm. There is not much variation in adult size within species: only a few species, notablyA. maculiferus,A. sinensis andA. entobaptus, have a variation in adult size that is greater than seven or eight millimeters in total.[4]
The single most major aspect of shell variation within the genus is the color patterning. In general, many arboreal snails are brightly colored, obvious examples being the bulimulid generaDrymaeus andLiguus, the cepolidPolymita, and the camaenidPapuina. However,Polymita,Liguus andAmphidromus are particularly noted for their color variations. The basic ground color ofAmphidromus appears to be yellow, and this color is usually (except forAmphidromus entobaptus) confined to the surface layers of the shell, since worn specimens appear to be nearly devoid of color. In some species the background color is whitish, and a few have dark background colors. Theapical whorls are pale, purple, brown, or black, and this sometimes varies within a population (as inA. quadrasi). A few species, for exampleA. schomburgki, have a deciduous greenperiostracum.[4]
Continuous zonal patterns can take the form of whitish subsutural bands (A. similis), heavy subperipheral pigmentation (A. perversus var.infraviridis), subsutural color lines (A. columellaris), broad spiral color bands (A. metabletus,A. webbi), or narrow spiral bands (A. laevus). Interrupted zonation can consist of the interruption of bands into spots in (A. maculatus); highly irregular splitting of zones (A. perversus vars.sultanus andinterruptus); formation of oblique radial streaks which run parallel to (inA. inversus) or cross (inA. latestrigatus) the incremental growth lines; or almost every conceivable combination and variation of these factors. Often the pattern will change radically from theapex to thebody whorl (inA. quadrasi vars.). The aperture,parietal callus,columella, lip, and umbilical region are variously marked with pink, brown, purple, white, or black. Haniel (1921)[15] includes several color plates which clearly demonstrate the extent of color variation within two species of theSyndromus type.A. perversus andA. maculiferus of the subgenusAmphidromus are equally variable, whereas species such asA. inversus andA. similis are almost uniform in coloration.[4]
In shells of most of the species in the subgenusAmphidromus, resting stages are marked by the deposition of a brown or black radial band called avarix. This appears to be rare in the subgenusSyndromus, although the shell ofA. laevus does show evidence of interruption of the spiral banding after a resting phase.[4]
Species recognition is based on combinations of minor structural variations in the shape, aperture, whorl contour, umbilical region, and color pattern. It appears to be the case that many species have a stable color pattern, while other species seem to vary tremendously. Adequate unselected field samples will enable a better understanding of the relative stability or variability of particular species in single localities.[4]
Information concerning the soft anatomy ofAmphidromus is widely scattered and fragmentary. The most complete account is that of Arnold Jacobi (1895)[19] on specimens fromGreat Natuna (Natuna Islands) andDjemadja (Anamba Islands). Unfortunately, although it is clear that anatomical differences exist in the two species Jacobi dissected, unfortunately we do not know which forms he worked on, because he had incorrectly identified his material. In his paper he referred to the two species asAmphidromus chloris and theinterruptus phase ofA. perversus. However, that is not possible, because in realityAmphidromus chloris is a species found only in the Philippine Islands, and theinterruptus phase ofA. perversus is not present in the Natuna Islands.[4]
Carl Arend Friedrich Wiegmann (1893, 1898)[20][21] discussed portions of the anatomy ofA. adamsii,A. porcellanus,A. contrarius, andA. sinistralis.Walter Edward Collinge (1901, 1902)[22][23] briefly noted features ofA. palaceus andA. parakensis (reported asA. perversus). Haniel (1921)[15] dissectedA. contrarius andA. reflexilabris, andBernhard Rensch published a few scattered notes in his various faunistic surveys. A few earlier notes are mentioned in Pilsbry (1900).[4][8]
Characters such as the long, narrow kidney with reflexed ureter and closed secondaryureter, the penial complex with distinct penis, which is continuous with the epiphallus, epiphalliccaecum (a flagellum and an appendix), unbranched gametolytic duct, lack of vaginal accessory organs, and the basic condition of the nervous and retractor muscle systems support the inclusion ofAmphidromus in the family Camaenidae.[17] This group of snails occur in a wide variety ofhabitats in thetropics ofEastern Asia andAustralasia, and is one of the most diverse families in thecladeStylommatophora.[24] ThoughLaidlaw &Solem (1961) provided no more additional details on the anatomy ofAmphidromus, subsequent studies by distinct authors, e.g., Bishop (1977)[25] and Solem (1983),[26] have demonstrated that the reproductive system can provide valuable data for species recognition.[4]
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| Phylogeny and relationships ofAmphidromus according to Sutcharit et al. (2007)[18] |
Prior to 1900, the similarity in shape of the shell ofAmphidromus to that of South American tree snails in the familyBulimulidae had misled taxonomists. However, the dissections made by Wiegmann and Jacobi clearly showed that the inner anatomical features ofAmphidromus were the same as those of the Asian-IndonesianCamaenidae, and that the resemblance of the shell ofAmphidromus to that of bulimulids was merely an example ofparallelism.[4]
Laidlaw and Solem (1961) recognized 75 species in the genusAmphidromus, and placed another seven names underincertae sedis. In 2010, 87 species in the genusAmphidromus were recognized.[18][27][28][4] Species within the genusAmphidromus are divided into two subgenera, as in the following list:[18]
Originally described asHelix perversus byLinnaeus in1758,Amphidromus perversus is thetype species of the genusAmphidromus, by the subsequent designation ofEduard von Martens (1860).[29] Species in the subgenusAmphidromus are amphidromine (left-handed and right-handed snails occur within the population) with a few exceptions. Four dextral taxa are:A. givenchyi,A. protania,A. schomburgki dextrochlorus andA. inversus annamiticus; and one sinistral:A. atricallosus classiaris.[18] These species usually have shells which have ht following characteristics: they are large (height often exceeding 35 mm (1.4 in)); they have a height/width ratio of less than 1.85; and a shell color which is yellowish or greenish. Anatomically they have a long epiphallus and flagellum, and an appendix is usually present.[4][17]
All but two species within the subgenusSyndromus are sinistral. The exceptions are the amphidromineA. glaucolarynx and the dextralA. kuehni.[28] The type species of the subgenusSyndromus isA. contrarius Müller, 1774, by the subsequent designation ofAdolf Michael Zilch (1960).[30] Species in the subgenusSyndromus have smaller shells (height usually less than 35 mm (1.4 in) and height/width ratio greater than 1.85), with variable color pattern. They also have a short epiphallus and flagellum, lacking an appendix.[4][17] A third possible subgenus,Goniodromus Bülow, 1905 (type speciesAmphidromus büllowi Fruhstorfer, 1905),[31] is also cited in the literature, though its subgeneric status is yet to be confirmed.[17]
Molecular analyses of partial sequences of16S rDNA of 18 distinct species carried out by Sutcharit and colleagues (2007)[18] indicate thatAmphidromus is amonophyletic group. In their study, differentcladograms obtained through distinct methods such asmaximum parsimony,neighbor joining andmaximum likelihood were congruent among themselves. Though thetopology obtained for the subgenusAmphidromus was fairly consistent with current taxonomy, the phylogeny of sinistralSyndromus species showed no such correspondence. Also according to their results,enantiomorphy seems to be theancestral state of shell coiling in the genusAmphidromus, which is contrary to the general expectation of dextrally coiled shells as an ancestral condition.[18]
Despite being morphologically identical, some specimens supposedly belonging to three species, namelyAmphidromus semitessellatus,A. xiengensis andA. areolatus, apparently had polyphyletic origins ofmtDNAhaplotypes. This resulted in the same species simultaneously appearing in distinct clades along the topology: for instance,A. areolatus can be found in two different clades in Sutcharit and colleague's (2007) cladogram, clustered respectively withA. xiengiensis and also withA. semitesselatus. According to the authors, these results could be explained byconvergent andpolymorphic shell color patterns (e.g., the shells of the specimens had very similar colors and shape, though the mtDNA markers showed significant differences). Alternatively, they could also be the result ofintrogressive hybridization or ancestral polymorphism of mtDNA. In any case, analyses ofphylogeography using other markers (nuclear markers or other mtDNA markers) or additional morphological characters would still be necessary to further clarify these issues.[18]
Currently, no reliable pre-human fossil occurrences ofAmphidromus have been recorded.Tera van Benthem Jutting (1932)[32] reported finding several specimens ofA. filozonatus which had been eaten in prehistoric times by natives, inSampoeng Cave, central Java; and a few years later (van Benthem Jutting, 1937, pp. 92–94)[33] the same author reported a single specimen ofA. palaceus from theTrinil Beds of Java. Neither record predates human occupancy, and therefore these shed no light on the pre-human history ofAmphidromus.[4]
The genusAmphidromus ranges from eastern India, in south-western Asia (limited to the north by theHimalayas), to northern Australia (limited eastward byWeber's Line).[17][26]Amphidromus species are found in localities as follows: from theGaro Hills andKhasi Hills of Meghalaya in northeasternIndia; throughoutBurma,Malay Peninsula,Thailand,Laos,Cambodia,Vietnam,Indonesia as far east as theSulawesi,Banda Islands,Timor and theTenimber Islands (but not on Ceram, Buru, Halmahera, Batjan Island, the Obi Islands, the Aru and Kei Islands or the Talaud Archipelago and some Celebesian satellite islands); in the southernPhilippines, notablyMindanao and theBalabac, Palawan;[4] and in northern Australia (solely represented byAmphidromus cognatus).[26]
Amphidromus species are arboreal land snails. Further information concerning the habits and mode of life of the species ofAmphidromus is almost non-existent, however, these snails have generally been collected while they were crawling on trees or shrubs. The diet ofAmphidromus is unknown, butAmphidromus atricallosus perakensis is thought to feed on microscopicfungi,lichens or terrestrialalgae.[4][34]
Despite the great diversity within this genus, as of 2017, comprehensive life-history studies ofAmphidromus species are still lacking; only a few observations of behavior of species within the genus exist, and these observations are scattered throughout the literature. A study byEugen Paravicini (1921)[35] describedegg-laying behaviour inAmphidromus palaceus var.pura atPalimanan,West Java. According to Paravicini's observations, in October, 1920, locals from West Java brought in two "nests" containing snails that had just begun depositing their eggs; one snail had folded the exterior leaves of a youngbamboo shoot and gummed them together into a pointed cornet. The shoot hung vertically with the narrow end pointed upward, and the wide opening below.[4] The upper part of the sack was filled with eggs when collected. The snail descended slowly, rotating around its longitudinal axis, and deposited eggs until the entire cavity was filled up. If a crack in the basket exposed eggs to the air, they quickly dried up. Two days after capture, egg-laying was finished, and the snail closed the opening by folding over more leaves. Probably four days were spent in egg-laying, since the cavity was half filled at the start of observations. A second nest of similarly foldedmango leaves contained 234 eggs. The volume of eggs in each case greatly exceeded the size of the snail, indicating that the eggs must be encapsulated just before deposition. The capsules were very thin, and dried quickly upon any exposure to the air. October marked the start of therainy season and probably this is the normal breeding period. Eggs ofA. porcellanus were reported by van Benthem Jutting (1950, p. 493)[13] to have started hatching only ten days after being laid. Similar nest-building habits have been reported for other species, but no complete study of a life cycle has been published. Up until 1961, no information was available on the cycle of activity, longevity, rate of growth, etc.[4]
Schilthuizen et al. (2005) described thespatial structure of a population ofA. inversus in Malaysia.[36] Schilthuizen et al. (2007) found that there issexual selection in mating with snails of the opposite chirality.[37] This means that the left-handed snails mate more often with right-handed snails than they do with snails of the same coiling. Additionally there are anatomical adaptations of thespermatophore and of the female part of thereproductive system for the success of these matings.[37]
Predators ofAmphidromus snails include the red-crowned barbetMegalaima rafflesii,[38] and probably otherbird species.[34] Asian snakes in the genusPareas are known to feed onAmphidromus species by removing the soft parts from the shells.[39][17] Many shells ofAmphidromus were found in the den of arat in Malaysia.[37]
This article incorporates public domain text from the reference.[4]
Albers J. C. (1850).Die Heliceen nach natürlicher Verwandtschaft: systematisch georduct: 138.Laidlaw F. F. &Solem A. (1961)."The land snail genusAmphidromus: a synoptic catalogue".Fieldiana Zoology41(4): 505–720.Martens E. von (1867).Die Preussische Expedition nach Ost-Asien. Zoologischer Theil.2: xii, 447 pp., 22 plates.Pilsbry H. A. (1900).Manual of Conchology, structural and systematic, with illustrations of the species. Second series: Pulmonata.Volume 13. Australasian Bulimulidae:Bothriembryon,Placostylus. Helicidae:Amphidromus. 253 pp., 72 plates,page 184.Bartsch P. (1917). "The Philippine land snails of the genusAmphidromus".U. S. Nat. Mus. Bull.100(1), part 1: 1–47, 22 plates.Bartsch P. (1918). "The land snails of the genusAmphidromus from the islands of thePalawan Passage".Jour. Washington Acad. Sci.8(11): 361–367.Bartsch P. (1919). "Critical remarks on Philippine Island land shells".Proc. Biol. Soc. Washington32: 177–184.(in German)Wiegmann C. A. F. (1863). "Beitrage zur Anatomie der Landschnecken des Indischen Archipels". In: Weber (1863).Zool. Ergeb. Reisen Indischen Arch.3: 112–259, plates 9–16.(in German)Wiegmann C. A. F. (1898). "Landmollusken (Stylommatophoren)".Zootomischer Teil. Abhl. Sencken. Naturf. Gesell.24(3): 289–557, plates 21–31.514-527.