Heterobranchia

Cornirostra pellucida, copyright Des Beechey.

Belongs within: Gastropoda.
Contains: Cimidae, Nerinellidae, Ceritellidae, Ptygmatididae, Nerineidae, Mathildidae, Khairkhaniidae, Acteonellidae, Donaldina, Murchisonellidae, Streptacididae, Valvatidae, Architectonicoidea, Prionoglossa, Ringipleura, Acteonimorpha, Euopisthobranchia, Sacoglossa, Siphonarioidea, Pylopulmonata, Acochlidimorpha, Hygrophila, Ellobioidea, Systellommatophora, Achatinina, Scolodontidae, Plectopyloidea, Punctoidea, Urocoptoidea, Rhytidoidea, Orthalicoidea, Clausilioidea, Arionoidea, Oleacinoidei, Succineoidei, Limacoidei, Helicoidei, Pupilloidea.

The Heterobranchia are a major clade of gastropods characterised by a reduction of the gill ctenidium. They also lack bolster cartilages in the radula or ciliated structures in the anterior oesophagus, and sperm cells are of the eupyrene type only (Salvini-Plawen & Steiner 1996). Many also exhibit a heterostrophic development with the whorls of the protoconch coiled in the opposite direction to those of the teleoconch. Basal members (outside the subsidiary clade Euthyneura) are mostly small, aquatic shells that were historically included in the grade ‘Mesogastropoda’ along with members of the Heterobranchia’s sister clade, Caenogastropoda. Examples include the Valvatoidea, minute marine and freshwater hermaphroditic snails with a secondary gill, pallial tentacle, and orthostrophic (not heterostrophic) development (Salvini-Plawen & Steiner 1996). The Mathildoidea have an elongate shell with many whorls, with a teleoconch ornament of spiral and axial elements. Shells of Murchisonellidae are similarly elongate but fragile, and the animal lacks a radula. Fossil heterobranchs include the Nerineoidea of the Jurassic and Cretaceous, which had large, turriculate to oviform shells that often bore internal protrusions of the walls within the whorls.

In the Euthyneura, the ctenidium was entirely replaced by a folded gill structure called a plicatidium (further modified or replaced in more derived subgroups); it has been debated whether the plicatidium represents an evolved derivative of the ctenidium or an entirely novel structure. The euthyneurans were historically divided between the air-breathing Pulmonata and the marine Opisthobranchia but recent phylogenetic analyses have indicated that the latter grouping is paraphyletic and the former is polyphyletic. Instead, molecular studies support the exclusion of the Acteonimorpha and Ringipleura (nudibranch sea slugs and related taxa) from a clade Tectipleura uniting the remaining opisthobranchs (bubble shells, sea hares, etc.) with the ‘pulmonates’. The majority of pulmonate taxa remain within a clade Eupulmonata, characterised by a contractile pneumostome and free head tentacles (Salvini-Plawen & Steiner 1996) within which the truly terrestrial lineages form the clade Geophila. The largest terrestrial lineage is the Stylommatophora, characterised by the possession of four retractable cephalic tentacles with eyes on the tips of the posterior tentacles. Molecular data supports the division of the Stylommatophora between three basal clades, treated by Bouchet et al. (2017) as the Achatinina, Scolodontidae and Helicina.

The Testacelloidea are a group of predatory snails and slugs, including predators of earthworms and other snails.

Snails, slugs and eye-stalks
Published 28 July 2008
Cepaea nemoralis, a highly variable terrestrial snail that has long been a model organism in heredity studies, from Palaeos.

In this section, we’ll be considering the Stylommatophora. While you may not be familiar with the name, Stylommatophora are actually the most instantly recognisable of all gastropod groups, for this is the group that includes the significant majority of land snails. Aydin Örstan has recently presented a series of posts discussing the difficulties of classing many gastropods (or other moisture-associated organisms for that matter) as “terrestrial” or “aquatic”, so I should probably qualify that last statement by stressing that “land snails” here refers to fully terrestrialised taxa that do not have an aquatic component to their life cycle. The name “Stylommatophora” refers to what must be the second thing that any child learns about snails (after learning that they carry their house on their back), that their eyes are on the end of stalks. More than one group of stylommatophorans has reduced or lost the shell—these, of course, are the slugs and semi-slugs (yes, “semi-slug” is a valid term, though unfortunately, to the best of my knowledge “slugi” is not). Such shell loss has occured multiple times. The most influential classification of stylommatophorans was the 1900 classification by Pilsbry that divided them into three groups based on the anatomy of the excretory system, the Orthurethra, Sigmurethra and Heterurethra. Pilsbry regarded the orthurethran straight ureter as ancestral to the sigmurethran sigmoid ureter, but more recent molecular phylogenies have supported the reverse—orthurethrans are a monophyletic group within the paraphyletic “sigmurethrans”, with the earliest division within the stylommatophorans being between the “achatinoid” and “non-achatinoid” clades (Wade et al. 2001, 2006). The Elasmognatha (≈Heterurethra) are a small group of two families, the shelled Succineidae and shell-less Athoracophoridae, whose status as a monophyletic group is well-supported but whose position relative to other stylommatophorans is not.

The giant African snail Achatina fulica, one of the largest terrestrial gastropods, photographed by Roberta Zimmerman. Introduced populations of Achatina snails (often imported for food) have become a serious problem in some parts of the world. Interestingly, snails are generally attracted to calcium, and chalk-based baits have often been used in their control. I once lived in a rather damp and disgusting house that had a problem with slugs crawling into the pantry through openings in the base. Once there they would invariably make a beeline direct for the flour. I still don’t really know why.

This newer division into achatinoids and non-achatinoids does not appear to be well-supported morphologically, though non-achatinoids tend to have better developed copulatory organs than achatinoids. For instance, those families with members that inject each other with calcareous “love darts” are all non-achatinoids. However, it is debatable whether and to what to degree this represents phylogenetic versus functional considerations. All stylommatophorans are functional hermaphrodites, but mating behaviour differs between taxa that mate face-to-face and inseminate each other simultaneously or those in which one individual mounts the other and insemination may be simultaneous, sequential or unilateral. As well as only occurring in achatinoids, love-darting only occurs in face-to-face copulators—and all face-to-face copulators are non-achatinoids. The function of the love darts is poorly known, but studies in Helix aspersa have shown that they induce faster uptake of received sperm by the darted individual, and one of the leading suggestions is that they discourage reproductive “cheats” that attempt to donate sperm while not taking up their partner’s. Such behaviour is really only a consideration in species that inseminate simultaneously, and while many achatinoids do have simultaneous insemination their shell-mounting behaviour may be less conducive to forcing reciprocity in sperm uptake (Davison et al. 2005).

Triboniophora graeffei, an athoracophorid slug. The large hole visible behind the head is the opening to the lung. Photo by Bill Rudman.

Their fully terrestrial habits (not to mention the absence of a shell in many species) mean that stylommatophorans have a much poorer fossil record than other gastropods, and their time of origin is a little doubtful. While Solem & Yochelson assigned some Carboniferous and Permian fossil snails to extant stylommatophoran families, this assignation is not well-supported and the next record of land snails is not until over 100 million years later in the Cretaceous (Wade et al., 2006). The elucidation of relationships between Palaeozoic and later gastropods and distinguishing true relationships from convergences is generally a process fraught with difficulty.

Systematics of Heterobranchia
<==Heterobranchia [Allogastropoda, Allomorpha, Architectibranchia, Dextrobranchia, Peracliones, Pulmobranchiata, Rhinophoralia]
    |--Valvatoidea [Valvatoideae, Valvatoidei]S-PS96
    |    |  i. s.: Palaeocarboninia Bandel & Heidelberger 2002B02
    |    |           `--P. jankei Bandel & Heidelberger 2002FB04
    |    |         Carboninia Bandel 1996B02
    |    |         Bandellina Schröder 1995B02
    |    |--ValvatidaeBR05
    |    |--Hyalogyrina Marshall 1988 [Hyalogryinidae, Hyalogyrinidae]BR05
    |    |    `--*H. glabra Marshall 1988BR17
    |    |--Provalvata Bandel 1991 [Provalvatidae]BR05
    |    |    |--‘Valvata (Cincinna)’ helicelloides Huckreide 1967 (see below for synonymy)B91
    |    |    `--P. sabaudiensis (Maillard 1884) [=Valvata sabaudiensis; incl. V. (Cincinna) proavia Huckriede 1967]B91
    |    `--Cornirostra Ponder 1990 [Cornirostridae]BR05
    |         |--*C. pellucida (Laseron 1954) [=Microdiscula pellucida]BR17
    |         `--C. floridana Bieler & Mikkelsen in Bieler, Ball & Mikkelsen 1998BC01
    `--+--+--ArchitectonicoideaBR05
       |  `--PrionoglossaS11
       `--Euthyneura (see below for synonymy)S11
            |  i. s.: Oscanius tuberculatusM62
            |         Aplysiella virescensPP64
            |         Tjaernoeia Warén & Bouchet 1988BR05 [Tjaernoeidae, TjaernoeiidaeBR17]
            |           `--*T. monterosati (Grillo 1877) [=Fossarus monterosati]BR17
            |         Aclesia Rang 1828G79
            |           `--A. areola Pease 1860K65
            |         ‘Strategus’ Cooper 1862 non Hope 1837C64
            |         Navarehus Cooper 1863C64
            |           `--N. inermis (Cooper 1862) [=Strategus inermis]C64
            |         Doridella obscuraF68
            |         PolycerellaF68
            |           |--P. conymaF68
            |           |--P. davenportiiF68
            |           `--P. emertoniF68
            |--RingipleuraBR17
            |--ActeonimorphaBR17
            `--TectipleuraBR17
                 |--EuopisthobranchiaBR17
                 `--Panpulmonata (see below for synonymy)BR17
                      |  i. s.: PromenetusB97
                      |           |--P. exacuous (Say 1821)B97
                      |           `--P. umbilicatellus (Cockerell 1887)P88
                      |         Prophysa Bandel 1991B91
                      |           `--*P. bristovii (de Loriol 1865) [=Physa bristovii; incl. Ph. wealdiana]B91
                      |         Proplanorbarius Bandel 1991B91
                      |           `--*P. sanctusclaudius Bandel 1991B91
                      |         Euplecta subdecussataPD78
                      |--SacoglossaBR17
                      `--+--SiphonarioideaBR17
                         |--PylopulmonataBR17
                         `--+--AcochlidimorphaBR17
                            `--+--HygrophilaBR17
                               `--Eupulmonata (see below for synonymy)BR17
                                    |--EllobioideaBR17
                                    `--GeophilaBR17
                                         |--SystellommatophoraBR17
                                         `--Stylommatophora (see below for synonymy)BR17
                                              |  i. s.: PhasisBR05
                                              |         Scalaxis Pilsbry 1909BR05 [ScalaxidaeBR17, Scalaxinae]
                                              |           `--*S. rillyensis (de Boissy 1848) [=Achatina rillyensis]BR17
                                              |         Cherusciola Huckriede 1967B91
                                              |           |--*C. nitida Huckriede 1967B91
                                              |           `--C. mojonia Bandel 1991B91
                                              |--AchatininaBR17
                                              |--ScolodontidaeBR17
                                              `--Helicina [Aulacopoda, Holopoda, Subnuda]BR17
                                                   |  i. s.: Coelociontidae [Coelociidae, Coelociontoidea]BR17
                                                   |           |--Perrieria Tapparone Canefri 1878BR17, BR05 [Perrieriinae]
                                                   |           |    `--*P. clausiliaeformis Tapparone-Canefri 1878BR17
                                                   |           `--Coelocion Pilsbry 1904 [Coelociontinae]SS10
                                                   |                |--*C. australis (Forbes 1852)BR17 (see below for synonymy)
                                                   |                |--C. circumumbilicata Stanisic in Stanisic, Shea et al. 2010SS10
                                                   |                `--C. craigeddiei Stanisic in Stanisic, Shea et al. 2010SS10
                                                   |         Papilloderma Wiktor, Martin & Castillejo 1990BR05 (see below for synonymy)
                                                   |           `--*P. altonagai Wiktor, Martin & Castillejo 1990BR17
                                                   |         PlectopyloideaBR17
                                                   |         PunctoideaBR17
                                                   |         Testacellidae (see below for synonymy)BR17
                                                   |           |--Parmacellina vitrinaeformis Sandberger 1872TTE93
                                                   |           `--Testacella Lamarck 1801BR17 (see below for synonymy)
                                                   |                |--*T. haliotidea Draparnaud 1801SS10 (see below for synonymy)
                                                   |                `--T. maugei [=Testacellus maugei]G40
                                                   |         UrocoptoideaBR17
                                                   |         ApulaE99
                                                   |           |--A. ambertiE99
                                                   |           |--A. escoffieraeE99
                                                   |           `--A. koehneiE99
                                                   |         MesodontopsisE99
                                                   |           |--M. chaixiE99
                                                   |           |--M. doderleiniE99
                                                   |           |--M. herlacensisE99
                                                   |           |--M. ludoviciE99
                                                   |           `--M. nehringiE99
                                                   |         PuisseguriaE99
                                                   |           |--P. idanicaE99
                                                   |           |--P. kowalczykiE99
                                                   |           `--P. zilchiE99
                                                   |         FrecheniaE99
                                                   |           |--F. ducrostiE99
                                                   |           |--F. nayliesiE99
                                                   |           |--F. quadrifasciataE99
                                                   |           `--F. reichenbachiE99
                                                   |--RhytidoideaBR17
                                                   |--OrthalicoideaBR17
                                                   |--ClausilioideaBR17
                                                   |--ArionoideaBR17
                                                   |--OleacinoideiBR17
                                                   |--SuccineoideiBR17
                                                   |--LimacoideiBR17
                                                   |--HelicoideiBR17
                                                   `--PupilloideaBR17
Heterobranchia incertae sedis:
  Micromelo undatusGO06
  Tricarilda striatissima Gründel 1999GK02
  PseudoceratodesBR05
  CimidaeBR17
  Dolomitella Bandel 1994 [Dolomitellidae]BR05
    `--*D. semiornata (Kittl 1894) [=fPHypsipleura semiornata]BR17
  Kuskokwimia Frýda & Blodgett 2001 [Kuskokwimiidae]FB01
    `--*K. moorei Frýda & Blodgett 2001FB01
  MisurinellidaeBR05
    |--Misurinella Bandel 1994BR05
    |    `--*M. sinistrorsa (Kittl 1894) [=Euchrysalis sinistrorsa]BR17
    `--Haszprunariella Kiel & Bandel 2001KB01
         |--*H. laevis Kiel & Bandel 2001KB01
         `--H. spiralis Kiel & Bandel 2001KB01
  Nerineoidea [Nerineacea, Nerineida, Nerineina]FB01
    |  i. s.: BrouzetiaY56
    |--NerinellidaeBR05
    |--CeritellidaeBR05
    |--PtygmatididaeBR17
    |--NerineidaeBR05
    |--Eunerinea Cox 1947 [Eunerineidae, Eunerineidae]BR17
    |    `--*E. castor (d’Orbigny 1850) [=Nerinea castor]BR05
    |--Pseudonerinea de Loriol 1890BR05 [PseudonerineidaeBR17]
    |    |--*P. blauenensis de Loriol 1890BR17
    |    |--P. stantoni Allison 1955TTE93
    |    `--P. sturtoni Allison 1955TTE93
    `--Itieriidae [Itieriacea, Itieriinae]BR17
         |--Itieria Matheron 1842BR05
         |    `--*I. cabaneti Matheron 1842BR17
         `--Itruvia Stoliczka 1867TTE93, BR05 [Itruviidae]
              |--*I. canaliculata (d’Orbigny 1842) [=Pyramidella canaliculata]BR17
              `--I. carinataTTE93
  Mathildoidea [Mathildoidei]FB01
    |  i. s.: Turristylus Blaschke 1905TE01
    |           `--*T. triadicus [=Eustylus triadicus]TE01
    |--MathildidaeBR05
    |--Gordenella Gründel 1990 [Gordenellidae]BR05
    |    `--*G. pommerana (Schmidt 1905) [=Cerithium pommeranum]BR17
    |--Trachoecus Kittl 1894 [Trachoecidae]BR05
    |    `--*T. gemmellaroi Kittl 1894BR17
    `--Schartia Nützel & Kaim 2014 [Schartiidae, Schartiinae]BR17
         `--*S. carinata Nützel & Kaim 2014BR17
  Damesia Holzapfel 1888BK03
    `--*D. cretacea (Müller 1851) [=Crepidula cretacea]KC60
  KhairkhaniidaeP08
  Loxebala Bandel 1996B02
    `--*L. vallandroensis Bandel 1996B02
  ActeonellidaeBR17
  MurchisonelloideaBR17
    |--DonaldinaBR17
    `--MurchisonellidaeBR05
  Rhodope Koelliker 1847BR05 (see below for synonymy)
    `--*R. veranii Koelliker 1847BR17
  StreptacidoideaFB01
    |  i. s.: Heteroloxonema Frýda 2000FB04
    |           `--*H. moniliformis (Goldfuss 1844)FB04 [=Turritella moniliformisFB04, Loxonema moniliformeFB01]
    |--StreptacididaeB02
    |--Cassianebala Bandel 1996 [Cassianebalidae]BR05
    |    `--*C. speciensis Bandel 1996B02
    `--Neodonaldina Bandel 1996TE01 [NeodonaldinidaeB02]
         `--*N. elongata (Zardini 1978) [=Spirocyclina elongata]TE01

*Coelocion australis (Forbes 1852)BR17 [=Balea australisSS10; incl. C. exigua Adams & Angas 1868SS10]

Eupulmonata [Acteophila, Actophila, Akteophila, Amphipulmonata, Ellobiiformes, Phyllovora]BR17

Euthyneura [Acera, Aceridae, Actaeonacea, Acteobranchia, Acteoniformes, Actopleura, Aiolobranchiata, Anangia, Androgyna, Angiophora, Anthobranchia, Apneumonophora, Aporobranchiata, Aptera, Aulacognatha, Aulocognatha, Bullariacea, Bulliones, Eleutherobranchia, Eleutherobranchiatae, Enterobranchiata, Haplomorpha, Hemiphyllidinae, Monostichoglossata, Notaspidea, Notobranchia, Opisthobranchia, Opisthobranchiata, Opisthopneumona, Pentaganglionata, Phlebenterata, Placoesophaga, Pleuroanthobranchia, Pomatobranchiata, Procephala, Scaphandracea, Scaphandroidei, Siphoglossa, Steganobranchia, Stegobranchia, Tectibranchia, Tetracerata, Tetradontogastra]S11

Panpulmonata [Adelopneumona, Aeropneusta, Basommatophora, Branchiopneusta, Coelopneumonata, Coelopnoa, Cilopnoa, Eupneumona, Heliciones, Inoperculata, Limaciones, Limnophila, Limnophilidae, Petrophila, Pulmonata, Pulmonifera, Saccobranchia, Siphonariiformes, Siphonariiformii, Siphonariiones, Siphonarioidei, Thalassophila]BR17

Papilloderma Wiktor, Martin & Castillejo 1990BR05 [Papillodermatidae, PapillodermatoideaBR17, Papillodermidae]

Rhodope Koelliker 1847BR05 [Apneusta, Rhodopacea, Rhodopadae, Rhodopemorpha, Rhodopidae, Rhodopida, Rhodopiformes, RhodopoideaBR17]

Stylommatophora [Achatinoinei, Agnathomorpha, Anurethra, Arioniformes, Ataeniae, Brachynephra, Dolichonephria, Geocochlides, Haplogona, Helixina, Helixinia, Holognatha, Holopodopes, Limaciformes, Limaciformii, Lissognatha, Mesurethra, Monogonophora, Nephropneusta, Oleacinina, Oxygnatha, Pupillina, Pupilloinei, Pycnognatha, Pycnognathae, Sigmurethra, Soleiferae, Stylommatophorida, Vasopulmonata]BR17

Testacella Lamarck 1801BR17 [incl. Testacelloides Wagner 1914SS10, Testacellus Férussac 1819SS10]

*Testacella haliotidea Draparnaud 1801SS10 [=Limax (Testacella) haliotoideaG20, Testacellus haliotideusG40; incl. Testacella europaeaG40, Testacella galliaeG40, Testacella scutulumG40]

Testacellidae [Testacellacidae, Testacellina, Testacellinae, Testacelloidea, Testacelloinei]BR17

‘Valvata (Cincinna)’ helicelloides Huckreide 1967 [=V. helicoides de Loriol 1865 non Stoliczka 1862, *Provalvata helicoides]B91

*Type species of generic name indicated

References

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[B02] Bandel, K. 2002. About Heterostropha (Gastropoda) from the Carboniferous and Permian. Mitteilungen des Geologisch-Paläontologischen Institutes der Universität Hamburg 86: 45–80.

[BK03] Bandel, K., & S. Kiel. 2003. Relationships of Cretaceous Neritimorpha (Gastropoda, Mollusca), with the description of seven new species. Bulletin of the Czech Geological Survey 78 (1): 53–65.

[BR05] Bouchet, P., & J.-P. Rocroi. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1–2): 1–397.

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