Heterobranchia Explained

Heterobranchia, the heterobranchs (meaning "different-gilled snails"), is a taxonomic clade of snails and slugs, which includes marine, aquatic and terrestrial gastropod mollusks.

Heterobranchia is one of the main clades of gastropods. Currently Heterobranchia comprises three informal groups: the lower heterobranchs, the opisthobranchs and the pulmonates.^[1]

Diversity

The three subdivisions of this large clade are quite diverse:

• The Lower Heterobranchia includes shelled marine and freshwater species.
• Opisthobranchia are almost all marine species, some shelled and some not. The internal organs of the opisthobranchs have undergone detorsion (unwinding of the viscera that were twisted during torsion).
• The Pulmonata includes the majority of land snails and slugs, many freshwater snails, and a small number of marine species. The mantle cavity of the Pulmonata is modified into an air-breathing organ. They are also characterized by detorsion and a symmetrically-arranged nervous system. The pulmonates almost always lack an operculum and are hermaphroditic.

Taxonomy

Current taxonomy^{[2] [3] [4] [5]}

• Heterobranchia
  • Valvatoidea Gray, 1840
  • Architectonicoidea Gray, 1850
  • Mathildoidea Dall, 1889
  • Omalogyroidea G. O. Sars, 1878
  • Allomorpha
    • Murchisonelloidea Casey, 1904
    • Rhodopoidea Ihering, 1876
  • Orbitestelloidea Iredale, 1917
  • Cimoidea Warén, 1993
  • Euthyneura
    • Actenonacea
      • Acteonoidea d'Orbigny, 1843
      • Rissoelloidea Gray, 1850
    • Tjaernoeiidae Warén, 1991
    • Ringipleura
      • Ringiculoidea Philippi, 1853
      • Nudipleura
    • Tectipleura
      • Euopistobranchia
      • Panpulmonata

Older taxonomy

The families currently included in Heterobranchia have historically been placed in many different parts of the taxonomic class of gastropods. Earlier authors (such as J.E. Gray, 1840) considered Heterobranchia to consist of only marine gastropods, and conceptualized it as a borderline category, intermediate between the Opisthobranchia & Pulmonata, and all the other gastropods.^[6]

The (sometimes recognized) category Heterostropha within the Heterobranchia, which includes such families as Architectonicidae, the sundial or staircase snails, is primarily characterized by a shell which has a heterostrophic protoconch, in other words the apical whorls are coiled in the opposite plane to the adult whorls. The classification of this group was revised by Ponder & Warén in 1988.^[7]

According to the older taxonomy of the Gastropoda (Ponder & Lindberg, 1997) the Heterobranchia were ranked as a superorder.

2005 taxonomy

Heterobranchia is currently one of the main clades of gastropods. For a detailed taxonomy, see Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)#Clade Heterobranchia.

2010 taxonomy

Jörger et al. (2010) have redefined major groups within the Heterobranchia: they created the new clades Euopisthobranchia and Panpulmonata.^[8]

A cladogram showing phylogenic relations of Heterobranchia as proposed by Jörger et al. (2010):^[8]

Further reading

• Dinapoli A. (2009). Phylogeny and Evolution of the Heterobranchia (Mollusca, Gastropoda). Thesis, Frankfurt am Main, 176 pp. PDF.
• Dinapoli A. . Klussmann-Kolb A. . 2010 . The long way to diversity – Phylogeny and evolution of the Heterobranchia (Mollusca: Gastropoda)". . . 55 . 1. 60–76 . 10.1016/j.ympev.2009.09.019 . 19778622.

Notes and References

1. Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. . . 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278
2. Bouchet . Philippe . Rocroi . Jean-Pierre . Hausdorf . Bernhard . Kaim . Andrzej . Kano . Yasunori . Nützel . Alexander . Parkhaev . Pavel . Schrödl . Michael . Strong . Ellen E. . 2017 . Revised Classification, Nomenclator and Typification of Gastropod and Monoplacophoran Families . . en . 61 . 1–2 . 1–526 . 10.4002/040.061.0201 . 0076-2997.
3. Pabst . Emily A . Kocot . Kevin M . 2018-08-01 . Phylogenomics confirms monophyly of Nudipleura (Gastropoda: Heterobranchia) . Journal of Molluscan Studies . en . 84 . 3 . 259–265 . 10.1093/mollus/eyy013 . 0260-1230. free .
4. Moles . Juan . Giribet . Gonzalo . 2021 . A polyvalent and universal tool for genomic studies in gastropod molluscs (Heterobranchia) . . en . 155 . 106996 . 10.1016/j.ympev.2020.106996. 33148425 . 226258146 .
5. Wilson . Nerida G . Jörger . Katharina M . Brenzinger . Bastian . Schrödl . Michael . 2017-11-01 . Phylogenetic placement of the enigmatic worm-like Rhodopemorpha slugs as basal Heterobranchia . Journal of Molluscan Studies . en . 83 . 4 . 399–408 . 10.1093/mollus/eyx031 . 0260-1230. free .
6. Haszprunar G. . The Heterobranchia ― a new concept of the phylogeny of the higher Gastropoda. 1985. Zeitschrift für zoologische Systematik und Evolutionsforschung. 23. 1 . 15–37 . 0044-3808.
7. Ponder, W. F. . Warén, A. . Classification of the Caenogastropoda and Heterostropha- A list of family-group names and higher taxa. 1988. Malacological Review Supplement . 4. 288–317.
8. Jörger K. M. . Stöger I. . Kano Y. . Fukuda H. . Knebelsberger T. . Schrödl M. . 2010 . On the origin of Acochlidia and other enigmatic euthyneuran gastropods, with implications for the systematics of Heterobranchia . . 10 . 323 . 10.1186/1471-2148-10-323 . 20973994 . 3087543 . free .