Hypsogastropoda

Lyocyclus solutus, from Thiele (1925).

Belongs within: Gastropoda.
Contains: Coelostylinidae, Pseudozygopleuridae, Goniospiridae, Zygopleuridae, Vermetidae, Pseudomelaniidae, Epitoniidae, Littorinina, Stromboidea, Capulidae, Hipponicidae, Calyptraeidae, Naticidae, Cypraeoidea, Tonnoidea, Neogastropoda.

The Hypsogastropoda are a major clade of caenogastropods possessing an exophallic penis positioned behind the right cephalic tentacle (Simone 2011). They are primarily marine though several lineages have diversified in fresh water. Basal relationships within the hypsogastropods remain poorly established. However, a clade Latrogastropoda including the neogastropods and related taxa may be recognised by the presence of a pair of retractor muscles in association with the snout, an enlarged mantle border that covers the head when active, and a sharp pointed apex on the marginal radular teeth. Latrogastropoda may be divided between the Stromboidea and Rhynchogastropoda with the latter clade united by the presence of a retractible proboscis. A clade containing the Capuloidea, Hipponicidae and Calyptraeoidea contains species with a hairy periostracum and nuchal flaps on both sides of the head. The remaining Rhynchogastropoda, forming the clade Adenogastropoda, show a tendency towards predatory behaviour with a simplified stomach and modified foregut. The Siphonogastropoda, including the Cypraeoidea, Tonnoidea and Neogastropoda, share a fusiform shell, determinate growth, and a well-developed siphonal canal. Finally, the Tonnoidea and Neogastropoda are united by synapomorphies including a terminal nucleus on the operculum and development of the incurrent siphon into an exploratory structure (Simone 2011).

The Late Palaeozoic high-spired Pseudozygopleuroidea represent possible early precursors of the Hypsogastropoda.

Hypsogastropods: gastropods on high
Published 26 February 2019

Historically, the classification of molluscs has been a challenging prospect. Early researchers focused almost entirely on the shell which provided a somewhat limited range of characters with a definite possibility for convergence. Over time, more attention came to be paid to features of the soft anatomy but that required access to freshly collected material that might be difficult or impossible to obtain. As such, it has only been in the last few decades that a well-structured classification for many molluscan groups has begun to develop, and even now many significant uncertainties remain.

Common periwinkles Littorina littorea, a pretty typical hypsogastropod, copyright Fritz Geller-Grimm.

Until maybe the late 1990s, gastropods were primarily classified using a heavily grade-based system that was established in the 1930s. Gastropods were divided between three subclasses: the torted, gill-breathing prosobranchs, the untorted opisthobranchs, and the lung-breathing pulmonates. Prosobranchs were in turn divided into three main groups whose names directly reflected the ‘level’ of evolution at which they were supposed to sit: the archaeogastropods, the mesogastropods and the neogastropods. Many of these subdivisions were implicitly assumed to be ancestral to others. As the philosophical underpinnings of biological classification came to favour recognition of monophyletic taxa, it was obvious that such a system had to change. The prosobranchs and archaeogastropods both faded away as formal taxa. A major clade uniting the neogastropods and most of the mesogastropods came to be recognised as the caenogastropods. And while many questions still remain about relationships within the caenogastropods, most recent analyses have agreed in supporting a clade that was dubbed the Hypsogastropoda by Ponder & Lindberg (1997).

False cowrie Dentiovula dosruosa, copyright Nick Hobgood.

The prefix ‘hypso-‘ means ‘high’ and was chosen because this clade corresponded to a group that had previously been known as the ‘higher’ caenogastropods (including the neogastropods and a fair chunk of the ‘mesogastropods’). Hypsogastropods include many of the best known marine gastropods, such as whelks, periwinkles, moon snails, cones, cowries, conches and doubtless a ton of other things beginning with C (they also include freshwater and terrestrial forms but these are mostly minute and lack the public image of their marine relatives). They are ecologically diverse, including grazers, detritivores, filter feeders, predators and even parasites. The violet snails of the genus Janthina are planktonic, using a raft of bubbles to float on the water’s surface so they can feed on Portuguese men-of-war. The similarly pelagic heteropods of the superfamily Pterotracheoidea have the foot extended and flattened to form a fin for active swimming.

Paraspermatozoon of violet snail Janthina, from Buckland-Nicks (1998). The arrow indicates the much smaller euspermatozoa attached to the tail.

Among the characters originally cited by Ponder & Lindberg (1997) as uniting the hypsogastropods were features of the spermatozoa. Most hypsogastropods have vermiform paraspermatozoa, sterile sperm cells that are released by the male together with the functioning euspermatozoa. The function of the paraspermatozoa seems to warrant further study. In some cases they may actively assist in the transport of the euspermatozoa; for instance, in violet snails a large number of euspermatozoa will be attached to a single super-sized paraspermatozoon able to swim harder and faster than any of the smaller cells could do on their own. In others, however, the two sperm cell types are not directly associated. It is possible that the paraspermatozoa act as a nuptial gift, providing nutrients to the female as a reward for mating, or that they somehow function to suppress sperm cells from any other males the female might made with (Buckland-Nicks 1998). Other synapomorphies of the clade include an external penis located behind the right cephalic tentacle, and statocysts (balance organs) each containing a single large statolith (Simone 2011).

Relationships within the Hypsogastropoda remain more poorly supported. Most researchers have agreed that the traditionally recognised neogastropods represent a clade united by numerous features, many of them related to the digestive system. The ‘mesogastropods’ included in the Hypsogastropoda mostly possess a taenioglossan radula with seven teeth in each row. In neogastropods, the number of teeth becomes more varied and the teeth themselves become modified so that the lateral teeth are strongly distinct in form from the central tooth. Some of these neogastropod modifications have been discussed in earlier posts on this site. A number of recent analyses have further associated the neogastropods with ‘mesogastropod’ taxa such as cowries and tun shells that they resemble in possessing an inhalent siphon forming a groove at the front of the shell (Simone 2011). A number of the remaining ‘mesogastropods’, such as the periwinkles of the Littorinidae and the Rissoidae, have been united by molecular analyses into a group that has been labelled the ‘asiphonate clade’ or the ‘GC group’ (the latter name chosen by Colgan et al., 2007, in reference to a particular genetic sequence motif). This clade is less universally recovered, however, and the scope for further investigation certainly remains.

Systematics of Hypsogastropoda

Synapomorphies (from Simone 2011): Nephridial gland present. Loss of pair of auxiliary muscle (m12) of horizontal muscle (m6). Exophallic penis present, situated behind and at right of right cephalic tentacle, with respective duct. Development of albumen and capsule glands at pallial oviduct. Each statocyst with single statolith.

<==Hypsogastropoda (see below for synonymy)
    |--+--PseudomelaniidaePC08
    |  `--EpitoniidaePC08
    `--+--‘Amauropsis’ rossiana Smith 1907S11
       `--+--LittorininaGS75
          `--Latrogastropoda [Convoluta, Neomesogastropoda, Strombogastropoda, Troschelina]BD12
               |  i. s.: EunaticaBD12
               |           |--E. papilla (Gmelin 1791)BD12
               |           `--E. telaaraneae (Melville 1901) [=Natica (Eunatica) telaaraneae]M01
               |--StromboideaS11
               `--Rhynchogastropoda [Capulacea]S11
                    |--+--CapuloideaBD12
                    |  |    |--CapulidaeS11
                    |  |    |--Gyrotropis Gabb 1877BR17 [GyrotropidaeBD12]
                    |  |    |    `--*G. squamosa Gabb 1877BR17 [=Trichotropis squamosaBD12]
                    |  |    `--Haloceras Dall 1889BR05 [HaloceratidaeBR17]
                    |  |         `--*H. cingulata (Verrill 1884) [=Cithna cingulata]BR17
                    |  `--+--HipponicidaeS11
                    |     `--Calyptraeoidea [Calyptaeiformes, Calyptraeiformi, Calyptraeiformii, Calyptraeoidei]BD12
                    |          |  i. s.: Thylacus Conrad 1860BD12
                    |          |           `--*T. cretaceus Conrad 1860BD12
                    |          |--CalyptraeidaeS11
                    |          `--Lyocyclus Thiele 1925BR05 [LyocyclidaeGS75, Lyocyclinae]
                    |               `--*L. solutus Thiele 1925BR17
                    `--Adenogastropoda [Epinephridia, Phaneropneumana, Phaneropneumona, Simrothina]S11
                         |--NaticidaeS11
                         `--Siphonogastropoda [Angyostomata, Siphonata]S11
                             |--CypraeoideaZLK11
                             `--PeogastropodaS11
                                  |--TonnoideaZLK11
                                  `--NeogastropodaZLK11
Hypsogastropoda incertae sedis:
  CoelostylinidaeBR05
  Pseudozygopleuroidea [Zygopleuroidea]BR17
    |--PseudozygopleuridaePC08
    |--GoniospiridaeBR17
    |--ZygopleuridaeBR17
    |--PommerozygiidaeBR17
    |    |--Pommerozygia Gründel 1998BR05
    |    |    `--*P. neckeritzensis Gründel 1998BR17
    |    `--Costazygia Gründel 1999G01
    |         `--C. bilzi Gründel 1999G01
    `--ProtorculidaeBR17
         |--Protorcula Kittl 1892BR05
         |    `--*P. subpunctata (Münster 1841) [=Turritella subpunctata, Undularia (*Protorcula) subpunctata]B91
         `--Battenizyga Nützel & Erwin 2002NE02
              `--*B. eotriassica (Batten & Stokes 1986) [=Anoptychia eotriassica]NE02
  VermetoideaBR17
    |--VermetidaeBR17
    `--Sakarahella Bandel 2006 [Sakarahellidae]BR17
         `--*S. angulata Bandel 2006BR17
  Confusiscala Boury 1909BS00

Hypsogastropoda [Acropththalma, Ancistroglossata, Caecoidei, Cerithiopsoidei, Circulopsoidei, Ctenoglossa, Cyclomyaria, Echinospiracea, Echinospirida, Haemiglossata, Hamiglossa, Hydrobioidea, Littorinacea, Littorinata, Littoriniformes, Littorinimorpha, Littorinoidei, Melanellida, Metamesogastropoda, Nudipeda, Peloridae, Pleurembolica, Ptenoglossa, Rissoacea, Rissooidei, Scaphoconchoidea, Semiproboscidifera, Truncatellacea, Tubulibranchiata, Vermivora]

*Type species of generic name indicated

References

[B91] Bandel, K. 1991. Über triassische “Loxonematoidea” und ihre Beziehungen zu rezenten und paläozoischen Schnecken. Paläontologische Zeitschrift 65 (3–4): 239–268.

[BD12] Bandel, K., & D. T. Dockery III. 2012. Protoconch characters of Late Cretaceous Latrogastropoda (Neogastropoda and Neomesogastropoda) as an aid in the reconstruction of the phylogeny of the Neogastropoda. Freiberger Forschungshefte C542 (psf 20): 93–128.

[BS00] Bandel, K., & W. Stinnesbeck. 2000. Gastropods of the Quiriquina Formation (Maastrichtian) in central Chile: paleobiogeographic relationships and the description of a few new taxa. Zbl. Geol. Paläont. Teil I 7–8: 757–788.

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

[BR17] Bouchet, P., J.-P. Rocroi, B. Hausdorf, A. Kaim, Y. Kano, A. Nützel, P. Parkhaev, M. Schrödl & E. E. Strong. 2017. Revised classification, nomenclator and typification of gastropod and monoplacophoran families. Malacologia 61 (1–2): 1–526.

Buckland-Nicks, J. 1998. Prosobranch parasperm: sterile germ cells that promote paternity? Micron 29 (4): 267–280.

Colgan, D. J., W. F. Ponder, E. Beacham & J. Macaranas. 2007. Molecular phylogenetics of Caenogastropoda (Gastropoda: Mollusca). Molecular Phylogenetics and Evolution 42: 717–737.

[GS75] Golikov, A. N., & Y. I. Starobogatov. 1975. Systematics of prosobranch gastropods. Malacologia 15 (1): 185–232.

[G01] Gründel, J. 2001. Neritimorpha und weitere Caenogastropoda (Gastropoda) aus dem Dogger Norddeutschlands und des nordwestlichen Polens. Berliner Geowissenschaftliche Abhandlungen, Reihe E 36: 45–99.

[M01] Melville, J. C. 1901. A few further remarks upon the Erythrean molluscan fauna, with descriptions of seven species from Aden, in the collection of Commander E. R. Shopland, R.I.M. Annals and Magazine of Natural History, series 7, 7: 550–556.

[NE02] Nützel, A., & D. H. Erwin. 2002. Battenizyga, a new Early Triassic gastropod genus with a discussion of the caenogastropod evolution at the Permian/Triassic boundary. Paläontologische Zeitschrift 76 (1): 21–27.

[PC08] Ponder, W. F., D. J. Colgan, J. M. Healy, A. Nützel, L. R. L. Simone & E. E. Strong. 2008. Caenogastropoda. In: Ponder, W. F., & D. L. Lindberg (eds) Phylogeny and Evolution of the Mollusca pp. 331–383. University of California Press: Berkeley.

Ponder, W. F., & D. R. Lindberg. 1997. Towards a phylogeny of gastropod molluscs: an analysis using morphological characters. Zoological Journal of the Linnean Society 119: 83–265.

[S11] Simone, L. R. L. 2011. Phylogeny of the Caenogastropoda (Mollusca), based on comparative morphology. Arquivos de Zoologia 42 (4): 161–323.

[ZLK11] Zou, S., Q. Li & L. Kong. 2011. Additional gene data and increased sampling give new insights into the phylogenetic relationships of Neogastropoda, within the caenogastropod phylogenetic framework. Molecular Phylogenetics and Evolution 61: 425–435.

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