Solenogastres

Solenogastres
Epimenia verrucosa
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	"Aplacophora"
Subclass:	Solenogastres
Superorders, orders & families
Aplotegmentaria Neomeniamorpha Hemimeniidae Neomeniidae Pholidoskepia Dondersiidae Gymnomeniidae Lepidomeniidae Macellomeniidae Meiomeniidae Sandalomeniidae Pachytegmentaria Cavibelonia Acanthomeniidae Amphimeniidae Drepanomeniidae Epimeniidae Notomeniidae Proneomeniidae Pruvotinidae Rhipidoherpiidae Rhopalomeniidae Simrothiellidae Strophomeniidae Syngenoherpiidae Sterrofustia Heteroherpiidae Imeroherpiidae Phyllomeniidae

The Solenogastres (less often referred to as Neomeniomorpha), common name solenogasters, are a subclass of worm-like, small, shell-less molluscs (Aplacophora), the other subclass being the Caudofoveata (Chaetodermomorpha).

Morphology

In contrast to all other molluscan classes, the Aplacophora have no shell, and are instead covered by aragonitic sclerites (calcareous spicules), which can be solid or hollow. These spicules can be arranged perpendicular one another within the cuticle to form a skeleton; or can stick up to form a pallisade; or can lay flat against the cuticle.^[1]

80% of solenogaster species have a radula, while in others it is secondarily lost. The radula may bear one or more teeth per row; where there is more than one tooth, there is no central radular tooth.^[1] The radula grows by dividing existing teeth in two, or by adding a new tooth at the centre of the radular row.^[1] The salivary glands are very elaborate, and are an important character for taxonomy. Next to the mouth they have a unique sense organ, the vestibulum.

The solenogastres do not have true ctenidia, although their gill-like structures resemble them.^[2]

Development

During development many solenogastres are covered by a spiny scleritome comprising spines or scale-like plates; this has been likened to the halwaxiid scleritome.^[3]

Sclerites of Epimenia start out solid before developing a hollow stem that subsequently solidifies.^[4]

Ecology

Diet

Solenogasters feed on cnidaria and ctenophores, either sucking their bodily fluids or eating their tissue.^[5] They do not use their radulae to rasp prey, as other molluscs do.^[6]

Phylogeny

There is some uncertainty regarding the phylogenetic position of the solenogasters. Traditionally considered to be the most basal molluscan group and the sister group to the Caudofoveata, alternatives to both of these statements have been proposed on various lines of evidence.^[7] Indeed, some molecular datasets plot Solenogastres as an outgroup to Mollusca.^[8]

References

1. ^ ^{a b c} Scheltema, A. H. (1999). "Two solenogaster molluscs, Ocheyoherpia trachia n.sp. From Macquarie Island and Tegulaherpia tasmanica Salvini-Plawen from Bass Strait (Aplacophora: Neomeniomorpha)". Records of the Australian Museum 51: 23–31. doi:10.3853/j.0067-1975.51.1999.1266.  edit
2. ^ Wilbur, Karl M.; Trueman, E.R.; Clarke, M.R., eds. (1985), "2. Early evolution and the Primitive Groups", The Mollusca, 10. Evolution, New York: Academic Press, ISBN 0-12-728702-7 
3. ^ Todt, C.; Wanninger, A. (2010). "Of tests, trochs, shells, and spicules: Development of the basal mollusk Wirenia argentea (Solenogastres) and its bearing on the evolution of trochozoan larval key features". Frontiers in Zoology 7 (1): 6. doi:10.1186/1742-9994-7-6. PMC 2828982. PMID 20181015. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2828982.  edit
4. ^ Okusu, A. (2002). "Embryogenesis and development of Epimenia babai (Mollusca: Neomeniomorpha)". The Biological bulletin 203 (1): 87–103. PMID 12200259.  edit
5. ^ Guralnick, R.; Smith, K. (1999). "Historical and biomechanical analysis of integration and dissociation in molluscan feeding, with special emphasis on the true limpets (Patellogastropoda: Gastropoda)". Journal of Morphology 241 (2): 175–195. doi:10.1002/(SICI)1097-4687(199908)241:2<175::AID-JMOR7>3.0.CO;2-0. PMID 10420163.  edit
6. ^ Scheltema, A. H.; Jebb, M. (1994). "Natural history of a solenogaster mollusc from Papua New Guinea,Epimenia australis(Thiele) (Aplacophora: Neomeniomorpha)". Journal of Natural History 28 (6): 1297. doi:10.1080/00222939400770661.  edit
7. ^ Todt, C.; Wanninger, A. (2010). "Of tests, trochs, shells, and spicules: Development of the basal mollusk Wirenia argentea (Solenogastres) and its bearing on the evolution of trochozoan larval key features". Frontiers in Zoology 7 (1): 6. doi:10.1186/1742-9994-7-6. PMC 2828982. PMID 20181015. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2828982.  edit
8. ^ Wilson, N.; Rouse, G.; Giribet, G. (2010). "Assessing the molluscan hypothesis Serialia (Monoplacophora+Polyplacophora) using novel molecular data.". Molecular phylogenetics and evolution 54 (1): 187–193. doi:10.1016/j.ympev.2009.07.028. PMID 19647088.  edit

Further reading

• Meyer A., Todt C., Mikkelsen N. T. & Lieb B. (2010). "Fast evolving 18S rRNA sequences from Solenogastres (Mollusca) resist standard PCR amplification and give new insights into mollusk substitution rate heterogeneity". BMC Evolutionary Biology 10: 70. doi:10.1186/1471-2148-10-70