The snail moment you’ve been waiting for …

Welcome to Blog 6, and yes, it’s June. Time marches ever onwards, and we’re half way through the year! Today is the day you’ve been waiting for. The day when I’m going to tell you all about Stephen’s master’s thesis. Thank you for your patience, but the long wait is finally over. Welcome to the discussion of “A classical taxonomic revision of Seraphsidae Jung 1974 (Gastropoda) using a pluralist approach to species assessment”.

Stephen’s thesis demonstrates that a “pluralistic approach to classic taxonomic practice can lead to increased cladistics resolution in a clade, including the recognition of new taxa at all nomenclatural levels”. Okay, so firstly, what is a pluralistic approach? Taxonomists and systematists have a tendency to name species based on particular species conceptions, such as the biological or phylogenetic species concepts. However, often the actual description of the species is not based on that conception. For example, many species are often described based on morphology, but the concept used to define them is based on reproductive compatibility. Pluralism allows a species to be described using multiple concepts, without the need to apply a particular definition that would be limiting. This leads to increased flexibility, and allows for use of all available evidence, rather than limiting the description to only a single kind (e.g. morphology), which often does not match the conception that was used to theoretically distinguish the taxa.

Fig. 1. The fighting conch Strombus pugilus

Stephen’s thesis had three aims: firstly, Stephen wanted to divide the Stromboidea into distinctive evolutionary crown clades using morphological evidence. The intention here was to reinstate the historical understanding of the internal cladistics relationships. A crown clade is defined based on living taxa. The first clade was easy, which is called the Neostromboidea. Animals in this clade contain taxa more closely related to Strombus pugilus (Fig. 1), Terebellum terebellum and Tibia fusus than members belonging to the Struthiolariidae and Aporrhaidae (Fig. 2). The other remaining members of the Stromboidea, the Struthiolariidae and the Aporrhaidae. Defining the other clade in its entirety is, currently, problematic as it would create meaningless ranks.

Fig. 2. The pelican's foot snail Aporrhais serresianus

Stephen’s second aim was to complete an alpha-taxonomic revision of the group defined by Jung (1974) known as the Seraphsidae using a pluralist approach to species conception. I should point out here that he looked at fossils. He first had to compile a list of all the defined taxa. Now this sounds easy, but in reality he had to look for all the synonyms too, so it made it quite a lot of work. He then had to reassess the validity of the synonyms using all available evidence, including morphological variation, historical distribution and temporal positioning. If the named synonymic species could not be validated in the literature, it was not included. Only those with a description that enabled clear resolution of the original author’s intent when describing the species were included. Once he had done this, he had to establish a set of characters for placement in a character state table. He then drew a phylogenetic tree that formed the basis of the internal resolution within the clade (Fig. 3).

Fig. 3. tnt generated maximum likelihood cladogram showing internal cladistic relationships within Seraphsidae Jung 1974 (Taken from Stephen's thesis)

Finally, Stephen’s third aim was to resolve the infrageneric relationships within the Seraphsidae using morphological cladistics. Simply put, what Stephen found here was a need to differentiate and organise this subclade into distinctive inclusive clades that provided an improved understanding of the evolutionary patterns within the group. The first clade represents the Neoseraphsinae nomen novem, with an involute terminal growth pattern. The second clade represents the Neoterebellinae nomen novem, with an evolute terminal growth pattern. Why is this growth pattern important in an evolutionary sense? Because it is related to an essential life history characteristic relating to burial, where the evolute pattern enables detection of burial. That all the Neoseraphsinae nomen novem are extinct indicates that this slight change in shell pattern in the Neoterebellinae nomen novem may have provided an evolutionary advantage, where burial detection may have allowed for additional protection from predation.

The most important message from Stephen’s thesis is that using a pluralistic approach can improve our understanding of internal cladistics relationships in evolutionary trees, and how that can then be reflected in the nomenclature.

You can read more about my research in my publications listed on my blog. You can also find me on ResearchGate, the James Cook University website and Twitter.