A different snail tale …

Welcome to May, and Blog 5. Time continues to fly, and we’re nearly half way through the year and still going strong! I’m going to continue with the current theme of marine gastropods, going back a little way to 2016 to introduce you to a brand new species that Stephen passionately described. Yes, I’m aware that the tension is mounting over his master’s thesis. Remember, patience is a virtue!

The family Cardiidae is an ancient clade that has its origins in the late Triassic. However, the internal resolution within the subclade Tachycardiinae is still unresolved. Within this subclade, two genera are recognised, namely Vasticardium and Acrostergima, and this paper, published in The Festivus, identified a new species falling within the genus Vasticardium.

The new species we describe is called Vasticardium swanae (Fig. 1) in honour of Beverly Swan from Townsville, Queensland, Australia. She made the initial discovery of the type, and has been collecting shells, and has provided support to Stephen, for many years.  

Fig. 1. Holotype of Vasticardium swanae (Maxwell et al. 2016)

V. swanae is located in tropical Queensland, with the type specimen being located on Bramble Reef (Fig. 2). This is currently the only known location of this species, potentially indicating a limited distribution.

Fig. 2. Location of Bramble Reef (Google Maps; 13/05/2019)

The shell (Fig. 1) is quite distinctive, and more colourful for a large Vasticardium (Fig. 3). The dorsum has dark to light brown blotches and flecks, sometimes appearing as ventral purple stain. The shell is moderately strong, equi-valved and ovate to quadrate. The rib morphology is also quite distinctive comparatively. The anterior ribs have strong spines that dorsoventrally increase in size. The ribbing is quite coarse and lacks colour in the aperture. Other characteristics include a fine ligament, fine and well developed anterior and posterior teeth, unequal cardinal teeth, a straight, serrated and interlocking margin that becomes elongated at the anterior dorsal margin and diminishes on the posterior margin, a concave and smooth lunacle, and white umbones (Fig. 1).

Fig. 3. The new species Vasticardium swanae (G) in comparison to other known species of Vasticardium (Maxwell et al. 2016)

The interpretation of new species is largely dependent on the observations of the taxonomist, and their own opinions. In this case, we used morphology to designate the species, while others may use different species concepts to interpret relationships. There aren’t too many important lessons to take away from this paper, although I suggest that we should always be aware that species delimitation and conception are sometimes mixed up, and it should be made clear from the outset how a species has been defined.

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.

Back to Laevistrombus …

It’s April, and we’re on to Blog 4. Progress is ever-onward, and I can’t believe how quickly the time is flying! Continuing with the current theme of marine gastropods, I’m going to continue with the story of Laevistrombus, discussing a paper that Stephen published in 2017. Yes, I know, I haven’t said anything about his masters thesis yet. All in good time!

Laevistrombus canarium (Maxwell et al. 2019)

Sex-ratio bias is common in gastropods, particularly in the Strombidae, with generally 0.75 males per female. In addition, this sex imbalance is variable on both spatial and temporal scales. Currently, the mechanisms driving sex-ratio bias are little explored. Therefore, in this paper, published in Memoirs of the Queensland Museum - Nature, we explored some of these mechanisms in Laevistrombus canarium (Fig. 1) from two populations.

Four Mile Beach and Alexandra Reefs (Google Maps; 14/04/2019)

We sampled individuals from two reefs in Far North Queensland, Australia, with different benthic compositions, namely Four Mile Beach and Alexandra Reef (Fig. 2). Snails were sampled over nine trips at low tide between June 2013 and May 2016. We collected individuals from bot mating and non-mating clusters when possible. For each individual, we recorded the substrate it occurred on and its sex.

We also found a strong bias towards females, which was consistent across both locations and across benthic substrates (Table 1). Our findings suggest that inherent genetic factors (possibly related to either ZQ-ZZ or XX-XY sex determination mechanisms) regulate natural patterns of sex imbalance in L. canarium. These findings also suggest that some life-history characteristics, yet to be clearly established, are associated with the origin and maintenance of this sex-ratio bias in L. canarium.

* Taken from Maxwell et al. 2017

Again, I hope that you realise that marine snails provide a really rich area for scientific scrutiny. And who knows how much more we will learn in the future. Perhaps the most important lesson that I take out of this paper is not a specific conclusion, or anything that is going to shatter the core of scientific thinking. I suggest that we shouldn’t just assume that patterns will be the same across closely related species. I suggest that we should explore with an open mind, and not just generalise that a snail will behave like any other snail. We really should admire these species, and indeed populations and even individuals within species, for what they are: unique.

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.

Recent news on the snail story …

It’s March, and we’re on to Blog 3, so still going strong. Continuing with the current theme of marine gastropods, we’ve just had a new piece that recent master’s graduate (and now PhD candidate) Stephen has had published. We still have to get onto a discussion of his masters thesis, but that will come in time!

Stephen’s third paper was published in Zootaxa, and evaluates the taxonomy of marine snails belonging to the genus Laevistrombus (Fig. 1). After the first major revision of the family Strombidae (Abbott 1960), Laevistrombus was considered monospecific (that is, only one extant species in the genus). This is where we could have a whole discussion on whether to lump or split organisms into distinct species. Abbott (1960) was a lumper, whereas recent revisions on this genus have considered Abbott (1960) to have been too conservative. While later authors suggest that there are three extant species, we suggest that further splitting is needed, proposing that L. taeniatus and L. vankorensis be elevated to species. We provide descriptions on the morphology and distribution to do this.

Fig. 1. The five extant members of the Laevistrombus: A) L. turturella; B) L. taeniatus; C) L. guidoi; D) L. canarium; and E) L. vanikorensis

Fig. 2. Morphology of a snail

We provide the description of five species of Laevistrombus in the paper. For each, we provide the taxonomic identification, the definition, type locality and distribution. We also identify the type material. Comparative analyses of this complex have been problematic specifically because there has been a lack of designation of the type material.  The shells of these animals are quite beautiful (Fig. 1). They are smooth, solid and quite round. The outer lip is quite thick and smooth, becoming a bit harder and rougher (calloused) towards the head region. The columella (the spiral bit that goes through the middle, Fig. 2) is smooth and thickened in the middle. To see what makes each of these species different, you can check out the paper by clicking on the link under List of Publications.

Hopefully you can see that there’s a lot more to marine snails that you probably thought. And there will definitely be more to come in the future. I think one of the most important lessons out of this paper is that lumping or splitting is perhaps a matter of opinion when there isn’t solid evidence or appropriate descriptions. If you state specifically why you think something is different to something else, and you provide evidence to support that observation, then there is no ambiguity in your rationale for splitting or lumping. However, if you just say that things look alike, and lump them together without taking a holistic view, then you introduce ambiguity, which causes confusion. 

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