Monthly Archives: April 2020

Stylommatophoran phylogenetics

Last year a large molecular study was published by Saadi & Wade, which aimed at studying the deep divisions at the base of the Stylommatophoran phylogenetic tree. Their abstract was “The deep divisions at the base of the stylommatophoran land snails and slugs have proved to be controversial, with the phylogenetic position of the Scolodontidae remaining unresolved. Here we present a phylogenetic analysis of 34 stylommatophoran genera based on a combined dataset (5782 sites) of four loci with the aim of resolving the position of the Scolodontidae and their relationship to the ‘achatinoid’ and ‘non-achatinoid’ clades. We also evaluate the phylogenetic utility of different genes and gene partitions. The deep phylogenetic relationships within the Stylommatophora are now clearly resolved. The Scolodontidae are shown categorically to be the sister group to all other stylommatophoran groups with robust support and with all phylogeny re-construction methods. The ‘achatinoid’ and ‘non-achatinoid’ clades are also strongly supported in the tree. The original LSU 1-5 fragment used extensively in studies of the Stylommatophora was found to be the most informative gene fragment and works well at resolving relationships at most levels in the Stylommatophora but does not reliably resolve the deep level relationships at the very base of the clade. The concatenated dataset of four genes employed in this study is not only informative at lower levels but also resolves the deep level relationships at the base of the Stylommatophora with robust support“.

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As this tree shows, the ‘Scolodontidae’ genera used herein are Guesteria and Systrophia. As Salvador & Cavalleri has recently shown, there is a clear distinction between the Scolodontidae and Systrophiidae to which the two mentioned genera belong. The authors may have been misled by the classification used by MolluscaBase which still classifies them with the Scolodontidae. As such not a disaster, but it shows that if the taxonomy is not up-to-date, even the conclusions of a thorough study are prone to failure.

Reference:
Saadi, A.J. & Wade, C.M., 2019. Resolving the basal divisions in the stylommatophoran land snails and slugs with special emphasis on the position of the Scolodontidae. Molecular Phylogenetics and Evolution 139: e106529 (9 pp.).

New Brazilian Rectobelus

A paper published last year describing a new species from Brazil is Simone & D’ávila. “Rectobelus levogyrus, a new species of subulinid, is described found in archaeological surveys in Amazon shell mounts (sambaquis) from Costa Marques, Rondônia, Brazil. It is the first sinistral subulinid species recorded in Brazil, and that is its main distinguishing character. A brief taxonomical treatment of the other congener species, R. rectus (Baker, 1927) (the type species, from Venezuela) and R. birabeni (Hylton Scott, 1946) (from Argentina) is included, with figures, as well as a discussion on the validity of the genus“.

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The title of this papers is curious, citing two different subfamily names, which are both outdated as the Subulininae are now considered as belonging to the Achatinidae. This is a very difficult group as the species are separated on minor details which are often not consistently studied in larger series. Many species from the ‘subulinid’ group are supposed to have continuous growth, making size differences difficult to use as a taxonomic characteristic. Moreover, for many species anatomical and molecular data are lacking. In this paper Simone disagrees with the opinion of Hausdorf, who considered Rectobelus H.B. Baker. 1927 as a synonym of Ischnocion Pilsbry, 1907. The latter is placed on MolluscaBase in the subfamily Coeliaxinae. Thus there remains ample room for further research.

Reference:
Simone, L.R.L. & D’ávila, 2019. The discovery of a sinistral Obeliscinae (Eupulmonata, Subulinidae) in Brazil, found in Amazon archaeological shell mounds of Rondônia. – Journal of Conchology 43(4): 327-336.

New streptaxid from Brazil

Salvador & Cunha just published a new paper, describing a new Brazilian species. “A new species of Streptartemon Kobelt, 1905 land snail from Santos, SE Brazil, is herein described as Streptartemon waukeen sp. nov., from specimens originally found in an urban garden. The new species is distributed along coastal urban areas from southern Espírito Santo state to São Paulo state. It can be diagnosed from its congeners by the following features: a comparatively small shell; the penultimate and body whorls bulging and rounded; a small and roughly circular aperture; and the lack of apertural lamellae/teeth. The new species also presents a bursa tract diverticulum, which is a plesiomorphic state in stylommatophoran snails, but absent in most streptaxid genera. Further details of the genital anatomy, as well as DNA barcoding information, are provided“.

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The discovery of this new taxon in urban areas is remarkable. Further collecting should show if this species is confined to anthropological habitats or not.

Reference:
Salvador, R.B. & Cunha, C.M., 2020. A new species of Streptartemon from southeastern Brazil (Gastropoda: Streptaxidae). – Journal of Conchology 43(5): 513-520.

Brazilian Obeliscus

Recently published by D’Avila e.a., a paper on Brazilian Obeliscus species. The abstract reads as follows: “Obeliscus agassizi Pilsbry, 1906 was described from specimens collected in Brazil, by J. G. Anthony, during the Agassiz expedition, in 1865. The type locality of the species was given simply as Brazil, without further information. More than a century after its description, this species was rediscovered during an expedition to the Biological Reserve of Pedra Talhada, Alagoas/Pernambuco states, Brazil. In the present study we provide detailed description of the anatomy of the soft parts of O. agassizi specimens, collected during this expedition, besides more precise data concerning the species occurrence. This work presents the first anatomical description for the genus. An annotated checklist of Obeliscus Beck, 1837 species is also provided. The species of Obeliscus have been traditionally distinguished by shell characteristics, mainly the general shell shape, number of whorls proportionally to the shell size, shell ornamentation, the shape of the protoconch and aperture size and shape. The distinction between species is often subtle. Considering that shell traits may be not sufficient as single taxonomic characters, other evidence for species boundaries, especially anatomical characters, is needed. Presently, it is not possible to discuss the taxonomic meaning of the set of anatomical characters described for O. agassizi, at the intra-genus level, as there is no information on the anatomy of the soft parts of other species of Obeliscus. The comparative analysis of the genital system of O. agassizi, Neobeliscus calcareus (Born, 1780), Stenogyra terebraster (Lamarck, 1822) and Rectobelus birabeni (Hylton-Scott, 1946) pointed out anatomical characters with potential diagnostic significance for the genus Obeliscus. However, the establishment of a definitive dif- ferential diagnosis for this genus, based in both conchological and anatomical traits, depends on the analysis of a greater number of species of Obeliscus, as well as species of other genera of Obeliscinae Thiele, 1931“.

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This is a useful paper, especially by providing anatomical details for this species and a checklist of other Brazilian species of the genus. However, the authors have missed the chance to add also molecular data to place this genus in the phylogentic data already available for the family. According to MolluscaBase the genus Obeliscus is classified in the Achatinidae (subfamily Stenogyrinae), no longer in the Subulinidae (subfamily Obeliscinae).

Reference:
D’ávila e.a., 2020. Resdiscovery of Obeliscus agassizi Pilsbry, 1906 (Gastropoda, Subulinidae, Obeliscinae), annotated checklist of species of Obeliscus beck, 1837 and first description of the anatomy for the genus. – Zoosystema 41(12): 159-172.

New Pantepui Plekocheilus

Freshly pressed: a paper with additional data on snails from the Eastern Pantepui region, with description of 3 new species. “Recent visits by a herpetologist to hitherto unexplored or ill–explored tepuis in the Pantepui area of Venezuela reveal three new species: Plekocheilus (P.) sanderi, P. (Eurytus) annetae, and P. (E.) timoi. This brings the total number of recognised species in the Pantepui to 27 land snails, of which 23 belong to the dominating superfamily Orthalicoidea“.

sanderi-annetae-timoi

 

Reference:
Breure, A.S.H., 2020. Additional data on Eastern Pantepui Orthalicoidea land snails (Mollusca, Gastropoda). – Journal of Conchology 43(5): 481-496.

New Argentinian Succinea

Recently Miquel et al. investigated the Succineidae from the southern tip of South America and found a new species.

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A new species of Succinea from Santa Cruz Province (Argentina) is described. Succinea argentina sp. nov. is characterized by the following features: a shell of regular growth, 3 to 3.25 whorls, length of 6.0 to 7.15 mm, shell not succineid, opaque walls and conspicuous axial ribs; straw­yellow opaque deciduous peri­ostracum; radular formula: 21-9-C-9-21, with central tooth tricuspid, lateral teeth bicuspid and marginal teeth tricuspid; penis with epiphallus, wrapped in a com­mon sheath, without appendices, and formed by two regions: a long proximal re­gion, which is lined by a mucosa with multiple transverse folds, and a short distal region, which opens into the atrium; vas deferens composed of three main regions – pre­prostatic, prostatic and post­prostatic –, entering the epiphallus subtermi­nally, and covered by a mucosa with multiple folds of different sizes; vagina long, thin and convolute; spermatheca globose, with a long duct that opens in the last portion of the vagina; atrium short“.

As with all succineid species the anatomy plays an important role. Nonetheless it is remarkable that the authors diagnose this species morphology as “not succineid”. There are several other related species occurring in this region from which it is, however, clearly different.

Reference:
Miquel, S.E. et al., 2019. A new species of Succinea Draparnaud from the extreme south of Argentina. – Spixiana, 42: 177-184.

New records from Santa Catarina state

In the just issued Tentacle there is another contribution of Agudo & Meyer on new records in the Brazilian state of Santa Catarina.

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Agudo is tireless in bringing data on the malacofauna of this state to light, making it without doubt the most thoroughly researched part of Brazil.

Reference:
Agudo-Padron, I. & Meyer, D., 2020. Conservation of non-marine molluscs in Central Southern Brasil: new additions to the inventory of Santa Catarina state. – Tentacle, 28: 20-21.

Internet trade and conservation

In the just published number of Tentacle, one of the interesting articles is about shell trade via the internet. It is to be applauded that Chinese authors have taken this hot topic to the open as shell trade is definitely a threat to molluscan diversity. The normal reaction from traders will be that they trade shells they found empty, but this has in most cases to be considered incorrect (as the perfect state of shells on offer tells otherwise). Unfortunately, even professional malacologists fall sometimes for the temptation of describing new species from material collected by traders, thereby reinforcing this questionable practice of dealers and their collectors.

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As the article shows a picture of Neotropical shells taken from a nature reserve in Florida, this is clearly a practice not limited to eastern Asia.

Reference:
Zhang, G. & Wu, M., 2020. Internet trade, a new threat to malacodiversity. – Tentacle, 28: 12-14.