Evolution Of Gastropods Research Articles

Miocene instead of Jurassic: the importance of sound fieldwork for paleontological data analysis—a reply

In their detailed comments, Das et al. (2023) try to discount our arguments that the strata cropping out at the so-called Jhura pond locality are not Late Jurassic in age but Miocene. We wrote this paper (Fürsich et al., 2023) because of the far-reaching conclusions that have been drawn from the molluscan fauna at that locality, in particular with respect to the evolution of turritellid gastropods and the evolution of drilling predation by naticid gastropods. We still maintain that the beds containing abundant turritellids are not Jurassic but Neogene, most probably Miocene, in age. In no way do we contest the various analyses on the material collected from the outcrop by the authors, but just the erroneous age assignment of the strata. In order to keep this reply short, we support our point by referring to just to two aspects: the position of the outcrop and the composition of the fauna. Rather than refuting each of the other arguments of Das et al. (2023), we think that a joint visit to the locality would be more productive for arriving at a consensus on the origin and age of the fauna of the Jhura pond locality.

The complete mitochondrial genome of the deep-sea paskentanid snail Alviniconcha marisindica (Caenogastropoda: abyssochrysoidea) from the Carlsberg Ridge

Alviniconcha marisindica Okutani 2014 is a deep-sea gastropod inhabited in hydrothermal vents of the Indo-Pacific. It belongs to superfamily Abyssochrysoidea. In the present study, we report the complete mitochondrial genome of A. marisindica, which is 15,979 bp in length and contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes. The nucleotide composition is 29.19% of A, 38.22% of T, 16.88% of G, and 15.71% of C. The phylogenetic analysis indicates that A. marisindica and A. boucheti clustered in the Abyssochrysoidea clade with high bootstrap support. The mitochondrial genome of A. marisindica provides valuable molecular data for further research on the evolution of deep-sea gastropods.

Transcriptomic response to salinity variation in native and introduced mud-tidal gastropod Batillaria attramentaria

The introduced Asian mud-tidal gastropod Batillaria attramentaria has been reported to quickly dominate its new habitat, Elkhorn Slough, USA, which has a different osmotic condition from its native habitat. This species has also been reported to have a substantial impact on the ecosystem of the new habitat. In this study, we compared the gene expression profiles in response to temporary salinity variation in native (Asian) and introduced (North American) snails and elucidated the genetic mechanism underlying such rapid adaptation of the introduced species. We examined the transcriptomes of four B. attramentaria populations, including three from the native habitats and one from the introduced habitat, in response to salinity variation. We found that 2,353, 2,505, 10,362, and 16,381 genes were differentially expressed due to their lineages (Kuroshio vs. Tsushima), origins (native vs. introduced), locations (Korea, Japan, or the USA), and salinity variations (stressful: 13, 23, and 43 PSU vs. optimal: 33 PSU), respectively. We found that GO-enriched differentially expressed genes involved in the detection of various abiotic and biotic stimuli through sensory perception and genes involved in response to abiotic stimulus and stress were upregulated when exposed to lower-salinity conditions in all locations. The results indicated that B. attramentaria has adapted well to varied salinity conditions and evolved after around 100 years of invasion in Elkhorn Slough. This study provides valuable transcriptomic data on salinity stress response genes in the tidal gastropod and contributes to the research on the adaptive evolution of coastal gastropods.

Core gut microbes Cloacibacterium and Aeromonas associated with different gastropod species could be persistently transmitted across multiple generations

BackgroundStudies on the gut microbiota of animals have largely focused on vertebrates. The transmission modes of commensal intestinal bacteria in mammals have been well studied. However, in gastropods, the relationship between gut microbiota and hosts is still poorly understood. To gain a better understanding of the composition of gut microbes and their transmission routes in gastropods, a large-scale and long-term experiment on the dynamics and transmission modes of gut microbiota was conducted on freshwater snails.ResultsWe analyzed 244 microbial samples from the digestive tracts of freshwater gastropods and identified Proteobacteria and Bacteroidetes as dominant gut microbes. Aeromonas, Cloacibacterium, and Cetobacterium were identified as core microbes in the guts, accounting for over 50% of the total sequences. Furthermore, both core bacteria Aeromonas and Cloacibacterium, were shared among 7 gastropod species and played an important role in determining the gut microbial community types of both wild and cultured gastropods. Analysis of the gut microbiota at the population level, including wild gastropods and their offspring, indicated that a proportion of gut microbes could be consistently vertically transmitted inheritance, while the majority of the gut microbes resulted from horizontal transmission. Comparing cultured snails to their wild counterparts, we observed an increasing trend in the proportion of shared microbes and a decreasing trend in the number of unique microbes among wild gastropods and their offspring reared in a cultured environment. Core gut microbes, Aeromonas and Cloacibacterium, remained persistent and dispersed from wild snails to their offspring across multiple generations. Interestingly, under cultured environments, the gut microbiota in wild gastropods could only be maintained for up to 2 generations before converging with that of cultured snails. The difference observed in gut bacterial metabolism functions was associated with this transition. Our study also demonstrated that the gut microbial compositions in gastropods are influenced by developmental stages and revealed the presence of Aeromonas and Cloacibacterium throughout the life cycle in gastropods. Based on the dynamics of core gut microbes, it may be possible to predict the health status of gastropods during their adaptation to new environments. Additionally, gut microbial metabolic functions were found to be associated with the adaptive evolution of gastropods from wild to cultured environments.ConclusionsOur findings provide novel insights into the dynamic processes of gut microbiota colonization in gastropod mollusks and unveil the modes of microbial transmission within their guts.1dB18pPYxP-ygVgUJj2q9BVideo

Diversity and evolution of parasitic gastropods

Diversity and evolution of parasitic gastropods

Chromosome-level genome of the venomous snail Kalloconus canariensis: a valuable model for venomics and comparative genomics.

Genomes are powerful resources to understand the evolutionary mechanisms underpinning the origin and diversification of the venoms of cone snails (Conidae: Caenogastropoda) and could aid in the development of novel drugs. Here, we used PacBio continuous long reads and Omni-C data to assemble the chromosome-level genome of Kalloconus canariensis, a vermivorous cone endemic to the Canary Islands. The final genome size was 2.87 Gb, with a N50 of 79.75 Mb and 91% of the reads located into the 35 largest scaffolds. Up to 55.80% of the genome was annotated as repetitive regions, being class I of transposable elements (16.65%) predominant. The annotation estimated 34,287 gene models. Comparative analysis of this genome with the 2 cone snail genomes released to date (Dendroconus betulinus and Lautoconus ventricosus) revealed similar genome sizes and organization, although chromosome sizes tended to be shorter in K. canariensis. Phylogenetic relationships within subclass Caenogastropoda were recovered with strong statistical support. The family Conidae was recovered as a clade, with K. canariensis plus L. ventricosus sister to D. betulinus. Despite the great diversity of cone snails (>900 species) and their venoms (hundreds of peptides per species), only 2 recently reported genomes are available for the group. The high-quality chromosome-level assembly of K. canariensis will be a valuable reference for studying the origin and evolution of conotoxin genes as well as whole-genome duplication events during gastropod evolution.

Comparison of Evolutionary Selection Acting on the Mitochondrial Protein-Coding Genes Between Intertidal and Deep-Sea Gastropods

Marine molluscs are ecologically and economically important group of organisms that survive in the challenging environments of different oceanic zones. Of all the classes of the phylum Mollusca, gastropods have radiated into marine, freshwater and terrestrial habitats, successfully adapting themselves to thrive in changing environmental conditions. Hence, marine gastropods can be considered as an ideal system to study stress adaptation. In order to withstand the constant fluctuations in temperature, salinity and shifts in oxygen concentration of the intertidal zone, the gastropods inhabiting here rely on a modified and adaptive energy metabolism. The same is applicable for gastropods living in the deep sea environment, which is characterized by high hydrostatic pressure, low oxygen concentrations and abundance of heavy metals. Therefore, survival of these organisms may be correlated to their adaptive mitochondrial genome which serves as the principal site for energy metabolism and production in the cell. Here, we estimated selection pressure acting on the mitochondrial protein-coding genes of 13 intertidal and 2 deep sea gastropods based on site and branch-site specific models. The results exhibited higher number of sites under diversifying selection for the mitochondrial protein-coding genes of intertidal gastropods compared to deep sea species. Overall, this study focusses on the adaptive mitogenome evolution of marine gastropods for survival in the dynamic environments of the intertidal zone as well as deep sea.

Mother snail labors for posterity in bed of mid-Cretaceous amber

When seldom life history events serendipitously get documented by exceptional preservation in the fossil record, a unique telescopic opportunity arises for interpreting fossils within their paleoenvironment as well as for understanding ancestral relationships of current life forms. We present a rare glimpse of live birth by a terrestrial mother snail, incidentally, engulfed by amber as she released her young in a tropical forest during the mid-Cretaceous (early Cenomanian). The exceptional finding featuring the preservation of a snail’s 99-million-year-old soft-body together with five neonate shells represents the earliest known fossilized incidence of viviparity in a terrestrial snail. Based on high-resolution photographs and µCT scans, we describe the mother snail as a new species of cyclophoroid, Cretatortulosa gignens sp. nov. Our finding provides remarkable perspectives for interpreting gastropod evolution 80 million years earlier than the fossil record has known up to now. It shows that viviparity was already a relevant reproductive strategy in the Cretaceous, probably increasing the offspring’s survival chance in a predator-lurking tropical forest.

Comparative analysis of the complete mitochondrial genomes in two limpets from Lottiidae (Gastropoda: Patellogastropoda): rare irregular gene rearrangement within Gastropoda

To improve the systematics and taxonomy of Patellogastropoda within the evolution of gastropods, we determined the complete mitochondrial genome sequences of Lottia goshimai and Nipponacmea fuscoviridis in the family Lottiidae, which presented sizes of 18,192 bp and 18,720 bp, respectively. In addition to 37 common genes among metazoa, we observed duplication of the trnM gene in L. goshimai and the trnM and trnW genes in N. fuscoviridis. The highest A + T contents of the two species were found within protein-coding genes (59.95% and 54.55%), followed by rRNAs (56.50% and 52.44%) and tRNAs (56.42% and 52.41%). trnS1 and trnS2 could not form the canonical cloverleaf secondary structure due to the lack of a dihydrouracil arm in both species. The gene arrangements in all Patellogastropoda compared with those of ancestral gastropods showed different levels of gene rearrangement, including the shuffling, translocation and inversion of single genes or gene fragments. This kind of irregular rearrangement is particularly obvious in the Lottiidae family. The results of phylogenetic and gene rearrangement analyses showed that L. goshimai and Lottia digitalis clustered into one group, which in turn clustered with N. fuscoviridis in Patellogastropoda. This study demonstrates the significance of complete mitogenomes for phylogenetic analysis and enhances our understanding of the evolution of Patellogastropoda.

Onshore-offshore trend in the evolution of calliotropid gastropods expressed in shell morphology

Two new species of calliotropid gastropods, Calliotropis (Riselloidea) faustiankensis sp. nov. and Calliotropis (Riselloidea) lukovensis sp. nov., are described from the Middle Jurassic (Middle Bathonian−Upper Callovian) of Poland. Additionally, new excellently preserved shells of Calliotropis (Riselloidea) biarmata (Münster) allow redefinition of this species. The new morphological information obtained from these three fossil species of Calliotropis in combination with the dataset assembled from 20 extinct and 24 living calliotropids is here summarized in quantitative multivariate and principal component analyses suggesting an onshore-offshore trend in calliotropid gastropod evolution from the Triassic to Recent times. This trend, which is expressed in the morphology of shells, shows that the Mesozoic species are mostly shallow water, while Cenozoic and Recent taxa are mostly deep water. The distinction supports earlier suggestions that the genus Calliotropis can be subdivided into two temporal subgenera belonging to the family Eucyclidae Koken.http://zoobank.org/urn:lsid:zoobank.org:pub:C8362FB8-966A-4322-95D5-7151CED20476

Genome sequence of pacific abalone (Haliotis discus hannai): the first draft genome in family Haliotidae.

Background: Abalones are large marine snails in the family Haliotidae and the genus Haliotis belonging to the class Gastropoda of the phylum Mollusca. The family Haliotidae contains only one genus, Haliotis, and this single genus is known to contain several species of abalone. With 18 additional subspecies, the most comprehensive treatment of Haliotidae considers 56 species valid [1]. Abalone is an economically important fishery and aquaculture animal that is considered a highly prized seafood delicacy. The total global supply of abalone has increased 5-fold since the 1970s and farm production increased explosively from 50 mt to 103 464 mt in the past 40 years. Additionally, researchers have recently focused on abalone given their reported tumor suppression effect. However, despite the valuable features of this marine animal, no genomic information is available for the Haliotidae family and related research is still limited. To construct the H. discus hannai genome, a total of 580-G base pairs using Illumina and Pacbio platforms were generated with 322-fold coverage based on the 1.8-Gb estimated genome size of H. discus hannai using flow cytometry. The final genome assembly consisted of 1.86 Gb with 35 450 scaffolds (>2 kb). GC content level was 40.51%, and the N50 length of assembled scaffolds was 211 kb. We identified 29 449 genes using Evidence Modeler based on the gene information from ab initio prediction, protein homology with known genes, and transcriptome evidence of RNA-seq. Here we present the first Haliotidae genome, H. discus hannai, with sequencing data, assembly, and gene annotation information. This will be helpful for resolving the lack of genomic information in the Haliotidae family as well as providing more opportunities for understanding gastropod evolution.

Putative structural-functional evolution of osphradial sensory surface in aquatic prosobranchian molluscs

At present, ecotoxicological studies use physiological reactions of invertebrates, based on diverse reflexes, as biomarkers. The primary link of the reflex chain is presented by the chemo-, mechano- and osmoreceptors located on the body surface and inside the mantle cavity. Previously we hypothesized that the polymodal osphradial organ in the pond snail may participate in adaptive reactions of aquatic molluscs to toxicants. A known homology of osphradial components allows extending this suggestion to marine representatives of various Mollusca subclasses, although a great diversity of their structural organization and feeding methods as well as multiplicity of aquatic molluscs may hamper the interpretation of the coming ecotoxicological studies. To elucidate this issue, we carried out a comparative electron microscopic study of the osphradial organs in different families of prosobranchian molluscs (Gastropoda). Depending on ultrastructural features, five sensory cell complexes (SCC) were identified in the osphradial organs, and a putative connection of these complexes with the known chemo-, mechano- and osmosensory modalities was demonstrated. The SCC structure becomes more sophisticated during evolution of gastropods depending largely on feeding methods. Thus, the primitively organized osphradium in the herbivorous mollusc Viviparus sp. is a polymodal receptor organ representing a prototype for further morpho-physiological modification. The osphradium in a winkle (Littorina sp.) is the next step in evolutionary transformation, combining osmo- and chemosensory SCC. In the novel, “ctenidial”, type of osphradia the total receptor surface increases and ultrastructural specialization of SCC occurs promoting the emergence of carnivorous feeding. In predatory marine molluscs which actively hunt for prey using odor, the accessory superficial SCC is distinguished. It is located on the lateral surfaces and ventral edge of the osphradial petals, near the supporting ciliated cells, and appears to be a mechanoreceptor organ sensing the direction and rate of liquid flowing along the osphradium. Association of SCC with a certain sensory modality and feeding method is suggested.

Unique digestive system, trophic specialization, and diversification in the deep-sea gastropod genusScaphander

Dietary specialization is known to be important for the evolution of Cephalaspidea gastropods, but still little is known about the overall trophic interactions of the group and the putative role of trophic ecology on diversification. The genus Scaphander is a group of predominantly deep-sea, infaunal cephalaspids with about 40% of its species (eight) occurring on the Atlantic Ocean. They are carnivorous and have a unique digestive system with a large, strongly muscularized gizzard containing three sizable and heavily calcified plates. This work aims to describe the diet of Scaphander, to evaluate if there is a functional relation between the anatomy of the digestive tract and exploitation of novel food resources, and to assess if dietary specialization may have played a role in the diversification of the Atlantic species of Scaphander. Gut contents were studied from 31 specimens representing seven of the Atlantic species using scanning electron microscopy and light microscopy. The chemical composition of the gizzard plates was analysed by X-ray microanalysis and X-ray powder diffraction. Foraminiferans, including agglutinating forms, were shown to be the most important food item for Scaphander; bivalves, gastropods, scaphopods, and polychaetes with calcareous tubes were also found to form part of the diet. The gizzard plates were shown to consist of a phosphate-rich amorphous component and a crystalline component identified as fluorite (hardness 4; Moh's scale). It is suggested that the ability of Scaphander gastropods to prey upon organisms with hard tests, particularly agglutinating foraminiferans, is not only due to the hardness of the gizzard plates but to the cumulative effect of shape and hardness of the gizzard plates and relative size of the gizzard and associated musculature. No interspecific differences were found in the diet and morphology of the digestive tract, indicating that dietary specialization probably has not played a significant role in the diversification of Atlantic species of Scaphander. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 512–525.

Evolution and classification of Mesozoic mathildoid gastropods

About 150 Mesozoic (mostly Early and Middle Jurassic) species of the heterobranch superfamily Mathildoidea are classified into four families and 27 genera. Most taxa are assigned to the families Mathildidae, Gordenellidae, and Tofanellidae while the Triassic family Anoptychiidae holds only a single genus and is restricted to the Late Triassic. Mathilda janeti is designated as type species for the genus Promathildia. Earlier designations are invalid because they refer to species which were not originally included in the genus Promathildia. As a consequence, Promathildia is transferred fromMathildidae to Gordenellidae. The generic assignment of numerous mathildoid species is changed. The suggested classification represents an arrangement which is based on shell characters; it is not based on a cladistic phylogenetic analysis.However, a great number of fossil taxa can only be classified based on shell characters. A high mathildoid diversity has been recognized from the Late Triassic Cassian Formation. Many o...

Phylogenetic relationships and evolution of pulmonate gastropods (Mollusca): New insights from increased taxon sampling

Phylogenetic relationships among higher clades of pulmonate gastropods are reconstructed based on a data set including one nuclear marker (complete ribosomal 18S) and two mitochondrial markers (partial ribosomal 16S and Cytochrome oxidase I) for a total of 96 species. Sequences for 66 of these species are new to science, with a special emphasis on sampling the Ellobiidae, Onchidiidae, and Veronicellidae. Important results include the monophyly of Systellommatophora (Onchidiidae and Veronicellidae) as well as the monophyly of Ellobiidae (including Trimusculus, Otina, and Smeagol). Relationships within Ellobiidae, Onchidiidae, and Veronicellidae are evaluated here for the first time using molecular data. Present results are compared with those from the recent literature, and the current knowledge of phylogenetic relationships among pulmonate gastropods is reviewed: despite many efforts, deep nodes are still uncertain. Identification uncertainties about early fossils of pulmonates are reviewed. Impacts of those phylogenetic and fossil record uncertainties on our understanding of the macro-evolutionary history of pulmonates, especially transitions between aquatic and terrestrial habitats, are discussed.

Expression of Hox genes during the larval development of the snail, Gibbula varia (L.)—further evidence of non-colinearity in molluscs

Hox transcription factors, a subfamily of homeobox genes, are expressed in distinct, often overlapping domains along the anterior-posterior body axis of animal embryos. Here, we report the sequence and expression pattern of Hox2, Hox3, Hox4, Hox5, Lox5, Hox7, Lox4, and Lox2 in different larval stages during the encapsulated development of the marine gastropod Gibbula varia. Our results show that all Gva-Hox genes are expressed in ectoderm-derived cells. Hox2, Hox3, Hox4, Hox5, and Hox7 are expressed in overlapping patterns in the pedal, pleural, oesophageal, and visceral ganglia, supporting the ancestral role of Hox genes in the neurogenesis processes in bilaterians. Gva-Hox1, Gva-Post2, and Gva-Post1 genes are involved in shell morphogenesis and have apparently lost their role in neurogangliogenesis. Lox5, Lox4, and Lox2 are expressed in different cells of the apical organ during the earlier larval stage (trochophore) and the cerebral ganglia during later larval stages (veliger). These results support the hypothesis that apical organ neurosensory cells contribute to the formation of cerebral ganglia commissures during metamorphosis. Gva-Hox7 and Gva-Lox4 are additionally expressed in the prototroch of the trochophore and in the velar area of the veliger larvae. This contradicts with the expression of these genes in the annelids, where most of Hox genes are expressed in the posttrochal area and are involved in segmental determination. Therefore, expression of Hox genes may serve as an example of co-option and plasticity of gene function during evolution of gastropods.

Mitochondrial genome of Thais clavigera (Mollusca: Gastropoda): Affirmation of the conserved, ancestral gene pattern within the mollusks

Class Gastropoda includes a large number of described species, many with extensively rearranged mitochondrial genomes. We sequenced the mitogenome of the rock shell, Thais clavigera (Gastropoda: Muricidae), an intertidal snail, using long PCR with primers designed on the basis of expressed sequence tags. The mitogenome of T. clavigera consists of 2 rRNAs, 22 tRNAs, and 13 protein-coding genes, but no control region. Structural comparisons revealed that the order Sorbeoconcha, including T. clavigera, have nearly identical mitochondrial gene patterns. However, they have an inversion between a tRNA(Phe)-tRNA(Glu) cluster that comprises 21 genes, but most of the remaining structure is similar to the putative mollusk ground pattern. These findings will provide a better insight into mitochondrial gene rearrangement over the course of gastropod evolution.

A global phylogeny of apple snails: Gondwanan origin, generic relationships, and the influence of outgroup choice (Caenogastropoda: Ampullariidae)

Apple snails (Ampullariidae) are a diverse family of pantropical freshwater snails and an important evolutionary link to the common ancestor of the largest group of living gastropods, the Caenogastropoda. A clear understanding of relationships within the Ampullariidae, and identification of their sister taxon, is therefore important for interpreting gastropod evolution in general. Unfortunately, the overall pattern has been clouded by confused systematics within the family and equivocal results regarding the family's sister group relationships. To clarify the relationships among ampullariid genera and to evaluate the influence of including or excluding possible sister taxa, we used data from five genes, three nuclear and two mitochondrial, from representatives of all nine extant ampullariid genera, and species of Viviparidae, Cyclophoridae, and Campanilidae, to reconstruct the phylogeny of apple snails, and determine their affinities to these possible sister groups. The results obtained indicate that the Old and New World ampullariids are reciprocally monophyletic with probable Gondwanan origins. All four Old World genera, Afropomus, Saulea, Pila, and Lanistes, were recovered as monophyletic, but only Asolene, Felipponea, and Pomella were monophyletic among the five New World genera, with Marisa paraphyletic and Pomacea polyphyletic. Estimates of divergence times among New World taxa suggest that diversification began shortly after the separation of Africa and South America and has probably been influenced by hydrogeological events over the last 90 Myr. The sister group of the Ampullariidae remains unresolved, but analyses omitting certain outgroup taxa suggest the need for dense taxonomic sampling to increase phylogenetic accuracy within the ingroup. The results obtained also indicate that defining the sister group of the Ampullariidae and clarifying relationships among basal caenogastropods will require increased taxon sampling within these four families, and synthesis of both morphological and molecular data. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 61–76.

Beiträge zur Torsion und Frühevolution der Gastropoden

Contributions to torsion and early evolution of the gastropods The phylogenetical model, which is presented here, is directed by trying to explain torsion of gastropods out of biomechanical conditions. It is based on morphological and functional reflexions upon the evolution of an ancestral mollusc out of an annelid-like segmented coelomate and further evolution of this to a monoplacophoran. Starting point of gastropod evolution is a high-arched monoplacophoran with serial pairs of dorsoventral muscles. There are always alternating one pair of vertically and one pair of obliquely running, crossed dorsoventral muscles. Evolution of higher arches causes a reduction of many dorsoventral muscles and a magnification of the pallial cavity. This gives place for a few pairs of massive gills instead of many serrated little monoplacophoran gills. A second consequence is a waist (“Taille”) between cephalopodium and visceral hump. It functions as an axis for at first little, with further muscle reductions greater torsional motions of the shell and the visceral hump. At last there exists only one pair of oblique and crossed dorsoventral muscles. This situation forces a fixation of the torted position, because it causes less energy consumption. There is also a lot of other advantages for the “torted gastropod”. The construction of a bilateral ancestor is the base for the evolution of recent asymmetric snails as a bundle of different phylogenetic lines.

Reassessment of the trophic position of Bullidae (Gastropoda: Cephalaspidea) and the importance of diet in the evolution of cephalaspidean gastropods

AbstractA review of the available data on the diet of species of Bullidae is presented. Their trophic level is reassessed through gut content analysis of worldwide species from various habitats. Gut contents were identified by light and scanning electron microscopy. The previous claims of omnivory and carnivory were not supported. Worldwide species of Bullidae feed preferentially on algae and secondarily on diatoms, and are therefore herbivorous. The influence of dietary specialization on the evolution of cephalaspidean gastropods was assessed by superimposing the diet onto a molecular family‐level phylogeny. Herbivory was found to be the plesiomorphic condition, with carnivory having arisen independently two or three times. This evidence suggests that dietary specialization has played a major role in the adaptive radiation of the group.