The origins of molluscs

The interrelationships and evolutionary history of molluscs have seen great advances in the last decade. Recent phylogenetic studies have allowed alternative morphology‐based evolutionary scenarios to be tested and, most significantly, shown that the aplacophorans are sister group to polyplacophorans (chitons), corroborating palaeontological and embryological evolutionary scenarios in which aplacophorans are secondarily simplified from a chiton‐like ancestor. Aplacophoran morphology therefore does not represent the plesiomorphic condition for molluscs as a whole. The mollusc crown group radiated in the Early Cambrian, and rapidly thereafter, stem lineages to the major molluscan classes emerged: cephalopods, gastropods, bivalves (= pelecypods), monoplacophorans, rostroconchs (inferred stem scaphopods) and aculiferans. This attests to the fast, adaptive radiation of the crown group during the Cambrian explosion. Kimberella from the latest Ediacaran exhibits several molluscan traits, which justifies its position as a molluscan stem‐group member, rather than as a more basal Lophotrochozoan. The interrelationships among the conchiferan molluscs are still a matter of contention and require further palaeontological and molecular phylogenetic scrutiny.     

Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. from the Early Cambrian of South China

Botting, J.P., Muir, L.A., Xiao, S., Li, X. & Lin, J.‐P. 2012: Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. from the Early Cambrian of South China. Lethaia, Vol. 45, pp. 463–475. The relationships of the extant sponge classes, and the nature of the last common ancestor of all sponges, are currently unclear. Early sponges preserved in the fossil record differ greatly from extant taxa, and therefore information from the fossil record is critical for testing hypotheses of sponge phylogenetic relationships that are based on modern taxa. New specimens of the enigmatic sponge Lenica sp., from the Early Cambrian Hetang Biota of South China, exhibit an unusual spicule structure. Each spicule consists of a siliceous core with an axial canal, an organic outer layer and a middle layer interpreted to have been originally calcium carbonate. This finding confirms previous work suggesting the existence of biminerallic spicules in early sponges. Combined with data from other early sponges, the new findings imply that the two fundamental spicule structures of modern sponges were derived from a compound, biminerallic precursor. Spicules are therefore homologous structures in Calcarea and Silicea, and if sponges are paraphyletic with respect to Eumetazoa, then spicules may also have been a primitive feature of Metazoa. □Calcarea, Early Cambrian, Hetang Biota, phylogeny, Silicea, taphonomy.     

Spicule structure and affinities of the Late Ordovician hexactinellid‐like sponge Cyathophycus loydelli from the Llanfawr Mudstones Lagerstätte,Wales

Exceptionally well‐preserved specimens of the reticulosan sponge Cyathophycus loydelli from the Sandbian (Late Ordovician) Llanfawr Mudstones Formation of Llandrindod, Waes, UK, have been examined using scanning electron microscopy (SEM). The specimens include exquisitely detailed pyritized spicules, and granular pyritization of surrounding soft tissues. Spicules frequently show axial canals of diameter similar to those of modern siliceous sponges, with hexagonal symmetry typical of modern demosponges rather than hexactinellids. In one case, the axial filament is also preserved. The largest spicules (ray diameter >20 μm) show a complex structure, with a laminar external region similar to that of the extant hexactinellid Monorhaphis. Some spicules preserve sub‐micron detail of the spicule surface, resembling the reticulate collagenous sheath of Monorhaphis. The hexagonal symmetry of the canal confirms that at least some Reticulosa are not crown‐group hexactinellids, but stem‐group Hexactinellida or Demospongea, or stem‐group Silicea. This suggests that a square canal is a sufficient diagnostic feature of total‐group Hexactinellida, but that hexagonal canals were more widely distributed among Early Silicea and were probably not restricted to demosponges. Alternatively, comparison with the structure of modern verongiid fibres suggests that these may be homologous with the outer layers of Cyathophycus spicules, and Cyathophycus may instead be a stem‐group demosponge. The preserved detail of the surface layer shows that pyritization can preserve certain material with extraordinarily fine resolution.     

Indigenous demosponge spicules in a Late Devonian stromatoporoid basal skeleton from the Frasnian of Belgium

This paper records the first example of a demosponge spicule framework in a single specimen of a Devonian stromatoporoid from the Frasnian of southern Belgium. The small sample (2.5 × 2 cm) is a component in a brecciated carbonate from a carbonate mound in La Boverie Quarry 30 km east of Dinant. Because of the small size of the sample, generic identification is not confirmed, but the stromatoporoid basal skeleton is similar to the genus Stromatopora. The spicules are arranged in the calcified skeleton, but not in the gallery space, and are recrystallized as multi‐crystalline calcite. The spicules fall into two size ranges: 10–20 μm diameter and 500–2000 μm long for the large ones and between 5–15 μm diameter and 50–100 μm length for the small ones. In tangential section, the spicules are circular, they have a simple structure, and no axial canal has been preserved. The large spicules are always monaxons, straight or slightly curved styles or strongyles. The spicules most closely resemble halichondrid/axinellid demosponge spicules and are important rare evidence of the existence of spicules in Palaeozoic stromatoporoids, reinforcing the interpretation that stromatoporoids were sponges. The basal skeleton may have had an aragonitic spherulitic mineralogy. Furthermore, the spicules indicate that this stromatoporoid sample is a demosponge.     

Growth patterns of Lower Palaeozoic sponges

Detailed studies of the growth patterns of modern siliceous sponges are restricted to demosponges and theoretical models. It is generally assumed that sponge growth is essentially incremental, with completion of one arbitrary unit being followed by external addition. All recent species are thick-walled, but Lower Palaeozoic sponges are dominated by thin-walled hexactinellids, with most Cambrian taxa consisting of a single spicule layer. Large populations of a primitive dictyospongiid have allowed the reconstruction of the growth patterns of their spicules and body morphology. The results indicate that growth occurred through continuous expansion of the globose body, accompanied by continuous enlargement of existing spicules, with a spicule size limit being reached only during the lifetime of a few individuals. It is noted that this skeletal growth pattern is otherwise restricted to deuterostomes. Consecutive appearance of successive spicule size orders appears to have maintained a maximum inhalant pore area. Comparisons with more limited data from two acanthose hexactinellids and a hazeliid demosponge indicate that an identical growth pattern operated in these species. The subsequent evolution of growth patterns is discussed, with various mechanisms producing the later thick-walled morphologies of hexactinellids and demosponges. The implications of these observations are discussed with reference to identification and systematics, since spicule size and arrangement are shown to vary during growth.     

Where's the glass? Biomarkers,molecular clocks,and microRNAs suggest a 200‐Myr missing Precambrian fossil record of siliceous sponge spicules

The earliest evidence for animal life comes from the fossil record of 24-isopropylcholestane, a sterane found in Cryogenian deposits, and whose precursors are found in modern demosponges, but not choanoflagellates, calcareans, hexactinellids, or eumetazoans. However, many modern demosponges are also characterized by the presence of siliceous spicules, and there are no convincing demosponge spicules in strata older than the Cambrian. This temporal disparity highlights a problem with our understanding of the Precambrian fossil record – either these supposed demosponge-specific biomarkers were derived from the sterols of some other organism and are simply retained in modern demosponges, or spicules do not primitively characterize crown-group demosponges. Resolving this issue requires resolving the phylogenetic placement of another group of sponges, the hexactinellids, which not only make a spicule thought to be homologous to the spicules of demosponges, but also make their first appearance near the Precambrian/Cambrian boundary. Using two independent analytical approaches and data sets – traditional molecular phylogenetic analyses and the presence or absence of specific microRNA genes – we show that demosponges are monophyletic, and that hexactinellids are their sister group (together forming the Silicea). Thus, spicules must have evolved before the last common ancestor of all living siliceans, suggesting the presence of a significant gap in the silicean spicule fossil record. Molecular divergence estimates date the origin of this last common ancestor well within the Cryogenian, consistent with the biomarker record, and strongly suggests that siliceous spicules were present during the Precambrian but were not preserved.     

Testing the phylogenetic position of Cambrian pancrustacean larval fossils by coding ontogenetic stages

The study of ontogeny as an integral part of understanding the pattern of evolution dates back over 200 years, but only recently have ontogenetic data been explicitly incorporated into phylogenetic analyses. Pancrustaceans undergo radical ontogenetic changes. The spectacular upper Cambrian “Orsten” fauna preserves phosphatized fossil larvae, including putative crown‐group pancrustaceans with amazingly complete developmental sequences. The putative presence and nature of adult stages remains a source of debate, causing spurious placements in a traditional morphological analysis. We introduce a new coding method where each semaphoront (discrete larval or adult stage) is considered an operational taxonomic unit. This avoids a priori assumptions of heterochrony. Characters and their states are defined to identify changes in morphology throughout ontogeny. Phylogenetic analyses of semaphoronts produced possible relationships of each Orsten fossil to the crown‐group clade expected from morphology shared with extant larvae. Bredocaris is a member of the stem lineage of Thecostraca or (Thecostraca + Copepoda), and Yicaris and Rehbachiella are probably members of the stem lineage of Cephalocarida. These placements rely directly on comparisons between extant and fossil larval character states. The position of Phosphatocopina remains unresolved. This method may have broader applications to other phylogenetic problems which may rely on ontogenetically variable homology statements.     

Early sponge evolution: A review and phylogenetic framework

Sponges are one of the critical groups in understanding the early evolution of animals. Traditional views of these relationships are currently being challenged by molecular data, but the debate has so far made little use of recent palaeontological advances that provide an independent perspective on deep sponge evolution. This review summarises the available information, particularly where the fossil record reveals extinct character combinations that directly impinge on our understanding of high-level relationships and evolutionary origins. An evolutionary outline is proposed that includes the major early fossil groups, combining the fossil record with molecular phylogenetics. The key points are as follows. (1) Crown-group sponge classes are difficult to recognise in the fossil record, with the exception of demosponges, the origins of which are now becoming clear. (2) Hexactine spicules were present in the stem lineages of Hexactinellida, Demospongiae, Silicea and probably also Calcarea and Porifera; this spicule type is not diagnostic of hexactinellids in the fossil record. (3) Reticulosans form the stem lineage of Silicea, and probably also Porifera. (4) At least some early-branching groups possessed biminerallic spicules of silica (with axial filament) combined with an outer layer of calcite secreted within an organic sheath. (5) Spicules are homologous within Silicea, but also between Silicea and Calcarea, and perhaps with Homoscleromorpha. (6) The last common ancestor of extant sponges was probably a thin-walled, hexactine-bearing sponge with biminerallic spicules. (7) The stem group of sponges included tetraradially-symmetric taxa that grade morphologically into Cambrian fossils described as ctenophores. (8) The protomonaxonid sponges are an early-branching group, probably derived from the poriferan stem lineage, and include the problematic chancelloriids as derived members of the piraniid lineage. (9) There are no definite records of Precambrian sponges: isolated hexactine-like spicules may instead be derived from radiolarians. Early sponges had mineralised skeletons and thus should have a good preservation potential: the lack of sponge fossils in Precambrian strata may be due to genuine absence of sponges. (10) In contrast to molecular clock and biomarker evidence, the fossil record indicates a basal Cambrian diversification of the main sponge lineages, and a clear relationship to ctenophore-like ancestors. Overall, the early sponge fossil record reveals a diverse suite of extinct and surprising character combinations that illustrate the origins of the major lineages; however, there are still unanswered questions that require further detailed studies of the morphology, mineralogy and structure of early sponges.     

Carboniferous Onychophora from Montceau‐les‐Mines,France, and onychophoran terrestrialization

The geological age of the onychophoran crown‐group, and when the group came onto land, have been sources of debate. Although stem‐group Onychophora have been identified from as early as the Cambrian, the sparse record of terrestrial taxa from before the Cretaceous is subject to contradictory interpretations. A Late Carboniferous species from the Mazon Creek biota of the USA, Helenodora inopinata, originally interpreted as a crown‐group onychophoran, has recently been allied to early Cambrian stem‐group taxa. Here we describe a fossil species from the Late Carboniferous Montceau‐les‐Mines Lagerstätte, France, informally referred to as an onychophoran for more than 30 years. The onychophoran affinities of Antennipatus montceauensis gen. nov., sp. nov. are indicated by the form of the trunk plicae and the shape and spacing of their papillae, details of antennal annuli, and the presence of putative slime papillae. The poor preservation of several key systematic characters for extant Onychophora, however, prohibits the precise placement of the Carboniferous fossil in the stem or crown of the two extant families, or the onychophoran stem‐group as a whole. Nevertheless, A. montceauensis is the most compelling candidate to date for a terrestrial Paleozoic onychophoran.     

Systematics and phylogenetic implications of the haplosclerid stromatoporoid Newellia mira nov. gen.

Wood, Rachel, Reitner, Joachim & West, Ronald R. 1989 01 15: Systematics and phylogenetic implications of the haploslerid stromatoporoid Newellia mira nov. gen. Lethaia, Vol. 22, pp. 85–93. Oslo. ISSN 0024–1164. The presence of spicules in a Palaeozoic stromatoporoid is here confirmed. Parallelopora mira Newell, 1935 from the Upper Carboniferous of the U.S.A. is redescribed as a calcified haplosclerid sponge with a primary siliceous spicule framework of isodictyally arranged styles, sub-tylostyles and strongyles and a secondary calcareous skeleton of stromatoporoid grade and probable aragonitic original mineralogy. P. mira is placed within a new genus Newellia, and family, the Newellidae. This form is postulated to have possessed large amounts of collagenous organic material which enveloped and bound the spicular framework in place. By the draping outline of the calcareous skeleton around the spicule framework and by analogy with the Recent demosponge genus Vaceletia, the calcareous skeleton is suggested to have formed by the direct mineralization of this collagenous template. Newellia mira nov. gen. is further proposed to constitute a member of a new clack of haplosclerid stromatoporoids, together with Euz-Miella erenoensis (Lower Cretaceous); a clade with some similarity to Recent non-calcified forms, e.g. Adocia. Most notably, the presence of different calcareous skeleton mineralogies and possibly microstructures in these two forms suggests the independent development of a calcareous skeleton at different times within this spicule clade. Demosponges appear to have produced calcareous skeletons independently in many different spicule clades. Calcified demosponges are now known from the Hadro-merida (Lower carboniferous; Upper Cretaceous - Recent), Axinellida (Upper Triassic - Lower Cretaceous; Upper Cretaceous; Recent), Poecilosclerida (Recent) as well as the Haplosclerida (Upper Carboniferous - Lower Cretaceous; Recent).□Upper Carboniferous, stromatoporoid, spicules, haplosclerid demosponges, calcareous skeleton biomineralization, demosponge clades, polyphyly.     

A placozoan affinity for Dickinsonia and the evolution of late Proterozoic metazoan feeding modes

SUMMARY Dickinsonia is one of the most recognizable forms in the Ediacaran fauna, but its phylogenetic position has been contentious, and it has been placed in almost every kingdom of life. Here, it is hypothesized that the affinities of Dickinsonia lie with the Placozoa (Metazoa), an understudied phylum that is widespread in tropical seas worldwide. Modern placozoans show obvious differences in size and axial organization compared with Dickinsonia, but these differences can be accounted for by the stem‐group/crown‐group distinction. The affinity with placozoans is evidenced primarily by the unique feeding mode of Dickinsonia, which is demonstrated by a series of feeding traces. These traces indicate that Dickinsonia moved over the Ediacaran matgrounds, and digested the mat using its entire lower sole. The ability of Dickinsonia to move negates an algal, fungal, or sponge affinity, while the feeding mode, external digestion with a ventral sole, rules out placement within any sponge or eumetazoan lineage. The only organisms that both move and feed in this manner are placozoans. Recent molecular phylogenetic studies have demonstrated that placozoans lie above sponges but below Eumetazoa. We hypothesize that Dickinsonia and other externally digesting Ediacaran forms are either stem‐placozoans, or a series of extinct lineages above sponges and below eumetazoans on the metazoan tree. We discuss the potential evolutionary transitions between the main metazoan feeding modes in the context of the emerging molecular phylogeny, and suggest that aspects of the sponge and placozoan feeding strategies are relicts of nonuniformitarian Proterozoic ocean conditions.     

An early Cambrian polyp reveals a potential anemone-like ancestor for medusozoan cnidarians

Cnidarians form a disparate phylum of animals and their diploblastic body plan represents a key step in animal evolution. Cnidarians are split into two main classes; anthozoans (sea anemones, corals) are benthic polyps, while medusozoans (hydroids, jellyfishes) generally have alternating life cycle stages of polyps and medusae. A sessile polyp is present in both groups and is widely regarded as the ancestral form of their last common ancestor. However, the nature and anatomy of the ancestral polyp, particularly of medusozoans, is controversial, owing to the divergent body plans of the extant lineages and the scarcity of medusozoan soft tissues in the fossil record. Here, we redescribe Conicula striata Luo & Hu from the early Cambrian Chengjiang biota, south China, which has previously been interpreted as a polyp, lophophorate or deuterostome. Through re-examination of the holotype and 51 exceptionally preserved specimens, we show that C. striata possessed features of both anthozoans and medusozoan polyps. A conical, annulated organic skeleton (periderm) fully encasing a polyp is found in fossil and living medusozoans, while a tubular pharynx extending from the mouth into a gut partitioned by c. 28 mesenteries, resembling the actinopharynx of anthozoans. Our phylogenetic analyses recover C. striata as a stem-group medusozoan, implying that the wealth of medusozoan diversity derived, ultimately, from an anemone-like ancestor.     

Middle and Late Cambrian sponge spicules from Hunan, China

Abundant and well-preserved assemblages of disarticulated sponge spicules occur in Middle and Late Cambrian platform carbonates of western Hunan, China. Assemblages recovered from 11 stratigraphic horizons include calcisponges, demosponges, and hexactinellids. Hexactinellida, in particular, are both abundant and diverse in Upper Cambrian carbonates. Comparison with spicule assemblages from Australia indicates that many of these taxa have long stratigraphic ranges, limiting their use in correlation. The morphological diversity of these spicules exceeds that known for living siliceous sponges, supporting the observation that during the Cambrian radiation, sponges, like other metazoans, evolved a variety of architectural forms not observed in later periods. Like conodonts, individual sponges can produce more than one spicule form; thus, an "apparatus genus" concept based on multiple co-occurring elements may eventually prove useful in the biostratigraphic and paleobiological interpretation of disarticulated sponge spicules. Four distinctive forms are recognized as new taxa: Australispongia sinensis new genus and species, Flosculus gracilis new genus and species, Pinnatispongia bengtsoni new genus and species, and Nabaviella paibiensis new species.     

Carbonaceous preservation of Cambrian hexactinellid sponge spicules

Early fossil sponges offer a direct window onto the evolutionary emergence of animals, but insights are limited by the paucity of characters preserved in the conventional fossil record. Here, a new preservational mode for sponge spicules is reported from the lower Cambrian Forteau Formation (Newfoundland, Canada), prompting a re-examination of proposed homologies and sponge inter-relationships. The spicules occur as wholly carbonaceous films, and are interpreted as the remains of robust organic spicule sheaths. Comparable sheaths are restricted among living taxa to calcarean sponges, although the symmetries of the fossil spicules are characteristic of hexactinellid sponges. A similar extinct character combination has been documented in the Burgess Shale fossil Eiffelia. Interpreting the shared characters as homologous implies complex patterns of spicule evolution, but an alternative interpretation as convergent autapomorphies is more parsimonious. In light of the mutually exclusive distributions of these same characters among the crown groups, this result suggests that sponges exhibited an early episode of disparity expansion followed by comparatively constrained evolution, a pattern shared with many other metazoans but obscured by the conventional fossil record of sponges.     

Description of a new long‐snouted beaked whale from the Late Miocene of Denmark: evolution of suction feeding and sexual dimorphism in the Ziphiidae (Cetacea: Odontoceti)

A new genus and species of Ziphiidae, Dagonodum mojnum gen. nov., sp. nov., from the upper Miocene Gram Formation (c. 9.9–7.2 Ma) represents the first occurrence of the family in Denmark. This long‐snouted ziphiid is characterized by two pairs of mandibular tusks, the Eustachian outlet that approximately levels with the dorsalmost margin of the posterior portion of the involucrum, and the left trapezoid nasal with a posteromedial projection into the frontal. A phylogenetic analysis including 25 species and 69 characters was conducted. Dagonodum mojnum is placed in a basal ziphiid clade as the sister taxon of Messapicetus. The specimen is probably a male, because it has enlarged tusks. Alternatively, females could also be involved in fights and develop erupted tusks as in the extant Berardius. Although less well supported, this interpretation proposes that aggressive interactions were not restricted to males in stem‐ziphiids. With a thickened thyrohyal and the presence of a precoronoid crest, D. mojnum was able to use suction feeding, but was less specialized to it compared to extant ziphiids. The elongated neck of D. mojnum less optimized to perform deep dives, and the shallow depth at which the Gram Formation was deposited corroborates the hypothesis that at least part of the stem‐ziphiids were not regular deep divers.     

Fedomia mikhaili—A new spicule-bearing organism of sponge grade from the Vendian (Ediacaran) of the White Sea, Russia

The Vendian fossil locality on the Solza River is one of the most productive in the White Sea Region. The fossiliferous deposits belong to the Upper Vendian Verkhovka Formation correlated lithologically with strata dated at 558 ± 1 to 555.3 ± 0.3 Ma in adjacent regions. This locality is characterized by yielding more than 10 well-represented Ediacaran genera. Elongated imprints of Fedomia mikhaili, n. gen. et n. sp., are common at the Solza River fossil locality. The new taxon is characterized by its six- to eight-rayed star-shaped concave structures with diameters of 2–5 mm. The organism can be reconstructed with sacciform thin-walled body attached basally to the substrate. The star-shaped structures may be spicules that appear to be rather flexible than rigid. The new genus, Fedomia, shows some similarities to Eiffelia Walcott, 1920 from the Middle Cambrian of British Columbia, and thus is interpreted as an organism of sponge grade. The new taxon could represent an additional phylogenetic link between the Ediacaran and Cambrian worlds.     

Early divergence dates of demosponges based on mitogenomics and evaluated fossil calibrations

Demosponges are among the most primitive biomineralized metazoans to appear first in the fossil record with hard skeletons; their confirmed earliest fossils are from the lower Cambrian rocks about 520 Ma, with putative demosponge biomarkers reported from 713 to 635 Ma sediments. In this study, we use mitogenomic data to approach the early divergence timescale of demosponges using relaxed molecular clock techniques and likelihood-evaluated fossil calibration strategies. We found that among various molecular dating models, the correlated rate model yielded time estimates of demosponges in this analysis which is most congruent with the fossil appearance dates of demosponges. Our dating analyses show that crown groups of Demospongiae appeared at about 704 (674–741) Ma, and the silicification in demosponges (divergence of spicular sponges) began about 633 (616–648) Ma indicating a gap of over 100 million years between the origin of silicification and their first unequivocal appearance of siliceous spicules in the fossil record (520–525 Ma); demosponges with tetraxon-type spicules (Tetractinellida) are dated here at about 514 (498–530) Ma, an estimate comparable with the earliest tetraxial megasclere fossil records (510–520 Ma, Ordian Age, middle Cambrian).     

The biology of the marine sponge Microciona prolifera (Ellis and Solander). III. Spicule secretion and the effect of temperature on spicule size

The secretion of siliceous spicules in the marine demosponge Microciona prolifera (Ellis and Solander) is by three different means. Styles are secreted by sclerocytes with archeocyte characteristics (nucleolate nucleus, phagosomes). chelas are formed by small sclerocytes with anucleolate nuclei, and toxas are apparently formed extracellularly within membranous material. Genetically and physiologically equivalent explants of this sponge were grown at 15, 20, and 25 C for four weeks. Analyses of spicule dimensions show little correlation of temperature with spicule length, except in the case of toxas. but a clear inverse relationship of spicule width with temperature. It is suggested that thicker spicules are formed at lower temperatures due to the more efficient entrapment of silicon rather than to effects upon silicon transport. Chela dimensions are very uniform implying an all or none process in their secretion. Differences in spicule dimensions between individual sponges grown at these temperatures may be due to the highly complex pathways of silicon transport and/or to genetic differences.     

Discordance between morphological and molecular species boundaries among Caribbean species of the reef sponge Callyspongia

Sponges are among the most species‐rich and ecologically important taxa on coral reefs, yet documenting their diversity is difficult due to the simplicity and plasticity of their morphological characters. Genetic attempts to identify species are hampered by the slow rate of mitochondrial sequence evolution characteristic of sponges and some other basal metazoans. Here we determine species boundaries of the Caribbean coral reef sponge genus Callyspongia using a multilocus, model‐based approach. Based on sequence data from one mitochondrial (COI), one ribosomal (28S), and two single‐copy nuclear protein‐coding genes, we found evolutionarily distinct lineages were not concordant with current species designations in Callyspongia. While C. fallax, C. tenerrima, and C. plicifera were reciprocally monophyletic, four taxa with different morphologies (C. armigera, C. longissima, C. eschrichtii, and C. vaginalis) formed a monophyletic group and genetic distances among these taxa overlapped distances within them. A model‐based method of species delimitation supported collapsing these four into a single evolutionary lineage. Variation in spicule size among these four taxa was partitioned geographically, not by current species designations, indicating that in Callyspongia, these key taxonomic characters are poor indicators of genetic differentiation. Taken together, our results suggest a complex relationship between morphology and species boundaries in sponges.