A Hypothesis on Suspension Feeding in Early Chelicerates (Offacolidae)

Abstract

The Cambrian–Ordovician Plankton Revolution played a crucial role in the Great Ordovician Biodiversification Event (GOBE) or Ordovician Radiation, as a driver of diversification. The emergence of new planktonic species enhanced primary productivity and improved nutrient cycling, fueling diversification across trophic levels. In this context, established plankton consumers like sponges and cnidarians thrived, and animals like euarthropods also radiated in response to these environmental conditions. Here, we hypothesize that Offacolidae, a small group of early chelicerates (the group including sea spiders, spiders, mites, and horseshoe crabs) known from the early Ordovician to the end of the Silurian, were suspension feeders that diversified within this changing ecosystem. Extant chelicerates are primarily predators or parasites, with no known cases of suspension feeding, which is also the case in extinct members. However, anatomical and environmental evidence suggest that Offacolidae may have adopted this feeding strategy. We examine the environmental conditions in which Offacolidae fossils were found, considering both biotic and abiotic factors such as paleolatitude, bathymetry, and the associated plankton community. We also assess the possible biomechanics of their unique appendages to determine their suitability for suspension feeding. Finally, comparisons with extant arthropods, such as the suspension-feeding crustaceans Limnomysis benedeni, Atya gabonensis, Subeucalanus pileatus, and the genus Emerita, provide insights into possible evolutionary analogies in their morphology, which may have served the same function. If confirmed, this hypothesis would make Offacolidae a unique case within chelicerates, illustrating how exceptional early Ordovician conditions fostered novel ecological adaptations and highlighting an interesting case of analogy between different lineages of euarthropods.

1. Introduction

The Cambrian–Ordovician Plankton Revolution marked a major turning point in marine ecology [1,2] and played a key role in shaping modern marine ecosystems [3]. During this time, a significant increase in phytoplankton primary production (e.g., acritarchs)—likely driven by a rise in nutrient availability in the water column—fueled the diversification of several zooplankton groups (e.g., radiolarians, graptolites, chitinozoans) [1,4]. The Cambrian–Ordovician Plankton Revolution (alongside other factors, e.g., [2,5,6]) contributed to triggering the so-called Great Ordovician Biodiversification Event (GOBE) or Ordovician Radiation, with many different animal groups radiating to colonize the water column during the same period [7,8,9,10]. Organisms such as radiolarians and graptolites underwent major evolutionary shifts, moving from bottom-dwelling (benthic) lifestyles to free-floating (planktonic—while ‘planktic’ is the proper derivative of the Greek, ‘planktonic’ is more widely used [11,12]) modes of life [1,13]. Even arthropods contributed to this ecological revolution; they likely played vital roles in early planktonic food webs, especially their larval stages as both main components and consumers [14,15]. This was already the case in the Cambrian [16], and they still play a major role nowadays [17]. The larvae of megacheiran arthropods have been interpreted as suspension feeders, possibly occupying a different ecological niche than the adults [18], while crustacean species entered the planktonic realm, likely filling mid-water ecological niches [14], and the larvae of several trilobite species were probably major components of the zooplankton as well [19,20]. Radiodonts, a group of large arthropod-related predators, diversified into suspension feeders and took advantage of the abundance of plankton [21,22,23,24], filling ecological niches similar to those of modern whales [25]. Suspension feeding is a food-gathering strategy consisting of capturing and ingesting food particles that are suspended in the water column. Suspension feeders feed alike on phytoplankton, zooplankton, bacteria, or detritus, and almost all the major groups of animals include species that suspension feed [26]. Suspension feeders can be broadly divided into passive types, which rely on ambient flow to capture particles—such as barnacles, crinoids, sponges, and corals—and active types, which generate their own feeding currents, typically including most suspension feeding arthropods [27]. This feeding strategy has been extensively studied, with fluid dynamics playing a crucial role in understanding its mechanisms. In this context, Rubenstein and Koehl [28] presented a theoretical framework based on Reynolds number and appendage motion, offering insights into particle capture beyond the simple concept of mesh or comb size and the pure anatomical comparisons. The increase in the number of suspension-feeding animals can be correlated to the growing complexity of planktonic communities [1,29]. As such, suspension-feeding animals are often associated with highly productive water bodies, which may provide them with a huge plankton community to feed on. Modern high-latitude waters and their richness of nutrients are one such example of a plankton-rich environment [30] in which suspension feeders thrive [31].

As for today, one group of well-established arthropods does not appear to have actively participated in the Cambrian–Ordovician planktonic revolution, neither as components of the plankton during their early developmental stages, nor as primary consumers of it as filter-feeding organisms. This is the case for chelicerates, a group of arthropods that are generally predators, opportunists, or parasites. Chelicerates include sea spiders, horseshoe crabs, arachnids, and the extinct eurypterids, chasmataspids, and synziphosurines. Synziphosurines have been considered for a long time as a suborder of the Xiphosura [32,33,34]. Subsequently, they have been shown to be a paraphyletic group including various forms scattered into the euchelicerates phylogeny [35]. The discovery of the anatomy of the appendages of some synziphosurines [36,37,38,39,40] has finally allowed researchers to group some of them into a monophyletic family at the root of Euchlicerata (Chelicerata minus Pycnogonida), the Offacolidae [36,39]. Offacolidae is a family made of four different genera: Setapedites abundantis [40] from the Lower Ordovician Fezouata Shale of Morocco [41]; Dibasterium durgae and Offacolus kingi from the middle Silurian Wenlock Series Lagerstätte of Herefordshire in the UK [36,37,38], and the most recent occurrence of the group is Bunaia woodwardi from the upper Silurian Bertie formation of Canada and the United States [39,42]. Offacolidae are minute chelicerates, with a known length of 4 to 32 mm. They all share a body made of a cephalic shield (Prosoma), a pre-abdomen, and an abdomen, ending with a bifurcated telson spine. On the ventral side, they show tiny, elongated chelicerae and biramous appendages in the prosoma. Book gills are present in the pre-abdomen. One of the main characters that distinguishes Offacolidae from other euchelicerates (called Prosomapoda, sensu [35]) is stenopodous exopods of six podomeres bearing a brush-like group of long and radially arranged setae on the distalmost podomere [40]. While the feeding habits and mechanics of other groups of chelicerates are well known [43,44,45], the function of the stenopodous exopods with setae of Offacolidae and the feeding strategies and ecology of the organisms bearing them remain unexplored. The only mention of feeding behavior in these animals concerns Offacolus, which was previously hypothesized to be a bottom-dwelling feeder [37]. However, this interpretation was proposed before its redescription and was based on an inaccurate initial understanding of its anatomy and a less precise systematic placement compared to its later reassessment [36].

Here, we present the hypothesis that Offacolidae were the only known suspension-feeding members of Chelicerata and expose the observations on which our hypothesis is based. First, we examine the anatomy of Offacolidae, including the stenopodous exopods bearing elongated setae. Second, we will explore paleoenvironmental data from the three Lagerstätten where Offacolidae fossils are known. Third, we analyze the paleobiogeographical patterns of those Lagerstätten. Fourth, we consider the chronological span in which Offacolidae fossils have been retrieved. These lines of observation will form the foundation of our hypothesis. We also integrate this information into a coherent ecological model for Offacolidae. Finally, we suggest two different approaches to test our hypothesis. The first approach would rely on the discovery of new evidence while the second, involves testing the biomechanical capabilities of Offacolidae. This work not only strengthens the interpretive framework for Offacolidae ecology and evolution but also demonstrates the value of hypothesis-driven research in paleobiology.

2. Observations

2.1. Observations on the Anatomy of Offacolidae

(1) Morphology of the chelicerae in Offacolidae: The chelicerae in Offacolidae are slender but likely extensively motile, presenting three (possibly four) elongated articles [40] (Figure 1). This is the case for all four known species belonging to the family [36,37,38,39,40]. Dibasterium and Offacolus present more elongated chelicerae than Setapedites and B. woodwardi.

(2) Measurements of Offacolidae setae maximum span: Fossil measurements were collected from figures available in the literature of already published specimens using ImageJ software, version 1.53k. The specimens measured are those of Figure 1 and Figure 2. One specimen (OUMNH C.29640) of Dibasterium, one specimen (MGL. 102247a) of Setapedites, and one specimen (OUM C.29557) of Offacolus were considered. The maximum space between setae is 0.20 mm for Setapedites, 0.40 mm for Dibasterium, and 0.28 mm for Offacolus; no measurements are available for B. woodwardi since no specimens show the brush-like setae.

(3) Setae topology: The setae are located on the exopods and not on the endopods. The endopods are naturally ventrally oriented, while the exopods are latero-dorsally oriented (Figure 1). In Offacolus, the exopods are dorso-frontally oriented (Figure 1), while the least clearly distinguished dorso-frontally oriented exopods are present in Dibasterium.

(4) Reduced gnathobases: The gnathobases of Offacolidae are typically reduced if compared with those of possible related Cambrian chelicerates such as Habelia optata and Mollisonia plenovenatrix [46,47], Ordovician chelicerates [48], or with modern horseshoe crabs [49,50]. This is the case for all four known species belonging to the family [36,37,38,39,40], but this pattern is remarkably well documented in Setapedites [40].

(5) Absence of eyes: No evidence for compound eyes has been found in Offacolidae. This is the case for all four known species belonging to the family [36,37,38,39,40]. However, B. woodwardi may possess simple ocelli on the ventral side [32,39].

Figure 2. Compared morphology of Offacolidae exopodites with modern crustacean endopodites. (A) The extant shrimp Atya gabonensis, photo credits Andre Montaut (Shrimply Canadian); (B) the extant shrimp Limnomysis benedeni, modified from Borza et al., 2023 [51]; (C) Specimen OUM C.29557 of Offacolus kingii in frontal view, modified from sketchfab.com (accessed on 20 March 2025) and Sutton et al., 2002 [36]; (D) Specimen OUM C.29557 of Offacolus kingii, detail of exopodial setae, modified from sketchfab.com and Sutton et al., 2002 [36]; (E) Specimen OUMNH C.29640 of Dibasterium durgae, detail of exopodial setae in green, endopod in blue, modified from Briggs et al., 2012 [38]; (F) Specimen MGL. 102247a of Setapedites abundantis, detail of the exopodial setae, modified from Lustri et al., 2024 [40]; (G) Emerita analoga by Peter J. Bryant (Natural History of Orange County); (H) Emerita talpoida by Eric A. Lazo-Wasem (Yale Peabody Museum), specimen YPM IZ 085053. Scale: (B) 200 μm; (C) 0.5 mm; (D) 0.25 mm; (E) 2 mm; (F) 0.5 mm; (H) 5 mm.

Figure 2. Compared morphology of Offacolidae exopodites with modern crustacean endopodites. (A) The extant shrimp Atya gabonensis, photo credits Andre Montaut (Shrimply Canadian); (B) the extant shrimp Limnomysis benedeni, modified from Borza et al., 2023 [51]; (C) Specimen OUM C.29557 of Offacolus kingii in frontal view, modified from sketchfab.com (accessed on 20 March 2025) and Sutton et al., 2002 [36]; (D) Specimen OUM C.29557 of Offacolus kingii, detail of exopodial setae, modified from sketchfab.com and Sutton et al., 2002 [36]; (E) Specimen OUMNH C.29640 of Dibasterium durgae, detail of exopodial setae in green, endopod in blue, modified from Briggs et al., 2012 [38]; (F) Specimen MGL. 102247a of Setapedites abundantis, detail of the exopodial setae, modified from Lustri et al., 2024 [40]; (G) Emerita analoga by Peter J. Bryant (Natural History of Orange County); (H) Emerita talpoida by Eric A. Lazo-Wasem (Yale Peabody Museum), specimen YPM IZ 085053. Scale: (B) 200 μm; (C) 0.5 mm; (D) 0.25 mm; (E) 2 mm; (F) 0.5 mm; (H) 5 mm.

2.2. Observations on the Geological, Chronological, Paleoenvironmental, and Paleogeographical Contexts of Offacolidae

(1) Fezouata biota: Specimens of Setapedites occur in the Lower Ordovician Fezouata Shale [13,52], in the Zagora province of the Moroccan Anti-Atlas [41,53]. This formation is composed of a ~1000 m thick succession of siltstone and mudstone [13,54,55,56]. The Fezouata Shale contains two main fossiliferous intervals that are Tremadocian and Floian in age, respectively [57,58]. Setapedites specimens are found in the Tremadocian fossiliferous interval [2,13,58,59]. From a paleoenvironmental perspective, the Fezouata Shale has been interpreted as a shallow marine environment dominated by wave and storm processes [54,60,61]. A well-developed suspension-feeding community within the Fezouata biota is documented (e.g., [21,61,62]). In the Fezouata Shale, animals were dead and decaying on the seafloor prior to their burial by storm or storm-induced deposits [56]. Following their burial, chemical conditions were conducive to authigenic pyritization or the replication of soft anatomies that survived pre-burial decay by pyrite minerals. This biota has been tentatively assigned to a polar latitude between 66 and 90° S in Western Gondwana [20,63].

(2) Williamsville Formation of the Bertie Group: Specimens of B. woodwardi occur in the Bertie Group, which extends from eastern New York to Ontario [64]. This unit consists of Silurian (middle–upper Pridoli) massive dolostones interbedded with occasional waterlime beds [65,66,67]. It includes several formations, among which the uppermost is the Williamsville Formation, the unit yielding B. woodwardi specimens. The Williamsville Formation is composed of laminated fine-grained dolostones and dolomitic mudstones, with lateral facies variation [65]. From a paleoenvironmental perspective, the Williamsville Formation has been interpreted to represent predominantly brackish to marine intertidal settings (occasionally becoming hypersaline) [68,69]. The exceptional preservation of the fossils was due to low oxygen levels, slightly anoxic environments of the Bertie Group, and possibly low temperature [70,71]. The Williamsville Formation has been tentatively assigned to a low paleolatitude between Laurentia and Avalonia [71,72].

(3) Herefordshire Lagerstätte: Specimens of Dibasterium and Offacolus occur in the Herefordshire Lagerstätte, located in the Welsh Basin, South Wales, UK. This deposit is lower Silurian in age. In this deposit, fossils are exceptionally preserved as calcitic void infills in early diagenetic carbonate concretions with a volcanistic horizon [73]. From a paleoenvironmental perspective, the Herefordshire Lagerstätte represents an outer shelf to upper slope setting [73]. Several species of radiolarians have been documented from this formation [74,75]. The Herefordshire Lagerstätte was deposited in tropical/subtropical paleolatitudes [76] and is probably one of the best sites to preserve exceptional fossils within concretions [77].

3. Discussion

3.1. Was the Anatomy of Offacolidae Suitable for a Suspension Feeder Feeding Strategy?

The chelicerae of Offacolidae were not adapted for a predatory lifestyle. Their slender shape [31,32,33,34,35] made them ineffective at immobilizing and penetrating or dismembering prey of a reasonable size. Their relatively small size compared to the body also suggests they were not well-suited for scavenging carcasses of animals similar in size, unless those remains were in an advanced state of decay, as they would have been unable to penetrate any protective coverings. On the other hand, their shape and size, likely allowing a high degree of mobility, could have enabled them to quickly capture and transfer small food particles to the mouth. As for the postcheliceral limb, the exopodites were associated with an endopodite, which likely served as the primary structure for locomotion. This interpretation is supported by the general role of endopods in arthropods for walking, as well as their inner positioning, oriented towards the ground. In contrast, exopods are typically not used for walking and are rather used for swimming, but this seems unlikely in the case of the elongated, slender, stenopodous exopods of Offacolidae. Moreover, their orientation in Offacolidae (latero-dorsal or dorsal, see Figure 2) makes them unsuitable for walking, and the absence of chelae may have made it difficult to use them in manipulating food. Furthermore, the exopods of Offacolidae are not oriented towards the substrate, favoring the exclusion of sediment sifting activities. Given their lack of a clear locomotory or respiratory role, a food-gathering function seems the most likely alternative. The probable ability of the chelicerae to reach the mouth could have worked in combination with the brush-like endites of the exopodial branches, which represent an adapted structure to trap particles in suspension. The chelicerae might then have been used to collect these trapped particles and bring them to the mouth. This interpretation is further supported by the maximum spacing measured between the setae observed in Dibasterium, Offacolus, and Setapedites, which falls in the suitable range for collecting mesoplankton (Figure 3). The measurements of setae and mesh-like structure maximum space have already been used to infer suspension feeding habits in extinct arthropods [21,22,23,24,78,79] and represent a further strong argument to sustain the hypothesis of suspension feeding in Offacolidae. Reduced gnathobases in the group also support the idea that they were unable to crush hard shells or manipulate food on the ventral side, as is typically done by arthropods feeding on particles on the substrate. Finally, the lack of evidence for compound eyes in all known species of Offacolidae suggests they may have relied on tactile strategies for food gathering, possibly in a stationary position, which would be consistent with the use of exopodite setae to collect suspended particles.

Figure 3. Measurements of Offacolidae setae maximum span and possible associated plankton size. Measurements of Setapedites, Offacolus, and Dibasterium overimposed on the modified graph shown in Potin et al., 2023 [21], modified from Vinther et al., 2014 [80]. Outline illustration of Offacolus and Dibasterium from phylopic.org.

Figure 3. Measurements of Offacolidae setae maximum span and possible associated plankton size. Measurements of Setapedites, Offacolus, and Dibasterium overimposed on the modified graph shown in Potin et al., 2023 [21], modified from Vinther et al., 2014 [80]. Outline illustration of Offacolus and Dibasterium from phylopic.org.

A comparison between the anatomy of Offacolidae and that of extant suspension-feeding crustaceans further supports the hypothesis of a suspension-feeding lifestyle for Offacolidae. Among the many possible examples of suspension-feeding crustaceans [81], we examine the shrimps Limnomysis benedeni (Malacostraca, Mysidae) and Atya gabonensis (Malacostraca, Atyidae), the copepods Subeucalanus pileatus (Copepoda, Eucalanidae), and the mole crabs of the genus Emerita (Malacostraca, Hippidae), as potential analogs for suspension-feeding adaptations. Limnomysis benedeni has been reported to primarily filter water by generating a current that passes through the center of the gnathobase, which is equipped with fine setae that trap suspended particles [51]. These particles are then transported to the mouth by the gnathobase [51]. This mechanism is not supported for Offacolidae, due to the reduced gnathobases. However, the second thoracic endopod in L. benedeni also bears a brush of setae on the endite (Figure 2), which has been proposed to directly capture suspended particles and transfer them to the mouth [51]. This second behavior can be considered analogous to the principal mechanism adopted by Offacolidae for gathering suspended particles from the water column. Likely, Offacolidae performed this direct capture of suspended particles in a more efficient way due to the use of more appendages (up to five [40]) and assistance of the chelicerae. Atya gabonensis is one such example of modern arthropods relying mainly on a direct capture of particles with well-adapted modified endites (Figure 2) on the appendages. In A. gabonensis, the first and second chelipeds are equipped with chelae covered in fine, soft setae that serve as a filtering apparatus [82], and are similarly used to directly collect suspended particles from the water [78]. We propose a similar function to those of the second thoracic endopod of L. benedeni and those of the highly specialized appendages of A. gabonensis for the stenopodus exopods of the members of the family Offacolidae. The suspension feeding mechanisms in the copepods Subeucalanus pileatus have been extensively studied and represent another insightful comparison. Subeucalanus pileatus, like other copepods, directs the water flow with food particles toward itself by moving four pairs of small limbs. When food gets close, it uses another pair of short limbs, the second maxillae, which have long bristles covered with tiny barbs, to catch the food. These limbs open up to let water in, then close tightly, pushing water out only through the small gaps between the bristles. This traps the food particles inside a sort of “basket” made by the bristles [83]. Whether or not an active creation of water flow during feeding was present in offacolids is beyond pure anatomical comparison and will require adequate study. However, what seems clear is that this strategy would require a pelagic lifestyle, which does not fit well with the anatomy of Offacolidae, which appear more suited for bottom-dwelling and a substrate-based suspension feeding activity. This is the case, for example, with the elongated telson, which could have acted as an anchorage, or the stout body shape of Offacolus. Indeed, the most compelling comparison is between Offacolus and the mole crabs. The genus Emerita (Figure 2G,H), as an example, shows an enlarged cephalic carapace as in Offacolus, with a series of appendages with setae protruding from the frontal part and being exposed in a passive way toward the sea currents [84], while the rest of the body is reduced, with the capability of enrolling on itself. The anatomies of Offacolus and the genus Emerita may represent a case of convergent evolution, reflecting anatomical adaptations that arose in order to exploit bottom, environmentally current-based suspension feeding mechanisms. This comparison suggests that Offacolus was the more specialized suspension feeder of the family, in accordance with its more developed exopods and reduced post-cephalic body. The last point worth mentioning is the fact that mole crabs are intertidal organisms [84]. While we will not assume such a behavior in Offacolus since it is not in accordance with its paleoenvironment, this could potentially have been the case for B. woodwardi, which inhabited tidal environments.

3.2. Was the Environment Inhabited by Offacolidae Suitable for a Suspension Feeder Feeding Strategy?

Offacolidae have been known from the late Tremadocian to the late Pridoli. This means they have evolved at the peak and through all of the plankton revolution [1,29] (likely starting to diversify in the Cambrian). This indicates that the oceans in which offacolids lived were going through massive changes in trophic networks, which offered opportunities to several lineages to radiate into a suspension feeding ecology. It is reasonable to assume that offacolids participated in this radiation as well. In this sense, the chronological framework represents mild but objective support for the interpretation of offacolids as suspension feeders.

Paleoenvironmental considerations, on the other hand, offer stronger support for the main hypothesis of this manuscript. The three Lagerstätten where Offacolidae fossils have been found to represent quite different paleoenvironmental conditions. Setapedites inhabited a shallow marine environment. B. woodwardi lived in brackish to marine intertidal settings, while Offacolus and Dibasterium are associated with an outer shelf to upper slope environments. Despite these differences, all of these environments share key characteristics: a general abundance of nutrients, high levels of productivity, and often significant amounts of suspended organic material, whether planktonic or detrital in origin, often derived from inland water bodies [85,86]. As such, the paleoenvironmental contexts in which offacolids have been discovered are consistent with those expected for suspension-feeding organisms. Further support for this hypothesis comes from the composition of the coeval faunas. In the Herefordshire Lagerstätte, a cluster of radiolarians was found between the appendages of another arthropod, Carimersa neptuni, providing direct evidence of radiolarians of suitable size for the setae of Dibasterium and Offacolus being present in the environment [74]. The presence of a well-developed suspension-feeding community within the Fezouata biota (e.g., [21,62]), on the other hand, represents indirect evidence of the presence of abundant meso- and zooplankton in the environment inhabited by Setapedites.

The last line of evidence supporting the suspension feeding in Offacolidae is paleobiogeographical. Setapedites likely inhabited high-latitude environments, which are well known to support huge communities of suspension feeders. This is in contrast with the tropical environment inhabited by B. woodwardi, Dibasterium, and Offacolus. Some tropical environments are, however, also known to rely on suspension feeding and meso/zooplankton communities to support them. The continental shelf of Western Gondwana for Setapedites, the debris from the continent of Laurentia and Avalonia for B. woodwardi, as well as from Avalonia for Offacolus and Dibasterium, could have been rich in upwelling currents and debris from the continent, phenomena commonly associated with plankton blooms and filter feeders.

3.3. Testing the Hypothesis of Suspension Feeding in Offacolidae

Paleontology operates within the realm of natural history, where interpretations often depend on singular, non-repeating events [87]. This makes fossil discoveries a crucial, though uncontrollable, part of hypothesis testing. To overcome the unpredictability of fossil discoveries, we suggest relying on both a historical approach and a more testable, experimental one.

Firstly, we proceed with the traditional, paleontological approach regardless. The most direct way to corroborate or refute our hypothesis is through the discovery of new fossil material. For instance, an Offacolidae specimen preserved with particles trapped in its setae would represent strong evidence for suspension feeding. Similarly, gut contents revealing zooplankton like small radiolarians would also provide compelling support. However, due to the rare and contingent nature of such finds, they cannot be systematically pursued.

Secondly, a biomechanical analysis of Offacolidae morphology, especially Offacolus, for which high-resolution 3D models already exist, offers an experimental test of our hypothesis. Simulating the hydrodynamics of their exopods in water flow and testing their particle-trapping capabilities could directly evaluate the plausibility of a suspension-feeding function. Similar methodologies have been successfully applied in studies of hydrodynamics and buoyancy in various arthropod groups, offering a promising path to test this hypothesis [88,89,90]. This could be used to test not only the capacity of the exopod setae to trap particles [80], but also whether Offacolidae were capable of actively generating water flow with their exopods or had to passively rely on environmental currents to capture suspended particles.

4. Conclusions

In this study, we proposed and explored the hypothesis that Offacolidae represents the only known suspension-feeding clade within Chelicerata. Through a synthesis of anatomical, paleoenvironmental, chronological, and paleogeographical evidence, we suggest that the unique morphology of Offacolidae—particularly their brush-like setae-bearing exopods, reduced gnathobases, and specialized chelicerae—reflects a specialized adaptation for suspension feeding. The environments in which they were preserved, ranging from shallow offshore settings to intertidal and outer shelf environments, were all nutrient-rich and likely supported planktonic communities capable of sustaining filter feeders. These findings align with the broader ecological backdrop of the Cambrian–Ordovician Plankton Revolution, during which several arthropod lineages diversified to exploit newly available trophic resources in the water column. By proposing a suspension-feeding ecology for Offacolidae, our work not only fills a notable gap in chelicerate ecological diversity during this time but also highlights the evolutionary plasticity of early euchelicerates. This reinterpretation of Offacolidae ecology may prompt a reevaluation of the ecological roles played by other early chelicerate groups. Future research—including direct evidence from gut contents or preserved feeding traces and experimental biomechanical modeling—will be crucial in testing the validity of our hypothesis. Ultimately, this hypothesis-driven approach reinforces the value of integrating anatomical, ecological, and taphonomical data to better understand the early evolution of marine ecosystems.