Infection prevalence, intensity, and tissue damage caused by the parasitic flatworm, Bdelloura candida, in the American horseshoe crab (Limulus polyphemus)

Parasite infection dynamics can have profound implications on a host’s fitness; yet, there is a dearth of information on parasites in the American horseshoe crab (Limulus polyphemus) (Linnaeus 1758), a species that has experienced population declines in recent decades. Therefore, we aimed to quantify the prevalence, intensity, and gill surface area coverage of the ectoparasitic flatworm (cocoon and adult stages), Bdelloura candida in adult (n = 29), sub-adult (n = 7) and juvenile (n = 32) horseshoe crabs collected from Moriches Bay, NY (40.7810° N, 72.7171° W) in 2019 and 2020. Subsamples of horseshoe crab gill tissue (10%) were collected from live specimen, then B. candida cocoons were enumerated across the gill subsamples using microscopy while the extent of tissue damage was quantified with histology. B. candida was present in all adult and sub-adult crabs (100%), whereas juveniles exhibited 6.2% prevalence. Cocoon intensities per sample ranged from 28 to 805 cocoons, with 4.0–94.0% of gill lamellae harboring cocoons. In infected individuals, the total cocoon surface area coverage on gill tissues ranged from 0.06–14.51%, with higher cocoon intensities observed in the ventral-most gill quartiles relative to the dorsal-most gill regions. Sex was strongly supported as a primary driver behind B. candida infection intensities with adult females harboring higher intensities. Among infected gill lamellae, cocoon intensity was lower in mitochondrial-rich regions relative to mitochondrial-poor regions. These results provide novel insight into B. candida infection dynamics across horseshoe crab demographics, but further research is necessary to quantify the physiological impacts of the infection on L. polyphemus.

A Novel Diagnostic Method for Invasive Fungal Disease Using the Factor G Alpha Subunit From Limulus polyphemus

Deaths due to invasive fungal disease (IFD) have been increasing every year. Early and rapid detection is important to reduce the mortality rate associated with IFD. In this study, we explored a novel diagnostic method for detecting IFD, which involves the G Factor α subunit (GFαSub) from Limulus polyphemus. The GFαSub double-sandwich method was developed to detect (1,3)-β-D-glucans in human serum using purified GFαSub and horseradish peroxidase-labeled GFαSub. The GFαSub double-sandwich method and the G test were performed and compared. Using GFαSub sequence analysis, the expression plasmid pET30a-GFαSub252-668 was synthesized, and GFαSub252-668 was expressed and purified via isopropyl-β-d-thiogalactoside induction and nickel-nitrilotriacetic acid affinity. The optimization method was established via the orthogonal method. Using this method, the sera of 36 patients with IFD and 92 volunteers without IFD underwent detection, and the receiver operating characteristic curve of the GFαSub252-668 double-sandwich method was described. The sensitivity and specificity of the GFαSub252-668 double-sandwich method were 91.67 and 82.61%, respectively, and there was good correlation with the G test for the serum specimens of 36 patients with pulmonary IFD (R2 = 0.7592). In conclusion, our study suggests that the GFαSub252-668 double-sandwich method was satisfactory at detecting IFD cases. This method can be promoted and further developed as a novel method for diagnosing IFD.

Correcting a 135-year error: Limulidae Leach, 1819 (Chelicerata, Xiphosura) is the proper authority, not Limulidae Zittel, 1885

The horseshoe crab Limulus polyphemus (Linnaeus, 1758) is a famous species, renowned as a ‘living fossil’ (Owen, 1873; Barthel, 1974; Kin and Błażejowski, 2014) for its apparently little-changed morphology for many millions of years. The genus Limulus Müller, 1785 was used by Leach (1819, p. 536) as the basis of a new family Limulidae and synonymized it with Polyphemus Lamarck, 1801 (Lamarck's proposed but later unaccepted replacement for Limulus, as discussed by Van der Hoeven, 1838, p. 8) and Xyphotheca Gronovius, 1764 (later changed to Xiphosura Gronovius, 1764, another junior synonym of Limulus). He also included the valid modern genus Tachypleus Leach, 1819 in the family. The primary authority of Leach (1819) is widely recognized in the neontological literature (e.g., Dunlop et al., 2012; Smith et al., 2017). It is also the authority recognized in the World Register of Marine Species (WoRMS Editorial Board, 2021).

Biomechanical analyses of Cambrian euarthropod limbs reveal their effectiveness in mastication and durophagy

Durophagy arose in the Cambrian and greatly influenced the diversification of biomineralized defensive structures throughout the Phanerozoic. Spinose gnathobases on protopodites of Cambrian euarthropod limbs are considered key innovations for shell-crushing, yet few studies have demonstrated their effectiveness with biomechanical models. Here we present finite-element analysis models of two Cambrian trilobites with prominent gnathobases— Redlichia rex and Olenoides serratus —and compare these to the protopodites of the Cambrian euarthropod Sidneyia inexpectans and the modern American horseshoe crab, Limulus polyphemus . Results show that L. polyphemus , S. inexpectans and R. rex have broadly similar microstrain patterns, reflecting effective durophagous abilities. Conversely, low microstrain values across the O. serratus protopodite suggest that the elongate gnathobasic spines transferred minimal strain, implying that this species was less well-adapted to masticate hard prey. These results confirm that Cambrian euarthropods with transversely elongate protopodites bearing short, robust gnathobasic spines were likely durophages. Comparatively, taxa with shorter protopodites armed with long spines, such as O. serratus , were more likely restricted to a soft food diet. The prevalence of Cambrian gnathobase-bearing euarthropods and their various feeding specializations may have accelerated the development of complex trophic relationships within early animal ecosystems, especially the ‘arms race' between predators and biomineralized prey.

The American Horseshoe Crab (Limulus polyphemus)

American horseshoe crabs (<em>Limulus polyphemus</em>) look prehistoric and in fact really have not changed very much in the 200 million years they have been around. This 3-page fact sheet written by Savanna Barry, Holly Abeels, and Shelly Krueger and published by the UF/IFAS Program in Fisheries and Aquatic Sciences, School of Forest Resources and Conservation tells the story of these interesting and valuable "living fossils," including their importance both to ecology and human medicine. It provides tips on how to find horseshoe crabs and a few ways you can help them.