The carapace was covered by triangular scales. The tergites and abdominal plates had mucrones (sharped points) typical of Adelophthalmidae, but these were considerably larger and more prominent than in related genera. In some places, the mucrones touched each other and formed a rhombic ornamentation, while in others, they were so elongated that they resembled the linear striations present in the more derived ("advanced") genus Adelophthalmus. The morphology of the genital operculum (a plate-like segment which contains the genital aperture) allows an easy differentiation between Bassipterus and the other adelophthtalmids.
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Bosmina longirostris has multiple morphotypes. The most common morphotypes in freshwater are cornuta, pellucida, similis, and typica. The morphotypes refer to the size and curve of the antennules of the organism, as well as the size of the mucrones.
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The third joint was very short and finished in two long points reminiscent of Eurypterus, a more basal genus. The appendage in its entirety was covered by triangular mucrones which pointed outwards. The genital operculum differentiates Bassipterus from other eurypterid genera and suggests a close relationship with Pittsfordipterus.
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Mycteroptids were medium-sized to fairly large mycteropoids with parabolic prosoma and a hastate telson with paired ventral keels. They had a culticular ornament of scales or mucrones and unlike the hibbertopterids, appendage IV was non-spiniferous. The first and second opisthosomal tergites were strongly developed and elongated. The heads of mycteroptids were subtrapezoid in shape with small compound eyes. 1955\. Merostomata.
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Should this interpretation be correct, the sparse mucrones of Megarachne might be because of its age, as Megarachne is significantly larger than Woodwardopterus. The smallest genus, Mycterops, has even more densely packed ornaments on its carapace and tergite and might thus be the youngest ontogenetic stage of the animal. Should Mycterops, Megarachne and Woodwardopterus represent the same animal, the name taking priority would be Mycterops as it was named first, in 1886.Dunlop, J. A., Penney, D. & Jekel, D. 2018.
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In this specimen, the entire telson measures 3.1 cm (1.2 in) in length and 1.3 cm (0.5 in) in width. Larger specimens are known however, with a specimen described by Henry Woodward in 1864 measuring 1.6 cm (0.6 in) in width. A small part of a tergite (specimen BGS GSM Zf-2866) preserves large and raised triangular mucrones (median spines on the outer surface). The largest such mucrone (0.4 cm, 0.15 in, in width) suggests that Salteropterus could grow much larger than the known small specimens would suggest.
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Though originally described as a giant spider, a multitude of features support the classification of Megarachne as a eurypterid. Among them, the raised lunules (the vaguely moon-shaped ornamentation, similar to scales) and the cuticular sculpture of the mucrones (a dividing ridge continuing uninterrupted throughout the carapace, the part of the exoskeleton which covers the head) are especially important since these features are characteristic of eurypterids. Megarachne possessed blade-like structures on its appendages (limbs) which would have allowed it to engage in a feeding method known as sweep-feeding, raking through the soft sediment of aquatic environments in swamps and rivers with its frontal appendage blades to capture and feed on small invertebrates. Megarachne also possessed a large and circular second opisthosomal tergite (the second dorsal segment of the abdomen), the function of which remains unknown.
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Fossilized remains of the second tergite of the mycteroptid Woodwardopterus were compared to the fossil remains of Megarachne by Selden and colleagues (2005), which revealed that they were virtually identical, including features previously not noted in Woodwardopterus, such as radiating lines covering the tergite. It was concluded that Megarachne and Woodwardopterus were part of the same family by Selden and colleagues (2005), with two primary differences; the tergites and the mucrones on the carapace are more sparsely packed in Megarachne and the protrusion of the anteroedian (i.e. before the middle) carapace, seen prominently in Megarachne, does not occur in Woodwardopterus. It has been suggested that three of the four genera that constitute the Mycteroptidae, Mycterops, Woodwardopterus and Megarachne, might represent different ontogenetic stages (different developmental stages of the animal during its life) of each other based on their morphology and the size of the specimens.
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