Male claspers in clam shrimps (Crustacea, Branchiopoda) in the light of evolution: A case study on homology versus analogy

Abstract

Male "clam shrimps" possess highly modified first (and second) trunk limbs for clasping the carapace of females during copulation. Claspers are present in all three clam shrimp taxa (Laevicaudata, Spinicaudata, and Cyclestherida) but despite striking similarities in their morphology and function, the matter of their homology is controversial. In this study, we address the question of the homology and evolution of these structures by comparing the developmental transformation of an unspecialized trunk limb into a clasper. In addition, we study the musculature and the nervous system in trunk limbs and claspers using confocal laser scanning microscopy. We establish that most (but not all) of the various parts of the claspers are homologous between clam shrimp taxa. We suggest that a single pair of claspers was already present in the ground pattern of Diplostraca, probably most comparable to those in Cyclestherida. The claspers, therefore, do not represent a case of analogy.

A new species of Leptestheria (Crustacea: Branchiopoda: Spinicaudata) from Western Maharashtra, India

“…Morphological description follows Kaji et al (2014), Shu et al (2015) and Timms (2016). The following references were consulted for data on Indian leptestheriids: Babu & Nandan (2010), Battish (1981), Daday (1923), Nayar & Nair (1968), Sars (1900), Simhachalam & Timms (2012), Tiwari (1966;1996).…”

Functional morphology of amplexus (clasping) in spinicaudatan clam shrimps (Crustacea, Branchiopoda) and its evolution in bivalved branchiopods: A video-based analysis

“…A) Is similar to F in Figure 9. The color coding is from Figure 9 in Kaji et al () and is used to indicated presumed homologous parts (same color = homology; same color coding is used in Figures 12 and 13).…”

“…The large palp is generally homologous in all three taxa, being composed of endite V, with the exception of the presence of a distal outgrowth in the Spinicaudata (Kaji et al, ). The large palp operates in a rather similar way during amplexus in both Spinicaudata and Laevicaudata (Fig.…”

“…). In Spinicaudata and Cyclestherida, the small palps are homologous as they are an outgrowth of endite IV, while in Laevicaudata the structure is endite IV (Kaji et al, ). The palp is unarticulated in all three taxa.…”

A new species of Lynceus Müller, 1776 from New Caledonia (Crustacea: Branchiopoda: Laevicaudata) from dolines, with remarks on zoogeography

“…10 pairs, first pair modified as claspers. Right and left claspers equal in size and shape, of typical Lynceus form (clasper terminology follows Sigvardt &Kaji et al 2014). Endite 1 of clasper limb typical for genus, lobiform, margined with short setae.…”