An expansion of the use of molecular data in the 21st C has accompanied a greatly increased number of amphibian and reptile species descriptions. Some of the newly discovered or recognised diversity has been considered ‘cryptic’. Islands and island endemic taxa represent worthwhile systems to address questions about cryptic species. Being comprised of multiple islands of partly Gondwanan origin, the Seychelles Archipelago offers the opportunity to address crypsis for a biota comprised of both deep-time vicariant and more recent overwater dispersed forms. We focus on the history of discovery, taxonomy, inter- and intraspecific variation, and phylogeography. Most recent studies investigating intraspecific variation in Seychelles herpetofauna have identified (often similarly) geographically structured, genetically divergent populations, and we note the potential of Seychelles herpetofauna in understanding lineage crypsis. We attempt to assess why some lineages have remained cryptic for so long; whether recently discovered lineages are truly cryptic and/or distinct taxa; and if ecology (vagility) and/or length of time on the islands can explain lineage crypsis. Patchy data and/or lack of sufficient study currently limit possible interpretations. Detailed ecological and environmental data, population genetic assessments, reconstruction of phylogeographic histories, and integration of phenotypic trait data will all aid future assessments.

Squamate hemipenes have yielded much systematic data, but there have been few, if any, attempts to infer changes across the lizard–snake transition. We assess external morphology of hemipenes of major extant squamate lineages. Summarizing information across Squamata from mostly published data is challenging because of (i) patchy coverage, (ii) uncertainty as to whether described organs are fully everted or inflated, (iii) interpreting mixed text, photographs and drawings, (iv) non-standardized terminology, (v) shifting views of squamate phylogeny. However, we provide suggestions towards a unified terminology for hemipenial morphology, and score 24 lineages for 10 traits. We infer likely ancestral states as follows. (1) Ancestral toxicoferan: slightly bilobed hemipenis; simple, flared sulcus spermaticus; lack of spines; possibly flounce-like transverse flanges on body. (2) Ancestral snake: simple, flared sulcus with closely spaced, symmetrical lips; lack of spines; lack of lobular calyces; possibly unilobed hemipenis. (3) Ancestral alethinophidian: moderately to deeply bilobed hemipenis; lobular flounces; lack of spines; centripetal, bifurcate sulcus reaching tips of lobes.

This brief chapter introduces the book. The rationale, scope, and coverage are summarized, including mention of topics that are not covered. Aspects of debate, disagreement, and consensus in the field are summarized before the chapter is concluded with a look to future potential progress.

The distinctiveness of their eyes has played a major role in debates about snake origins and early evolution, having been interpreted as providing evidence for nocturnal and/or fossorial (and to a lesser degree, aquatic) origins. Much of this evidence came from anatomical studies of snake retinas in the 1900s. More recent morphological and molecular studies have provided further evidence for the distinctness of the snake eye that lacks many of the traits present in lizards. Data remain patchy and are particularly sparse for extant lineages (scolecophidians and non-caenophidian alethinophidians) that bear special importance for inferring traits of the ancestral snake. However, evidence is strong for: (1) the ancestral snake having lost multiple anatomical and molecular genetic components present in the eyes of the ancestral squamate and retained by most lizards; (2) the eye of the ancestral snake being adapted for low-light environments and/or activity cycles but being notably less regressed than that of extant scolecophidians; (3) an elaboration and diversification of the eye within endoglyptodont caenophidian snakes.