A happy family: systematic revision of the endemic Theridion spiders (Araneae, Theridiidae) of the Hawaiian Islands

Abstract

Since the description in 1900 of the iconic Happy Face spider, Theridion grallator, Simon, along with nine relatives, the Theridion fauna of the Hawaiian Islands has remained unstudied. Here, we present a systematic revision of the Hawaiian Theridion, which includes the examination of abundant material collected during the last 50 years, with scanning of the genitalia of several species using SEM techniques, and a cladistic analysis based on 22 morphological characters, to provide a first hypothesis of the phylogenetic structure of the group. We describe eight new species, namely T. ariel, sp. nov., T. caliban, sp. nov., T. ceres, sp. nov., T. ferdinand, sp. nov., T. juno, sp. nov., T. miranda, sp. nov., T. prospero, sp. nov. and T. sycorax, sp. nov. Additionally, we provide new diagnoses for former species and illustrate and describe for the first time the male of T. kauaiense Simon, 1900 and the female of T. praetextum Simon, 1900. We further propose that T. campestratum Simon, 1900 is a junior synonym of T. melinum Simon, 1900 and T. praetextum concolor Simon, 1900 is a junior synonym of T. praetextum. Finally, we provide updated information on the distribution of the species. Most species are easily diagnosed based on the male and female genitalia, but we also reveal the existence of somatic characters that differ among species, such as the body size and the shape and size of the chelicerae, which may have played a role in the diversification and coexistence of some of the species. The preferred cladogram from the cladistic analysis, although compatible with a progression rule, also suggests a complex pattern of multiple back and forward colonisations, albeit most of the clades are poorly supported.