Darwinulidae, Brady & Robertson, 1885

Smith, Robin James & Chang, Cheon Young, 2022, Two new species of non-marine Ostracoda (Crustacea) of the genera Vestalenula Rossetti & Martens, 1998 (Darwinuloidea) and Microloxoconcha Hartmann, 1954 (Cytheroidea) from Tsushima, Japan, and a summary of the non-marine ostracod fauna of the island, Zootaxa 5150 (4), pp. 529-555 : 546

Darwinulidae

Although Penthesilenula brasiliensis is globally widespread, known from seven of the world’s zoogeographical regions ( Meisch et al. 2019), it has not been previously recorded in East Asia. Vestalenula gravata sp. nov., Vestalenula sp. and the new record of P. brasiliensis herein, bring the total of Darwinuloidea species known from Japan to nine, representing almost a quarter of the total number of extant species in this superfamily. Three of these, P. brasiliensis , Darwinula stevensoni ( Brady & Robertson, 1870) , and Microdarwinula zimmeri ( Menzel, 1916) , are globally widespread, while two of the Vestalenula species, Vestalenula lundi and Vestalenula molopoensis , are known from more than one zoogeographical region ( Meisch et al. 2019). The other four species, Vestalenula cornelia , Vestalenula gravata sp. nov., Vestalenula cylindrica and Vestalenula sp. , may be endemic to East Asia, although V. cylindrica is known as fossils from elsewhere, and may represent a relic endemic (Smith et al. 2006; Smith & Janz 2009). The small size and lack of a pigmented eye indicates that Vestalenula gravata sp. nov. may be a stygobiont, which was washed to the surface in heavy rains prior to collecting. The distributions of stygobionts can be difficult to determine as direct access to groundwater is usually limited, and thus it is plausible that Vestalenula gravata sp. nov. is more widespread, but difficult to collect.

Vestalenula is divided into two groups, the boteai -group, which includes species with a short keel on the right valve, and the danielopoli -group, consisting of species with a longer keel ( Rossetti & Martens 1998). The boteai - and danielopoli -groups are both widespread, with each found in the Afrotropical, Australasian, Neotropical, Palaearctic regions, and with the boteai -group also found in the Pacific Oceanic Islands region ( Meisch et al. 2019). Five of the Vestalenula species found in Japan belong to the danielopoli -group of Vestalenula ( V. cornelia , V. cylindrica , Vestalenula gravata sp. nov., V. lundi , and Vestalenula sp. ), but it is unknown if they represent a distinct lineage within the genus. Vestalenula gravata sp. nov. lacks a post-abdomen and a pigmented eye, whereas these are present in V. cornelia , V. lundi , and V. cylindrica . The post-abdomen is a feature useful for species discrimination (e.g. Rossetti & Martens 1998), but it is not clear if it is only present in particular lineages within the genus. The absence of a pigmented eye is not a widely used taxonomic character in Vestalenula (the presence or absence of an eye is sometimes not noted in descriptions, Table 3), and could potentially be a homeomorphic character influenced by habitat, rather than having phylogenetic significance. The extra setae on both the antennule and antenna of Vestalenula sp. are features previously only known in three other Vestalenula species, belonging to the boteai -group, from Brazil. Species of the genera Alicenula Rossetti & Martens, 1998 , Darwinula Brady & Robertson, 1885 and Penthesilenula Rossetti & Martens, 1998 have the extra setae on the antennule and antenna, while Isabenula Rossetti et al., 2011 and Microdarwinula Danielopol, 1968 only have the extra seta on the antenna. As these setae are taxonomically widespread in the family, their absence in most species of Vestalenula is possibly an apomorphy. Their loss could be a result of convergent evolution in both groups of Vestalenula , or species of Vestalenula retaining these setae could represent a distinct phylogenetic lineage. This latter scenario would indicate that keel length, and hence the boteai - and danielopoli -groups, is not phylogenetically significant.