Sphaeromatidea

Abstract: Isopoda is a highly diverse order of crustaceans with more than 10,300 species, many of which are parasitic. Taxonomy and phylogeny within the order, especially those of the suborder Cymothoida Wagele, 1989, are still debated. Mitochondrial (mt) genomes are a useful tool for phylogenetic studies, but their availability for isopods is very limited. To explore these phylogenetic controversies on the mt genomic level and study the mt genome evolution in Isopoda, we sequenced mt genomes of two parasitic isopods, Tachaea chinensis Thielemann, 1910 and Ichthyoxenos japonensis Richardson, 1913, belonging to the suborder Cymothoida, and conducted comparative and phylogenetic mt genomic analyses across Isopoda. The complete mt genomes of T. chinensis and I. japonensis were 14,616 bp and 15,440 bp in size, respectively, with the A+T content higher than in other isopods (72.7 and 72.8%, respectively). Both genomes code for 13 protein-coding genes, 21 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs), and possess a control region (CR). Both are missing a gene from the complete tRNA set: T. chinensis lacks trnS1 and I. japonensis lacks trnI. Both possess unique gene orders among isopods. Within the CR of I. japonensis (284 bp), we identified a repetitive region with four tandem repeats. Phylogenetic analysis based on concatenated nucleotide sequences of 13 protein-coding genes showed that the two parasitic cymothoids clustered together and formed a basal clade within Isopoda. However, another parasitic cymothoid, Gyge ovalis Shiino, 1939, formed a sister group with the suborder Limnoriidea Brandt & Poore in Poore, 2002, whereas two free-living cymothoid species were located in the derived part of the phylogram: Bathynomus sp. formed a sister group with the suborder Sphaeromatidea Wagele, 1989, and Eurydice pulchra Leach, 1815 with a clade including Bathynomus sp., Sphaeromatidea and Valvifera G. O. Sars, 1883. Our results did not recover the suborders Cymothoida and Oniscidea Latreille, 1802 as monophyletic, with parasitic and free-living cymothoidans forming separate clades. Furthermore, two parasitic cymothoidans formed the sister-clade to all other isopods, separated from Epicaridea Latreille, 1825, which challenges currently prevalent isopod phylogeny. Additional mt genomes of parasitic and free-living isopods might confer a sufficient phylogenetic resolution to enable us to resolve their relationships, and ultimately allow us to better understand the evolutionary history of the entire isopod order.

Abstract: Crustacean specimens (Isopoda, Anomura and Brachyura) from the upper Albian lithographic limestone of the Tlayua Formation are reviewed, providing new morphologic data for taxa previously reported from this locality. Description of mouth parts and other carapace details of the isopod Archaeoniscus aranguthyorumFeldmann, Vega, Applegate, and Bishop are provided for the first time. Following the recently proposed Brandt and Poore classification of the Isopoda, the Late Jurassic-Late Cretaceous monogeneric family Archaeoniscidae is placed into the suborder Sphaeromatidea. A right chela of Pagurussp. is the first report for pagurid remains from this locality. The brachyuran crab Tepexicarcinus tlayuaensisFeldmann, Vega, Bishop and Applegate is moved to the Dorippidae, as previously suggested by Larghi. Dorsal carapace morphology, and fourth and fifth pereiopods are described and illustrated for this species. Based on preservation features of the crustaceans here described, paleoenvironmental interpretation of the site being a shallow restricted lagoon is reinforced.

Abstract: Exosphaeroides quirosi is described from a karstic stream and its associated cave sink located 390 m above sea level and 23.5 km inland from the east coast of Espiritu Santo (Vanuatu, SW Pacific ocean). This is the first purely freshwater sphaeromatid isopod reported from an oceanic island, and is a new example of colonization of an oceanic island freshwater habitat by a typically marine taxon. E. quirosi differs from any other representative of the family in the peculiar condition displayed by the exopod of pleopod 4, which has a falcate outline, is distinctly longer than the corresponding endopod, and has the medial margin of the proximal segment produced into a foliaceous endite. Seemingly, the sexual dimorphism expressed in the presence/absence of a setulose fringe on the pereopods has not been recorded in any other sphaeromatid. Even though the peculiar pleopod 4 and the fusion pattern of pleonites—with complete incorporation of pleonite 1 to rest of pleonites—could suggest a new genus to accommodate the new species, it is included here in the broad Exosphaeroma s. l. cluster, from which most freshwater sphaeromatids seem to derive. This is done with the caveat that it is incertae sedis in Exosphaeroides until such time as a comprehensive revision of Exosphaeroma and related genera has been undertaken. E. quirosi appears to be a Exosphaeroma -derived species with an unusual pleopod 4 and fusion of pleonite 1 to the remainder of the pleon; these features being here regarded as species-level apomorphies within a morphologically diverse genus.

Abstract: Paradella tiffany sp. nov., from the high intertidal of Baja California, Mexico, is described and figured. It is the first record of a species of Paradella with a posteriorly-directed median process on pereonite 7, this character distinguishing males of the species from all other species in the genus and all other sphaeromatids known from the East Pacific. A further unique character, in the male only, is the presence of short, stout and rigid plumose marginal setae on the distal margin of the pleopod 1 endopod.