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Complete 18S rDNA sequences of two species of the Tantulocarida Arcticotantulus pertzovi (Basipodellidae) and Microdajus tchesunovi (Microdajidae) were obtained and used for estimating the relationship of the class with other Crustacea. This constitutes the first use of tantulocaridan gene sequences, and we conclude that the Tantulocarida are very close relatives of the class Thecostraca, which comprise cirripedes, ascothoracidans and the enigmatic facetotectans. With much lower confidence, the Tantulocarida are also indicated as nested within the Thecostraca, being sister group to the Cirripedia. We therefore discuss morphological similarities and differences between tantulocaridans and the thecostracans in search of potential synapomorphies, including a possible relation to the parasitic barnacles (Rhizocephala). We conclude that the cement gland of the tantulus larva and the cirripede cyprid might be homologous structures, but that similarities in host infection and root systems between the Tantulocarida and the Rhizocephala are, on present evidence, likely to be homoplasies evolved by convergent evolution into advanced parasitism. The precise position of the Tantulocarida in relation to or within the Thecostraca must be pursued by a more extensive database of genetic markers.

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Transcriptional dynamics following freezing stress reveal selection for mechanisms of freeze 3 tolerance at the poleward range margin in the cold water intertidal barnacle Semibalanus 4 balanoides 5 6 Running title: Transcription following freezing in S. balanoides 7 Abstract 22The ability to survive freezing has repeatedly evolved across multiple phyla. This suggests that 23 the mechanisms of freeze tolerance must be readily evolvable from basal physiological traits. 24While several biochemical correlates to freeze tolerance have been described, the mechanism that 25 confers freeze tolerance is still not well understood. To understand both the basic biochemical 26 mechanisms of freeze tolerance as well as their role in local adaptation at the poleward range 27 edge, we conducted a transcriptomic study on two populations (one from the poleward range 28 margin in the White Sea, Russia, and one from the central coast of British Columbia, Canada) of 29 the cold water acorn barnacle Semibalanus balanoides on a time series following a freezing 30 event. We found that the British Columbia population (at the equatorward range margin) was 31 significantly less freeze tolerant than the White Sea population (at the poleward range margin). 32After assembling and annotating a de novo transcriptome for S. balanoides, we found that the 33 patterns of differential transcript expression following freezing were almost entirely non-34 overlapping between the two populations, with the White Sea population expressing a series of 35 heat shock proteins in response to freezing stress as well as several aquaporins, while the British 36 Columbia population expressed a series of proteases instead, indicating severe protein damage. 37 We found strong evidence of purifying selection on the significantly upregulated transcripts in 38 the White Sea population, suggesting local adaptation to freezing threat. Taken together, this 39 shows the importance of freeze tolerance to population survival at the poleward range margin, 40 and highlights the central roles of aquaporins and heat shock proteins to the trait of freeze 41 tolerance across taxa. 42

A new ascothoracidan species has been discovered off Taiwan in the north part of the west Pacific at SCUBA depths. Twelve specimens including both sexes of the new species, described herein as Synagoga arabesquesp. nov., were collected from colonies of the antipatharian Myriopathes cf. japonica Brook, 1889. Three previously described species of Synagoga, morphologically the least specialized ascothoracidan genus, have been found as ectoparasites of antipatharians and an alcyonarian, whereas all other records of this genus have been based on specimens collected from the marine plankton. This is the second study of a new form of Synagoga to be based on more than a few mature specimens of a single sex or on a single juvenile. Furthermore, it is the second in which SEM has been used to document the fine-scale external morphology. The position of terminal pores in the anterior pairs of the lattice organs is different in Synagoga arabesquesp. nov. than those in S. grygieri Kolbasov & Newman, 2018 and S. millipalus Grygier & Ohtsuka, 1995. Species of Synagoga are small, host-specific predators or ectoparasites of antipatharians. This genus exhibits a major Tethyan reliction pattern.