Alexandra S. Petrunina

Two new species of Tantulocarida from the Atlantic deep sea with first CLSM pictures of tantulus larva

During the deep-sea expedition ANTARKTIS XIII/5 of RV Polarstern in 1996, abundant material on Tantulocarida was collected. Here, we present a description of the two new species Tantulacus coroniporus sp. nov. and Polynyapodella thieli sp. nov. The genus Tantulacus is characterized by a prominent spine on endopods of thoracopods 2–5 in tantulus larva. The new species is placed in this genus on the account of this character and represents the first Tantulacus from the Atlantic deep sea. Thus, the genus now comprises five species, showing wide distribution in the World ocean. The monotypic species Polynyapodella ambrosei Huys, Møbjerg, & Kristensen, 1997 is known to have only one seta on the exopod of thoracopods 1–5, which is unique among tantulocaridans except monophyletic family Microdajidae having reduced rami on thoracic limbs. The new species is assigned to Polynyapodella based on this character; however, it could be distinguished from P. ambrosei in the pore formula and morphology of furcal setae. Confocal laser scanning microscopy (CLSM) is, for the first time, used to study the external morphology of tantulus larva and is proved to be helpful to detect even smaller elements of cuticle ornamentation and setation of appendages. Some details of tantulocarid anatomy could also be studied using CLSM.

Transcriptional dynamics following freezing stress reveal selection for mechanisms of freeze tolerance at the poleward range margin in the cold water intertidal barnacle Semibalanus balanoides

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

Anatomy of the Tantulocarida: first results obtained using TEM and CLSM. Part I: tantulus larva

The morphology of Tantulocarida, a group of minutely sized ectoparasitic Crustacea, is described here using for the first time transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). This enabled a detailed analysis of their internal anatomy to a level of detail not possible with previous light microscopic investigations. We studied the infective stage, the tantulus larva, attached on the crustacean host in two species, Arcticotantulus pertzovi and Microdajus tchesunovi, and put special emphasis on cuticular structures, muscles, adhesive glands used in attachment, sensory and nervous systems, and on the organs used in obtaining nutrients from the host. This allowed description of structures that have remained enigmatic or unknown until now. A doubly folded cuticular attachment disc is located at the anterior-ventral part of the cephalon and used for gluing the larva to the host surface with a cement substance released under the disc. Four cuticular canals run from a cement gland, located ventrally in the cephalon, and enter an unpaired, cuticular proboscis. The proboscis can be protruded outside through a separate opening above the mouth and is used for releasing cement. An unpaired and anteriorly completely solid cuticular stylet is located centrally in the cephalon and is used only for making a 1-μm-diameter hole in the host cuticle, through which passes a rootlet system used for obtaining nutrients. The rootlet system is a direct extension of the anterior gut of the tantulus, but inside the host, it consists of cuticle only. Several muscular systems seem to degenerate very quickly after the tantulus has settled on the host. The central nervous system is reduced to an absolute minimum in terms of both cell size and number. We discuss the morphology of the tantulus in light of the Tantulocarida being a sister group to the Thecostraca or even nested within that taxon.