Examinando por Autor "Leander, Brian"

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Insights into mud dragon morphology (Kinorhyncha, Allomalorhagida): myoanatomy and neuroanatomy of Dracoderes abei and Pycnophyes ilyocryptus.
(Springer, 2020-07) Herranz, Maria; Sørensen, Martin V.; Park, Taeseo; Leander, Brian; Worsaae, Katrine
Comprehensive morphological investigations covering the diversity of metazoan lineages are needed to obtain a complete picture of organ system evolution. Despite the increased amount of studies on lesser-known phyla during the last decades, the gap in knowledge for these lineages is still remarkable. This is the case for kinorhynchs, or mud dragons, where only a few genera, mainly belonging to the major clade Cyclorhagida, have undergone detailed morphological examinations. Here, we explore the neuroanatomy and myoanatomy in the other major clade, Allomalorhagida, through studies of Dracoderes abei and Pycnophyes ilyocryptus by immunochemistry, CLSM, and computational 3D reconstruction. The current phylogenetic position of Dracoderes as a sister group to all the remaining allomalorhagids makes it a key taxon for understanding the evolution of organ systems within Kinorhyncha. Clear segmental arrangement of muscles and nerves was found in the trunk of D. abei and P. ilyocryptus, excluding modifications observed in the posteriormost segments. When comparing current and previous studies of allomalorhagids and cyclorhagids, the nervous system shows a conserved pattern across kinorhynchs, while the musculature shows significant variation among genera. Segmentation in kinorhynchs is restricted to the trunk, including mesoderm (muscles) and ectoderm derivated structures (nerves and glands). The nervous system shows a segmental arrangement in the first eight trunk segments, whereas the last three segments show some deviating arrangements most likely related to a post-hatching development of these segments. The presence of non-segmental trunk muscles is interpreted as adaptations for increased introvert motility and trunk flexibility.
Redescription of Echinoderes ohtsukai Yamasaki and Kajihara, 2012 and E. kozloffi Higgins 1977 from the northeastern Pacific coast, including the first report of a potential invasive species of kinorhynch
(Elsevier, 2016-11) Herranz, Maria; Leander, Brian
Although the dispersal ability of kinorhynchs is known to be limited, the distribution of certain kinorhynch species appears to extend over vast geographical areas. Combining molecular phylogenetic data with biogeographical investigations can test this paradox by discerning cryptic species with restricted distributions from species with potentially large geographical distributions. In this paper, we (1) redescribe two species of kinorhynchs (Echinoderes ohtsukai and E. kozloffi) found in the northeastern Pacific Ocean using molecular and morphological data and (2) provide the first evidence for a disjunct geographical distribution in kinorhynchs that is consistent with the introduction of an invasive species. Although we collected E. ohtsukai from the northeastern Pacific Ocean (British Columbia, Canada), this species was originally described from Japan. We demonstrated that specimens of E. ohtsukai collected from Japan and British Columbia have identical DNA sequences for the mitochondrial cytochrome c oxidase subunit 1 (COI) gene. These results are most consistent with a recent introduction of this species into one of the habitats on the opposite side of the Pacific Ocean through human-mediated dispersal.
Revisiting kinorhynch segmentation: variation of segmental patterns in the nervous system of three aberrant species
(BMC, 2021-10) Herranz, Maria; Park, Taeseo; Di Domenico, Maikon; Leander, Brian; Sørensen, Martin V.; Worsaae, Katrine
Background: Kinorhynch segmentation differs from the patterns found in Chordata, Arthropoda and Annelida which have coeloms and circulatory systems. Due to these differences and their obsolete status as ‘Aschelminthes’, the microscopic kinorhynchs are often not acknowledged as segmented bilaterians. Yet, morphological studies have shown a conserved segmental arrangement of ectodermal and mesodermal organ systems with spatial correspondence along the anterior-posterior axis. However, a few aberrant kinorhynch lineages present a worm-like body plan with thin cuticle and less distinct segmentation, and thus their study may aid to shed new light on the evolution of segmental patterns within Kinorhyncha. Results: Here we found the nervous system in the aberrant Cateria styx and Franciscideres kalenesos to be clearly segmental, and similar to those of non-aberrant kinorhynchs; hereby not mirroring their otherwise aberrant and posteriorly shifted myoanatomy. In Zelinkaderes yong, however, the segmental arrangement of the nervous system is also shifted posteriorly and misaligned with respect to the cuticular segmentation. Conclusions: The morphological disparity together with the distant phylogenetic positions of F. kalenesos, C. styx and Z. yong support a convergent origin of aberrant appearances and segmental mismatches within Kinorhyncha.