No abstract

Postembryonic development in the kinorhynch species Antygomonas incomitata was examined using scanning electron microscopy. The morphology of the six juvenile stages, J-1 to J-6, varies at numerous details, but they can also be distinguished by a few key characters. Juvenile stage 1 by its composition of only nine trunk segments; J-2 by the combination of possessing 10 trunk segments, but no cuspidate spines on segment 9; J-3 by the presence of cuspidate spines on segment 9, but only one pair of cuspidate spines on segment 8; J-4 by the combination of 10 trunk segments only, but having two pairs of cuspidate spines on segment 8; J-5 by possessing 11 trunk segments and same spine compositions as adults but is still maintaining postmarginal spiculae; J-6 specimens closely resemble adults and are most easily identified by their reduced trunk lengths. New segments are formed in a growth zone in the anterior part of the terminal segment. The complete number of segments is reached in J-5. Development of cuticular head and trunk structures are described through all postembryonic stages and following developmental patterns could be outlined: the mouth cone possesses outer oral styles from J-1, but in J-1 to J-3, the styles alternate in size. Scalids of the introvert are added after each molt, and scalids appear earliest in the anterior rings, whereas scalids in more posterior rings are added in older postembryonic stages. The early J-1 stage is poor in spines and sensory spots and both structures increase in number after each molt. The complete spine composition is reached in J-4, whereas new sensory spots appear after all molts, inclusive the final one from J-6 to adult. Sensory spots in the paraventral positions often appear as Type 3 sensory spots but are through development transformed to Type 2. This transformation happens earliest on the anterior segments.

2017). A molecular approach to arthrotardigrade phylogeny (Heterotardigrada, Tardigrada). -Zoologica Scripta, 46, 496-505. The marine order Arthrotardigrada (class Heterotardigrada, phylum Tardigrada) is known for its conspicuously high morphological diversity and has been traditionally recognized as the most ancestral group within the phylum. Despite its potential importance in understanding the evolution of the phylum, the phylogenetic relationships of Arthrotardigrada have not been clarified. This study conducted molecular phylogenetic analyses of the order encompassing all families except Neoarctidae using nuclear 18S and 28S rRNA fragments. Data from two rare families, Coronarctidae and Renaudarctidae, were included for the first time. The analyses confirmed the monophyly of Heterotardigrada and inferred Coronarctidae as the sister group to all other heterotardigrade taxa. Furthermore, the results support a monophyletic Renaudarctidae + Stygarctidae clade, which has been previously suggested on morphology. Our data indicated that two subfamilies currently placed in Halechiniscidae are only distantly related to this family. We propose that these taxa are each elevated to family level (Styraconyxidae (new rank) and Tanarctidae (new rank)). The morphology of tardigrades is discussed in the context of the inferred phylogeny.

Detailed information revealed through combined use of light-and scanning electron microscopy, is given for two species of kinorhynchs, representing the cyclorhagid genera Semnoderes and Antygomonas. The two species have not previously been examined using SEM, and the new observations point out several similarities between species of the two genera, which could indicate a potential close relationship. The generated data is meant to be incorporated in a future phylogenetic analysis in order to clarify the phylogenetic relationships among kinorhynchs.

The tardigrade fauna of Condor Seamount, west of the Azores, is relatively rich, and species from at least seven genera are represented. A new species of the rare marine genus Neostygarctus (Arthrotardigrada) was found at 206 m depth at the summit of the seamount. This is the first record of the genus from the Atlantic Ocean, and also the deepest record of the genus. The new species Neostygarctus oceanopolis sp. nov. is easily distinguished from the Mediterranean type species N. acanthophorus by the number of middorsal spines. N. acanthophorus has five dorsal spines, whereas the adult of N. oceanopolis sp. nov. has seven. The cave tardigrade from Japan, Neostygarctus lovedeluxe also has dorsal spines on all five segments, but only the cephalic and the caudal segments have a middorsal spine, while the three other trunk segments have two spines on each of the dorsal segmental body plates. For the first time, ventral plates are recorded for a species of Neostygarctus. A membranous coating of the all spines of the cephalic segment, the lateral processes of the first three trunk segments, and the spines of the fourth leg pair are unique for Neostygarctus.

No abstract

A large number of specimens (1563) of a new Florarctus species were collected in a single intertidal sample from the Ionian Sea, Italy. The postembryonic development of the new species was studied with emphasis on external morphology and functional anatomy. The new Florarctus species was recognized as having two distinct larval stages, during which the anus is formed and the gonads mature prior to the development of a gonopore. The larval stages are followed by one adult stage in females and two adult stages in males. Cuticular structures change in morphology during postembryonic development, so that they exhibit a juvenile and an adult appearance. The accelerated growth in gonadal development could be the result of paedomorphosis, which was observed in the tendency of adult males of the new Florarctus species to maintain juvenile character conditions.

We re-examined the type material of five of the seven described species of the marine tardigrade genus Angursa Pollock, 1979, namely, A. abyssalis Renaud-Mornant, 1981, A. bicuspis Pollock, 1979 (type species), A. capsula Bussau, 1992, A. lanceolata Renaud-Mornant, 1981, and A. lingua Bussau, 1992. In addition, we describe A. seisuimaruae sp. nov. from the Sea of Kumano, Japan. Based on new data obtained, we amend the diagnosis of this genus, provide a taxonomic key to species, and discuss their geographical distributions.