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1

The discovery of acanthocephalans parasitizing chaetognaths

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Lozano-Cobo H., Gomez-Gutierrez J., Franco-Gordo C., Prado-Rosas M. C. G.
Acta Parasitologica
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2017
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tom 62
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nr 2
2
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The Burges Shale animal Oesia is not a chaetognath: A reply to Szaniawski [2005]

100%
Morris S. C.
Acta Palaeontologica Polonica
|
2009
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tom 54
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nr 1
175-179
The Middle Cambrian Oesia disjuncta, a monospecific genus, is known only from the celebrated Burgess Shale of British Columbia. It has been re−interpreted by Szaniawski (Acta Palaeontologica Polonica 50:1–8; 2005) as a chaetognath, a distinctive phylum whose exact position in the protostomes is still controversial. Unequivocal chaetognaths, that have no similarity to Oesia, are already known to occur in the Chengjiang Lagerstätte (Lower Cambrian, S.W. China), and here I describe the first example of a chaetognath from the Burgess Shale itself. Comparisons between Oesia and chaetognaths fail to find any significant homologies. Whilst the phyletic position of Oesia is very uncertain, a place in the hemichordates may be worth exploring.
3

Derogenes varicus [Muller, 1784] from chaetognaths [Chaetognatha] caught in Kongsfjorden, West Spitsbergen

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Rolbiecki L., Walkusz W.
Oceanological and Hydrobiological Studies
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2005
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tom 34
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nr 4
4

Status of arrow worms [Chaetognatha] in the Southern Baltic Sea

100%
Maciejewska K., Margonski P.
Bulletin of the Sea Fisheries Institute
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2001
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nr 1
5

The differential expression of ribosomal 18S RNA paralog genes from the chaetognath Spadella cephaloptera

84%
Barthelemy R. M., Grino M., Pontarotti P., Casanova J.-P., Faure E.
Cellular and Molecular Biology Letters
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2007
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tom 12
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nr 4
573-583
Chaetognaths constitute a small marine phylum of approximately 120 species. Two classes of both 18S and 28S rRNA gene sequences have been evidenced in this phylum, even though significant intraindividual variation in the sequences of rRNA genes is unusual in animal genomes. These observations led to the hypothesis that this unusual genetic characteristic could play one or more physiological role(s). Using in situ hybridization on the frontal sections of the chaetognath Spadella cephaloptera, we found that the 18S Class I genes are expressed in the whole body, with a strong expression throughout the gut epithelium, whereas the expression of the 18S Class II genes is restricted to the oocytes. Our results could suggest that the paralog products of the 18S Class I genes are probably the “housekeeping” 18S rRNAs, whereas those of class II would only be essential in specific tissues. These results provide support for the idea that each type of 18S paralog is important for specific cellular functions and is under the control of selective factors.
6
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Cambrian chaetognaths recognized in Burgess Shale fossils

84%
Szaniawski H.
Acta Palaeontologica Polonica
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2005
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tom 50
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nr 1
Oesia disjuncta, one of the species of the soft−bodied fauna collected and described by Walcott (1911) from the Middle Cambrian Phyllopod Bed (Burgess Shale, British Columbia, Canada) is recognized as a chaetognath. For anatomical comparisons many specimens of Recent chaetognaths were specially compressed and dried to obtain forms similar to the fossils preserved in shales. The most characteristic features shared by the fossil and Recent specimens include: strongly elongated, transversely striated and very flexible body, large size, and characteristically diversified shape of head, pronounced intestine and horizontally oriented caudal fin. Possible traces of other chaetognath structures—grasping apparatus, lateral fins, seminal vesicles, ventral ganglion, ovaries and anus—are also present but preserved in one specimen only. Among extant genera, those showing the closest similarity to Oesia Walcott, 1911 are the hyperbenthic Archeterokrohnia Casanova, 1986¹, and Heterokrohnia Ritter−Záhony, 1911, which are considered by some authors as evolutionarily most primitive.
7
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Fossil chaetognaths from the Burgess Shale: A reply to Conway Morris [2009]

67%
Szaniawski H.
Acta Palaeontologica Polonica
|
2009
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tom 54
|
nr 2
361-364
Walcott (1911) erected the new genus and species Oesia disjuncta and assigned them to the polychaete annelids, based on a small collection of similar fossils from the famous Middle Cambrian Burgess Shale. In 2002 I suggested that the species is “possibly related to chaetognaths” (Szaniawski 2002: 405). Later, after obtaining new photos of the specimens and making comparative investigations with the extant chaetognaths, I was able to describe many significant similarities, and came to the conclusion that O. disjuncta indeed is an ancestral chaetognath (Szaniawski 2005). This interpretation already has been accepted in several publications (Vannier et al. 2005; Ball and Miller 2006; Hu et al. 2007. Giribet 2008). Ball and Miller (2006: 594) confirmed not only its “... remarkable resemblance to modern chaetognaths” but also correctness of recognition of all its organs. They even reproduced a part of my illustration showing them (Ball and Miller 2006: fig. 2). Vannier et al. (2006: 629) combined the problem with the open question of the systematic position of another Burgess Shale fossil Amiskwia sagittiformis Walcott, 1911, and expressed their reservation based on “...the lack of clear evidence of a grasping apparatus...”. Only Conway Morris (2009) firmly disagreed with this diagnosis and even devoted a special “discussion” article addressing the issue. However, that article contains several ambiguities and misunderstandings which need clarification.
8
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Chaetognath grasping spines from the Upper Mississippian of Arkansas [USA]

67%
Doguzhaeva L. A., Mutvel H., Mapes R. H.
Acta Palaeontologica Polonica
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2002
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tom 47
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nr 3
Previously unidentified tiny (about 0.5 mm in length), hollow, gently curved, serrated spines probably originally composed of horny, organic fibers from the Upper Mississippian (Middle Chesterian = Namurian A equivalent or lower Serpukhovian) of Arkansas (USA) are described, and their probable chaetognath affinities are discussed. The specimens are preserved in an oval accumulation (about 15 mm long and 6 mm wide) of approximately 200 specimens within a small (about 25 mm in length) phosphatic concretion. For comparison, the grasping spines of the Recent chaetognath Eukrohnia hamata were examined. The Arkansas specimens are named Eoserratosagitta serrata gen. et sp. nov., and this genus is assigned to the Phylum Chaetognatha. The Upper Mississippian spines are also compared with protoconodonts. This comparison supports the hypothesis that the chaetognaths may have existed in the Cambrian.
9
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New evidence for the protoconodont origin of chaetognaths

67%
Szaniawski H.
Acta Palaeontologica Polonica
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2002
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tom 47
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nr 3
An earlier hypothesis concerning the origin of chaetognaths from protoconodonts found additional support in new discoveries and in recent structural, chemical and molecular investigations. The new findings show that the head armature of protoconodonts was composed not only of grasping spines but also of much smaller spicules corresponding in size and shape to the chaetognath teeth. Grasping spines of protoconodonts were originally built mainly of an organic substance. Their original composition was changed by secondary phosphatisation. The thickest layer of the protoconodont spines was originally constructed of organic fibrils, similar to those in the corresponding layer of chaetognaths. Recent molecular investigations show that the chaetognath lineage separated in the early stage of metazoan radiation, which fits the presented hypothesis. Described are some previously unknown structural details of chaetognath grasping spines, including composition of the outer layer and the origin of their distinctive tips.
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