Tactopoda
| Tactopoda | |
|---|---|
| |
| The tardigrade Hypsibius dujardini | |
| |
| The blue crab Callinectes sapidus, an arthropod | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Subkingdom: | Eumetazoa |
| Clade: | ParaHoxozoa |
| Clade: | Bilateria |
| Clade: | Nephrozoa |
| (unranked): | Protostomia |
| Superphylum: | Ecdysozoa |
| (unranked): | Panarthropoda |
| (unranked): | Tactopoda Budd, 2001 [1] |
Tactopoda is a proposed clade of protostome animals that includes the phyla Tardigrada and Euarthropoda, supported by various morphological observations.[1][2]
The competing hypothesis is that Arthropoda sensu lato[3] (= Euarthropoda + Onychophora, the arthropods and the velvet worms) is monophyletic.[4]
Anatomic arguments for the tactopoda monophyly include similarities in the anatomies of head, legs, and muscles between the arthropods and the tartigrades. Anatomic arguments against it include that tartigrades lack the kind of circulatory system (including a dorsal hart) which the arthropods and the velvet worms share. Graham Budd argued that the lack of this system in recent tartigrades is due to their miniature size, which makes a complex circulatory system superfluous; thus, the loss of this feature would be a secondary property, acquired as tartigrade stem group turned smaller, and both the Euarthropoda+Onychophora circulatory system and a relatively large size should be a feature of the last common ancestor of all three groups.[1] However, Edgecombe also invokes phylogenomic evidence in favour of the alternative Euarthropoda+Onychophora grouping.[4]
Proposed classification
- Phylum Tardigrada
- Class Eutardigrada
- Class Heterotardigrada
- Class Mesotardigrada
- Phylum Arthropoda
- Class Pycnogonida (?)
- Clade Arachnomorpha
- Class †Trilobita
- Order †Aglaspida
- Order †Strabopida
- Class Pycnogonida (?)
- Order †Cheloniellida
- Subphylum Chelicerata
- Class Xiphosura
- Class †Eurypterida
- Class †Chasmataspidida
- Class Pycnogonida (?)
- Class Arachnida
- Clade Mandibulata
- Order †Euthycarcinoidea
- Subphylum Myriapoda
- Clade Pancrustacea
- Clade Oligostraca
- Class Ostracoda
- Some of polyphyletic class Maxillopoda
- Clade Altocrustacea
- Clade Multicrustacea
- The rest of polyphyletic class Maxillopoda
- Class Malacostraca
- Clade Allotriocarida
- Class Branchiopoda
- Clade Miracrustacea
- Superclass Xenocarida
- Class Cephalocarida
- Class Remipedia
- Subphylum Hexapoda
- Paraphyletic class Entognatha
- Clade Ectognatha
- Class Insecta
- Superclass Xenocarida
- Clade Multicrustacea
- Clade Oligostraca
Phylogeny
| Panarthropoda |
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References
- ^ a b c Graham E. Budd (2001). "Tardigrades as 'stem-group arthropods': the evidence from the Cambrian fauna" (PDF). Zoologischer Anzeiger. 240 (3–4): 265–279. doi:10.1078/0044-5231-00034. Archived from the original (PDF) on 2016-03-03.
- ^ Smith, M. R.; Ortega Hernández, J. (2014). "Hallucigenia's onychophoran-like claws and the case for Tactopoda". Nature. 514 (7522): 363–366. doi:10.1038/nature13576. PMID 25132546.
- ^ J. Ortega-Hernández, "Making sense of 'lower' and 'upper' stem-group Euarthropoda, with comments on the strict use of the name Arthropoda von Siebold, 1848," Biol. Rev., vol. 91, no. 1, pp. 255–273, 2016.
- ^ a b Gregory D. Edgecombe (2010). "Arthropod phylogeny: An overview from the perspectives of morphology, molecular data and the fossil record". Arthropod Structure & Development. 39: 74–87.
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