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Mesonacinae
Taxonomy
Mesonacidae was named by Walcott (1891).
It was synonymized subjectively with Olenellidae by Riccio (1952); it was reranked as the subfamily Mesonacinae by Lieberman (1999).
It was assigned to Opisthoparia by Walcott (1910); and to Olenellidae by Lieberman (1999).
It was synonymized subjectively with Olenellidae by Riccio (1952); it was reranked as the subfamily Mesonacinae by Lieberman (1999).
It was assigned to Opisthoparia by Walcott (1910); and to Olenellidae by Lieberman (1999).
Synonymy list
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
Subfm. †Mesonacinae Walcott 1891
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G. †Mesolenellus Palmer and Repina 1993
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†Mesolenellus hyperborea Poulsen 1974
†Mesolenellus svalbardensis Kielan 1960
G. †Mesonacis Walcott 1885
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†Mesonacis bonnensis Resser and Howell 1938
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Invalid names: Olenellus brevoculus Resser and Howell 1938 [synonym], Olenellus terranovicus Resser and Howell 1938 [synonym]
†Mesonacis cylindricus Palmer and Halley 1979
†Mesonacis eagerensis Best 1952
†Mesonacis fremonti Walcott 1910
†Mesonacis hamoculus Cowie and McNamara 1978
†Mesonacis vermontanus Hall 1859
†Mesonacis wileyi Gapp and Lieberman 2014
Invalid names: Angustolenellus Palmer and Repina 1993 [synonym], Fremontia Raw 1936 [synonym], Schmidtia Moberg 1899 [synonym]
Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| C. D. Walcott 1910 | Cephalon very large, wider than long, genal angles with spines ; intergenal spines developed in young and may be pres- ent in adult. Facial suture rudimentary, .or in a condition of syn- thesis. Eyes crescentic or semicircular and attached more or less closely to the anterior lobe of the glabella by a rounded ridge ; visual surfaceofeyeswithfacetsarrangedinquincunxorder. Hypostoma usually with more or less spinose posterior margin. Thorax long, composed of from 13 to 27 free segments. Pygidium siuall, margin usually entire but may have from one to three spines. Surface of test in adult specimens granular and usually with network of very fine thread-like raised inosculating ridges. | |
| B. S. Lieberman 1999 | The Mesonacinae can be defined by the possession of the following diagnostic char- acters in combination (thoracic and pygidial characters are not preserved in all species as- signed to the Mesonacinae): 1. anterior part of ocular lobe close to L4; 2. ocular lobe with prominent furrow; 3. width (tr.) of interocular area approximately equal to width of ocular lobe; 4. axial part of L0 with node; 5. extraocular area flattened, lacking prominent anasto- mosing ridges (except in M. svalbardensis); 6. extraocular region opposite L1 40% to 50% width (tr.) of glabella at L1 (except in M. fremonti); 7. intergenal angle directed anteriorly at angle greater than or equal to 30 degrees relative to transverse line; 8. anterior margin of thoracic pleural furrow on third segment parallels a transverse line before flexing strongly posteriorly when proceeding from proximal to distal edge; 9. width (tr.) of thoracic pleural spines T5 to T8 at spine midlength less than or equal to half length (exsag.) of correspond- ing segment between spine and axis; 10. segments of opisthothorax with prominent pleu- rae (except in M. fremonti); 11. pygidium length (sag.) 1.5 times width (tr.). None of these characters are unique to the Mesonacinae, meaning they all show some homoplasy or are symplesiomorphic within the Olenelloidea. |