Archoxynaspis, Van, Robert J. & Dekelboum, Allen M., 2011

Van, Robert J. & Dekelboum, Allen M., 2011, Oxynaspididae (Crustacea, Cirripedia): phylogenetics and evolutionary ecology, with descriptions of three new genera and six new species, Zootaxa 3103, pp. 1-32 : 3

Genus Archoxynaspis gen. nov.

Figure 1

Type species. This mono-typic genus contains only the extinct species, Archoxynaspis eocenica ( Withers, 1935) .

Type locality. Middle Eocene of England.

Diagnosis. All 5 plates completely and thickly calcified; plates closely approximate, not separated by uncalcified areas. Scutum with distinct ridge running from umbo to apex. Tergum with distinct ridge running from umbo (apex) to basal tip. Scutal adductor muscle pit lacking. Carina with basal end recurved; basal margin rounded, not forked.

Etymology. From the Greek arch -, beginning, oxyno -, to sharpen, and aspi -, shield (scutum).

Remarks. The lack of an adductor muscle pit on the scutum of Archoxynaspis gen. nov. distinguishes it from Minyaspis gen. nov., Pycnaspis gen. nov. and Oxynaspis . The lack of a scutal adductor muscle pit in Archoxynasipis eocenica and the two species used as outgroups in our phylogenetic analysis, Dosima fascicularis Ellis & Solander, 1786 and Lepas anatifera Linnaeus, 1758 , indicate that it is a plesiomorphic character state. In addition, this earliest known representative of the Oxynaspididae exhibits other plesiomorphic capitular plate morphology such as complete shell coverage of the capitulum, with no gaps between calcified plates and the basal end of the carina rounded, not forked as it is in Minyaspis .

Figures

FIGURE 1. Archoxynaspis eocenica (Withers, 1935), copy of Plate XVI from Withers, 1935. Wither’s original caption follows: EXPLANATION OF PLATE XVI. Lepas eocenica, sp. n. Middle Eocene, Ledian, Upper Bracklesham Beds: Selsey Bill, Sussex. Figs. 1 – 3. Scuta. Holotype (fig. 1), a. outer view; b, inner view. Figs. 4 – 11. Carina (incomplete). Figs. 4, 10, outer view of two plates showing basal plate; fig. 5, outer view of apical part; figs. 6, 7, inner view of two basal parts, showing variation in outward curvature of basal plate; figs. 8, 9, side view of two plates, fig. 8 showing cross-section; fig. 11, plate with basal plate broken away. Figs. 12 – 14. Terga, outer views. Fig. 15. Reconstruction. (Figs. 1 – 15, x 6 diam.)