Coronula bifida Bronn, 1831

Buckeridge, John Stewart, Chan, Benny K. K. & Lee, Shih-Wei, 2018, Accumulations of Fossils of the Whale Barnacle Coronula bifida Bronn, 1831 (Thoracica: Coronulidae) Provides Evidence of a Late Pliocene Cetacean Migration Route through the Straits of Taiwan, Zoological Studies 57 (54), pp. 1-12 : 4-6

Coronula bifida Bronn, 1831

( Fig. 3 )

Coronula bifida Bronn, 1831: 126 .

Coronula barbara Darwin, 1854a: 421 .

Coronula dormitor Pilsbry and Olsson, 1951: 202 .

Coronula bifida bifida Menesini, 1968: 387 .

Coronula bifida barbara Menesini, 1968: 395 .

Coronula bifida Collareta et al., 2018a: 15 .

Coronula bifida Collareta et al., 2018b: 147

Distribution: Late Pliocene to early Pleistocene (Piacenzian to Gelasian, Taiwan - this work); Middle Pliocene to mid-lower Pleistocene (Calabrian, Western Europe; California; Ecuador). As C. barbara : Marquet et al. 2009; Zullo 1969; Beu 1971 Pilsbry and Olsson 1951; Darwin 1854b; De Alessandri 1960 Bianucci et al. 2006b; Collareta et al. 2016 2018a b (see full references in Collareta et al. 2018a).

Material Examined: Taiwan. 0860-0869: 10 complete shells (without opercula), 17.4-37.0 mm C-R diameter, 13.6-31.2 height; CIMFO0047- CIMFO0058 and NMMSTM000125: 13 complete shells (without opercula), 41.2-78.5 mm C-R diameter, 25.0- 54.8 mm height; ASIZCR000400- ASIZCR000409: 10 complete shells (without opercula) 21.0- 56.5 mm C-R diameter, 18.3- 44.7 mm height; G.340: one specimen (without opercula), C-R diameter 47 mm, height 38 mm ( Table S1). All specimens were collected by Mr Wen-Ji Xue between 1980 and 2000 and from an actively eroding escarpment at Chaiyi Niupu - 23°25'40.8"N, 120°33'25.7"E.

Diagnosis: Coronula with globose shell; compartments with convex longitudinal parietal ribs that often bifurcate, and with strong transverse ridges; radii broad, flat, becoming narrower in their lowermost third; body chamber relatively shallow, sub-cylindrical; sheath less than half that of the total shell height.

Description: Shell globose; in adults, lower half of compartments developing five to six convex longitudinal parietal ribs; parietal ribs with strong transverse ridges in which bifurcation is rare; ridges spaced by at least their own height; basal edges of ribs crenated; orifice narrower than basal opening; compartments (i.e. ribs) noticeably worn in upper third of shell; radii broad, flat, summits horizontal; centrally radii are slightly wider than paries, becoming narrower in their lowermost third; body chamber relatively shallow, sub-cylindrical; sheath less than half of the total height of the shell. Opercula unknown.

Remarks: Coronula bifida is close to Coronula diadema ; a phyletic lineage from C. bifida to C. diadema has been proposed by Dominici et al. (2011: 99), and as the ranges of these species are not known to overlap, this seems a reasonable conclusion. It differs from C. diadema in its more widely spaced transverse ridges on the parietal ribs and a shallower body chamber. In general C. bifida has more parietal ribs on each compartment than observed in C. diadema (i.e. the ribs branch less frequently in the latter species). The worn (= exposed) portion of the compartments suggests that the shell was embedded into the cetacean skin by slightly more than half of its height. Specimens of C. diadema in the collection at RMIT tend to show a proportionately greater worn zone, permitting us to conclude that C. bifida was buried deeper into the whale’s skin. These observations are consistent with specimens of C. bifida recovered from the Mediterranean ( Collareta et al. 2018a).

It is noteworthy that both Darwin (1854a: 420) and later Dominici et al. (2011: 97) commented that the differences between C. diadema and Coronula reginae are minimal. Darwin considered C. reginae more closely related to C. balaenaris than C. diadema , which is interesting, as C. balaenaris is now recognized as Cetopirus (see above). What this does is demonstrate the significant variation in whale barnacle morphology due to crowding and location on the whale. This variation is also demonstrated by the rather broad spectrum of shell morphologies in this collection of C. bifida .

Figures

Fig. 3. Coronula bifida Bronn, 1831 from Niupu, Chiayi, Western Central Taiwan, Liuchungchi Formation (Plio-Pleistocene). Specimens (#0860-0869) held by the Chia-Yi Municipal Museum, Chaiyi City, Taiwan.