Hibernicoceras hibernicus Moore & Hodson, 1958

Hibernicoceras hibernicus Moore & Hodson, 1958

Figs 15–17 View Fig View Fig View Fig ; Tables 9–10 View Table 9 View Table 10 , A 5 View Table 5

Hibernicoceras hibernicus Moore & Hodson, 1958: 87 , pl. 3 figs 1–2, text-fig. 1.

Hibernicoceras hibernicus – Kumpera & Lang 1975: pl. 3 fig. 6, pl. 4 fig. 2.

Hibernicoceras hibernicum – Korn 1997: 54, pl. 6 figs 3–5, text-fig. 44.

non Hibernicoceras hibernicum – Liang & Wang 1991: 98, pl. 24 figs 15–16, text-fig. 69.

Diagnosis

Species of Hibernicoceras with a thickly pachyconic conch at 5 mm diameter (ww/dm ~ 0.80), a thickly pachyconic conch at 10 mm diameter (ww/dm ~ 0.80) and a thickly pachyconic conch at 30 mm diameter (ww/dm ~ 0.75). Umbilicus very wide in early juvenile stage (uw/dm ~ 0.50 at 2 mm dm) and becoming continuously narrower throughout ontogeny (uw/dm ~ 0.20–0.28 at 10 mm dm, uw/dm ~ 0.20 at 30 mm dm); umbilical wall sigmoidal in section with shallow spiral groove. Ornamentation at 20 mm conch diameter with wide-standing, rectiradiate growth-lines with low lateral projections. Spiral lines in a moderately wide zone on the inner flank; growth lines crenulated on the flank but almost smooth on the venter. Suture line with a weakly Y-shaped, moderately wide external lobe in the adult stage (0.60–0.70 of the external lobe depth; 1.45 of the adventive lobe width), and moderate median saddle (almost 0.45 of the external lobe depth). Ventrolateral saddle narrowly rounded, adventive lobe with slightly sinuous flanks.

Type material

Holotype

IRELAND – County Leitrim • Townland of Carraun, north-east slope of Dough Mountain , two miles south-west of Kiltyclogher ; beds a few feet above the highest beds with G. sphaericostriatus ( Late Viséan) ; Moore and Hodson Coll.; GSM ZI3025 View Materials ; illustrated by Moore & Hodson (1958: pl. 3 figs 1–2), re-illustrated here in Fig. 15A View Fig .

Material examined

MOROCCO – Central Meseta • 24 specs; Sidi Amar , southern side of the Tabaïnout mountain ridge; Late Viséan ; 2011; Korn and Ebbighausen leg.; MB.C. 32217.1 to MB.C. 32217.24 .

Description

Specimen MB.C.32217.1 is the largest of the available specimens, with a conch diameter of 42 mm ( Fig. 15B View Fig ). The specimen is fully chambered and has undergone two phases of corrosion. The first phase occurred during embedding, which resulted in the destruction of the body chamber and the erosion of much of the shell surface. After this, the specimen acted as a ‘benthic island’, serving as a substrate for crinoids to attach. The second phase of erosion and corrosion occurred more recently, during the weathering of the surrounding shales. Consequently, only small fragments of the shell ornamentation have been preserved. The specimen is thinly pachyconic and involute (ww/dm = 0.70; uw/dm = 0.12); the preserved shell fragments exhibit fine spiral lines on the inner flank and widely spaced, apparently uncrenulated growth lines on the venter.

Specimen MB.C.32217.2 is a somewhat corroded, fully septate conch with a diameter of 23 mm ( Fig. 15C View Fig ). It is thickly pachyconic and subinvolute (ww/dm = 0.82; uw/dm = 0.23) with a moderately depressed whorl profile (ww/wh = 1.84) and a low coiling rate (WER = 1.54). Although much of the shell surface has eroded, some details are well preserved in the dorsal whorl area. The specimen possesses very coarse growth lines that curve backwards from the umbilicus, along with around ten spiral lines on the inner flank, which are much finer than the growth lines.

The six sectioned specimens (MB.C.32217.4–MB.C.32217.9) show remarkable similarity in both conch geometry and ontogeny ( Figs 16 View Fig , 17A–F View Fig ), resulting in minimal variation in the conch parameter diagrams ( Fig. 17G–I View Fig ). All specimens display a continuous transition from the early juvenile stage, characterised by a kidney-shaped whorl profile, to the middle ontogenetic stage, where the whorl profile becomes C-shaped. This shift is clearly reflected in the ontogenetic trajectories. The ww/wh ratio increases nearly to 3.00 up to a conch diameter of 3 mm, then decreases almost continuously to around 1.60 at a diameter of 20 mm. Similarly, the uw/dm trajectory rises to 0.50 by 2.5 mm in conch diameter, followed by a gradual decline to 0.20 at 30 mm. A common feature across in all cross sections is the sinuous umbilical wall, which becomes more pronounced in varying degrees once the conch reaches a diameter larger than 9 mm.

Remarks

Moore & Hodson (1958) described the type species as Hibernicoceras hibernicus , using a masculine ending, although Hibernicoceras actually requires a neuter ending. The authors consistently used this spelling, so it must be assumed that it was intentional. Since Moore & Hodson (1958) did not clarify whether they used “ hibernicus ” as an adjective (“Irish”) or as a noun (“the Irish”), the ending probably does not require a correction to “ hibernicum ” according to Article 34.2 of the ICZN Code ( ICZN 1999).

The specimen illustrated by Liang & Wang (1991) as Hibernicoceras hibernicum does obviously not belong to this species, as it exhibits spiral lines on the flank.

Hibernicoceras hibernicus is distinguished from most other species in the genus primarily by its stout conch. The ww/wh ratio of approximately 0.75 at a 30 mm conch diameter is higher than that of many other species, which typically do not exceed a value of 0.70. This is especially true for species such as H. mediocre , H. carraunense , and H. alentejoense ( Korn & Ebbighausen 2008) , which have longdistance growth lines. The species is particularly characterised by a sigmoidal umbilical wall with a spiral groove, rarely seen in other species.