Spiroloculina Mamo, 2016, sensu

Spiroloculina sp. cf. S. depressa d’Orbigny 1826 (Fig. 6:20, 21)

Description. See Debenay (2012, p. 133, pl. 5).

Remarks. This species was classified under S. depressa due to its rounded lateral view, nearly parallel sides giving a flat to slightly compressed cross-section and its round, terminal aperture on a short neck with a small lip and single tooth. Classification remains uncertain due to low abundance, the inflated peripheral chambers and the lack of both compression towards the test’s centre and of raised inner margins that are frequently found with this species (Cuvier et al. 1834; Debenay 2012).

Despite the lack of raised margins and compression causing uncertainty with CG specimens, these features both vary within the species. For instance, compare specimens of Cuvier et al. (1834: pl. 6. fig. 7) and Debenay (2012: p. 133) with strongly raised inner margins between chambers to Brady’s (1884: pl. 9, fig. 7) and Cushman’s (1921, p. 81, fig. 2) where there are none.

Spiroloculina sp. cf. S. depressa bears similarity to Spiroloculina sp. 1 in possessing a short neck and parallel sides, giving the test a flat cross-section. They differ in that Spiroloculina sp. 1 has massiline coiling and does not have inflated chambers and therefore a less rounded and more carinate periphery.

D’Orbigny (1826) originally collected fossil forms of S. depressa from Castell’Arquato, Italy and has since been extensively reported globally (Bay of Biscay, Irish Sea, Guam, North Atlantic, United States, Mediterranean Sea, Japan, Red Sea—Brady 1884 and Gross 2014; Philippines—Cushman 1921b; New Caledonia from 10–411 m—Debenay 2012).

Distribution within study area. Spiroloculina sp. cf. S. depressa does not occur in high abundance within the CG—no more than six specimens were collected per site. The greatest abundance was from site 53 of One Tree Lagoon 2 and was collected from only one site within Heron Lagoon. This species was absent from both Sykes Reef and the channel sample.

Spiroloculina foveolata Egger 1893 (Fig. 7:1, 2)

1893 Spiroloculina foveolata Egger, p. 224, pl. 1, figs 33, 34.

1918 Spiroloculina elegans Cushman, p. 290, pl. 96, figs 1, 2.

1988 Spiroloculina foveolata Egger; Haig, p. 234, pl. 10, figs 14, 15. 1994 Spiroloculina foveolata Egger; Loeblich & Tappan, p. 43, pl. 66, figs 9, 10. 1995 Spiroloculina foveolata Egger; Lobegeier, p. 68, pl. 1, figs 11, 12. 2009 Spiroloculina foveolata Egger; Parker, p. 346, fig. 250a–f.

Description. See Cushman (1918, p. 290, pl. 96, figs 1,2) and Parker (2009, p. 346, fig. 250a–f).

Remarks. This spiroloculine taxon is characterised by a long neck that terminates in a rounded aperture and distinct wall ornament of regular elliptical depressions (Fig. 7:1, 2).

Original illustrations of Spiroloculina foveolata by Egger (1893, pl. 1, figs 33, 34) do not show typical spiroloculine coiling, nor does the distinctive reticulate ornamentation extend completely to the tip of the neck to the aperture. Millett (1898), who actually considered S. foveolata to be a variety of S. nitida d’Orbigny 1826, indicated that Egger’s (1893) material only represented juvenile specimens. This confusion was possibly behind Cushman’s (1918) decision to establish Spiroloculina elegans, which he thought was sufficiently different from S. foveolata as illustrated by Egger (1893). It is now clear however, that Cushman’s (1918, p. 209, pl. 96, figs 1, 2) description and illustrations are accurate representations of S. foveolata sensu stricto, and so all specimens from the CG and previous published specimens described as S. elegans Cushman 1918 should be referred to S. foveolata based on priority (Haig 1988; Loeblich & Tappan 1994; Lobegeier 1995; Parker 2009).

Egger’s (1893) type specimens of S. foveolata were collected from a depth of 137 m off Mauritius and Cushman’s (1918) specimens came from Murray Island, GBR. Whilst there are differences between Egger’s (1893) illustrations and specimens collected from the CG, Cushman’s (1918) illustrations show a test with the aperture and neck tip broken off, so it is difficult to discern aperture characteristics. The CG specimens most closely resemble those illustrated by Haig (1988) from the Papuan Lagoon and Lobegeier (1995) from Low Isles, GBR. By having a long neck that terminates with a moderate lip and dentition consisting of two short, nub-like, directly opposing teeth; one or both teeth are split at the tip to become bifid. The tip of the neck, directly beneath the peristomal rim, has scute-like marks which are likely undeveloped reticulate ornament (Fig. 7:2). The individual pits of the ornament are very closely spaced on all specimens reported by Haig (1988), Lobegeier (1995) and CG specimens reported here.

Haig (1988) reported this species as a common constituent in back-reef, channel and fore-reef environments. Lobegeiger (1995) lists S. foveolata as a common species from the Low Isles Reef Flat, mangrove and shallow water sediments. Loeblich & Tappan’s (1994) specimens retrieved at a depth of 30 m from the central Timor Sea have more compressed tests, the individual reticulate pits are smaller, the sutures are far less distinct and the overlapping nature of external chambers over the inner is far less obvious than in the Papuan Lagoon and GBR specimens (Cushman 1918; Haig 1988; Lobegeier 1995). In addition, the neck of the Timor (Loeblich & Tappan 1994) specimens is short and stout, with only a very thin peristomal rim; the circular aperture is smaller and the dentition consists of a single, proportionally larger Y-shaped bifid tooth. Parker’s (2009) specimen from Ningaloo Reef is similar to those collected from the CG except that its elliptical depressions are spaced further apart and the dentition consists of a single nub-like tooth that is not bifid and has no second tooth positioned directly opposite.

Distribution within study area. Spiroloculina foveolata was recovered in relatively low numbers within the CG with no more than four specimens per sample. It is the third most abundant Spiroloculina species. This species was not collected from Sykes Reef and was rare on the Heron Reef flat. Site 48 in One Tree Lagoon 3 had the greatest abundance of S. foveolata.