Fungiacyathus (Fungiacyathus) stephanus (Alcock 1893)

Fungiacyathus (Fungiacyathus) stephanus (Alcock, 1893)

Bathyactis symmetricus.—Moseley, 1881:189 [in part: Challenger 194].—?Wood-Mason and Alcock, 1891a:8.—?Alcock, 1898:28; 1902a:37 [in part: Siboga 12, 18].

Bathyactis stephanus Alcock, 1893a:149, pl. 5: figs. 12, 12a.

Bathyactis stephana.—Alcock, 1898:28–29, pl. 3: figs. 5, 5a; 1902a:38; 1902b, fig. 93.—Gardiner and Waugh, 1939:232.

?Bathyactis sibogae Alcock, 1902a:38 [in part: specimen 57 mm in calicular diameter, Siboga 95 or 159].

Bathyactis symmetrica.—Gardiner and Waugh, 1939:230–231.

Fungiacyathus stephana.—Wells, 1977:7.

?Fungiacyathus sibogae.—Van Soest, 1979:109 [in part: probably Siboga 95 or 159].

Not Fungiacyathus sp. cf. F. stephanus.—Wells, 1984:207, pl. 1: figs. 3, 4 [= F. paliferus].

DESCRIPTION.—The study material contains specimens representing two morphological forms: one with a concave base and very exsert septa, referred to as the typical form; the other with a flat base and less prominent septa, referred to as the flat-based form.

Corallum of typical form up to 39 mm in diameter and 18 mm tall, often with an extremely concave base. Flat-based form up to 50 mm in diameter and 14 mm tall, with a perfectly flat base. Coralla of both forms extremely fragile, but corallum porosity not evident in well-preserved coralla. Costae consist of thin (0.8–1.0 mm wide), finely serrate ridges, which become more prominent (up to 0.75 mm tall) and slightly sinuous toward calicular edge. Costal dentition fine, each tooth roughly cylindrical, about 51 μm in diameter and 0.10 mm tall. Intercostal area about 0.75 mm wide and smooth peripherally, somewhat granular near epicenter. C5 originates about 6 mm from epicenter, corresponding to inception of S5 on basal plate.

Septa hexamerally arranged in five complete cycles. Six S1 largest septa, each forming a very tall internal lobe, which decreases in size abruptly, often having a vertical outer edge but continuing to the calicular edge as a low ridge. S1 of typical form composed of 20–23 trabeculae that steadily increase in size from the columella to the 10th or 11th trabeculum and then rapidly decrease in size peripherally. In contrast, in the larger corallum and longer septa of the flat-based form there are fewer trabeculae, e.g., 14–19, the tallest trabeculae occurring in the 7th to 9th positions. S2 only slightly smaller than, S1, but more obliquely inclined from the fossa and therefore having a septal apex farther from the fossa and slightly lower than that of the S1. S3 inclined even farther, with a crown of 12 septal lobes positioned lower and more peripheral than those of the S2. Septal lobes of S4 considerably smaller; S5 lack septal lobes. All septa are highly corrugated, corresponding to the underlying trabeculae, each crest bearing a row of fine triangular teeth, each tooth about 0.11 mm tall and spaced about 0.28 mm apart; however, in well-preserved specimens it is clear that the corrugations attenuate at the upper septal edges forming smooth, straight, continuous upper septal borders. S1 independent, united to adjacent septa only by synapticular plates; septa of all other cycles joined to one another by porous triangular canopies. Canopies linking S3 to S2 occupy about of calicular radius, those linking S4 to S3 about of calicular radius, and those linking S5 to S4 occupy about of calicular radius and are the lowest and best developed of the canopies. Canopies uniting the larger septa are better developed in the flat-based form. Each S1 of the typical form has 10–13 T-shaped synapticular plates gradually increasing in size from the columella to the 6th or 7th position, and then decreasing in size peripherally. Probably because of its larger size, the flat-based form has 13–15 synapticular plates per S1, with the largest in the 7th to 9th position. In both forms, the tallest synapticular plate is equal in height to an adjacent S4. Synapticulae do not form rings; they are rarely continuous across a septum. Both septal trabeculae and synapticular plates are obliquely inclined away from the fossa, but the former more so, such that in the typical form it is not unusual for the 6th synapticular plate to reinforce and obliquely intersect the 11th trabeculum at the height of the septal lobe. In well-preserved coralla, which are rare in this fragile species, a marginal shelf is present beyond the outler edges of the outer septal lobes. The shelf is about 5 mm wide, composed of the outer edges of the 96 septa, all of which are about 1.5 mm tall at this radius.

Frequently there is a crown of six acute P2 near the columella originating from the S2–S3 canopies. A ring of 12 P3 is also sometimes present near the S3–S4 canopies; however, there is great variation in both size and presence of paliform lobes. If present, the P2 are about 1.0 mm broad; the P3, 2.5–3.0 mm broad. Columella a low, loose fusion of inner septa about 4.5 mm in diameter.

Fungiacyathus (F.) stephanus (Alcock, 1893)

Bathyactis stephanus Alcock, 1893:149, pl. 5: figs. 12, 12a.

Bathyactis stephana.—Alcock, 1898:28–29, pl. 3: figs. 5, 5a; 1902c:38.

Fungiacyathus stephanus.—Cairns, 1989a:7–9, pl. 1: figs. a-k; pl. 2: figs. a,b [synonymy].—Cairns and Keller, 1993:230:

DESCRIPTION.—Corallum circular and quite fragile, the more typical concave-base form up to 39 mm in diameter and 20 mm in height (D:H = 1.95), whereas the flat-base form attains 45 mm in diameter but only 16–17 mm in height (D:H = 2.7). Costal ridges thin, finely dentate, and straight to slightly sinuous. Corallum white.

Septa hexamerally arranged in 5 complete cycles according to the formula: S1>S2>S3>S4>S5. S1 composed of an extremely tall inner lobe bearing 12–14 vertical, finely dentate ridges (trabeculae) and a lower outer marginal shelf about 5 mm wide and only about 1.5–2.0 mm in height. Ten to 13 synapticulae occur along an S1 of a large specimen, the largest synapticulae being 6th or 7th from columella, which rise about to level of adjacent S4. Each S2 bears a prominent paliform lobe internally, followed by a tall septal lobe (but smaller than that of the S1) composed of 10–12 trabeculae, and a similar outer marginal shelf. Each S3 also has an inner paliform lobe but more recessed from the columella, a smaller and lower septal lobe, and a peripheral marginal shelf. S4 joined to adjacent S3 in a canopied structure, lack paliform lobes, and have only a small septal lobe and low marginal shelf. S5 quite small, lacking both paliform and septal lobes, and merge with adjacent S4 via a long, low canopied structure; their outer shelf region is only about 0.5 mm in height. All septal faces corrugated, but upper septal edges are often straight. Columella a low, circular trabecular mass 4–5 mm in diameter.

azooxanthellate

245-2000 m

Known from seamounts and knolls

bathyal