Comprehensive DescriptionRead full entry
Alatotrochus rubescens (Moseley, 1876), comb. nov.
Platytrochus rubescens Moseley, 1876:553.
Sphenotrochus rubescens.—Moseley, 1881:157-159, pi. 6: figs. 8, 8a.
DESCRIPTION.—Corallum compressed, very much resembling the shape of Tropidocyathus lessoni, with thin, solid (not hollow) edge crests extending as much as 4 mm from the thecal edge. Largest Japanese specimen examined 16.1 x 10.5 mm in calicular diameter and 14.7 mm in height; however, the syntypes are larger: up to 20 x 16 mm in calicular diameter and 17-19 mm in height. Costae thin (about 0.8 mm wide), high, serrate ridges, one corresponding to each septum, and another of equal size corresponding to each interseptal space. Near calice the costae that correspond to septa widen at the expense of the interseptal costae. Additional costae, also uncorrelated to septa, cover the thecal edge crests, oriented at right angles to face costae. Many, but not all, costae are continuous from calice to base. The 2 principal costae extend along the outside of each lateral crest and are continuous along the sharp-edged base of the corallum, meeting one another at base epicenter. Intercostal spaces broad (0.18-0.20 mm) but diminish in width near calice. Theca, calicular edge, and exsert portion of septa reddish brown.
Septa hexamerally arranged in 4 cycles (48 septa) according to the formula: S1>S2>S3>S4; however, some larger syntypes have pairs of S5 in end half-systems, for a total of 56 septa. S1 highly exsert (up to 4 mm) and quite thick (0.25 mm), with straight, vertical inner edges that fuse with the columella low in fossa. S2 only slightly less exsert (about 3.5 mm), but otherwise similar to the S1. S3 2.0-2.2 mm exsert and about two-third width of an S1-2, with finely sinuous inner edges that do not attain the columella. S4 1.3-1.5 mm exsert and only about one-third width of an S3. All septal faces covered with very low, rounded granules, producing an apparently smooth aspect. Fossa shallow but commodious, caused by widely spaced septa and the absence of pali. Columella papillose, composed of 5 or 6 tall, cylindrical, finely granulated, aligned pillars, each pillar 0.4-0.7 mm in diameter and reaching almost to level of calice.
DISCUSSION.—This is only the second report of this rare and beautiful species, heretofore known only from four syntypes from the type locality. Aside from the six specimens reported herein from Bungo Strait, a Pleistocene specimen (USGS 17633) is tentatively assigned to this species. It differs only in that its four lateral C1 are swollen into robust protuberances near the calicular edge.
MATERIAL EXAMINED.—New Records: TM (KT9015, BS2), 5, USNM 92776, 1, ORI; TM (KT9309, AM7), 4, ORI; TM (KT9309, AM8), 1 ORI; USGS 17633, 1 km southwest of China, Chinen Peninsula, Okinawa, Ryukyu Islands, Pleistocene, 1, USNM 88672. Previous Records: 1 syntype of P. rubescens, BM.
TYPES.—Four syntypes of Platytrochus rubescens, one illustrated in Plate 29h,i,l, are deposited at the BM (1 numbered 18188.8.131.52). Type Locality: Challenger-192: 5°49' 15"S, 132°14'15"E(off Kei Island, Banda Sea), 136 m.
DISTRIBUTION.—Same as that for genus.”