Reteporellina denticulata (Busk, 1884)

Reteporellina denticulata (Busk, 1884) View in CoL

Figure 59 View FIGURE 59

v. 1884 Retepora denticulata Busk , p. 109, text-fig. 18, pl. 26, fig. 13.

v. 1934 Reteporellina denticulata (Busk) ; Harmer, p. 581, figs. 25D, 33, pl. 35, figs. 21–23, pl. 38, figs. 27–32.

v. 2010 Reteporellina denticulata (Busk) ; Hirose, p. 73, pl. 127A–H.

Figured material. PMC EDM-Collection J.H.B.148a, sample 19044 ( Figure 59A–B View FIGURE 59 ) and sample 19021 ( Figure 59C–I View FIGURE 59 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony erect, non-fenestrate, dichotomously branching with bifurcations occurring at angles of 60–80º; branches generally narrow, widest at bifurcations (145–700 µm wide), bi- to quadriserial. Autozooids distinct, separated by thin raised margins, arranged in alternating longitudinal rows, rectangular to rhomboidal, elongate (mean ZL/ZW 1.99). Frontal shield flat, faintly nodular, imperforate except for two marginal pores, slit-like and adjacent to the lateral sides, or rounded and located a certain distance from the margins, in both cases positioned in the proximal third of zooid, 8– 30 µm in maximum dimension. Primary orifice concealed by a deep, curved peristome extending away from the branch axis at an angle of approximately 90º to the frontal surface, having a flared rim with rounded crenulations and a narrow Ushaped medioproximal notch. Avicularium present or absent, adventitious, suboral, transversely placed, occupying the entire length of the proximal margin of the peristome; rostrum duckbill-shaped with crenulated tip directed laterally on either side; crossbar complete. Ovicell pyriform, elongate (mean OvL/OvW 1.22), occupying half to two-thirds of the frontal shield of the distal zooid, gradually covered by secondary calcification except for a median slit-like or upside-down drop-shaped fissure, 65–100 µm long by 20–40 µm wide; aperture rectangular with a narrow semicircular to semielliptical labellum. Dorsal side nodular to coarsely granular, with smooth, raised vibices outlining irregularly polygonal sectors of varying size; each sector with one or two sparse circular pores; avicularia uncommon, obliquely and randomly placed within the dorsal surface, usually adjacent to the proximal corner of a sector, triangular, elevated and hump-shaped, with a needle-like rostrum directed proximally to proximolaterally, and complete crossbar.

Measurements (µm). ZL 434±35, 366–504 (5, 27); ZW 218±56, 147–306 (5, 27); PeL 168±34, 120– 241 (5, 16); AvL (suboral) 131±16, 107–150 (3, 9); AvW (suboral) 46±7, 36–60 (3, 9); AvW (suboral; rostral tip) 65±10, 46–75 (3, 9); AvL (dorsal) 142±31, 124–178 (2, 3); AvW (dorsal) 46±5, 43–52 (2, 3); OvL 194±17, 162–222 (5, 17); OvW 159±14, 134–182 (5, 17).

Remarks. Reteporellina denticulata was first described from the Sandwich Islands at depths ranging from 36 to 73 m. Since then, it has been reported across a wide geographical range, from Australia (e.g., Hayward and Ryland, 1995) to the Indo-Pacific (e.g., Harmer, 1934), and into the North Pacific, with multiple records from Japan (Okada, 1920; Buchner, 1924; given in both publications as R. misakiensis (Okada, 1920) synonymized by Harmer, 1934; Hirose, 2010). Despite its seemingly implausible widespread distribution, the only notable morphological variation seems to be in the number of rows of autozooids in the branch, and the presence or absence of trabeculae lacking autozooids. Trabeculae are reported to be present in the type specimens, but we did not observe them in our samples. While their presence cannot be entirely ruled out due to the fragmented nature of our samples, the sheer number of fragments available (thousands) makes their presence highly unlikely. However, we prefer not to use these observed differences as the basis for introducing a new species currently, as a more thorough study, beyond the scope of this work, is needed.