Adeonellopsis arculifera (Canu & Bassler, 1929)

Fig. 6

Adeona arculifera Canu & Bassler, 1929: 377, pl. 52, figs 1–2.

Adeonellopsis arculifera – Harmer 1957: 800, text-figs 82C, 84A, pl. LIII, figs 13–14.

Adeonella subsulcata – Thornely 1905: 125.

Material examined

JAPAN: many branches collected from Hirase, southwest of Yakushima Island, 87–88 m depth (NSMT- Te781, Te783, Te784, Te785, Te786, Te787, Te788, Te789); single colony collected from South of Nagannu Island, 47–52 m depth (NSMT-Te782).

Measurements

Autozooids. ZL: 505̅762 (590±62); ZW: 207̅387 (288±53); n = 39. SOrL: 54̅91 (71±10); SOrW: 62̅103 (83±9); n = 30. SAvL: 76̅147 (100±13); SAvW: 50̅85 (64±7); n = 38. SpL: 12̅27 (20±4); SpW: 16̅25 (20±3); n = 28.

Description

Colony small, slender, dichotomously branching (Fig. 6A); yellowish white. Branches subcylindrical or flat (Fig. 6B); slender, on average 1 mm wide (0.9–1.3 mm, n = 8), multiserial, zooids opening on both sides. Zooids oval, boundaries indistinct, delineated by shallow groove and opposing single rows of tiny, irregular areolar pores (Fig. 6D). Frontal shield smooth, or finely granulate and slightly wrinkled. Zooids raised distally towards a low peristomial rim; primary orifice D-shaped, with straight or convex proximal margin; secondary orifice broader than long. Spiramen small, uniporous, circular, situated close to center of frontal shield proximal to orifice, often in depressed frontal zone (Fig. 6C). Suboral avicularium abutting proximal margin of peristome, smaller in area than secondary orifice, rostrum slightly raised and sometimes hooked distally, slightly curved toward distal side, directed distolaterally; no crossbar; mandible equilaterally triangular (Fig. 6C). No other types of avicularia observed. Autozooids distal to branch bifurcations elongate, sometimes bearing up to three umbonate bosses 47–76 μm in diameter (average 61 μm, n = 18), on one or both sides proximolateral to orifice and toward proximal end of frontal shield (Fig. 6D). Older autozooids in basal part of branch broad, irregular in outline; zooidal boundaries indistinct; frontal shield heavily secondarily calcified; spiramen often lacking; suboral avicularium lies in depression in thickened frontal shield (Fig. 6F). Rarely, kenozooids occur at basal bifurcations (Fig. 6E); same size as autozooids. Gonozooids not found.

Remarks

Canu & Bassler (1929) originally described Adeona arculifera from Jolo and Sulade Islands, Sulu Archipelago, Philippines, on the basis of the single spiramen, although the branched colony resembles the condition in Adeonellopsis . Harmer (1957) then transferred the species to Adeonellopsis on the basis of the operculum, which is not widely sinuate. Adeonellopsis arculifera resembles A. subsulcata (Smitt, 1873) in the arrangement of the suboral avicularia but differs from the latter in having a circular spiramen in the center of the frontal shield.

Distribution

Adeonellopsis arculifera has previously been reported from the Philippines, Indonesia, and the Indian Ocean, at depths of 38– 53 m. In Japan, it has been detected only in the southwestern region, from Okinawa and near Yakushima Island, at depths of 47– 88 m. Although this is the first Recent record for Japan, Hayami (1971) reported the species from the Pliocene Shinzato Tuff on Okinawa Island.