Aspidostoma sarcophagus, Boonzaaier-Davids & Florence & Gibbons, 2020

Boonzaaier-Davids, Melissa K., Florence, Wayne K. & Gibbons, Mark J., 2020, Novel taxa of Cheilostomata Bryozoa discovered in the historical backlogs of the Iziko South African Museum, Zootaxa 4820 (1), pp. 105-133 : 110-111

Aspidostoma sarcophagus n. sp.

( Fig. 3 C–F, Table 2)

zoobank.org/ 489350B7-CC68-4B37-98F3-5567DC116C47

Material examined. Holotype: SAMC-A 029067 (dry), AFR273 A31605 (34°25’22.4”S, 22°52’58.7”E), off Mossel Bay, South Coast, South Africa, trawl, depth 100–102 m, 16 April 2011. Additional comparative material: Aspidostoma magna, NHMUK 1978.2.2.31, station SM 41 (28°41’42.0”S, 32°34’30.0”E), off Richard’s Bay, East Coast, South Africa, bongo, depth 880 m, 29 June 1975. Aspidostoma livida , SAMC-A 026420 (holotype), station SM 239 (32°14.8’S, 29°00.8’E), off Mbhanyana River Mouth, Southeast Coast, South Africa, RV Meiring Naude Survey, double beam trawl, depth 90 m, 25 June 1979. ‘ Aspidostoma livida’ (= A. giganteum ), SAMC-A 028660, station ANO183 (33°56’S, 18°22’E), off Clifton Beach, West Coast, collected by G. Harkins, depth 95 m, 30 May 2000.

Etymology. From sarcophagus (anglicized spelling of a Greek word to indicate the ancient Egyptian anthropoid coffins), referring to the hexagonal (sarcophagus-like) shape of the zooids. Used as a name in apposition.

Diagnosis. Colony erect, bilaminar, thickly calcified. Autozooids with extensive, granular cryptocyst with scattered pits in the centre; antler-like processes developing in late ontogeny at zooidal distal corners. Opesia with ‘axe head-shaped’ lip and paired opesiular channels proximally. Avicularia absent. Ovicell globular, prominent; ooecium helmet-shaped formed by the distal autozooid. Kenozooids present.

Description. Colony erect, rigid, forming broad, bilaminar, (seemingly) anastomosing branches; the largest of three fragments about 46 mm long by 30 mm wide; dark maroon colour in dried material. Autozooids roughly hexagonal, large, 1.17 mm long by 0.78 mm wide, distinct by wavy sutures. Frontal shield convex; cryptocyst with scattered pits concentrated in the centre, a few pits (if any) distally above the opesia. Opesia rounded triangular or semicircular, the proximal border forming a thick ‘axe head-shaped’ lip about 0.23 ± 0.01 mm wide (N T = 9) with paired opesiular channels. Distal end of autozooids forming a raised rim, frequently with blunt processes developing on each corner, in later ontogeny becoming antler-like processes about 0.38 mm long, persisting in ovicelled autozooids. Ovicell prominent; ooecium formed by distal autozooid, comprised of membranous ectooecium and thick calcified entooecium, helmet-shaped, longer than wide, with convex lip proximally, imperforate with finely granular surface in cleaned specimens, lateral sides becoming covered by secondary calcification formed by the maternal zooid. Kenozooids hexagonal, scattered throughout the colony, often as large as autozooids; frontal wall granular with cryptocystal pits. Avicularia not observed.

Remarks. Aspidostoma Hincks, 1881 is an ancient genus reported since the Cretaceous ( Canu 1900, 1911), and also known from the early Cenozoic deposits of Patagonia, Australia and New Zealand ( Brown 1952; Gordon & Taylor 1999). Only four extant species are known today, namely A. giganteum Busk, 1854 , A. coronatum Thornely, 1924 , A. magna Hayward & Cook, 1979 , and A. livida Hayward & Cook, 1983 ; the latter two species considered endemic to South Africa.

Aspidostoma giganteum has a widespread distribution in the South Atlantic Ocean, from Magellan Strait to the Falkland Isles, across the southern Patagonia Shelf, and also recorded in Gough Island, ranging as south as the South Shetland Isles in the Antarctic ( Hayward 1995). This species is characterised by hexagonal-shaped autozooids, a proximal raised lip notched on each side, and small interzooidal avicularia sparsely distributed throughout the colony ( Hayward 1995). Upon further inspection, one of the colonies (SAMC-A028660, in ethanol) in the SAMC Bryozoa collection (previously identified as A. livida ) is, in fact, the only known record of A. giganteum from the West Coast of South Africa.

The Antarctic species A. coronatum , also reported in Eocene material ( Hara 2001; Hayward 1995), is similar to A. sarcophagus n. sp. in having distolateral horns, sporadic kenozooids, irregularly distributed frontal pits, finely granular surface and convex hexagonal autozooids ( Hayward 1995). However, A. coronatum differs from A. sarcophagus n. sp. in forming thick nodular fronds, as well as in having interzooidal avicularia and distinct marginal pores.

The present material was also compared to both A. magna and A. livida found in South Africa. Aspidostoma magna differs from A. sarcophagus n. sp. in having erect, subcylindrical colonies, a frontal umbo on the ooecium and a conical knob proximal to the opesia ( Hayward & Cook 1979, p. 74). Aspidostoma livida differs also from A. sarcophagus n. sp. in having sporadic distolateral interzooidal avicularia and fenestrulae rimmed by a single series of sizeable kenozooids. Additionally, A. livida has smaller autozooids (0.89 mm long by 0.73 mm wide, see Hayward & Cook 1983, p. 36) than A. sarcophagus n. sp. (1.07–1.35 mm long by 0.63–0.87 mm wide, see also Table 2).

Aspidostoma sarcophagus n. sp. is only known from the South Coast of South Africa, off Knysna, at 100–102 m depth.

Figures

FIGURE 3. A–B. Chaperiopsis familiaris n. comb. (SAMC-A026415) A. Group of zooids, some with ovicells (scale bar = 0.4 mm, magnified x120). B. Closer view of some ovicelled zooids (scale bar = 0.2 mm, magnified x250). C–F. Aspidostoma sarcophagus n. sp. (SAMC-A029067). C. Zooids and kenozooids with cryptocystal pits (scale bar = 0.5 mm, magnified x35). D. Close-up of the orifice (scale bar = 0.2 mm, magnified x150). E. Developing antler-like processes (scale bar = 0.2 mm, magnified x100). F. Ovicelled zooid with well-developed antler-like processes (zooid on the left) (scale bar = 0.4 mm, magnified x50).