Heliodoma goesi Silen 1942

Heliodoma goesi Silén, 1942a

(Fig. 15; Table 15)

Heliodoma goësi Silén, 1942a: 2, fig. 2, pl. 1, figs 3, 4.

Setosellina goesi: Lagaaij 1963: 172, pl. 2, fig. 1.

Material examined. Lectotype SMNH-Type-1892a [designated here (Fig. 15A, B); this specimen was illustrated in Silén (1942a, pl. 1, fig. 4)], Caribbean Sea, Virgin Islands, West Indies; depth 366–549 m. Leg. A. Goës 1869. Paralectotypes SMNH-Type-1892b (Fig. 15C, D), c (Fig. 15E–I), and d (Fig. 15J), same details as lectotype. Paralectotypes SMNH-Type-1892e-j (not figured).

Other species material for comparison: Heliodoma implicata Calvet, 1906 SMNH-128026 and SMNH-128027 (Fig. 16E–G; see also Silén 1942a, pl. 1, fig. 2), including two colonies each; North Atlantic Ocean, Sao Miguel, off Vila Franca do Campo, Azores. Gravel with clay. Leg. Josephine Expedition 1869, station e35-42. SMNH-127828 (Fig. 16A–D; see also Silén 1942a, pl. 1, fig. 1), one colony; North Atlantic Ocean, Sao Miguel, off Vila Franca do Campo, Azores. Gravel and volcanic rocks. Leg. Josephine Expedition 1869, station e2-10.

Description. Colony encrusting substrates less than 2 mm in diameter (colony size: 1.099 –1.491 mm long by 1.057 –1.450 mm wide; L/ W 0.77 –1.23; N 10), S-shaped (Fig. 15A), flat, including 10–16 autozooids in addition to the ancestrula; in some colonies the peripheral zooids growing beyond the substrate to a limited extent, without enveloping the underside (Fig. 15A, C, J).

Ancestrula elliptical, budding one distolateral vibraculum and two autozooids, one distal and the other distolaterally at a right angle from each other, giving origin to two concentric clock-wise spirals of zooids and associated vibracula (Fig. 15A, C, E); ancestrula, 258–280 µm long by 185–230 µm wide (measured from the gymnocystal rim, gymnocystal boundaries undefined) with the frontal surface occupied almost entirely by the oval opesia (230–270 µm long by 170–185 µm wide); first budded zooids 280–335 µm long by 180–230 µm wide including the gymnocyst (230–300 µm long by 180–210 µm wide if measured from the gymnocystal rim), opesia oval (195–230 µm long by 150–175 µm wide) narrower distally; ancestrula and first budded zooids sometimes sealed by a nodular lamina leaving a more or less centrally placed elliptical opening (Fig. 15A, B).

Autozooids oval, longer than wide (mean L/ W 1.53). Gymnocyst smooth, convex, extensive proximally, narrow laterally, minimal distally, forming a raised mural rim outlining the autozooids (Fig. 15B, D, F, G); gymnocystal boundaries mostly undefined, sometimes with narrow grooves. Cryptocyst beaded, very thin proximally and laterally (10–15 µm), disappearing distally (Fig. 15G, H). Interzooidal communication through depressed multiporous septula, two elliptical, 30–70 µm long by 18–30 µm wide, visible on lateral walls (one proximolateral and one distolateral) of external zooids (Fig. 15D, E arrowed). Intramural buds common in autozooids, visible through the opesia as concentric rims (Fig. 15B, I). Opesia oval, narrower distally, occupying almost the entire length of the frontal surface (Fig. 15F, G); operculum semicircular (Fig. 15B).

A vibraculum present distolaterally to each autozooid, those at the periphery of the colony globular, often with a more developed cystid (Fig. 15D, F); opesia occupying most of the length of the frontal surface but much narrower, figure-8-shaped with two small teeth in the middle; seta thin and curved, about 350 µm long (Fig. 15B).

Ovicells terminal, cap-like, closed by the operculum; ooecium smooth with a central pore on the centre of a depression of variable size, not always visible in frontal view (Fig. 15H, I arrowed).

Kenozooids absent.

Remarks. Silén (1942a) placed this species in Heliodoma acknowledging that the differences between the genera Heliodoma and Setosellina Calvet, 1906 were vague, and that the type species of the genus, H. implicata Calvet, 1906, differed from his new species in having a more extensive cryptocyst proximally and laterally (Fig. 16F), as well as nodular closure plates sealing the opesia of the first generations of zooids except for the area occupied by the operculum (Fig. 16A, B). Closure plates, although different in appearance, can be seen also in the central zooids of H. goesi (Fig. 15A, B). In this case the calcification starts from the periphery of the opesia towards the centre, leaving a central, oval opening.

In the diagnosis of Heliodoma, Calvet (1906, p. 157) mentioned the double, concentric spiral arrangement of the zooids, while in the diagnosis of Setosellina (Calvet 1906, p. 157) the main character mentioned is the position of the vibracula, corresponding with the longitudinal axis of the zooid; there is no mention of the development of the cryptocyst. In Silén’s species, zooids are arranged in a double spiral pattern, and vibracula are placed distolaterally not distally, therefore leaning more on one side, not corresponding to the zooidal axis. The vibraculum is distally placed in the type species, S. roulei Calvet, 1906 (see also Calvet 1907, pl. 26, fig. 5, 6; Di Martino & Taylor 2014b, pl. 22, fig. 2a, b for additional non-type material), and also in other species, e.g. S. constricta Harmer, 1926 (see Di Martino & Taylor 2018, figs 23, 24).

Harmelin (1977) highlights the undivided zooidal spirals in Heliodoma, observed also in the syntypes of H. goesi and previously pointed out by Silén (1942a) as the main difference between the two genera.

The development of the cryptocyst was never mentioned as a generic diagnostic character. In the two species currently included in Heliodoma, the extension of the cryptocyst varies from moderate in the type species, to narrow in the Pleistocene H. angusta Rosso, 1998 which appears similar to H. goesi.

Based on these considerations, the original combination Heliodoma goesi is here reinstated. The first attribution of the species to Setosellina rather than Heliodoma is in Lagaaij (1963) but the reasons leading to this action are not stated. Since then, it has always been reported as Setosellina (e.g. Cook 1965; Cook 1985; Rosso 2008).

Molecular data will be essential to confirm the difference between the two genera. Unfortunately, representatives of the Heliodomidae have not been sequenced yet, likely due to the difficulty in obtaining suitable samples, given the small size of the colonies and their occurrence in deep water settings.

Heliodoma goesi was reported from a variety of sand-sized substrates, including quartz grains and carbonate bioclasts such as foraminifera tests (Lagaaij 1963; Cook 1985; Rosso 2008). Colonies examined here were encrusting tests of Globorotalia menardii (d’Orbigny in Parker, Jones & Brady, 1865). The extension to which the colonies are able to grow independently of the substrate varies depending on the species in both Heliodoma and Setosellina. In H. implicata and H. angusta, up to several generations of autozooids can be budded free from the substrate (e.g. Silén 1942a; Rosso 1998), while in H. goesi only the last generation of zooids can be partially free from it (Fig. 15J; see also Silén 1942a). Among Setosellina species, some such as S. capriensis (Waters, 1926), are able to grow extensively away from the substrate (see Håkansson & Zagoršek 2020, fig. 12.4), while others, such as S. constricta, are able to envelop the underside of the substrate producing clusters of kenozooids (Di Martino & Taylor 2018, figs 23, 24; Di Martino et al. 2019, fig. 2).

All paralectotypes were SEMed, and additional images not published here will be made available through the SMNH online catalogue.