Smittipora abyssicola

Smittipora abyssicola (Smitt, 1873)

(Fig. 3; Table 3)

Vincularia abyssicola Smitt, 1873: 6, pl. I, figs 60, 61.

Smittipora abyssicola: Jullien 1882: 284.

Material examined. Lectotype [designated here; figured in Smitt (1873, fig. 61)] SMNH-Type-1815, North Atlantic Ocean, Florida, United States, depth 124 m, on a solitary coral. Leg. Gulf Stream Explorations 1868–69, coll. L.F. De Pourtales. Paralectotype SMNH-Type-9104, North Atlantic Ocean, off Cojima, Cuba, depth 824 m, on a phidoloporid bryozoan. Leg. Gulf Stream Explorations 1868–69, coll. L.F. De Pourtales.

Description. Colony starting with a more or less developed encrusting base (Fig. 3A, B), and later becoming erect, forming cylindrical branches, about 1 mm in diameter, comprised of 4–6 alternating longitudinal series of autozooids and vicarious avicularia (Fig. 3B, C, E), oligo- to multiserial (depending on the substrate available), unilaminar.

Ancestrula elliptical, similar to later autozooids but smaller (Fig. 3A, D), c. 500 µm long by 380 µm wide; cryptocyst extensive, finely granular, sloping inwards laterally, depressed and flat centrally; opesia rounded quadrangular, almost equidimensional, 176 µm long by 188 µm wide; three zooids budded directly from the ancestrula, one distally and two distolaterally, either exclusively autozooids (Fig. 3A), or both autozooids and vicarious avicularia (Fig. 3D), smaller than subsequent generations (first budded zooid: c. 525 µm long by 350 µm wide; first vicarious avicularium: c. 375 µm long by 295 µm wide); ancestrula later surrounded by six zooids.

Autozooids distinct with raised margins and shallow grooves, those of the encrusting base quincuncially or irregularly arranged, those forming the cylindrical branches arranged in alternating longitudinal series (Fig. 3C, E); semi-elliptical, elongate with V-shaped proximal edge, sometimes rounded hexagonal, longer than wide (mean L/ W 1.56). Cryptocyst concave, finely granular, extensive (Fig. 3F). Opesia rounded quadrangular to rounded trapezoidal with proximal margin slightly concave (Fig. 3F) but slightly convex in periancestrular zooids (Fig. 3D).

Avicularia vicarious, smaller than autozooids, symmetrical, lozenge-shaped with acutely pointed proximal margin and rounded rostrum tip (Fig. 3D, F); mandible triangular (Fig. 3C), c. 600 µm long; cryptocyst concave and finely granular as in autozooids; opesia centrally located, oval to elliptical.

Fertile zooids not observed.

Remarks. In his description of Vincularia abyssicola, Smitt (1873) refers only to two specimens he obtained from Pourtales, one collected in deep waters off Cuba and encrusting a phidoloporid bryozoan (Fig. 3A), the other collected off Florida at a much lower depth and encrusting a coral (Fig. 3B). An additional specimen found in the collection (Fig. 4; SMNH-Type-1786 North Atlantic Ocean, Florida, United States, depth 124 m, encrusting bivalve shell. Leg. Gulf Stream Explorations 1868–69, coll. L.F. De Pourtales) and catalogued as an additional syntype of S. abyssicol a belongs instead to S. americana (Canu & Bassler, 1928). This species has leaf-shaped mandibles with long, pointed tips (Fig. 4A), and marked opesiular indentations (Fig. 4B).

Smittipora abyssicola, originally described from the western tropical Atlantic, was subsequently recorded pantropically, including the Pacific and Indian oceans. Some of these records were revised during the years, e.g. S. abyssicola sensu Harmer (1926) from Malaysia became the type species of S. harmeriana (Canu & Bassler, 1929), but some others await a revision. For instance, the specimen illustrated in Taylor et al. (2018, fig. 29) as Smittipora abyssicola from the west of East Channel, off Aldabra Island in the Indian Ocean, differs from the type specimens in having proportionally smaller opesiae with distinct opesiular indentations, and avicularia with pointed rostra.

Onychocellid genera are all very similar and there is a limited number of characters to distinguish one genus from the other. The main features used to distinguish Smittipora from Onychocella are the relatively smaller opesiae and the symmetrical avicularia in the former genus. In the type specimens of Smittipora studied here, the opesiae are proportionally smaller but simply quadrangular/trapezoidal in shape, without proximal indentations or lateral constrictions. Nonetheless, a great number of species with proximal opesiular indentations are currently assigned to the genus.

As already highlighted by Taylor et al. (2018), a thorough revision is needed of the 42 Recent and fossil species currently assigned to Smittipora (Bock 2022), considering that some of these species have, in addition to the marked opesiular indentations, also asymmetrical vicarious avicularia.