Microporella sp. A

Fig. 9

Examined material.

Italy • 1 dead colony fragment consisting of ca. 14 zooids (some incomplete), none fertile; Tyrrhenian Sea, Palinuro Cape, Scaletta submarine cave; sediment sample; 40°1'35"N, 15°16'7"E; 46 m; 14 Sep. 2009; R. Leonardi leg.; scuba diving; PMC Rosso Collection I. H. B. 88a .

Description.

Colony encrusting, multiserial, unilaminar.

Autozooids irregularly polygonal, rounded, 435-676 (510 ± 80, N = 7) × 255-427 µm (342 ± 68, N = 7) (mean L/W = 1.49), distinct, with interzooidal boundaries marked by a narrow, raised, gymnocystal rim (Fig. 9A). Frontal shield nearly flat to slightly convex, densely and coarsely granular and irregularly pseudoporous; granules 5-25 µm in diameter; 20-30 pseudopores, circular (5-12 μm in diameter), sparse in the proximal two-thirds of the zooid; 4-6 marginal areolae, usually visible at zooidal corners, circular to elliptical (10-40 µm long).

Orifice transversely D-shaped, 90-107 (94 ± 5, N = 10) × 118-143 (132 ± 9, N = 10) µm (mean OL/OW = 0.71; mean ZL/OL = 5.43); hinge-line straight, smooth to slightly crenulated; in each corner a short, blunt, triangular condyle directed distally (Fig. 9B). Oral spine bases four or five, 10-18 µm in diameter, evenly spaced, the proximalmost pair at about one-third of orifice length (Fig. 9B).

Ascopore field a narrow, elliptical area of smooth gymnocystal calcification (33-44 × 39-55 μm), placed 22-30 μm below the orifice, slightly depressed relative to the adjacent frontal shield; ascopore opening divided by thin radial septa, usually with a distinct tongue extending proximally from the distal edge (Fig. 9B).

Avicularium single, sometimes absent (two out of 14 zooids without avicularium in the fragment available), 93-123 (107 ± 12, N = 9) × 70-87 (79 ± 6, N = 9) μm (mean AvL/AvW = 1.36), located distolaterally, on either side; crossbar complete; rostrum short, triangular, not channelled, directed distolaterally, sometimes slightly raised distally (Fig. 9A, B). Mandible, ovicells and ancestrula not observed. Subsequent intramural budding observed in avicularia.

Remarks.

This species differs from its Mediterranean congeners in having a finely reticulate ascopore but it is left in open nomenclature owing to the availability of a single, infertile colony fragment. Similar ascopores can be found in M. arctica Norman, 1903 from Norway, M. ketchikanensis Dick, Grischenko & Mawatari, 2005 from Alaska, M. santabarbarensis Soule, Chaney & Morris, 2004 from southern California, and M. stellata (Verril, 1879) from Maine, USA. Microporella arctica differs from Microporella sp. A in having a finely granular frontal shield pierced by a greater number of marginal areolae that are always very distinct from pseudopores, in the lack of oral spines, and in having a smooth gymnocystal area laterally and proximally to the orifice that is continuous with the gymnocyst of the ascopore field ( Kukliński and Taylor 2008). The ascopores of both M. ketchikanensis and M. santabarbarensis have a similar, delicate cribrate aspect but lack the distal tongue extending from the distal edge (Dick et al. 2005; Soule et al. 2004). Microporella stellata differs in having only two oral spines and a proximal orifice margin with broad, rectangular condyles (Winston et al. 2000).

Distribution and ecology.

Presently known only from the Palinuro Peninsula, along the Tyrrhenian coast of Campania (southern Italy). A dead colony was collected from the biogenic muddy sediment covering the floor of a completely dark sector of the Scaletta submarine cave, at 46 m depth where the colony presumably lived.