Microporella pachyspina, Martino & Rosso, 2021

Martino, Emanuela Di & Rosso, Antonietta, 2021, Seek and ye shall find: new species and new records of Microporella (Bryozoa, Cheilostomatida) in the Mediterranean, ZooKeys 1053, pp. 1-42 : 1

Microporella pachyspina sp. nov.

Fig. 8

Type material.

Holotype: Italy • 1 living colony consisting of about 50 zooids, several fertile; Sicily Strait, Egadi Islands, Marettimo Island; 37°56'59"N, 12°3'56"E; sample ECE5; 8 m; summer 2007; A. Sinagra leg.; IA and HP Biocoenoses; scuba diving; PMC. B31a.3.12.2020. Paratypes: Italy • ECE5, 2 living, fertile colonies, one including the ancestrula on a Posidonia oceanica leaf; same details as the holotype; PMC. B31b. 3.12.2020.

Other material.

Italy • a few living colonies, Sicily Strait, Egadi Islands, Marettimo Island ; 37°56'43"N, 12°5'3"E; sample EBE4; 19 m; summer 2007; A. Sinagra leg.; IA-HP Biocoenoses; scuba diving; PMC Rosso Collection I. H. B. 87a .

Diagnosis.

Colony encrusting, multiserial. Autozooid frontal shield granular and centrally pseudoporous. Orifice transversely D-shaped; hinge-line smooth with rectangular condyles at corners; five (more commonly) to eight oral spines, the proximalmost pair placed slightly below the orifice hinge-line and very large in diameter. Ascopore field reniform to elliptical, developing a mucro proximally; ascopore opening transversely C-shaped, with tongue and radial spines. Avicularium single, located at half zooidal length, directed distolaterally; crossbar complete; rostrum triangular, channelled. Ovicell produced by distal autozooid, non-personate.

Description.

Colony encrusting, multiserial, unilaminar, forming subcircular patches less than 1 cm in diameter, consisting of several tens of zooids, typically on Posidonia leaves; interzooidal communications through pore chamber windows along lateral walls (44-99 × 12-20 μm), two elliptical pairs placed proximolaterally and distolaterally, and a single distal one more rounded.

Autozooids hexagonal, 374-510 (442 ± 50, N = 24) × 257-346 (290 ± 31, N = 24) µm (mean L/W = 1.52), distinct with interzooidal boundaries marked by deep grooves between salient vertical walls (Fig. 8A ), often exposing the smooth, lateral gymnocyst. Frontal shield nearly flat proximally, slightly convex disto-centrally, finely to coarsely granular and pseudoporous (Fig. 8C, D ); granules 5-10 µm in diameter, irregularly spaced; 6-18 pseudopores, circular (7-25 μm in diameter), irregularly arranged, mostly centrally in the proximal half of the zooid; 3-6 marginal areolae, usually visible at zooidal corners, those placed proximally and laterally fissure-like (up to 90 μm long), the single or paired distal ones rounded (20 µm in diameter).

Orifice transversely D-shaped, 75-93 (84 ± 6, N = 15) × 89-127 µm (108 ± 12, N = 15) (mean OL/OW = 0.78; mean ZL/OL = 5.17), outlined by a thin and smooth raised rim; hinge-line straight, smooth, with a pair of rectangular condyles at corners (Fig. 8B ). Five (Fig. 8B ) (occasionally 6-8: Fig. 8G ) oral spines; the proximalmost pair robust, the base 36-51 µm in diameter, horn-shaped, terminally tapering and bending, placed slightly below the level of the orifice hinge-line, persisting in ovicellate autozooids (Fig. 8E ); the three (occasionally 4-6) distal spines thinner (base diameter 13-32 μm).

Ascopore field a reniform to elliptical area of smooth gymnocystal calcification (39-78 × 45-102 μm), more extensive proximally, developing a pointed, upward directed mucro not concealing the ascopore opening, placed 30-60 μm below the orifice, slightly depressed relative to the adjacent frontal shield (Fig. 8D ); opening transversely C-shaped, 32-64 × 7-18 μm, with subcircular tongue projecting from distal edge and radial, tiny denticles.

Avicularium single, often absent (e.g., 40% of zooids without avicularium in a colony of 42 zooids), moderately large, 76-115 (94 ± 10, N = 33) × 48-78 μm (63 ± 9, N = 33) (mean AvL/AvW = 1.50), located laterally, on either side, at about half zooidal length; crossbar complete; rostrum short, rounded triangular, channelled, directed distolaterally, often raised distally on a smooth, gymnocystal cystid (Fig. 8C ). Mandible 143-224 μm long, pointed, with a hook at about one-third of its length that clamps it to the rostrum tip, lying proximally to ascopore when open (Fig. 8G ).

Ovicell non-personate, subglobular, prominent, 216-320 (251 ± 23, N = 20) × 241-312 (288 ± 22, N = 20) μm (mean OvL/OvW = 0.87), obscuring half to two-thirds of the zooidal orifice, formed by and continuous with frontal shield of distal zooid (Fig. 8E ) (occasionally of two zooids), lateral gymnocystal margins raised, exceeding boundaries of the autozooid on which it lies; calcification fabric similar to frontal shield but with smaller and more widely-spaced granules, sometimes completely smooth centrally and with a rounded mucro (Fig. 8A, E ); imperforate except for 12-18 large pseudopores aligned in a peripheral row, closely and evenly spaced, separated by radial ridges, rounded quadrangular, 17-42 μm in diameter, plus an additional, discontinuous inner row of 4-6 smaller, circular pseudopores (5-10 μm).

Ancestrula tatiform, oval (300 × 218 μm), gymnocyst moderately developed, more extensive proximally (Fig. 8F ); opesia subcircular, surrounded by a well-developed, smooth cryptocyst, more extensive proximally, narrowing distally, outlined by a thin elevated rim indented by ten gymnocystal spines (six distal, two median, two proximal). Ancestrula budding two distolateral autozooids, followed by two lateral and two proximolateral ones.

Etymology.

From the Greek pachys, meaning thick, and the Latin spina meaning spine, referring to the robust proximalmost pair of oral spines.

Remarks.

The main diagnostic character of Microporella pachyspina sp. nov. is the great size of the proximalmost pair of oral spines, as well as their position, halfway below the level of the orifice hinge-line. Among Microporella species known worldwide, M. alaskana Dick & Ross, 1988 from the eastern Pacific, M. echinata Androsova, 1958, and M. trigonellata Suwa & Mawatari, 1998, both from off Japan, share similar features. In M. alaskana the proximalmost pair of spines are larger in diameter compared to the remaining spines but they are placed more distally compared to the new species, approximately at orifice mid-length ( Dick and Ross 1988); in addition, this species has paired avicularia, the ascopore is placed very close to the orifice hinge-line, and there is a prominent umbo centrally on the frontal shield ( Dick and Ross 1988). Microporella echinata differs in having an evenly pseudoporous frontal shield, with pseudopores visibly larger, and tubercular ( Mawatari et al. 1991). Microporella trigonellata shows the same number, relative size, arrangement and position of spines but differs from the new species in having the avicularium placed distolaterally, directed distally, with a pointed, non-channelled rostrum; also, the ridges and grooves on the ovicells are distinctly defined and more marked, and the ancestrula has a narrower proximal gymnocyst ( Suwa and Mawatari 1998).

The general appearance of those zooids lacking avicularia in M. pachyspina sp. nov. reminds those of Fenestrulina joannae (Calvet, 1902), which are also similar in having the proximalmost pair of spines long, robust and rounded, non-stellate pseudopores sparse on the frontal shield, centrally smooth ovicells, sometimes with peripheral radial ridges, developing a mucro ( Chimenz Gusso et al. 2014: 165, fig. 82a-c). This latter species, originally described as Microporella by Calvet (1902), was reassigned to Fenestrulina by Gautier (1962: 171) apparently based on a suggestion made by Hastings without any supporting statement, instead highlighting the different type of pseudopores (non-stellate) compared with those of the type species of the genus Fenestrulina malusii Audouin, 1826. Subsequent authors followed Gautier (1962). Fenestrulina species have large, stellate pseudopores mostly occupying the area of the frontal shield between the ascopore and the orifice, a sector that is usually imperforate in Microporella . Based on these observations, Fenestrulina joannae seems to have more affinities with Microporella and here we suggest its displacement.

Dry specimens on organic substrates (i.e., Posidonia leaves) appear with the zooids disconnected or almost disconnected, giving to the colony a slightly disjunct appearance because the zooids were less packed hence exposing a more extensive, smooth gymnocyst laterally (Fig. 8F ). This loose packing is a common adaptation in species growing on flexible substrates to reduce the potential breakage of the zooidal skeletons.

Distribution and ecology.

Presently known only from shallow waters off Egadi Islands, at the western limit of the Sicily Strait in the Mediterranean Sea, associated with Posidonia meadows and the Infralittoral Algae Biocoenosis.

Figures

Figure 8. Microporella pachyspina sp. nov. from Sicily Strait, Egadi Islands A-E holotype PMC. B 31 a. 3.12.2020 F, G paratype PMC. B 31 b. 3.12.2020 A colony general view B close-up of orifice with proximolateral rectangular condyles, smooth hinge-line, and five oral spine bases. Note the giant proximolateral pair of spine bases located at hinge-line level and at some distance from the thinner, distal ones C close-up of avicularium with truncated, channelled rostrum projecting laterally outside its edge affecting the shape of the adjacent zooid margin D close-up of ascopore with proximal mucro E ovicells smooth and imperforate centrally, finely granular and with a row of large pores peripherally. Radial buttresses between marginal pores converge towards the median umbo F Ancestrula budding one distal and two distolateral autozooids. Two larger, proximolateral, curved autozooids complete the periancestrular region G autozooids from the colony growing margin with six or seven oral spines. Scale bars: 1 mm (A); 50 µm (B-D); 200 µm (E-G).