Microporella ichnusae, 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 ichnusae sp. nov.

Figs 5 , 6

Microporella sp. A Fraschetti et al. 2010: table 27.

Type material.

Holotype: Italy • 1 living colony consisting of more than 100 zooids, including some complete and some broken ovicells; Iberian-Provençal Basin, NW Sardinia, Capo Caccia-Isola Piana MPA, Bisbe submarine cave; sample Bisbe 2; 40°34'15"N, 8°12'55"E; 8 m; 2009; V. Di Martino leg.; scuba diving; GSO Biocoenosis; PMC. B30a. 20.11.2020. Paratypes: Italy • 9 living colonies, each consisting of a dozen zooids; Iberian-Provençal Basin, NW Sardinia, Capo Caccia-Isola Piana MPA, Bisbe, Falco and Galatea caves; samples Bisbe 1, Bisbe 2, Falco 2, Galatea 1 and Galatea 2; Bisbe, same details as the holotype; Falco: 40°34'09"N, 8°13'14"E; Galatea: 40°34'09"N, 8°13'54"E; 4-8 m; 2008; V. Di Martino leg.; scuba diving; GSO Biocoenosis; PMC. B30b. 20.11.2020.

Diagnosis.

Colony encrusting, multiserial. Autozooid frontal shield densely pustulose and sparsely pseudoporous. Orifice transversely D-shaped; hinge-line smooth with blunt condyles close to corners; four thin oral spines, hidden in ovicellate zooids. Ascopore field semi-elliptical; ascopore opening an arched fissure marked by a distal tongue with radial spines. Avicularium usually single, same level as or proximal to the ascopore, occasionally paired, directed distolaterally; crossbar complete; rostrum lanceolate, channelled. Ovicell non-personate.

Description.

Colony encrusting multiserial, unilaminar (Fig. 5C, D ) with zooids arranged in alternate rows often disrupted on particularly irregular substrata; interzooidal communications through 6-8 elliptical pore chamber windows (40-65 × 18-26 µm).

Autozooids usually hexagonal to rhomboidal but sometimes irregularly shaped, 307-587 (434 ± 73, N = 20) × 284-439 (357 ± 59, N = 20 µm) (mean L/W = 1.21), boundaries marked by narrow grooves and raised rims of lateral walls (Figs 5F , 6B, G ). Frontal shield slightly convex with polygonal and flat-topped pustules giving a tessellate appearance, and pierced by circular (diameter 6-12 µm), irregularly distributed pseudopores, usually numbering 10-30 but more numerous in some colonies; 2-4 marginal areolae, elliptical to fissure-like, barely visible or distinguishable from pseudopores (Figs 5F , 6B ).

Orifice transversely D-shaped, 75-94 (81 ± 5, N = 20) × 109-145 (122 ± 10, N = 20) µm (mean OL/OW = 0.67; mean ZL/OL = 5.33), outlined by a thin, slightly raised rim; hinge-line straight, smooth, with a pair of small triangular, blunt condyles close to corners (Fig. 5F ). Oral spines four, occasionally five or six (diameter of the bases 10-14 μm), evenly spaced, the proximal pair located at orifice mid-length; spines hidden in ovicellate autozooids (Fig. 6B, E ).

Ascopore field a small and very narrow, transversely semi-elliptical area marked by a thin raised gymnocystal rim, 28-36 × 30-50 μm, located 25-50 μm below the orifice, at the same level as the frontal shield; opening transversely C-shaped, 20-30 × 6-10 μm, with a subcircular tongue projecting from distal edge, and relatively few, tiny, radial denticles.

Avicularium most often single (Figs 5E, F , 6B, D ), occasionally paired (Fig. 5C ) or absent (Figs 5C, E , 6C ), relatively large, 75-120 (98 ± 13, N = 20) × 55-91 (71 ± 11, N = 20) μm (mean AvL/AvW = 1.39), located laterally, on either side, in the distal zooidal half, same level as or proximally to the ascopore (Figs 5B, F , 6B, E ) but on irregularly shaped zooids occasionally placed in the proximal part; crossbar complete, thin; rostrum triangular, channelled and open-ended, directed laterally or distolaterally, often distally raised on a smooth, gymnocystal cystid (Fig. 5F ). Mandible 160-180 μm long, setiform, with a hook at about one-third of its length that clamps it to the rostrum tip, crossing the whole zooid when open (Fig. 5A, B ).

Ovicell subglobular and prominent, 185-241 (214 ± 25, N = 4) × 290-314 (297 ± 11, N = 4) μm (mean OvL/OvW = 0.72), produced by and continuous with frontal shield of distal zooid, obscuring distal part of the orifice; calcification fabric similar to frontal shield but with smaller and more prominent pustules; pseudopores small (diameter 5-10 μm), densely packed at the periphery, absent centrally (Fig. 6B, E ).

Kenozooids smaller than or nearly as large as autozooids, lacking openings such as orifices and ascopores but sometimes equipped with avicularium (Fig. 6A, F ).

Ancestrula not observed.

Etymology.

From Ichnusa the Latinized form of the ancient Greek name for Sardinia.

Remarks.

Size and shape of autozooids vary remarkably within and between colonies, including dwarf-like autozooids, about half the size of the more regular ones, as well as extremely large and irregularly shaped autozooids, appearing as the result of the fusion of contiguous autozooids (Fig. 5C, E ). In this latter case the avicularium can be placed much more proximally than in regular autozooids. Irregularly-shaped autozooids also occur in M. browni ( Harmelin et al. 2011: fig. 3b). These unusual autozooids and the kenozooids observed in this species seem to be particularly common in zones of contact between colonies or lobes of the same colony, and in damaged areas, also associated with evidences of reparation (Figs 5D , 6A, D ), such as regeneration of broken autozooids, patches of calcification to close holes in the frontal shield, or orifices of presumably not functional autozooids (Fig. 6G ). Intrazooidal budding, a feature that is common in bryozoans from submarine caves (e.g., Rosso et al. 2020a, 2020b), has been more commonly observed in avicularia (Fig. 6C, D ) than autozooids (Fig. 6F, G ). The occurrence of ovicells seems rare, observed only on the colony selected as the holotype.

The general appearance of this new species is very similar to M. ciliata . However, the orifice in M. ciliata , although of comparable size (0.06-0.08 mm long by 0.11-0.15 mm wide), is proportionately shorter, the hinge-line shows a series of median denticles and the two lateral condyles are more prominent and more laterally placed (Fig. 4E ; see also Kukliński and Taylor 2008: fig. 1G). The type and position of the oral spines are similar but the number of spines is 4-6 (more commonly four) in M. ichnusae sp. nov. and 1-4 (and occasionally lacking in the zone of astogenetic repetition) in M. ciliata ( Kukliński and Taylor 2008). In M. ciliata the frontal avicularium is constantly single, only lacking in the first autozooid budded from the ancestrula, and no kenozooids were reported ( Kukliński and Taylor 2008). Furthermore, the ovicells in M. ciliata have length comparable with those of M. ichnusae sp. nov. but are much narrower.

Distribution and ecology.

Microporella ichnusae sp. nov. is presently known only from submarine caves in the Capo Caccia-Isola Piana MPA, in NW Sardinia. However, it is possible that some previous records of M. ciliata , to date the only Microporella species with a single avicularium considered as widespread in the Mediterranean, belong to this species.

Figures

Figure 4. Microporella ciliata (Pallas, 1766) from the Ionian Sea, Gulf of Noto, PMC Rosso-Collection I. H. B. 85 a A general view of the colony B autozooids at the colony margin showing distal and distolateral pore chamber windows C ovicellate autozooids D autozooid with the characteristic four, thin, oral spine bases. Note how commonly avicularia regenerate E close-up of the orifice showing a series of median denticles and two lateral condyles. Scale bars: 500 µm (A); 250 µm (B); 200 µm (C); 100 µm (D); 50 µm (E).

Figure 5. Microporella ichnusae sp. nov. from the Iberian-Provencal Basin, NW Sardinia, Capo Caccia-Isola Piana MPA, Falco Cave, Paratype PMC. B 30 b. 20.11.2020 A unbleached colony B avicularium with open mandible, showing the channelled rostrum. The straight, short, setiform mandible has a hook at about one-third of its length which clamps it to the rostrum tip C bleached autozooids showing size and shape variability. Note that the majority of autozooids has a single avicularium, while few autozooids have paired avicularia (white asterisks) or none (black asterisks) D irregularly-shaped autozooids and kenozooids along the contact zone of lobes E autozooids and kenozooid (asterisk) near the colony margin with pore-chamber windows visible along exposed lateral walls F autozooid at the growing edge showing the morphology of the orifice and four, thin spine bases. Scale bars: 500 µm (A, C, D, E); 50 µm (B); 100 µm (F).

Figure 6. Microporella ichnusae sp. nov. from the Iberian-Provencal Basin, NW Sardinia, Capo Caccia-Isola Piana MPA, Bisbe Cave, Holotype PMC. B 30 a. 20.11.2020 A colony portion with broken ovicells, autozooids showing evidences of reparation, and kenozooids with (white asterisk) and without (black asterisk) avicularia B autozooids with complete or broken ovicells C paired autozooids, seemingly repaired, one lacking avicularium D close-up of a colony portion with evidence of zooidal repair. Note the occluded orifice indicated by the partly protruding spines (see arrow) E group of zooids (two ovicellate), some with open or closed mandibles and one lacking an avicularium F close-up of two zooids. Owing to the absence of an ascopore, which is usually placed at the same level as the avicularium, the upper one is more likely to be a kenozooid equipped with an avicularium than an autozooid with obliterated orifice. Note also the different frontal shield texture of its proximal margin, likely due to ovicell resorption G close-up of an autozooid with sealed orifice (central zooid), and an orifice with a thin secondary rim, indicating intramural budding presumably as a result of predation. Scale bars: 500 µm (A); 200 µm (B-G).