Ascophorina, Levinsen, 1909

Kuklinski, Piotr & Taylor, Paul D., 2008, Arctic species of the cheilostome bryozoan Microporella, with a redescription of the type species, Journal of Natural History 42 (27 - 28), pp. 1893-1906 : 1894-1898

Suborder ASCOPHORINA Levinsen, 1909

Superfamily SCHIZOPORELLOIDEA Jullien, 1882

Family MICROPORELLIDAE Hincks, 1879

Genus Microporella Hincks, 1877

Type species: Eschara ciliata Pallas, 1766 .

Diagnosis

Colony encrusting or erect bifoliate. Pore chambers usually present. Ancestrula tatiform or ascophoran. Frontal shield cryptocystal, perforated by pseudopores and marginal areolae, pustulose or granular, with an outer layer of aragonite in most species. Ascopore subcircular, transversely elliptical, reniform or crescentic, often partly occluded by marginal teeth, radial septa or a sieve plate, located adjacent to proximal edge of orifice or separated from it by an area of frontal shield lacking pseudopores. Orifice semielliptical, the almost straight proximal edge bearing small teeth or a pair of condyles or both; oral spines present or absent, basally articulated. Ovicell surface cryptocystal, variably porous, in some species personate and associated with a peristome in the maternal zooid. Avicularia adventitious, single or paired, sometimes lacking in particular zooids, varying in location from close to mediolateral margin of autozooid to adjacent to orifice, oriented distally, distolaterally or laterally, cross bar complete, rostrum a high-sided triangle, sometimes with an open channel at tip, mandible simple, setiform with a basal beak or lanceolate with a pair of hooks near base.

Remarks

Microporella is characterized by autozooids with cryptocystal frontal shields perforated by pseudopores over most of the surface, a semielliptical orifice with a straight proximal edge, an ascopore, and adventitious avicularia that are either single or paired and located laterally or proximolaterally of the orifice on the frontal shield of the autozooid. Most of the other characters in the diagnosis vary according to species.

As mentioned above, morphological differences between species of Microporella can be subtle and, as yet, no molecular sequence data are available that might assist in distinguishing between species. Suwa and Mawatari (1998) have shown how detailed morphological and anatomical study can enable distinctions to be made between species of Microporella . Characters of importance include the number, location and morphology of the avicularia, the form of their mandibles, the position and morphology of the ascopore, ovicell porosity, and the occurrence of teeth, condyles and oral spines associated with the autozooidal orifice. Unfortunately, these features are often inadequately described or illustrated in earlier taxonomic works.

Soule et al. (2003) introduced a new genus, Microporelloides (type species M. mazatlanica ), for species of Microporella having ovicells with pores widely spaced and as large as, or larger than, the pseudopores on the frontal shield. Based on ovicell variability within and between species of Microporella , this is unlikely to be a valid reason for distinguishing a new genus and Microporelloides is here provisionally regarded as a junior synonym of Microporella . In another cheilostome, Celleporella , the number of ovicellular pores has been found to be inversely correlated with sea water temperature and, probably, the level of dissolved oxygen in the water ( Navarrete et al. 2005). Similar physiological factors may perhaps determine ovicell porosity in Microporella .

Microporella ciliata ( Pallas, 1766)

( Figures 1A–I )

Eschara ciliata Pallas 1766, p. 38

Type material

Neotype (chosen here): NHM 2008.02.06.1, Penta Palummo Bank, Bay of Naples, on shell, collected using a gill net from a fishing boat by F. Toscano, 4 July 1984. Note that the exact locality in the Mediterranean Sea from where Pallas obtained his material of Eschara ciliata is unknown. Attempts to locate the collection used by Pallas for his 1766 publication have been unsuccessful despite enquiries to museums in Berlin , Göttingen , Leiden and St Petersburg.

Other material

NHM 2008.02.06.2 (on shell of Laevicardium norvegicum ), 2008.02.06.3 (on fragment of shell of Pecten jacobaeus ), 2008.02.06.4 (on shell of Cardium deshayesi ); 2008.02.06.5 (on shell of Astarte fusca ), 2008.02.06.6 (on shell of Glycymeris sp. ), 2008.02.06.7 (on shell of Cardium sp. ), 2008.02.06.8 (on shell of Arca tetragona ), 2008.02.06.9 (on shell of Arca tetragona ), 2008.02.06.10 (on shell of Pitar rudis ); locality and collection details as for neotype but collected 7 July 1984. 2008.02.06.11, dredged off Posillipo, Villa Rosbery, collected by P. Sordino and F. Toscano, October 2005, 50 m depth, muddy bottom, on shell of Turritella communis .

Description

Colony encrusting, developing extensive unilaminar sheets. Pore chambers with elliptical windows, generally one on each proximolateral and one on each distolateral zooid wall, two, occasionally three, on distal wall. Ancestrula tatiform, longer than wide, bordered by narrow cryptocyst and about 10 spines, sometimes with closure plate perforated by about six small pores in ring close to border. Two distolateral zooids budded from ancestrula, the smaller one of the two without an associated avicularium and bearing six oral spines. Subsequent buds encircle ancestrula.

Autozooids rounded rhombic in frontal outline, separated by deep grooves, 0.51–0.82 mm long (average 50.62 mm, n 520) by 0.26–0.51 mm wide (average 50.39 mm, n 520). Frontal shield coarsely pustulose, perforated by pseudopores decreasing in density outwards and often absent from a band around border of frontal shield; areolae larger than pseudopores, elongated parallel to zooid margin, typically numbering five or six. Orifice small relative to zooid size, wider (0.11– 0.15 mm, average 50.13 mm, n 520) than long (0.06–0.08 mm, average 50.07 mm, n 520), semielliptical, proximal border straight, condyle present in each proximolateral corner, numerous very fine teeth between the condyles. Oral spines numbering one to four or occasionally absent in zooids from zone of astogenetic repetition, hidden in ovicellate autozooids. Ascopore moderately large, averaging 0.03 mm long by 0.04 mm wide (n 510), crescentic, margins crenulate with short tooth-like spines projecting from border into lumen, set within a reniform or transversely elliptical smooth depression; situated proximally of orifice by a distance approximately equivalent to height of orifice; umbo lacking. Basal walls with or without uncalcified windows. Ovicell hyperstomial, prominent, moderately large, wider (0.24–0.28 mm, average 50.26 mm, n 515) than long 0.18–0.22 mm wide (average 50.20 mm, n 515); frontal surface pustulose, porous, with about 30 pores close to distal and lateral edges, imperforate centrally; narrow ridge defining concave proximal edge above orifice.

Avicularia adventitious, single (unpaired), moderately large, 0.07–0.12 mm long (average 50.10 mm, n 520) by 0.06–0.08 mm wide (average 50.07 mm, n 520), placed on the right or left, between ascopore and mediolateral corner of autozooid; opesia semielliptical; crossbar calcified, straight; rostrum triangular with slightly concave edges, acute to the frontal plane of the autozooid, directed distolaterally or rarely laterally, tip channelled; mandible setiform.

Distribution

This species is possibly endemic to the Mediterranean Sea but a thorough restudy of the numerous records of putative M. ciliata from elsewhere needs to be undertaken for this claim to be confirmed or refuted (see comments in the next section).

Remarks

Re-examination using an optical microscope of material in the CNM from Arctic Canada regarded by Powell (1968) as Microporella ciliata suggests that his identification is, like that of Kluge (1975), incorrect and that true M. ciliata is absent from the Arctic.

Because of the lack of adequate illustrations in most of the literature, no attempt is made here to assess critically the accuracy of the multitude of other occurrences of supposed M. ciliata elsewhere in the world, living and fossil. However, even in the type region of the Mediterranean it is possible that more than one species closely similar to M. ciliata , as redefined in the previous section, may exist. Hayward and McKinney (2002) provided a well-illustrated description of putative M. ciliata from the northern Adriatic Sea off Rovinj. Several minor differences are evident between their material and that described here, leading to the suspicion that they may represent separate species. Compared to the neotype, the Adriatic Microporella has proportionally larger avicularia, an ascopore with a prominent thickened rim, no teeth on the proximal edge of the orifice between the condyles, and five or six oral spines. A British specimen of putative M. ciliata figured by Hayward and Ryland (1999, fig. 134C-D) more closely resembles the Adriatic material than it does the material from the Bay of Naples described here. Clearly, a thorough study of morphological variation within and between populations, coupled with molecular data, will be needed to determine the true geographical distribution of M. ciliata .

Figures

Figure 1. Microporella ciliata (Pallas, 1766), Bay of Naples, bleached. (A) Group of zooids, some ovicellate; (B) autozooid and avicularium; (C) ovicellate autozooid; (D) colony margin showing pore chamber windows; (E) ancestrula and early zooids; (F) ancestrula with closure plate; (G) tilted orifice with one oral spine base, condyles and small hinge teeth; (H) avicularium; (I) ascopore. (A, B, C, E, G, H, I), neotype, NHM 2008.02.06.1; (D, F), NHM 2008.02.06.3. Scale bars: 200 mm (A); 30 mm (B); 100 mm (C, D, E, F); 20mm (G, H); 10 mm (I).