Akatopora leucocypha ( Marcus, 1937 )

Harmelin, Jean-Georges, 2014, Alien bryozoans in the eastern Mediterranean Sea — new records from the coast of Lebanon, Zootaxa 3893 (3), pp. 301-338 : 309-312

Akatopora leucocypha ( Marcus, 1937)

( Fig. 3 A–F; Table 5 )

? Flustra savartii Audouin, 1926: 240 [ Savigny 1817: pl. 10, fig. 10.].

Crassimarginatella leucocypha Marcus, 1937: 46 , pl. 8, fig. 20A, pl. 9, figs 20B,C;? Mawatari 1952: 269, fig. 3.

? Conopeum lacroixii: Balavoine 1959: 264 , pl. 1, figs 8–9.

Antropora leucocypha: Shier 1964: 613 ; Winston 1982: 123, fig. 36; Winston & Håkansson 1986: 9, figs 14–16.

? Conopeum reticulum: Zabala & Maluquer 1988: 76 , pl. 1E (not fig. 65); Abdel Salam & Ramadan 2008: 6, fig. 2. Not Conopeum reticulum ( Linnaeus, 1767) : Prenant & Bobin 1966: 124, fig. 32; Hayward & Ryland 1998: 120, figs 9A,B, 23, 24.

? Membranipora savartii: d’Hondt 2006: 62 .

Akatopora leucocypha: Winston & Vieira 2013: 110 , fig. 7.

Material examined. Specimens from Lebanon: 1) Stn 2A, 1 colony on barnacle; 2) Stn 2B, 1 colony on pottery debris; 3) Stn 16A, 1 small colony on Spondylus shell. Other material examined: 1) MNHN no. 10 299, labelled Conopeum reticulum, Y.V. Gautier coll., Biguglia Lagoon, Corsica, August 1950 [= C. seurati (Canu, 1928) ]; 2) MNHN no. 7851, labelled Conopeum lacroixii Aud. 1826 , Gulf of Suez, Dollfus coll., studied by Balavoine (1959), Al Sayad Stn XI, 25–31 m (possibly conspecific with the Lebanese specimens); 3) MNHN no. 10 297, labelled Conopeum lacroixii, St Aygulf Lagoon (French Riviera) , October 1953, Y.V. Gautier coll. (= C. seurati ); 4) Antropora cf. leucocypha , northern Bay of Safaga, Egypt, SEM photos by Ostrovsky et al. (2011a).

Description. Colony small, encrusting, unilamellar, occasionally partly bilamellar, consisting of autozooids with adventitious kenozooids inserted in corners between them. Autozooids separated by distinct grooves, with thick, well-calcified walls including basal wall. Frontal membrane transparent; orifice relatively large; operculum with narrow thickening (sclerite?) bordering its free edge. Gymnocyst smooth, developed proximally, variably sized and shaped, often not visible in frontal view, occasionally with a knob. Cryptocyst a broad, sloping rim, narrower distally around orifice, ornamented with hemispherical granulations in 3–5 ranks, inner one forming denticulate inner edge of opesia. Opesia roughly oval, often a little wider proximally. Basal wall complete. Lateral communications comprising 6–10 large, irregularly shaped recesses in lateral walls, each with a uniporous septulum. No spines, even in young autozooids. Ooecia partially immersed, present in young autozooids near growing margin, their calcified wall visible frontally as a narrow, convex, crescentic structure on distal edge of autozooid, sometimes a little thicker and prolonged downwardly by curved distal wall that forms a narrow floor. Kenozooids triangular or irregularly shaped, variably sized, often paired and contiguous between successive autozooids, sometimes partly overlying ooecium; gymnocyst relatively broad; cryptocyst narrow, granular; opesia round to irregularly oval, variably sized. Avicularia not observed.

Remarks. An obvious morphological convergence between species belonging to different genera and families has posed some challenges to the taxonomic assignment of the Lebanese specimens. This resemblance involves (i) two electrid species, Conopeum reticulum ( Linnaeus, 1767) from northern European waters and Craspedopora scalprata Taylor & McKinney, 2006 , a fossil species from North America; and (ii) a western Atlantic antroporid, Akatopora leucocypha ( Marcus, 1937) . Their common features are an encrusting growth-form, a colony structure with many triangular or irregularly shaped kenozooids inserted at the corners of the autozooids, the general shape of autozooids, opesia and kenozooids, and the wall structure of both kenozooids and autozooids with a reduced gymnocyst and a coarsely granular cryptocyst forming a sloping rim. Arguments for ascribing the Lebanese specimens to Akatopora leucocypha and the cases of species with similar morphological features are discussed below.

1) Assignment to Akatopora leucocypha . The genus Akatopora Davis, 1934 includes fossil and Recent encrusting species with large, oval opesiae, no spines, small avicularia and kenozooids between the zooids, and immersed ovicells ( Gordon 1986; Taylor & McKinney 2006). In A. leucocypha , avicularia have a semicircular mandible ( Marcus 1937, pl. 8, fig. 20A) and no condyles (Winston & Vieira 2013). They were not observed in the Lebanese specimens but, as suggested by the scarcity of their representation in the literature, their occurrence is likely very occasional. Ovicells are immersed in Akatopora species ( Ostrovsky et al. 2009) and ooecia thus may be poorly visible. In A. leucocypha , ooecia occur only in young colonies and are visible frontally as a narrow crescentic lip at the distal edge of the maternal zooid ( Winston & Håkansson 1986, fig. 16; Winston & Vieira 2013). The same pattern was observed in young zooids of a relatively large colony from Lebanon (Stn 2B), which presented several ooecia. Besides this key character, the general features of autozooids and kenozooids of A. leucocypha reported in the literature (e.g. Marcus 1937, pl. 9, fig. 20B; Winston 1982, fig. 37; Winston & Vieira 2013, fig. 7) are strikingly similar to those of the Lebanese specimens. Moreover, the zooidal dimensions of the latter are close to those given by Winston & Vieira (2013). Thus, considering (i) the rarity of avicularia in A. leucocypha and (ii) the small number of colonies available in the Lebanese material, the apparent lack of avicularia in the latter is not considered significant.

This is the first record of a Recent Akatopora species in the Atlanto-Mediterranean region. Akatopora leucocypha is known from the western Atlantic, from Cape Hatteras to Brazil (Winston & Vieira 2013). The possible occurrence of this species in the Red Sea has to be verified by a closer examination of morphologically similar specimens, e.g. from the Gulf of Suez in Balavoine's collection (labelled Conopeum lacroixii ) and from the northern Bay of Akaba, recorded as Antropora cf. leucocypha by Ostrovsky et al. (2011a).

2) Possible misidentifications. Because ooecia are inconspicuous in A. leucocypha , specimens from the Atlanto-Mediterranean region may have been formerly confused with the electrid Conopeum reticulum . The most obvious difference from northern European specimens of C. reticulum is the absence of three features: (i) spines at the border of the frontal membrane, even in young zooids; (ii) multiporous septula in lateral walls (cf. Hayward & Ryland 1998, figs 9A,B, 24D); and (iii) operculum with a folded, membranous structure ( Hayward & Ryland 1998). Conopeum reticulum is a boreal species, well known from the British Islands and the North Sea (e.g. Prenant & Bobin 1966; Hayward & Ryland 1998), but also reported from various regions with contrasting climatic environments. The surprisingly wide distributional range attributed to C. reticulum , including records from both marine and brackish environments (e.g. Hayward & Ryland 1998) may be an indication that several cryptic species are included in this species name. On the other hand, Menon (1972) showed from laboratory experiments that colonies of C. reticulum from the North Sea displayed a particularly high thermal tolerance and aptitude to acclimatization to temperatures higher than that of their native environment. This trait could facilitate humanmediated transport of propagules outside the boreal zone and therefore might explain at least part of the vast geographical range attributed to this species. There is no evidence that C. reticulum belongs to the native fauna of the Mediterranean despite the assertion of Calvet (1906) that Membranipora reticulum is “très commune dans la Méditerranée.” Calvet’s (1902) unillustrated record of C. reticulum on a mussel from Biguglia Lagoon ( Corsica) was probably based on a misidentification of C. seurati (Canu, 1928) ; this was the case for a specimen from the same lagoon labelled by Y.V. Gautier (MNHN no. 10 299). According to Zabala & Maluquer (1988), the occurrence of C. reticulum on aquacultured mussels at Minorca (Balearic Islands) probably resulted from an introduction with mussel spat from Atlantic coasts. Unfortunately, it is not indicated if their figure 65 showing autozooids with spines was made from a Balearic specimen or from a boreal specimen. The report of C. reticulum from fouling panels at El-Dekheila harbour (Alexandria, Egypt) by Abdel-Salam & Ramadan (2008), figured without spines, may correspond to the species collected in Lebanon. A Red Sea specimen from the Gulf of Suez (MNHN no. 7831) recorded by Balavoine (1959) as Conopeum lacroixii ( Audouin, 1826) is probably conspecific with the Lebanese specimens in having autozooids with a broad, coarsely granular cryptocyst and triangular or quadrangular kenozooids inserted between them and without spines.

Savigny’s illustration (1817, pl. 10, fig. 10) of Flustra savartii Audouin (1826) also recalls the Lebanese specimens. It depicts zooids with large, oval opesiae with a denticulate edge (well calcified cryptocyst?) and a rounded structure at the proximolateral corners of the autozooids that may be either a tubercle (on gymnocyst?) or a kenozooid. However, this illustration by Savigny has been diversely interpreted ( Tilbrook 2006, p. 19) and the name savartii is generally attributed to species with a diverging morphology, particularly a cryptocyst with a distally-flared expansion with denticles (e.g. Acanthodesia savartii in Marcus 1937).

The genus Craspedopora Canu & Bassler, 1929 comprises three fossil species (Eocene and Cretaceous) that resemble both Conopeum and Akatopora in having small kenozooids inserted between the autozooids ( Gordon 1986). For example, C. scalprata Taylor & McKinney, 2006 , from the Maastrichtian of North Carolina ( Taylor & McKinney 2006, pl. 60, fig. 2A,B) presents apparent similarities with the Lebanese specimens. However, no ooecium has been observed in this genus ( Gordon 1986; Taylor & McKinney 2006).

Figures

FIGURE 3. Akatopora leucocypha (Marcus, 1937), Lebanon, Stn 2 B: A, part of colony with autozooids and variously shaped kenozooids; B, autozooid with five adjacent triangular kenozooids; C, three kenozooids adjacent to autozooids [note the difference in width of the cryptocyst between the distal (right) and proximal (left) parts of autozooids]; D, E, zooids with narrow crescentic ooecia; F, recesses for communication pores, one showing a uniporous septulum. Scale bars: A, 200 µm; B, 100 µm; C – F, 50 µm.

Tables

TABLE 5. Akatopora leucocypha, morphometrics of three colonies from Stns 2 A, 2 B, 16 A.

A. leucocypha	X	SD	Range	N
Az L	321	37	220–375	30
Az W	241	29	195–315	30
Op L	246	28	205–325	30
Op W	151	19	120–180	30
Ov L	61	4	55–65	8
Ov W	129	8	120–140	8