Mucropetraliella thenardii ( Audouin, 1826 )

Harmelin, Jean-Georges, 2014, Alien bryozoans in the eastern Mediterranean Sea — new records from the coast of Lebanon, Zootaxa 3893 (3), pp. 301-338 : 324

Mucropetraliella thenardii ( Audouin, 1826)

( Fig. 12 A–C)

Flustra thenardii Audouin, 1826: 240 [ Savigny 1817: pl. 10, figs 31–33.].

Cellepora thenardii: d’Orbigny 1852: 402 .

Mucropetraliella thenardii: Harmer 1957: 714 (part), non pl. 46, figs 10–12, text-figs 62G, 64; Balavoine 1959: 270, pl. 4, figs 1–2; Dumont 1981: 635; d’Hondt 2006: 54, figs 3.1–3.3.

Non Mucropetraliella thenardii: Liu et al. 2001: 642 , pl. 62, figs 3–4 (= M. bifidata Tilbrook, 2006 ).

Material examined. Specimens from Lebanon: Stn 17B, 5 small colonies on biogenic concretions and skeleton of Phyllangia mouchezi . Other material examined: Red Sea, Egypt: South Sinai, Ras Mohammed, Yolanda wreck, 18 m, 15 May 1983, several colonies on aluminium plates (JGH).

Description. Colony encrusting, unilamellar, forming light-brown patches loosely attached to substratum. Frontal shield convex, evenly perforated by large pseudopores. Orifice rounded, slightly longer than wide, with a pair of well-developed, pointed, down-curved condyles and a relatively tall, narrow lyrula, both gutter-shaped, formed by folding of lamellar proximal edge of orifice. Anter of non-ovicellate orifices edged by low, crescentic blade recumbent on border with distally adjacent autozooid. Oral spines lacking. Suboral tall, antler-like mucro basically composed of bulging collar encircling proximal half of orifice from which is produced a medioproximal, vertically raised, compressed umbo bearing tubular processes: one vertical digitate process associated with a pair of longer, arched, lateral branches directed distally, and up to 3 digitate processes raised from trunk or lateral branches. Avicularian apparatus including 2 types of adventitious avicularia: 1) at tip of tubular processes of umbo, several constant small, oval avicularia; 2) at distal corners of peristomial collar an infrequent large spatulate avicularium, frontally curved, borne by suboral mucro on which it replaces a lateral ramification, with rostrum upwardly directed, rounded and bulbous, denticulate distally. Both small oval and large spatulate avicularia have a complete crossbar. Ooecium hyperstomial, large, globular; ectooecium finely granular and punctuated by tiny pseudopores.

Remarks. The specimens collected in southern Lebanon agree perfectly with Savigny’s beautiful drawings in all physiognomic characters. They are also similar to Red Sea specimens from the Gulf of Suez ( Balavoine 1959) and south Sinai (Ras Mohammed, pers. colln.) in having the same type of branched mucro and median denticle (narrow and rectangular, lacking acute lateral processes) and no oral spines. Mucropetraliella thernardii was redescribed by Harmer (1957) from various Indian Ocean localities. He considered the species to show high variability between localities, particularly in the shape of the suboral mucro. He also noted the frequent occurrence of 2–6 long slender spines (up to 8 in a specimen from Borneo) and a ‘bidentate lyrula’ (median denticle sensu Tilbrook & Cook 2004). Harmer’s redescription of M. thenardii clearly encompasses several species. As noted by Tilbrook (2006), although most species of Mucropetraliella Stach, 1936 have oral spines, the species group to which M. thernardii belongs differs in having no oral spines.

The species was only found at the southernmost station south of Tyre on relatively deep-water substrata (36–42 m). This single record probably does not reflect the actual distribution of M. thenardii along the whole Lebanese coast as only three sites below 30 m depth were visited and were poorly sampled. Mucropetraliella thenardii is the first species of Petraliellidae to be found in the Mediterranean Sea, a family which is particularly present in the Indo-Pacific and Australian regions ( Tilbrook 2006). The geographic distribution of M. thenardii is most probably less vast than indicated by Harmer (1957) and may have been restricted to the Red Sea ( Balavoine 1959; Dumont 1981) prior to introduction into the Mediterranean.

Figures

FIGURE 12. Mucropetraliella thenardii (Audouin, 1826), Lebanon, Stn 17 B: A, oblique view of colony showing elevated suborificial antler-like processes; B, ovicelled zooids and large avicularia with raised rostra; C, distal part of non-ovicelled zooid showing orifice with paired condyles and narrow lyrula, and three small avicularia borne by branched suboral process. Scale bars: A, B, C, 200 µm.