Pleuromucrum Vigneaux, 1949

Martino, Emanuela Di & Taylor, Paul D., 2017, Some Miocene cheilostome bryozoan genera of Michel Vigneaux - systematic revision and scanning electron microscopic study, Geodiversitas 39 (4), pp. 783-796 : 791-794

Genus Pleuromucrum Vigneaux, 1949

Lifuella Gordon & d’Hondt, 1997: 21 , n. syn.

Allorhynchozoon Liu in Liu, Yin & Ma, 2001: 821, n. syn.

TYPE SPECIES. — Pleuromucrum saucatsense Vigneaux, 1949 by original designation.

EMENDED DIAGNOSIS. — Colony encrusting. Zooids with convex frontal shield, nodular, imperforate apart from occasionally sparse marginal areolar pores. Primary orifice bell-shaped, with a broadly arcuate, smooth-rimmed anter and more or less developed condyles. Oral spines present in both fertile and infertile zooids.A suboral mucro often developed.Adventitious avicularia, when present, triangular and latero-oral or sparse on the frontal shield, budded from marginal areolar pores. Ovicells subimmersed, globular, with a widely arched opening.

REMARKS

Since its introduction by Vigneaux (1949) the genus Pleuromucrum has been largely overlooked, although Cheetham (1963: 73) placed it in synonymy with Pleurolyrula Vigneaux, 1949 . However, Pleurolyrula as the name suggests possesses a lyrula which is absent in Pleuromucrum . Examination of the type species of Lifuella Gordon & d’Hondt, 1997 , Lepralia multidentata Thornely, 1905 ( Fig. 7 ), and the type species of Pleuromucrum , P. saucatsense Vigneaux, 1949 ( Fig. 9 ), allowed us to ascertain the close similarity between these two genera, and consequently Lifuella is here considered as a junior subjective synonym of Pleuromucrum .

Gordon & d’Hondt (1997: 58) introduced Lifuella for Lepralia calyciformis Philipps, 1900 , as well as all of the tropical and warm-temperate species previously attributed to Hippoporella Canu, 1917 , which seemingly had little in common with the boreal-arctic type species of Hippoporella , H. hippopus ( Smitt, 1868) , including the type species of Lifuella , L. multidentata ( Thornely, 1905) . Subsequently, Tilbrook et al. (2001: 95) assigned Lifuella calyciformis to the new genus, Fodinella Tilbrook, Hayward & Gordon, 2001 , which differs from Lifuella in having a beaded anter. Allorhynchozoon Liu in Liu, Yin & Ma, 2001 is a junior subjective synonym of Lifuella (http://bryozoa.net by P. Bock, accessed 10.I.2017) and therefore also of Pleuromucrum . The type species of Hippoporella , H. hippopus , dif- fers from the type species of Pleuromucrum , P. saucatsense , in the ovicell originating from the distal zooid and in the presence of distinct basal pore-chambers (not obvious in Pleuromucrum ).

Of the seven species currently included in Lifuella , we are able to reassign two – L. multidentata ( Thornely, 1905) and L. gorgonensis ( Hastings, 1930) (see Di Martino et al. 2017) – to Pleuromucrum based on the re-examination of the type material, while a further three can be transferred to Pleuromucrum based on SEM images published in the literature: L. porelliformis ( Kirkpatrick, 1888) sensu Tilbrook et al. (2001: 96 , fig. 20C), L. lepralielloida ( Pleuromucrum lepralielloidum n. comb.; Liu in Liu et al. 2001: pl. 80, figs 1-3) and L. granulata ( Pleuromucrum granulatum n. comb.; Liu in Liu et al. 2001: pl. 80, figs 4-6). Re-examination of the type material of Lifuella articulata ( Fodinella articulata n. comb.; Philipps 1900) revealed a beaded anter ( Fig. 8 ) typical of Fodinella , to which it is here reassigned. Lepraliella moorabolensis ( MacGillivray, 1895) sensu Gordon (1984) was tentatively placed in Lifuella byTilbrook et al. (2001). Based on Gordon’s (1984: 123) description the anter of this species as “smoothly rounded distally with no beading”, this species fits within the diagnosis of Pleuromucrum . However, the specimen figured by ( Gordon 1984: pl. 50, fig. D) shows small oval adventitious avicularia with serrated rostrum tips more typical of species of Fodinella . Restudy of the type material of L. mooraboolensis is needed to ascertain whether this fossil Australian species is conspecific with the Recent New Zealand species, and into which genus it should be referred.

Two further fossil species of Pleuromucrum were found in the early Miocene Chipola Formation of Florida ( Di Martino et al. 2017).

Pleuromucrum saucatsense Vigneaux, 1949 ( Fig. 9 )

MATERIAL EXAMINED. — Figured syntypes ( Vigneaux 1949: 105, pl. 10, figs 6, 7), C.B.317-1 and C.B.318-2. C.B.318-2 is here designated as the lectotype of the species.

TYPE LOCALITY. — Saucats, Pont-Pourquey, Gironde, Aquitaine, France.

AGE. — Burdigalian, early Miocene.

DESCRIPTION

Colony encrusting, multiserial, unilaminar ( Fig. 9A ). Autozooids distinct, delineated by narrow interzooidal furrows, quincuncially arranged, hexagonal, longer than wide (mean L/ W 1.45). Frontal shield convex, granular, imperforate except for a single row of subcircular to elliptical, marginal areolar pores, 15-25 µm long ( Fig. 9B ). Orifice bell-shaped, almost equidimensional ( Fig. 9C, D ); four distal oral spine bases in both ovicellate and non-ovicellate zooids, about 10 µm in diameter ( Fig. 9C, D ). Suboral mucro conical with a rounded tip ( Fig. 9C ). Adventitious avicularia single or absent, laterooral, rounded triangular, distolaterally directed ( Fig. 9D ); crossbar not observed. Ovicells subimmersed, with the same granular appearance as the frontal shield, imperforate, with a widely arched opening ( Fig. 9E ).

MEASUREMENTS

ZL 368 ± 34, 308-435 (20); ZW 254 ± 29, 211-319 (20); OL 85 ± 4, 79-82 (20); OW 105 ± 4, 103-108 (20); OvL 105 ± 4, 103-108 (2); OvW 133 ± 11, 126-141 (2); AvL 72 ± 8, 66-78 (2); AvW 37 ± 2, 36-39 (2).

REMARKS

In the two type specimens available for study we observed only two avicularia, both lacking a pivotal bar, which may be a preservational artifact rather than a genuine absence. As the presence of a single latero-oral avicularium may be related to the age of the colony, we cannot exclude the possibility that older colonies of this species could develop paired latero-oral avicularia, as well as other avicularia sparse on the frontal shield and budded from marginal areolar pores, as observed for other species of the genus. Pleuromucrum saucatsense differs from P. multidentatum ( Thornely, 1905) n. comb. in having four oral spine bases instead of six, a bell-shaped orifice without well defined condyles, and a slender and shorter suboral mucro. Furthermore, zooids in P. multidentatum n. comb. are generally smaller (ZL 298 ± 50, 209-389 [20]; ZW 274 ± 41, 202-341 [20]), although highly variable in size, and with a lower mean ratio L/W (1.09 vs 1.45) than those of P. saucatsense . Among other species here assigned to Pleuromucrum , P. gorgonensis ( Hastings, 1930) n. comb. and P. porelliformis ( Kirkpatrick, 1888) n. comb. differ in having two and eight oral spine bases respectively. P. gorgonensis n. comb. also differs in having a trifid suboral mucro and elongate adventitious avicularia. Pleuromucrum porelliformis n. comb. is characterised by a finely serrated lip on the distal edge of the suboral mucro.

Figures

FIG. 7. — Pleuromucrum multidentatum (Thornerly, 1905) n. comb.A–C, lectotype NHMUK 1906.12.3.4,Recent, Ceylon.A, general view of the colony;B, group of zooids; C, close-up of an autozooid showing six oral spine bases, orificial condyles, stout broken-off suboral mucro and multiple adventitious avicularia budded from marginal areolar pores. D–F, syntype, NHMUK 1975.7.28.24, Recent, Ceylon. D, general view of the colony; E, group of autozooids and ovicellate zooids; F, close-up of two ovicellate zooids. Scale bars: A, 500 μm; B, C, D, 200 μm; E, F, 100 μm.

FIG. 9. — Pleuromucrum saucatsense Vigneaux,1949,figured syntype C.B.318-2,Burdigalian,early Miocene,Saucats,Pont-Pourquey,Gironde,Aquitaine,France. A, general view of the colony; B, group of autozooids; C, close-up of an autozooid showing the suboral mucro; D, two autozooids with adventitious avicularia; E, close-up of an autozooid and an ovicellate zooid. Scale bars: A, 500 μm; B, C, D, E, 100 μm.

FIG. 8. — Fodinella articulata (Philipps, 1900) n. comb., syntypes NHMUK 1999.3.9.7a, b, Recent, Lifu, Loyalty Island, Sandal Bay. A, group of zooids; B, two ovicellate zooids; C, close-up of the distal part of a zooid showing the ovicell in formation, seven spine bases and the distolateral avicularia with serrated rostrum tips; D, close-up of an orifice showing the beaded anter and proximal mucro. Scale bars: A, 200 μm; B, 100 μm; C, 50 μm; D, 30 μm.