Gephyrotes convexus Canu & Bassler, 1920

Martino, Emanuela Di & Rosso, Antonietta, 2015, Revision of the bryozoan genus Gephyrotes Norman, 1903 (Cheilostomata, Cribrilinidae) with the description of two new taxa, Zootaxa 3941 (2), pp. 261-283 : 273

Gephyrotes convexus Canu & Bassler, 1920

( Figs 30–33 ; Table 6 )

Gephyrotes convexa Canu & Bassler 1920: 302 , pl. 42, figs. 2–3.

Material examined. Cotypes: USNM 64030 A–B, two specimens, Late Eocene, Alabama, USA. USNM 64030 B is chosen as lectotype.

Description. Colony encrusting unilaminar, multiserial ( Figs 30–31 ). Ancestrula not observed; zooids in early astogeny smaller than later autozooids, lacking oral structures ( Fig. 31 ). Autozooids distinct, with deep interzooidal furrows, arranged quincuncially, elliptical, slightly longer than broad (mean L/W = 1.14). Gymnocyst smooth, forming marginal portions of frontal shield, usually narrow laterally and more extensive proximally, often hidden in frontal view by adjacent zooids and visible only proximally as a rounded triangular area; larger and equally developed in early astogeny ( Figs 31, 33 ). Frontal shield markedly convex, formed by 12–18 costae, not including the 2 distalmost pairs participating in the proximal peristomial rim. Costae 40–50 µm broad, apparently closely united along their length, with 3 small, circular, prominent pelmatidia on each. Proximal peristomial rim formed by conjunction of 2 pairs of raised costae, one pair originating from the bifurcation of those most proximal to orifice and projecting frontalwards, the second pair originating lateral to orifice as a continuation of avicularian rostra, if present; the collar-like structure exhibiting a single semicircular intercostal lacuna, centrally placed ( Fig. 32 ). Primary orifice slightly broader than long, subquadrangular with concave proximal margin ( Fig. 33 ); secondary orifice semilunar with markedly concave proximal margin ( Fig. 32 ). Oral spine bases not observed. Ooecium subglobular, small, slightly wider than long, immersed in distal zooid ( Fig. 32 ). Adventitious avicularia small, paired, teardrop-shaped with complete pivot bar ( Figs 30, 32 ), laterally placed or transversely projecting across proximal end of orifice, proximomedially directed; associated with ooecium, lacking in non-reproductive zooids. Sporadic, hollow, tubular kenozooids along zooidal margins. Uniporous septula visible in inner vertical walls at colony margin ( Fig. 33 ).

Remarks. This species is readily distinguishable from the other encrusting congeners in the general appearance of the frontal shield, with numerous broad costae very close to each other. This feature is shared with G. quadriserialis , which has an erect growth morphology and well-developed marginal kenozooids. The presence of four oral spines, as reported by Canu & Bassler (1920), is rejected. The scars, sometimes observed at the oral margins, are interpreted as the breakage points of the collar-like structure.

Distribution. Late Eocene of Alabama, USA ( Fig. 1 ).

N, Number of colonies and number of zooids measured; SD, standard deviation.

Figures

FIGURE 1. Map showing the spatial and temporal distribution of all the studied species. 1, Gephyrotes nitidopunctatus (Smitt, 1868); 2, Gephyrotes fortunensis Pouyet, 2000; 3, Gephyrotes moissettei n. sp.; 4, Gephyrotes spectabilis Canu & Bassler, 1920; 5, Gephyrotes quadriserialis Canu & Bassler, 1920; 6, Gephyrotes convexus Canu & Bassler, 1920; 7, Tricephalopora saillans (Canu & Bassler, 1920); 8, Tricephalopora levigata (Canu & Bassler, 1920); 9, Spiniflabellum spinosum Canu & Bassler, 1928. Open circles, Recent; solid circles, Miocene; diamond, Oligocene; stars, Eocene; triangles, Danian.

FIGURES 30 – 33. Gephyrotes convexus Canu & Bassler, 1920, USNM 64030, Late Eocene, Alabama, USA, fig. 30 of lectotype USNM 64030 B; figs 31 – 33 of paralectotype USNM 64030 A: 30, well-preserved colony ephebic with autozooids, ooecia and avicularia; 31, neanic colony of small sterile autozooids; 32, part of colony in fig. 30 with ooecia, peristomial avicularia and frontal shields showing slit-like lacunae and numerous pelmatidia; 33, close-up of distalmost autozooid in fig. 31, with the broken collar-like structure leaving only the basal portion of the costae. Scale bars: Figs 30, 31, 500 µm; Figs 32, 33, 200 µm.

Tables

TABLE 6. Measurements (in Μm) of Gephyrotes convexus Canu & Bassler, 1920, USNM 64030.

	N (colonies, zooids)	Mean	SD	Range
Zooid length	2, 10	530	62	441–602
Zooid width	2, 10	467	36	426–524
Orifice length	2, 6	97	4	94–100
Orifice width	2, 6	121	4	118–124
Ovicell length	2, 4	170	3	166–172
Ovicell width	2, 4	204	1	203–204
Avicularia length	2, 8	126	16	107–151
Avicularia width	2, 8	58	7	47–65