Locality B86

Reptamsassia divergens n. gen. n. sp. is present in a 0.8-m-thick thrombolite bed capped by thin grainstone; the thrombolite is flanked by dolomitized burrowed limestone. The top is an undulating erosion surface overlain by dolomite intraclasts in the depressions, followed by a dolomitized microbial laminite that passes laterally to a breccia of angular laminite clasts. The Reptamsassia-bearing bed is ~4 m above the Boat Harbour disconformity marking the base of the Barbace Cove Member of the Boat Harbour Formation, and ~47 m below the Catoche Formation (unit 190 in Pratt, Reference Pratt1979, p. 217; just above sample site BH-42 at +84 m in Knight et al., Reference Knight, Azmy, Boyce and Lavoie2008, fig. 4, column E; Fig. 2).

Locality B97

Reptamsassia divergens n. gen. n. sp. and R. minuta n. gen. n. sp. are present in a 2.3-m-thick thrombolite bed recorded in the field as a burrowed wackestone. This occurrence is ~15 m above the Boat Harbour disconformity marking the base of the Barbace Cove Member of the Boat Harbour Formation, and ~34 m below the Catoche Formation (unit 207 in Pratt, Reference Pratt1979, p. 216; between sample sites BH-45 and BH-46 at +92 m in Knight et al., Reference Knight, Azmy, Boyce and Lavoie2008, fig. 4, column E; Fig. 2).

Lithology

The thrombolite framework at both localities (B86 and B97) consists of irregular to crudely columnar masses of microbialite composed of clotted micrite and micrite with embedded skeletons of Reptamsassia n. gen., some preserved in growth position (Fig. 3.1–3.3). Microbialite locally exhibits centimeter-scale surfaces of abrasion. Flanking sediment is mainly a grainstone consisting of micrite, peloids, small intraclasts of clotted micrite, and bioclasts, all of which are sporadically incorporated in the microbialite. The similarity between the framework and matrix and places where matrix grades into microbialite make it somewhat difficult to distinguish between the two.

Figure 3.

(1–3) Representative dolomitic limestone fabrics of thrombolite mounds containing Reptamsassia n. gen. in the Barbace Cove Member (Floian) of the Boat Harbour Formation, Isthmus Bay, Port au Port Peninsula, western Newfoundland; back-lit photographs of thin sections oriented horizontally (1; locality B86) and vertically (2, 3; locality B97) with respect to bedding; scale bar (shown in 1) = 10 mm. (1) Rudstone composed of peloids, rare bioclasts, a fragment of nautiloid (lower center), a turriform gastropod (right), and intraclasts of biolithite, including one containing Reptamsassia n. gen. (top center). (2) Boundstone composed of Reptamsassia n. gen. (center and right) encased in microbialite, flanked by wackestone composed of sparse biomicrite and locally pelsparite, with burrows conforming to Palaeophycus and Planolites where backfilled. (3) Boundstone composed of Reptamsassia n. gen. in upright growth position, mostly enveloped by a thin microbialite coating and flanked by lime mudstone consisting of burrowed micrite and locally pelsparite. (4) Direct association of Reptamsassia n. gen. species; back-lit photograph of thin section. Transverse view of large-module species R. divergens n. gen. n. sp. (left; GSC 142673) and the small-module species R. minuta n. gen. n. sp. (right; GSC 142674) from floatstone/rudstone at locality B97; scale bar = 5 mm.

Small intraclasts range from rounded to angular. Some peloids are hollow capsules. Bioclasts are sparse, broken, and commonly abraded, and include trilobite sclerites, brachiopod valves, gastropods, and nautiloids, along with rare Nuia Maslov, Reference Maslov1954, stylophoran echinoderm ossicles, rounded fragments of the radiating calcimicrobe Botomaella Korde, Reference Korde1958, and blunt-tipped calcisponge spicules. Gastropods have turbinate, turriform, and planispiral shapes; nautiloids are orthocones. Micrite envelopes on bioclasts are common. Small monaxon and hexactine siliceous sponge spicules are present in some micritic areas and intraclasts. Subrounded clasts of microbialite and Reptamsassia n. gen. are also present. Both the matrix and micritic areas of microbialite are penetrated by spar- and partly sediment-filled burrows conforming to Palaeophycus Hall, Reference Hall1847; local backfilled burrows at locality B97 conform to Planolites Nicholson, Reference Nicholson1873. Inclusion-rich, isopachous fibrous calcite cement is confined to portions of the Reptamsassia n. gen. skeletons.

Paleoenvironment

Reefal deposits at both localities (B86 and B97) record a relatively high-energy setting, where parts of the microbial framework, including some of the incorporated Reptamsassia n. gen. skeletons, were subjected to physical breakage and disintegration. Fragments were variably rounded by wave action, and small areas of the reef surface were abraded. Vigorous water movement through the elevated framework elements promoted submarine cementation in the Reptamsassia n. gen. skeletons. The reef surface was populated sparsely by invertebrates. Shells and sclerites also suffered breakage and rounding, commonly with bioerosion forming micrite envelopes. Quiescent periods allowed accumulation of lime mud on the accreting reef surface, locally accompanied by growth of small siliceous sponges. Both the microbial framework and matrix were affected by burrowing before sufficient cementation stiffened the sediment.

Genera

Amsassia Sokolov and Mironova, Reference Sokolov and Mironova1959 (type genus), and Reptamsassia n. gen.

Diagnosis

Growth form massive, structure phacelocerioid; growth direction of modules upward, lateral, or reptant. Transverse shape of modules polygonal to subpolygonal in densely packed areas, subcircular to circular in loosely packed areas, or irregular. Adjoining modules have back-to-back walls. Species have maximum module diameters ranging from 0.28–1.66 mm. Module increase by longitudinal fission involving infolding(s) of wall: bipartite, tripartite, quadripartite, or hexapartite. Modules resulting from fission remain in contact, separate slightly, or diverge in opposite directions with an inter-module angle up to 90°. Tabulae absent. Tabula-like structures form incomplete to complete, concave-up bases of rejuvenated or regenerated modules. Calices shallow to deep with concave-up bottoms.

Remarks

Amsassia was originally considered to be a tabulate coral and assigned to Family Cryptolichenariidae Sokolov in Sokolov and Mironova, Reference Sokolov and Mironova1959. Sokolov and Mironova (Reference Sokolov and Mironova1959) noted the similarity of Amsassia to representatives of Lichenariidae Okulitch, Reference Okulitch1936, Tetradiidae Nicholson, Reference Nicholson1879, and Chaetetidae Milne-Edwards and Haime, Reference Milne-Edwards and Haime1850. Since then, Cryptolichenariidae (including Amsassia) has been placed in the orders Lichenariida Sokolov, Reference Sokolov1950 (e.g., Yu and Zhang, Reference Yu, Zhang, Yu, Wu, Zhao and Zhang1963), Tetradiida Okulitch, Reference Okulitch1936 (e.g., Sokolov, Reference Sokolov, Sokolov and Orlov1962; Lin et al., Reference Lin, Tchi, Jin, Li and Yan1988), and Chaetetida Okulitch, Reference Okulitch1936 (Hill, Reference Hill and Teichert1981, who noted that Amsassia is possibly a tetradiid). The nominative lichenariid genus, Lichenaria, is definitely a tabulate coral (Laub, Reference Laub, Oliver, Sando, Cairns, Coates, Macintyre, Bayer and Sorauf1984; Elias et al., Reference Elias, Lee and Woo2008, Reference Elias, Lee and Pratt2021). The nominative cryptolichenariid genus, Cryptolichenaria Sokolov, Reference Sokolov1955, was included by Scrutton (Reference Scrutton, Oliver, Sando, Cairns, Coates, Macintyre, Bayer and Sorauf1984) in Tetradiida, which he later removed from Tabulata Milne-Edwards and Haime, Reference Milne-Edwards and Haime1850 (Scrutton, Reference Scrutton1997). The nominative tetradiid genus, Tetradium Dana, Reference Dana1846, has since been interpreted as a calcareous florideophyte red alga (Steele-Petrovich, Reference Steele-Petrovich2009a, Reference Steele-Petrovichb), necessitating the replacement name Prismostylus Okulitch, Reference Okulitch1935, and erection of Family Prismostylaceae Steele-Petrovich, Reference Steele-Petrovich2011 (Steele-Petrovich, Reference Steele-Petrovich2011). Chaetetids are now regarded as calcareous sponges (West, Reference West2011a). West (Reference West2011b) rejected Amsassia and Cryptolichenaria from chaetetid-type sponges.

Based on morphologic comparisons in previous studies, Amsassia has been excluded from corals and calcareous sponges, as well as cyanobacteria, and referred to calcareous algae (Sun et al., Reference Sun, Elias and Lee2014; Lee et al., Reference Lee, Park, Tien, Choh, Elias and Lee2016, Reference Lee, Elias, Choh and Lee2018, Reference Lee, Elias and Pratt2021; Elias et al., Reference Elias, Lee and Pratt2021). Infolding of the module wall during longitudinal fission in both Amsassia and Reptamsassia n. gen. is consistent with simple branching of the module occupant (di-, tri-, quadri-, and hexachotomous in Amsassia; di-, tri-, and probably quadrichotomous in Reptamsassia n. gen.). Dichotomous to polychotomous branching is common in algae. Steele-Petrovich (Reference Steele-Petrovich2009a) interpreted module increase in Tetradium as branching. Increase by longitudinal fission in tetradiids was typically quadripartite, but could also be tripartite and bipartite (Sun et al., Reference Sun, Elias and Lee2014). Increase in Cryptolichenaria was bipartite (Hill, Reference Hill and Teichert1981).

Unlike Amsassia and Reptamsassia n. gen., in which module increase involved infolding of the wall, increase in Tetradium and Cryptolichenaria involved the development of one or more skeletal partitions inside the module (Hill, Reference Hill and Teichert1981). Horizontal skeletal elements in tetradiids (e.g., Paenetetradium Copper and Morrison, Reference Copper and Morrison1978; see Copper and Morrison, Reference Copper and Morrison1978) and Cryptolichenaria (see Sokolov, Reference Sokolov1955) are true tabulae, which are platforms having edges attached to the inner surface of the module wall (Hill, Reference Hill and Teichert1981). Amsassia and Reptamsassia n. gen., however, lack true tabulae. Their tabula-like structures are bases of rejuvenated or regenerated modules, which are structurally continuous with the vertical module wall (Elias et al., Reference Elias, Lee and Pratt2021; Lee et al., Reference Lee, Elias and Pratt2021). Thus, Amsassia and Reptamsassia n. gen. differ significantly from tetradiids, and are regarded as a distinct group of extinct calcareous algae for which the Family Amsassiaceae n. fam. is here erected.

In considering the biologic affinity of Amsassia, Lee et al. (Reference Lee, Elias and Pratt2021) made comparisons with the unmineralized extant green alga Cladophora Kützing, Reference Kützing1843. They suggested that if branching filaments such as those of Cladophora were tightly to loosely arranged and the cell walls became calcified during growth, phacelocerioid skeletons of modules with tabula-like structures at constrictions could result, like those of Amsassia. Such tabula-like structures also occur in Reptamsassia n. gen. Maximum module diameters in species of Reptamsassia n. gen. (0.30–0.53 mm) are within the range of maximum cell diameters in species of Cladophora (0.07–1.00 mm). Dichotomous to hexachotomous branching occurs in Cladophora; in Reptamsassia n. gen., the types of module fission indicate di-, tri-, and probably quadrichotomous branching. Angles of ramification are variable within and among species of Cladophora (e.g., see Leliaert and Coppejans, Reference Leliaert and Coppejans2003). Although modules resulting from fission remain in contact in Amsassia, they may also separate slightly or diverge from one another in Reptamsassia n. gen. Lee et al. (Reference Lee, Elias and Pratt2021) inferred that the tops of modules in Amsassia would have remained uncalcified to allow elongation of filaments during growth, and for release of gametes and zoospores as in Cladophora. Therefore, upon death and decomposition of Amsassia, calices with an open top and a concave-up tabula-like structure at the base would have been present on the distal surface of the skeleton and become filled with sediment. Such calices are also observed in Reptamsassia n. gen. On the basis of the foregoing, it is concluded that the Family Amsassiaceae n. fam. may belong to the green algae (Phylum Chlorophyta Reichenbach, Reference Reichenbach1828).

Type species

Reptamsassia divergens n. gen. n. sp.; Barbace Cove Member (Floian; Tulean) of Boat Harbour Formation, localities B86 and B97 in Isthmus Bay, eastern Port au Port Peninsula, Newfoundland, Canada.

Other species

Reptamsassia minuta n. gen. n. sp.; Barbace Cove Member (Floian; Tulean) of Boat Harbour Formation, locality B97 in Isthmus Bay, eastern Port au Port Peninsula, Newfoundland, Canada.

Diagnosis

Growth habit encrusting; growth direction of modules highly variable, upward to lateral and reptant. Transverse shape of modules extremely variable, commonly irregular. Species have maximum module diameters ranging from 0.30–0.53 mm. Module increase bipartite, tripartite, and probably quadripartite. Some modules resulting from fission separate slightly, or diverge in opposite directions with an inter-module angle up to 90°. Calices of modules moderately deep to deep.

Etymology

The name recognizes the similarity of this new genus to Amsassia, while noting its distinctive, reptant growth habit.

Remarks

Reptamsassia n. gen. resembles Amsassia in its massive growth form, phacelocerioid structure, back-to-back walls of adjoining modules, module increase by longitudinal fission involving infolding(s) of the wall, calices with concave-up bottoms, and absence of tabulae. Tabula-like structures forming the bases of regenerated or rejuvenated modules in Reptamsassia n. gen. occur at the same levels in adjacent modules, as in species of Amsassia. Maximum module diameters in species of Reptamsassia n. gen. (0.30–0.53 mm) fall within the range of Amsassia (0.28–1.66 mm; Lee et al., Reference Lee, Elias and Pratt2021). The new genus is differentiated from Amsassia by its encrusting habit, the highly variable growth direction of modules ranging from upward to lateral and reptant, the extremely variable and commonly irregular shape of modules, and module increase resulting in modules that separate slightly or diverge from one another in some cases.

Types

Holotype GSC 142679 (thin section; Fig. 6.1) and paratype GSC 142680 (thin section, Fig. 6.2) occur in boundstone and floatstone/rudstone, respectively, Barbace Cove Member (Floian; Tulean) of Boat Harbour Formation, locality B97 in Isthmus Bay, eastern Port au Port Peninsula, Newfoundland, Canada.

Figure 6.

Thin-section photomicrographs showing transverse (2, 3, 5–7) and both transverse and longitudinal (1, 4) views of Reptamsassia divergens n. gen. n. sp. from localities B86 (4, 6, 7) and B97 (1–3, 5). (1) Skeleton showing phacelocerioid structure and variable growth directions of modules, ranging from upward to lateral and reptant; some small areas of sediment accumulation or microbial encrustation (left of center, lower right of center) seem to have been accommodated by diverted growth of modules without mortality; note module undergoing bipartite fission (arrow); holotype GSC 142679; scale bar = 5 mm. (2) Skeleton showing variable growth directions of modules; paratype GSC 142680; scale bar = 5 mm. (3) Skeleton showing partial growth interruptions associated with peloids and micritic clots likely of microbial origin (arrows); GSC 142681; scale bar = 5 mm. (4) An intraclast consisting of skeleton encrusted by microbialite; longitudinal fission resulting in pairs of modules (arrows); deep calices with concave-up bottoms (outlined area; enlarged in Fig. 8.3); GSC 142682; scale bar = 2 mm. (5) Cerioid area showing low size and shape variability of densely packed, polygonal to subpolygonal modules; GSC 142683; scale bar = 1 mm. (6) Loosely packed area showing high size variability of subcircular to circular modules, some flanked by micrite (dark colored); outlined area enlarged in 7; GSC 142684; scale bar = 0.5 mm. (7) Enlargement of outlined area in 6, showing back-to-back walls between adjoining modules (pairs of white arrows); GSC 142684; scale bar = 0.5 mm.

Diagnosis

Reptamsassia n. gen. with maximum module diameter 0.53 mm.

Description

Growth form massive, shape predominantly irregular; structure phacelocerioid (Figs. 6.1–6.4, 7.1). At locality B97, complete skeletons not observed due to development of stylolites and partial diagenetic dissolution; many apparently in growth orientation, some fragmentary and abraded skeletons evidently transported; size over 80 × 80 mm across and 55 mm high. Many skeletons at locality B97, predominantly in boundstone, were overgrown by and intergrown with comparatively small-module species Reptamsassia minuta n. gen. n. sp. (Figs. 4, 5), and contain various amounts of peloids and micritic clots likely of in situ microbial origin (arrows in Fig. 6.3). At locality B86, most skeletons occur as heavily abraded, transported grains in rudstone; original form and size unknown (Fig. 6.4).

Figure 7.

Thin-section photomicrographs showing transverse views of Reptamsassia divergens n. gen. n. sp. from localities B86 (1, 2, 6) and B97 (3–5, 7, 8). (1) Modules irregularly shaped where they encrust substrate during initial stage of skeletal growth (black arrow) and at base of skeleton during subsequent lateral expansion (white arrows); outlined area enlarged in 2; GSC 142685; scale bar = 2 mm. (2) Enlargement of outlined area in 1, showing variably sized modules, some flanked by micrite, in loosely packed area; module shapes subcircular to circular, or irregular due to interference from adjacent modules; note module undergoing bipartite fission involving infolding of wall (arrow); GSC 142685; scale bar = 0.5 mm. (3–6) Modules undergoing bipartite fission (white arrows) and probable quadripartite fission (black arrow in 5) involving infolding(s) of wall; GSC 142686a, GSC 142687, GSC 142686b, and GSC 142688, respectively; scale bars = 0.5 mm. (7) Module undergoing tripartite fission; GSC 142686a; scale bar = 0.5 mm. (8) Module probably undergoing tripartite fission involving infoldings of wall; GSC 142689; scale bar = 0.5 mm.

In transverse section, module shape extremely variable: polygonal to subpolygonal in densely packed areas (Fig. 6.5); subcircular to circular in loosely packed areas where partially or completely separated by micrite (Figs. 6.6, 7.2); shape irregular where modules encrust substrate, including initial stage of skeletal growth (black arrow in Fig. 7.1) and base of skeleton during subsequent lateral expansion (white arrows in Fig. 7.1); irregular due to highly variable growth directions of modules, ranging from upward to lateral and reptant (Figs. 3.4, 6.1–6.3); irregular due to interference from adjacent modules (Figs. 6.6, 7.2). Adjoining modules have back-to-back walls (Fig. 6.7). Module size extremely variable throughout skeletal growth, especially in loosely packed areas with modules partially or completely separated by micrite (Figs. 6.6, 7.2); diameter of largest 10% of modules 0.40–0.53 mm (Table 1). Module increase by longitudinal fission (arrows in Fig. 6.4) involving infolding(s) of wall (white arrows in Figs. 6.1, 7.2–7.6), which extend(s) to divide module; predominantly bipartite (white arrows in Figs. 6.1, 7.2–7.6), rarely tripartite (Fig. 7.7, 7.8) and probably quadripartite (black arrow in Fig. 7.5). In oblique or longitudinal section, some modules resulting from fission separate slightly (arrows in Fig. 6.4; Fig. 8.1, 8.3) or diverge from one another in opposite directions with an inter-module angle up to 90° (arrows in Fig. 8.5, 8.6). In longitudinal section, module walls usually undulate (Fig. 8.6, 8.7). Tabulae absent. Regeneration or rejuvenation, usually following constriction of modules (white arrows in Fig. 8.7), recorded by typically concave-up tabula-like structures forming bases of subsequent module growth, structurally continuous with vertical module wall, commonly developed at same levels in adjacent modules (black arrows in Fig. 8.7). Calices of modules deep with concave-up bottoms (white arrow in Fig. 8.2; Fig. 8.3, 8.4), similar in shape to the tabula-like structures (black arrows in Fig. 8.2).

Figure 8.

Thin-section photomicrographs showing longitudinal views of Reptamsassia divergens n. gen. n. sp. from localities B86 (3, 4) and B97 (1, 2, 5–7). (1) Longitudinal fission resulting in modules that separate slightly; GSC 142690; scale bar = 0.5 mm. (2) Deep calice with concave-up bottom (white arrow) similar in shape to tabula-like structures within modules (black arrows); GSC 142691; scale bar = 1 mm. (3) Enlargement of outlined area in Figure 6.4, showing longitudinal fission resulting in modules that separate slightly (left side); note deep calices of modules; GSC 142682; scale bar = 1 mm. (4) Deep calices with concave-up bottoms; GSC 142692; scale bar = 1 mm. (5, 6) Longitudinal fission resulting in modules that diverge (arrows); GSC 142693 and GSC 142694, respectively; scale bars = 1 mm and 0.5 mm, respectively. (7) Tabula-like structures forming bases of regenerated modules, usually following constriction of modules (e.g., white arrows), commonly developed at same levels in adjacent modules (black arrows); GSC 142695; scale bar = 2 mm.

Table 1.

Diameter (mm) of modules of Reptamsassia divergens n. gen. n. sp., based on 12 skeletons from locality B86 and 11 (including holotype and paratype) from locality B97. In transverse thin-sections, diameter was measured internally in the largest 10% of modules; module diameter = (long axis + short axis) ÷ 2 (see Scrutton, Reference Scrutton1981). Abbreviations: Min. = minimum; Max. = maximum; Avg. = average; S.D. = standard deviation; N = number of modules.

Etymology

The name of the new species refers to the divergent growth patterns of modules following longitudinal fission.

Remarks

The most distinctive feature of Reptamsassia divergens n. gen. n. sp. is the high degree of variability in shape and size of modules, related in part to the encrusting base of the skeleton and the highly variable growth directions of modules, ranging from upward to lateral and reptant. Reptamsassia divergens n. gen. n. sp. is the large-module species of this genus; diameters of the largest 10% of modules are 0.40–0.53 mm for R. divergens n. gen. n. sp. versus 0.19–0.30 mm for R. minuta n. gen. n. sp. Although diameters of subcircular to circular modules in R. divergens n. gen. n. sp. tend to be smaller at locality B86 than at locality B97, the ranges of values overlap (Table 1). Many skeletons of R. divergens n. gen. n. sp. were overgrown by and intergrown with R. minuta n. gen. n. sp. at locality B97, predominantly in the boundstone.

Types

Holotype GSC 142675a (thin section; Figs. 4.1, 5.1, 9.1, 10.4), 142675b (thin section; Figs. 4.2, 9.3, 9.6), and 142675c (thin section; Fig. 9.2, 9.4), and paratype GSC 142677a (thin section; Figs. 4.4, 10.5) and 142677b (thin section; Fig. 4.5) occur in boundstone, Barbace Cove Member (Floian; Tulean) of Boat Harbour Formation, locality B97 in Isthmus Bay, eastern Port au Port Peninsula, Newfoundland, Canada.

Figure 9.

Thin-section photomicrographs showing transverse views of Reptamsassia minuta n. gen. n. sp. from locality B97. (1) Mostly polygonal to subpolygonal modules showing variable shapes and sizes, with one module undergoing bipartite fission involving infolding of wall (white arrow); adjoining modules have back-to-back walls (black arrows); holotype GSC 142675a; scale bar = 0.5 mm. (2) Shape and size variability of subcircular to circular and irregularly shaped modules, some flanked by sediment (dark area left of center); holotype GSC 142675c; scale bar = 0.5 mm. (3) Module undergoing bipartite fission (arrow) where modules are relatively densely packed; holotype GSC 142675b; scale bar = 0.2 mm. (4, 5) Modules undergoing bipartite fission involving infolding(s) of wall (arrows); holotype GSC 142675c and GSC 142696a, respectively; scale bars = 0.2 mm. (6) Module undergoing tripartite fission involving infoldings of wall (arrows); holotype GSC 142675b; scale bar = 0.2 mm. (7) Module probably undergoing quadripartite fission involving infoldings of wall (arrows); GSC 142697; scale bar = 0.2 mm.

Figure 10.

Thin-section photomicrographs showing longitudinal views of Reptamsassia minuta n. gen. n. sp. from locality B97. (1–3) Longitudinal fission resulting in modules that separate slightly or diverge (white arrows); note calice of a module (black arrow in 1); GSC 142696b (1, 2) and GSC 142698 (3); scale bars = 0.2 mm. (4, 5) Modules having moderately deep calices (arrows); holotype GSC 142675a and paratype GSC 142677a, respectively; scale bars = 0.2 mm and 0.5 mm, respectively.

Diagnosis

Reptamsassia n. gen. with maximum module diameter 0.30 mm.

Description

Growth form massive, shape irregular; overall structure phacelocerioid, predominantly cerioid with inconspicuous phaceloid areas. Size (difficult to determine in most cases) up to 10 × 8 mm across and 4 mm high. All observed skeletons grew in direct association with R. divergens n. gen. n. sp. (Figs. 3.4, 4, 5); occasional partial mortality was followed by rejuvenation/regeneration (Fig. 4.5). In transverse section, modules predominantly polygonal to subpolygonal in densely packed areas (Fig. 9.1), subcircular to circular in more loosely packed areas (Fig. 9.2); shape of modules typically irregular, especially where in contact with R. divergens n. gen. n. sp. (Figs. 3.4, 4.2, 5.1). Growth direction of modules variable, ranging from upward to lateral and reptant (Fig. 4.1). Adjoining modules have back-to-back walls (black arrows in Fig. 9.1). Module size highly variable throughout skeletal growth; diameter of largest 10% of modules 0.19–0.30 mm (Table 2). Module increase by longitudinal fission (white arrows in Fig. 10.1–10.3); predominantly bipartite (white arrows in Fig. 9.1, 9.3–9.5), rarely tripartite (Fig. 9.6) and probably quadripartite (Fig. 9.7), involving infolding(s) of wall seen where module is not constrained by tight packing (white arrows in Fig. 9.1, 9.3–9.7). In oblique or longitudinal section, some modules resulting from fission separate slightly or diverge from one another in opposite directions with an inter-module angle up to 60° (white arrows in Fig. 10.1–10.3). In longitudinal section, module walls highly undulate (Fig. 4.4) and conform with modules of R. divergens n. gen. n. sp. where in contact (Figs. 4.3, 5.2). Tabulae absent. Regeneration or rejuvenation, usually following constriction of modules, recorded by typically concave-up tabula-like structures forming bases of subsequent module growth, structurally continuous with vertical module wall, commonly developed at same levels in adjacent modules (between black arrows in Fig. 4.4). Calices of modules moderately deep with concave-up bottoms (black arrows in Fig. 10.1, 10.4, 10.5).

Table 2.

Diameter (mm) of modules of Reptamsassia minuta n. gen. n. sp., based on five skeletons (including holotype). In transverse thin-sections, diameter was measured internally in the largest 10% of modules; module diameter = (long axis + short axis) ÷ 2 (see Scrutton, Reference Scrutton1981). Abbreviations: Min. = minimum; Max. = maximum; Avg. = average; S.D. = standard deviation; N = number of modules.

Etymology

The name of the new species refers to the small size of its modules.

Materials

In addition to holotype and paratype (see above), thin sections of the following six skeletons are figured. GSC 142674 (Fig. 3.4) occurs in floatstone/rudstone, GSC 142676 (Fig. 4.3), GSC 142678 (Fig. 5.2), GSC 142696a (Fig. 9.5) and 142696b (Fig. 10.1, 10.2), GSC 142697 (Fig. 9.7), and GSC 142698 (Fig. 10.3) occur in boundstone, Barbace Cove Member (Floian; Tulean) of Boat Harbour Formation, locality B97 in Isthmus Bay, eastern Port au Port Peninsula, Newfoundland, Canada.

Remarks

Reptamsassia minuta n. gen. n. sp. is the small-module species of this genus; diameters of the largest 10% of modules are 0.19–0.30 mm for R. minuta n. gen. n. sp. versus 0.40–0.53 mm for R. divergens n. gen. n. sp. Reptamsassia minuta n. gen. n. sp. is only known to occur in direct association with R. divergens n. gen. n. sp., overgrowing and intergrown with the latter species.