Carolinapecten corpulentus Waller, 2018
WALLER, T. R. 2018. Systematics and biostratigraphy of Chesapecten and Carolinapecten (Mollusca: Bivalvia: Pectinidae) in the upper Miocene and Pliocene "lower Tamiami Formation" of southwestern Florida. Bulletin of the Florida Museum of Natural History, 56 (1): 1-47, figs. 1-11. [p. 23, figs. 9A-9D]
2018 Carolinapecten corpulentus Waller, 2018
T. R. Waller, 2018, figure 9.
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«Zoobank Nomenclatural Act.— 81615907-5C80-4779-A0C7-80973FA14465.
Diagnosis.— Gibbous, right-convex Carolinapecten with right umbo projecting well above hinge and left valve nearly as well inflated as right; disk with 15–18, most commonly 16, rounded to slightly flattened ribs that are about twice as wide as interspaces on right valve and about equal in width to interspaces on left valve. Secondary costae absent on disk and disk flanks; right anterior auricle commonly with only three radial costae. Description.— Shell large, maximum ob-served height 108 mm, moderately thick shelled, with moderately large anterior and posterior disk gapes; height about 90% of length, both valves well inflated but with right valve more convex than left; maximum convexity of right valve ranging from 25 to 30% of valve height, that of left valve commonly about 20%; convexity of articulated shell about 50% of shell height with maximum convexity occurring dorsal to midpoint of shell; byssal notch of right valve deep in small shells, becoming shallower in late ontogeny, its depth at maturity about 25% of length of anterior hinge, with active ctenolium commonly disappearing at valve heights greater than about 70 mm; byssal fasciole moderately broad and slightly arched, crossed by commarginal growth lines and rarely by one or two radial costellae. Disks with 15–18 low, rounded to slightly flattened radial ribs, most commonly 16 on right valve and 17 on left, with lateralmost ribs on each valve tending to fade out distally or to break up into low costellae; commarginal growth lines arched dorsally on ribs and ventrally in rib interspaces; disk flanks rounded, not steep, without radial costae but with fine costellae adjacent to lateralmost faded ribs. Total hinge length 65–70% of shell length, with anterior hinge slightly shorter than posterior hinge; dorsal folds of auricles weakly developed, with anterior dorsal fold of greater amplitude than posterior fold; anterior margin of right anterior auricle curving into rounded apex of byssal notch; anterior margin of left anterior auricle rather sharply rounded dorsally, then recurving into broad, shallow byssal sinus; margins of posterior auricles very shallowly outwardly convex, with overall trend forming an angle that is commonly perpendicular to dorsal margin, rarely slightly acute; right anterior auricle commonly with three broad radial costae (63% of specimens, n=32), these costae sometimes faintly striate near margin, less commonly with four costae, the ventralmost narrower than others; left anterior auricle with five to eight radial costae, most commonly six or seven, costae on posterior auricles very weak and difficult to count, not known to exceed eight. Hinge dentition of right valve consisting of strong resilial teeth extending laterally nearly parallel to hinge line, dentition of left valve consisting of strong infradorsal and infraresilial teeth. Umbonal cavity extending beneath resilifers of both valves; auricular denticles well developed at distal ends of ridges on shell interior at ventral edge of auricles. Pallial line well inset from ventral margin at about one-third height of valve. Umbonal inner foliated calcite layer extending ventrally to about mid-adductor level. Etymology.— Name based on the Latin adjective meaning fat or stout. Type material and measurements.— Holotype: USNM 716593, closed pair of valves, Ht 83.0 mm, L 90.5 mm, convexity of articulated shell 45.4 mm (Fig. 9A–D). Type locality.— USGS 26939, Charlotte County, Florida. Sixth canal west of Murdock [Jupiter Waterway], lower zone, possibly equal to “mold bed” at North Port Charlotte. M. E. Hunter, probably collected in early 1960s. Other material.— About 50 specimens (single valves plus pairs of matching valves) from four localities in the Port Charlotte area. Comparisons.— Carolinapecten corpulentus differs from all other species of the genus in having both valves well inflated, with the umbo of the right valve extending well above the dorsal margin. It is closest to Ca. murdockensis druidwilsoni n. sp. and n. ssp. (Fig. 9E–H), but that taxon is strongly inequivalve, with its left valve much less convex than that of Ca. corpulentus. Although some right valves of Ca. corpulentus and Ca. murdockensis druidwilsoni may be difficult to distinguish, the latter more commonly has four radial costae on its right anterior auricle, its ribs tend to be squared rather than rounded, and it does not attain the large size of Ca. corpulentus. Occurrence.— Port Charlotte area, west of Murdock: Como Waterway: USGS 26922; Jupiter Waterway: USGS 26925, CH108; Apollo Waterway: CH022. Distribution.— Known only from the Port Charlotte area in the southwestern Florida Peninsula in the lower Bayshore Clay Member of the lower Tamiami Formation of Hunter (1968), now regarded as within the upper Peace River Formation of late Miocene (Tortonian) age. The new species is assigned to pectinid zone PZ1 (see Biostratigraphy section). Remarks.— The determination that Carolinapecten corpulentus belongs in the genus Carolinapecten is surprising considering the highly gibbous shape of this species. The generic placement is supported, however, by the folded dorsal hinge margin of the right valve, the arcuate rather than strongly sigmoidal shape of the posterior margins of the posterior auricles, the fairly prominent disk gapes, and the rather shallow byssal notch in mature specimens. The generic placement is further supported by the inferred succession of Carolinapecten species in the Port Charlotte area, with Ca. murdockensis druidwilsoni n. sp. and ssp. forming an intermediate step (gibbous right valve, but low-convexity left valve) between Ca. corpulentus and the more equiconvex Ca. murdockensis murdockensis and Ca. murdockensis parawatsonensis. At its type locality on the Jupiter Waterway and at a second locality on the Apollo Waterway, Carolinapecten corpulentus is represented by abundant paired valves greater than 70 mm in size. Small juvenile shells are apparently absent, and there are few associated calcitic fossils. One of these associates is a large specimen (Fig. 4D) of Ecphora cf. gardnerae whiteoakensis Ward and Gilinsky, 1988, a taxon previously known only from the Claremont Manor Member of the Eastover Formation of early Tortonian Miocene age in Virginia (Ward, 1992b: 124). A second calcitic associate at the type locality of the new species (USGS 26925) is a large pycnodonteine oyster that Wilson (1987:15) identified as Pycnodonte (Gigantostrea) aff. leeana Wilson, 1987. He regarded this taxon as being very close to P. (G.) leeana from the early to middle Miocene Pungo River Formation of North Carolina and to be “the last known Gigantostrea Sacco, 1897, in the Coastal Plain.” Wilson noted that the specimen from Charlotte County was probably from Hunter’s (1968) Bayshore Clay Member, an assessment that is reinforced by the stark white color of the specimens, a feature that Hunter (1968) observed in the Bayshore Clay.» THOMAS RICHARD WALLER, 2018
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