Carolinapecten murdockensis murdockensis 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. 26, figs. 10A-10D]
2018 Carolinapecten murdockensis murdockensis Waller, 2018
T. R. Waller, 2018, figure 10.
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«Zoobank Nomenclatural Act.— 10C8F80C-454A-4122-86C6-B28F5E6E2733.
Diagnosis.— Moderately inflated, equiconvex to slightly right-convex Carolinapecten with right umbo not projecting far above dorsal margin and dorsal margins on auricles of right valve not strongly folded; disks with 15–18 ribs, most commonly 17, with variable rib profiles ranging from distinctly squared to rounded; commarginal lamellae closely spaced in rib interspaces and on rib crests, secondary radial costae absent on disk and disk flanks; right anterior auricle commonly with four radial costae. Description.— Shell moderately large, equilateral or with slightly extended posterior, maximum observed height 108 mm but most specimens less than 80 mm, moderately thick shelled, disk gapes absent or very narrow; height about 90% of length, both valves moderately inflated, either equiconvex or with right valve slightly more convex than left; maximum convexity of right valve less than 25% of valve height, that of left valve commonly less than 20%; convexity of articulated shell commonly less than 40% of shell height; 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 80 mm, rarely minimally present at shell heights up to 90 mm; byssal fasciole narrow, either flat or slightly depressed, becoming narrowly raised along suture and crossed by commarginal growth lines. Disks with 15–18, most commonly 17, high ribs having profiles that vary among populations, squared at least in early ontogeny and commonly throughout ontogeny in some, but high and rounded in others, consistently wider than interspaces on right valve and about equal to interspaces on left, with lateralmost ribs on each valve tending to persist to margin; commarginal growth lines closely spaced in rib interspaces, tending to disappear on rib crests; disk flanks lacking radial striae, narrow, flat, and steep in square-ribbed forms, broader and more sloping in rounder ribbed forms. Total hinge length variable, 55–75% of shell length, with anterior hinge slightly shorter than posterior hinge; dorsal folds of auricles of right valve weakly developed, with anterior dorsal fold of greater amplitude than posterior fold; anterior margin of right anterior auricle curving into apex of byssal notch; anterior margin of left anterior auricle evenly rounded to shallowly sigmoidal, producing a shallow byssal sinus; margins of posterior auricles very shallowly outwardly convex, with overall trend variable, forming distinctly acute angle with dorsal margin in some populations but perpendicular in others; right anterior auricle commonly with four radial costae, rarely with three; 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.— Named for the Murdock area of northwestern Port Charlotte, Charlotte County, Florida. Type material and measurements.— Holotype: USNM 716595, pair of matching valves, Ht 69 mm, L 71 mm, convexity of articulated shell 29.6 mm (Fig. 10A–D). Type locality.— USGS 26933, Charlotte County, Florida, spoil banks of canal [Lion Heart Waterway] at north edge of Port Charlotte Information Center, northwest edge of Port Charlotte, US 41 (Sec. 17, T40S, R22E). Collectors: H. E. and E. H. Vokes, 1969. Other material.— 185 specimens (single valves plus pairs of matching valves) from 32 localities mainly in the Port Charlotte area. Comparisons.— Carolinapecten murdockensis murdockensis differs from Ca. murdockensis druidwilsoni n. ssp. in being nearly equiconvex rather than strongly right convex, having a more inflated left valve, and having a much greater percentage of specimens with four costae on the right anterior auricle. Carolinapecten murdockensis murdockensis differs from Ca. murdockensis parawatsonensis n. ssp. in having more squared ribs, a less equilateral shell with its posterior side slightly extended, much narrower or absent disk gapes, and in lacking lateralmost ribs that fade out and/or subdivide before reaching the shell margin in mature specimens. Occurrence.— Port Charlotte area, west of Murdock: Cocoplum Waterway: SO010C; Auburn Waterway: USGS 22256, USGS 26906, CH104B, CH018; Como Waterway: USGS 22926, USGS 23202, USGS 26922, CH106, CH120; Bayshore Waterway: USGS 26932, USGS 26910, USGS 26917, USGS 26923, USGS 26938, CH030B; Jupiter Waterway: USGS 26916, CH113. Port Charlotte area, east of Murdock: Pellam Waterway: USGS 22911, USGS 22912, USGS22913; Lion Heart Waterway: USGS 26928, USGS 26933; Sunset Waterway: USGS 23118, USGS 26912. Other localities: Charlotte County: CH026; DeSoto County: USGS 21258, USGS 26920, USGS DE006. Distribution.— Known mainly from the Port Charlotte area in the southwestern Florida Peninsula in pectinid zone PZ2 in the upper Bayshore Clay Member and lower Murdock Station Member of the lower Tamiami Formation of Hunter (1968), now regarded as within the upper Peace River Formation of late Miocene (Tortonian) age. Remarks.— Carolinapecten murdockensis murdockensis is highly variable in rib profiles. These range from squared throughout ontogeny as in the holotype (Fig 4A–D) and in specimens in CH113 marked by Hunter as “type Pecten biostrome,” to forms that have squared ribs limited to early ontogeny. Abundant specimens at Locality CH026 have rib profiles that vary from rounded to squared and differ from other populations of Ca. murdockensis murdockensis in having a higher percentage of right valves with three rather than four costae on the right anterior auricle (54% with three, 46% with four in a measured sample of 13 right valves). Calcitic associates of Carolinapecten murdockensis murdockensis include Chesapecten middlesexensis hunterae, broad-ribbed Ecphora in the E. gardnerae complex, the non-auriculate oyster, Mansfieldostrea compressirostra brucei, and the pectinid Euvola smithi, all regarded as indicators of late Miocene (Tortonian) age.» THOMAS RICHARD WALLER, 2018
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