Carolinapecten murdockensis parawatsonensis 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. 29, figs. 11A-11F]
2018 Carolinapecten murdockensis parawatsonensis Waller, 2018
T. R. Waller, 2018, figure 11.
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«Zoobank Nomenclatural Act.— E5F6ACA3-C651-4C3B-9279-C672F9A0CC97.
Diagnosis.— Equilateral Carolinapecten with 15–19 subrounded ribs with low, steep sides, with lateralmost rib on each side subdividing and becoming lower near margin; secondary radial costellae or striae absent from ribs and interspaces; close-set commarginal lamellae commonly limited to rib interspaces or forming a fringe along sides of rib crests; byssal notch remaining moderately deep throughout ontogeny. Description.— Shell moderately large, maximum observed height 104 mm, moderately thick shelled, equilateral or with slightly extended posterior, disk gapes moderately broad; height and length nearly equal or with length slightly longer than height, hinge length about 60–70% of shell length, with anterior hinge length nearly equal to posterior hinge length or slightly shorter; valves about equally convex or slightly right-convex, with convexity of each valve not exceeding 20% of valve height, convexity of articulated shell about 40% of shell height. Disks with 15–19 ribs, most commonly 17 or 18, with shallowly rounded crests and low, steep sides, broader than interspaces on both valves or equal in width to interspaces on left valve; lateralmost ribs commonly becoming lower and subdividing near margin; commarginal lamellae closely spaced in rib interspaces and on edges of rib crests, with smooth centers of rib crests slightly elevated above lamellae on sides of crests (Fig. 11E–F), secondary radial costae absent on disk and disk flanks. Disk flanks narrow and steep, crossed by commarginal growth lines. Right anterior auricle commonly with four radial costae, rarely three or five; byssal notch remaining moderately deep with angular apex in late ontogeny, its depth at maturity about 20% of length of anterior hinge, with active ctenolium commonly weakly developed at valve heights greater than about 80 mm, rarely present with only one or two teeth at shell heights up to 100 mm; byssal fasciole broad, slightly raised and crossed by commarginal growth lines; radial costae on posterior auricles and left anterior auricle weakly developed and difficult to count, about six or seven, commonly stronger on dorsal part of these auricles; dorsal folds of auricles of right valve moderately developed, with anterior dorsal fold of greater amplitude than posterior fold. 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 its close morphological resemblance to Carolinapecten eboreus watsonensis. Type material and measurements.— Holotype (Fig. 11A–F): USNM 716596, pair of matching valves, Ht 79 mm, L 88.5 mm, convexity of articulated shell 31.2 mm. Type locality.— USGS 26931, Charlotte County, Florida, Port Charlotte development, spoil banks, canal [Bayshore Waterway] north side of US 41, 5.3 km (3.3 miles) west of SR 776 at old Murdock junction, sec. 3, T40S, R21E. H. E. and E. H. Vokes, 1969. Other material.— About 250 specimens (single valves plus pairs of matching valves) from 13 localities in the Port Charlotte area. Comparisons.— Carolinapecten murdockensis parawatsonensis resembles other subspecies of Ca. murdockensis in having closely spaced commarginal lamellae in rib interspaces, a moderately deep byssal notch, an active ctenolium that tends to persist into late ontogeny, and low dorsal folds on its right anterior auricles. It differs from the other subspecies in having moderately wide disk gapes (Fig. 11B), subrounded ribs with low, steep sides, and in many specimens rib crests that have a smooth center slightly raised above flanking lamellate fringes (Fig. 11–F). Carolinapecten murdockensis parawatsonensis differs from Ca. eboreus watsonensis in having higher, more steeply sided ribs, more closely spaced commarginal lamellae throughout ontogeny, a deeper byssal notch, a more persistent active ctenolium, and less deeply folded dorsal margins of right-valve auricles. Occurrence.— Port Charlotte area, west of Murdock: Como Waterway: USGS 22931; Crestwood Waterway: USGS 22916; Eastwind Waterway: USGS 26909; Bayshore Waterway: USGS 23858, USGS 26910, USGS 26911, USGS 26923, USGS 26931, CH029. Port Charlotte area, east of Murdock: Crestview Waterway: CH119; Sunset Waterway: USGS 23117, USGS 26915; Morningstar Waterway: USGS 26929. Generalized Murdock localities: USGS 26938. Distribution.— Carolinapecten murdockensis parawatsonensis is known only from the Port Charlotte area, where it occurs in biozone PZ3 (see Biostratigraphy section) associated with Ch. middlesexensis bayshorensis. Remarks.— Carolinapecten murdockensis parawatsonensis is regarded as the youngest and most derived member of the Ca. murdockensis lineage in the Port Charlotte area. It co-occurs at most localities with Ch. middlesexensis bayshorensis, regarded as the latest member of the Ch. middlesexensis lineage in Florida. Other co-occurring calcitic fossils corroborate a position near the Miocene-Pliocene boundary. At locality USGS 23117 on the Sunset Waterway east of Murdock, associated barnacles include Arossia glyptopoma (Pilsbry, 1916) and Tamiosoma advena Zullo, 1992b, both previously regarded as Pliocene species (Zullo, 1992b), but Chesaconcavus myosulcatus Zullo, 1992b, a Miocene species, is also present at the same locality as well as the non-auriculate oyster Mansfieldostrea compressirostra geraldjohnsoni (Ward, 1992b) and the pectinid Euvola smithi.» THOMAS RICHARD WALLER, 2018
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