Squires—Northeast Pacific Oniscidia


ratio 1.4–1.6; teleoconch widest where outer lip makes prominent deflection adaxially. Spire angle 94–112°. Spire moderately low. Protoconch missing. Teleoconch up to 4.5 whorls (incomplete); strongly shouldered and upper part of last whorl flat sided. Suture covered by thin collar, becoming taller, especially on dorsal side of last whorl and in vicinity of posterior end of outer lip. Base (neck) constricted. Axial sculpture (costae) more prominent than spiral sculpture; costae becoming increasingly prominent but less numerous with increasing size of shell: 15–16 on ante-penultimate whorl, 14–15 on penultimate whorl, and 10 to 12 (not counting varix) on last whorl. Axial costae present on moderately shallow ramp, have swollen (noded) terminations at shoulder, continue across most of face of last whorl and gradually narrow before becoming weak to obsolete on base. Only tips of costae exposed on penultimate and ante-penultimate whorls. Axial costae slightly prosocline near suture and orthocline or slightly opisthocline across most of face of last whorl. Axial costae tend to align with those on previous whorl, especially on spire whorls. Spiral ribs mainly confined to interspaces, which becomewider on successive whorls. Interspaces on upper spire whorls narrower or same width as axial ribs; interspaces on penultimate whorl approximately same width or wider than axial ribs; interspaces on last whorl two to three times wider than axial costae ribs. On uppermost spirewhorls, spiral ribs missing or obsolete; on penultimate whorl and shelf of last whorl, spirals small and very closely spaced, creating micro-cancellate sculpture at intersections with growth lines. On last whorl, spirals can cross axial costae and increasingly so toward base of shell, where spirals noticeably increase in size, especially on dorsal side of shell. Aperture high and moderately narrow. Columellar lip callused, becoming thin posteriorly where axial costae covered by callus, but show through somewhat on parietal area of callus; columellar callus extending to anterior end of shell. Columellar lip without folds. Outer lip varix smooth, flat, wide, and high (extending to slightly posterior of suture). Outer lip interior smooth. Siphonal fasciole (twisting) moderately distinct. Anterior end of shell recurved. Growth line prosocline at suture, orthocline across most of face of last whorl, and strongly prosogyral near anterior end.


Remarks.—The examined material consists of three specimens, including the holotype. They show collectively a range in preservation from moderately poor to excellent, with the Sepultura Formation specimen having the best preservation. This species has the morphologic characteristics of Oniscidia and is its earliest unequivocal record. Waring’s species is most


similar to Oniscidia bruuni (Powell, 1958, p. 80–81, pl. 11, fig. 5; Glass and Foster, 1987, p. 67, figs. 1, 28–29), which is a rare species found living today in southeast Australia, New Zealand, and New Caledonia (Emerson, 1990, p. 148–149, figs. 10, 11). Oniscidia bruuni is unlike other modern-day species because it lacks cancellate sculpture. Oniscidia plectata differs from O. bruuni by having more obvious spiral sculpture. Aspecimenof Harpa? n. sp., reported by Zinsmeister (1974,


799


whorl rather than near the suture. Zinsmeister (1983, pl. 4, fig. 29) reported this same specimen to be the west coast Cretaceous species Cancellaria crassa Waring (1917, p. 66, pl. 9, fig. 5), a homonym (non Nomland, 1917, Pliocene, California) renamed by Hanna (1924, p. 160) as Cancellaria simiana.


Discussion


Habitat preference.—Detailed information about the inferred in situ habitats of fossilOniscidia is lacking. It is necessary to rely, therefore, on what little is known about the habitats of living species. Based on rare, live-collected specimens of cancellate species formerlyreferredtoas Morum, Oniscidia is knowntobe mostly found in depths of 250–360m(Dance and Emerson, 1967; Hughes and Emerson, 1987; Emerson, 1990). Although a few living species of Oniscidia are found in depths of 25–30 m (Emerson, 1990), most species have been collected from subtidal sediments, predominantly in relatively deep, offshore water (Hughes and Emerson, 1987). The rarity of most of the living species ofOniscidia suggests, furthermore, that they prefer a deep- water existence (Dance and Poppe, 1999). Oniscidia specializes probably in preying on crabs (Hughes and Emerson, 1987). Specimens of Oniscidia plectata all occur in turbidite-


generated, siltstone-enclosed storm deposits associated with very abundant shallow-marine mollusks. Specimens of O. plectata are rare, whereas most of the other mollusks are common to abundant. The silty environment, rarity of O. plectata specimens, and preference for deep water of living species of Oniscidia are suggestive that O. plectata lived most likely in outer sublittoral depths where muds and silts accumulated. The associated shallow-marine mollusks under- went post-mortem transport into the living space of O. plectata. At LACMIP loc. 41691 in Simi Valley, it is likely that the turbidites likewise ‘invaded’ the living space of raninid crabs and spiny lobsters (Squires et al., 2017), which probably lived in the deeper water community inhabited by O. plectata. Emerson (1990, p. 149) reported that the standard condition


in the majority of extant Indo-Pacific Oniscidia species (formerly placed in Morum) is non-planktotrophy, whereas Bouchet (2002) reported the opposite and maintained that planktotrophy is the standard condition and non-planktotrophy is a derived character state present in only a few species. In contrast to Oniscidia, the cylindrical/nodose shells of


Morum are commonly found in shallow depths. The mode of development ofMorumhas been observed in onlyMorumoniscus (Linnaeus, 1767), which has a paucispiral protoconch and non- planktotrophic development (Hughes and Emerson, 1987).


p. 156, pl. 17, figs. 13, 14) from the middle Santa Susana Formation (Selandian = ‘Martinez Stage’), north of Meier Canyon, south side of Simi Valley in Ventura County, somewhat resembles O. plectata, but there are important differences. UnlikeO. plectata, the outer lip on the Meier Canyon specimen is not thickened, and the posteriormost part of its aperture is near the middle of the last


Paleobiogeographic considerations.—Oniscidia and Eocithara are the only harpids known to have a Paleocene and/or Eocene fossil record. The late early Paleocene occurrence of O. plectata in southern California and Baja California is the unequivocal FAD (First Appearance Datum) of this genus. It is also the only occurrence of Oniscidia in western North America previous to the modern-day appearance of Oniscidia veleroae (Emerson, 1968) at Isla del Coco, an oceanic island west of Costa Rica in the eastern tropical Pacific (Emerson, 1968; Keen, 1971). The FAD of Eocithara is Thanetian in Greenland (Merle and Pacaud, 2004). In the northeast Pacific, Eocithara occurs in lower


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