Kaparachlamys Boreham, 1965
BOREHAM, A. U. E. 1965. A revision of F. W. Hutton's pelecypod species described in the Catalogue of Tertiary Mollusca and Echinodermata. New Zealand Geological Survey Paleontological Bulletin, 37: 1-125, pls. 1-20. [p. 24]
«Genus KAPARACHLAMYS nov.
Type species: Pecten hectori Hutton, 1873, Cat. Tert. Moll., p. 30. Pleistocene New Zealand.
Shell moderate to large, thin-walled, equilateral, subcircular in outline. Valves little inflated, but left valve slightly more inflated than right. Ears subequal, byssal sinus obsolete in adult. Sculpture of numerous very fine, subequal, thread-like riblets, which become obsolete towards the ventral margin. Ribbing on right valve flatter, less distinct, and dying out at an earlier growth stage than on left valve. Valves of some specimens fold'ed round the apex into six or seven shallow radial plications, which die out distally.
Kaparachlamys is distinguished from Chlamys and other genera of Pectinidae in New Zealand chiefly by its sculpture of numerous very fine, subequal ribs, which become obsolete towards the distal shell margin, particularly on the right valve. The new genus Kaparachlamys (feminine gender; Kapara = Maori word for comb) is proposed for a small and local New Zealand group, including K. mariae (Finlay) and K. hectori (Hutton), which is thought to have diverged from Phialopecten in the early Pliocene. The suffix "Chlamys" was chosen because Phialopecten itself is probably derived from a group of Chlamys-like shells; the name Kaparachlamys, like Phialopecten, is ranked as a full genus rather than as a subgenus of Chlamys for the sake of greater convenience and brevity. Evidence for the origin of Kaparachlamys can be seen in the variation of a sample of 12 shells collected from the Opoiti Limestone, Mangaroa Survey District, Gisborne (GS 2604, age Opoitian). The sample shows a complete range of variation in sculpture between that of Phialopecten and of Kaparachlamys: six specimens have about 30 low primary ribs with strong intercalary riblets, and are indistinguishable from the Opoitian - lower Waitotaran Phialopecten n.sp. aff. triphooki (Zittel); one specimen has about 50 narrow, flat, subequal ribs becoming obsolete on the distal part of the disc, and is very similar to some specimens of Kaparachlamys mariae; the remaining five specimens are intermediate between the two extreme forms and show in varying degrees the tendency for primary and secondary (i.e., intercalary) ribs to become subequal and obsolete on the distal part of the disc. K. mariae occurs in upper Waitotaran - lower Nukumaruan rocks of the Wairarapa and Hawke's Bay: for example, at Castle Point (GS 81, 1820); at Whangaimoana, Palliser Bay (GS 5491); in the shelly limestone on the Gladstone - East Coast main highway (GS 6670); at the junction of Ruakokopatuna and Makara Streams (GS 2619); in the Makara Stream upstream from the Ruakokopatuna junction (GS 7848); and in the Te Aute Limestone (GS 2440). The species has not been collected from the Wanganui-Rangitikei basin, or elsewhere west of the main divide. Doubtless, the species will be recorded more widely in the future: owing to the loss of the holotype (recently found) the species has been misinterpreted in the past, having been referred in many cases to "Placopecten" hectori or not recognised at all, while the name mariae has been used for a fossil species of Mesopeplum close to the Recent M. convexum (Q. and G.) (Finlay, 1927b, p. 526; Marwick, 1931, p. 62). The confusion probably arose because the two figures of Pecten semiplicatus Hutton published by Suter (1915, pI. 1, fig. 7; pI. 6, fig. 4) somewhat resemble a Mesopeplum species; one figure was Buchanan's idealised drawing of the lost lectotype from Napier, and the other a photograph of a juvenile right valve from Castle Point, where both Kaparachlamys mariae Fin. (= semiplicatus Hutt.) and Mesopeplum cf. convexum are common. Kaparachlamys mariae retains some features of Phialopecten, notably the inflated left valve and less inflated or almost flat right valve – in which it resembles Chlamys and differs from Mesopeplum, which has the right valve more inflated than the left. Kaparachlamys mariae, like some specimens of Phialopecten, has the disc radially folded near the apex. Sculpture of some specimens resembles that of some specimens of Phialopecten n.sp. aff. triphooki from the Opoiti limestone (GS 2604), but on most specimens of Kaparachlamys mariae the ribs are considerably finer, more numerous, more even, and flatter than on any specin1en referable to Phialopecten; on Kaparachlamys mariae, moreover, the ribbing tends to become completely obsolete towards the valve margins, at an earlier growth stage on the right valve than on the left. Kaparachlamys hectori, from the ? upper Waitotaran - lower Nukumaruan of Pitt Island, Chatham Islands, is probably penecontemporaneous with, and unlikely to be later than, K. mariae. Morphologically, K. hectori represents the culmination of Kaparachlamys evolution, having a fragile, very little inflated shell with entire sharp margins and very fine, flat, uniform radial ribbing that is almost obsolete on the right valve. On a few specimens the disc is weakly radially folded near the apex. On the basis of the specimens so far examined, K. hectori and K. mariae appear to be sufficiently distinct to warrant specific separation. However, most specimens of K. mariae have so far been collected from shell-beds, often containing large Pectens and oysters, in detrital shelly limestones such as that at Castle Point, whereas all the specimens of K. hectori have come from the tuffs on Pitt Island. Future collecting from a wider range of facies may show that the mainland population includes some shells like K. hectori; this was suggested by the collection, from a siltstone containing scattered Pelicaria, Alcithoe, and other fossils (GS 7848, Makara Stream), of a single, incomplete specimen that is thinner shelled and finer sculptured than typical K. mariae and resembles K. hectori. Kaparachlamys hectori is remarkably similar to the eastern North American Placopecten clintonius (Say), type species of Placopecten Verrill, of which there are in the New Zealand Geological Survey collection specimens from the Miocene of Yorktown, Virginia. Both Kaparachlamys hectori and P. clintonius have thin, little inflated shells with numerous very fine, flat, subequal riblets; ears are subequal with obsolete byssal notch in the adult. Verrill (1899, p. 49) considered that "some of the modern thin smooth forms have probably descended from ribbed species by the gradual reduction of the ribs. This appears to be the case with Placopecten... in which the ribs have become nearly obsolete, though it is in other respects nearly allied to Chlamys". Similarly, Kaparachlamys hectori has probably evolved from a more strongly ribbed Chlamys-like shell in New Zealand, and the resemblance of K. hectori to Placopecten clintonius appears to be an example of parallel evolution in separate stocks, as Marwick (1928, p. 451) originally surmised when provisionally locating Kaparachlamys hectori in Placopecten. Possibly the trend towards a thin, scarcely inflated shell with obsolescent sculpture is an adaptation to an active, free-living mode of life, like that of Amussium. Whatever the biological significance, the conchological evolution of Kaparachlamys is in the opposite direction to that of Phialopecten, from which Kaparachlamys is thought to have been derived, for the trend of Phialopecten evolution, also culminating in Waitotaran - lower Nukumaruan times, is towards an increasingly massive, strongly inflated shell having few, coarse, heavy ribs.» ANNE URSULA ENID BOREHAM, 1965
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Kaparachlamys hectori (F. W. Hutton, 1873); A. U. E. Boreham, 1965, A revision of F. W. Hutton's pelecypod species described in the Catalogue of Tertiary Mollusca and Echinodermata, plate 6, figures 3, 5, 6.
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