Talochlamys dichroa (Suter, 1909)
SUTER, H. 1909. Descriptions of new species and subspecies of New Zealand Mollusca, with notes on a few species. Proceedings of the Malacological Society of London, 8: 253-265 [p. 264, pl. 11, fig. 31]
1909 Pecten (Chlamys) dichrous Suter, 1909
1915 Chlamys consociata Smith, 1915
1924 Chlamys campbellicus Odhner, 1924 [partim]
1952 Chlamys (Mimachlamys) taiaroa Powell, 1952
1915 Chlamys consociata Smith, 1915
1924 Chlamys campbellicus Odhner, 1924 [partim]
1952 Chlamys (Mimachlamys) taiaroa Powell, 1952
H. Suter, 1909, plate 11.
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«Shell triangularly orbicular, moderately inflated, sub- equilateral, somewhat inequivalve, with rather distant rounded radial ribs; valves differently coloured, ears very unequal, the anterior large, the posterior very small. Beaks approximate, the prodissoconch small, oval, smooth. Anterior and posterior ends similar, slightly concave above, then forming a half-circle with the basal margin; right valve slightly more convex than the left, with a rather large triangular anterior ear with four radial costae, crossed by strong and close imbricating growth-lines, a distinct byssal sinus below, and a row of teeth below it on the anterior margin (ctenobium); the posterior ear very small, triangular, with a few concentric riblets; left valve with the anterior ear also triangular, the anterior side straight or lightly sinuous, with about six scaly radiate riblets, the intercostal spaces with one or two fine scaly lines. Sculpture consisting of sub-equidistant rounded radial ribs, indenting the margins, their number varying from, sixteen to twenty on each valve; they are broadly or acutely rounded, sometimes ornamented with scales, more prominent on the left valve; towards the margin the ribs have often one or several grooves, and in the interstices one to three radial fine riblets may be present; besides this sculpture there are minute divaricating radial lines (the so-called Camptonectes striation). The concentric sculpture consists of very fine and rather close undulating and slightly imbricating layers. Colour of right valve whitish, lightly tinged with pink, rarely yellowish-brown all over; left valve always much darker coloured, white with red concentric spots and bands, or reddish or yellowish-brown, sometimes mottled with white. Inside shining, white or stained with red, strongly grooved, the margins sharp, dentate, or crenulate. Hinge-line long and straight, the resilifer triangular, not very deep, its margins rather sharply raised. Ligament external, narrow. Length 32, height 36, diam. 10 mm.
Hab.— A number of valves were found in the stomach of a Blue-Cod {Parapercis colias, Forster) caught in Port Pegasus, Stewart Island, and kindly given to me by Captain Bollons. This fish is found in New Zealand waters only: East of Jones Head, in 20 fathoms; 19 miles south of Oamaru, in 40 fathoms; off Lyttelton, in 100 fathoms (Mr. Edgar E. Waite). This species is allied to the Miocene P. Chathamensis, Hutton (Cat. Tert. Moll. N. Zeal., p. 29), but this form has the ribs more scaly, the scales more distant; the ribs show no tendency to division towards the margins. The anterior ear of the right valve is not large, has no byssal sinus, and there is of course no ctenobium. The form and size of the shell and the number of ribs are about the same as in the recent species. Type in my collection.» HENRI SUTER, 1909
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«Until now, T. dichroa has generally been regarded as a scarce southern species, though in fact a form morphologically identical to southern specimens is common and the dominant pectinid off the Three Kings Islands, and on Ranfurly Bank, East Cape, where it appears to replace T. gemmulata. Although having a wider north-south distribution than both T. gemmulata and T. zelandiae, T. dichroa is evidently a stenothermal, cool-adapted species, and northern populations are probably able to thrive where they do because of local upwelling (Marshall 1998: 120). Upwelling may explain its presence on Wanganella Bank, though whether or not it still lives there remains to be established (only 5 valves known).
Chlamys taiaroa and Pecten dichrous are based on two forms in which sculpture diverges strongly after the shell attains about three mm in height. In the typical dichroa morph (Fig. 42, 43) the radial ribs become broader than high from an early stage of growth, with broadly rounded summits. On the left valve, the summits of generally each third rib are set with imbricating scales, while on the right valve few or all ribs develop typically closely-spaced, imbricating scales, the interspaces on both valves having thin, commarginal lamellae and finer radial threads. The commarginal lamellae range from low and simple, to high with summits that lean ventrally to contact the next lamella, so that a secondary exterior surface is formed over the interspaces (typically more or less incomplete, however, because of extreme fragility of the lamellae—which sonication will destroy). In the typical taiaroa morph (Fig. 44A–D) the radial ribs remain angulate in section throughout, a secondary rib may or may not appear on one or both sides of each primary, the radials have rather widelyspaced scales, and interstitial commarginal lamellae may be prominent or obsolete, typically vanishing when the shell attains a height of about five millimetres. Both morphs occur off the Three Kings Islands, and patchily off the northeastern North Island, where the taiaroa morph includes the type material of C. consociata. Whereas most individuals tend to be distinctly one form or the other, intermediates exist, not only in series, but also as occasional individuals in which sculpture changes abruptly from characteristically dichroa to taiaroa (Fig. 42C, D) (never vice versa). All specimens of the taiaroa morph are thinly encrusted with sponge, whereas, all specimens of the dichroa morph are naturally sponge-free and either clean or partly covered with living bryozoans. As discussed with respect to Zygochlamys delicatula (see below), the transition is evidently a response to settlement of sponge on the shell. We presume that settlement by sponge is advantageous to these bivalves by reducing predation (see Marin and López Belluga 2005). Since there is fluid intergradation in shell morphology within and between northern and southern populations, it seems clear to us that a single highly variable species is involved. The southern Australia T. pulleineana (Tate, 1887), which shows similar variation, differs markedly in having much weaker sculpture on the early dissoconch (Beu and Darragh 2001: 95, figs 29A–I). Whereas the nominal form of dichroa is distinctive, the taiaroa form is superficially similar to T. gemmulata, from which it differs in that radial ribs are more narrowly and sharply angulate in section, with considerably more prominent and sharper scales at equivalent stages of growth, in that the secondary ribs that appear beside the primary ribs remain markedly weaker than the adjacent primaries (enlarging to resemble primaries in T. gemmulata), and in that the spaces between adjacent secondaries are considerably broader. Populations of T. dichroa occur within the geographic and bathymetric ranges of T. gemmulata (sympatric), though they have never been taken living together, and even shells are rarely found together (asyntopic). Some forms of Z. delicatula have very similar sculpture (especially up to about 10 mm height—Figs 53, 54). However T. dichroa differs in these characteristics: lighter build, less inflated, less highly arched in the middle and less oblique, smaller resilium, narrower hinge, and with radial undulations typically more deeply concave. Moreover, the summits of the primary radial ribs are typically smooth in Z. delicatula, but develop sharp spines in the taiaroa and consociata forms of T. dichroa.» DIJKSTRA, H. H. & B. A. MARSHALL. 2008. The recent Pectinoidea of the New Zealand region (Mollusca: Bivalvia: Propeamusiidae,Pectinidae and Spondylidae). Molluscan Research, 28 (1): 1-88, figs. 1-70. [p. 55, 56]
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Talochlamys dichroa (Suter, 1909); H. H. Dijkstra & B. A. Marshal, 2008, The recent Pectinoidea of the New Zealand region, figure 43: typical dichroa morphotype.
Talochlamys dichroa (Suter, 1909), typical taiaroa morphotypes; H. H. Dijkstra & B. A. Marshal, 2008, The recent Pectinoidea of the New Zealand region, figures 44A, 44B: virtual topotype of Chlamys taiaroa Powell, 1952; figures 44C, 44D: virtual topotype of Chlamys consociata E. A. Smith, 1915.
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«Type material. IGNS, TM 209 (1 RV), TM 210 (1 LV figured by Suter, 1909, pl. 11. fig. 3i), TM 211, 212 (2 pairs), syntypes of Pecten (Chlamys) dichrous ("holotype" [TM 209] and "paratypes" in Boreham, 1959; however, none were selected as such by Suter, 1909); two other syntypes (1 LV, 1 RV; "cotypes") are kept at ZMB (ZMB 61885) (H.H. Dijkstra, pers. comm. 2002).
The holotype of Chlamys taiaroa, from the Recent off Otago, New Zealand, was illustrated by Powell, 1952, pl.35, fig. 1 (1 pair, VH 43 mm; specimen at AM); paratypes: 2 pairs; specimens at AM. The pair labelled "paratype" at NMNH (USNM 763695, ex A. W. B. Powell) must be considered as a topotype since the two paratypes cited by Powell (1952) are both larger. The four lots of Talochlamys taiaroa at NMNH (USNM 617440, 617444, 763694, 763695) seem to originate from a single population (perhaps just from one collection?), as suggested by the similarity of their collection details, and thus can all be considered topotypes. The specimens figured by Odhner (1924) as Chlamys campbellicus belong to two taxa: Beu (1995, p. 17) designated the specimen in Odhner's fig. 36 as the lectotype of C. campbellica (= Psychrochlamys delicatula subantarctica) and referred the two left valves in figs. 37 and 38 to T. dichroa. Odhner's fig. 39 shows sculptural details of the specimen in fig. 37. Material examined. 38 pairs, 4 LV, 2 RV from the Recent of the southern New Zealand region; lodged at HHD, NMNH, and ZMUC (see Appendix). Description. Shell of small size (mean VH c. 34 mm; maximum observed VH 42.4 mm [USNM 763694]; maximum reported VH 43 mm [holotype of C. taiaroa; Powell 1952]), almost acline, highly asymmetrical, with anterior part of shell much shorter than posterior part (VLA/VLP 0.81); moderately convex, with both valves nearly equally convex (RV occasionally more convex than LV); umbonal angle narrow (c. 95º). Colour pink to orange, with white chevron-shaped markings. Radial macrosculpture of up to c. 20 scaly costae, main ribs simple, broad and rather flat, or tripartite with up to two costellae in rib interspaces. Microsculpture made up of narrow antimarginal ridgelets. Auricles highly asymmetrical (OLA/OLP 2.3); LV anterior auricle with true byssal sinus and up to about 10 costellae; RV anterior auricle with relatively deep byssal notch (BND/VH 0.087); mean number of byssal teeth in functional ctenolium 5.7. Measurements and counts. VH 33.7± 0.9 mm (n = 34), VHA 18.0 ± 0.4 mm (n = 34), VHP 18.9 ± 0.5 mm (n=34),VL 31.5 ± 1.0 mm (n = 34), VLA 13.9 ± 0.4 mm (n = 34), VLP 17.6 ± 0.7 mm (n = 34), C (LV) 5.9 ± 0.2 mm (n = 34), C (RV) 6.0 ± 0.3 mm (n = 33), OL 14.7 ± 0.4 mm (n = 32), OLA 10.2 ± 0.2 mm (n = 32), OLP 4.5 ± 0.2 mm (n = 33), AHA (LV) 8.5 ± 0.2 mm (n = 35), AHA (RV) 6.2 x 0.1 mm (n = 34), AHP 6.0 ± 0.3 mm (n = 34), BND 2.9 ± 0.1 mm (n = 34), UA 95.3º t ±1.0 (n = 34), BT 5.7 ± 0.2 (n = 31). Stratigraphical age and distribution. Recent, Campbell Island to Chatham Islands; also at the Three Kings Islands (Beu, 1995, p. 18; Fig. 22). According to Powell (1955), Odhner's (1924) record from off the Auckland Islands refers to juvenile Psychrochlamys delicatula subantarctica, with which species it is sympatric. Remarks. Chlamys taiaroa was proposed by Powell (1952) for shells that are similar in size, shape and coloration to those of Pecten (Chlamys) dichrous Suter, 1909. Shell colour of both dichroa and taiaroa varies from pink to orange, with white chevron-shaped markings and blotches, but shells of taiaroa differ in being more inflated and in having finely scaly radial ribs that are broadly angulate and which on each side are flanked by a secondary riblet; also, there are one or two low costellae in rib interspaces (and in these respects, the sculpture of taiaroa resembles that of Psychrochlamys delicatula subantarctica) (Plate 11, figs. j, k). Sculpturally typical T. dichroa is altogether simpler, with ribs being broad and flat-topped, becoming tripartite with age, and there are no (or very few) riblets in rib interspaces; rib scales are coarse (Plate 11, figs. h, i). This distinction appears to break down in populations away from the type area of taiaroa: Powell (1952) stated that material from the Chatham Islands includes both delicately and strongly ribbed shells, and he had difficulty in assigning this to either taiaroa or dichroa. Incidentally USNM 763964, also from there, includes a coarsely ribbed left and a finely ribbed right valve, and was identified as T. dichroa. According to Waller (1991, p. 29, and pers. comm. 2001) dichroa and taiaroa differ also in microsculpture in the rib interspaces: whereas commarginal lirae persist throughout ontogeny in dichroa, with antimarginal ridgelers ontogenetically preceding the commarginally lirate stage, such lirae terminate early in taiaroa, and antimarginal ridgelets only appear after the end of the lirate stage. Despite these differences Beu (1995, p. 1B) synonymized dichroa and taiaroa: he observed identical sculptural detail in juveniles, whereafter coarseness starts to vary in adults, with a complete range of variation between extremes (pers. comm. 1998). Morphometry of material at NMNH seems to support this synonymy. Similarities are found in size, width of umbonal angle, length of outer ligament, auricular symmetry, depth of byssal notch and byssal sinus, and number of functional byssal teeth. The chief morphometric difference between dichroa and taiaroa is the higher convexity of left valves of taiaroa (by c. 1 mm in specimens of 35 mm valve height; right valves are equally convex), but it should be emphasized that all measured taiaroa specimens represent a single population (see earlier comment on NMNH material), and it may well be that finely ribbed forms elsewhere have left valves that are equally convex to those of typical dichroa. Regional variation in shell convexity has also been reported for Talochlamys gemmulata (Reeve, 1853) (Beu & Maxwell, 1990, p. 336). T. dichroa is distinguished from Psychrochlamys delicatula subantarctica by (1) its smaller maximum shell size (<50 mm), (2) a higher VH/VL ratio, (3) nearly equally convex left and right valves, (4) a narrower umbonal angle, (5) a less opisthocline shell (Fig. 27), (6) greater auricular asymmetry (7) a comparatively deeper byssal notch, (8) presence of a true byssal sinus, and (9) a higher average number of functional byssal teeth (Fig. 34), without a tendency towards lower numbers in mature individuals.» JONKERS, H. A. 2003. Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions. Monographs of Marine Mollusca, 5: i-viii + 1-125 pp, 17 pls. Backhuys Publishers, Leiden. [p. 56, 57]
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TalochIamys dichroa (Suter); H. A. Jonkers, 2003, Late Cenozoic-Recent Pectinidae of the Southern Ocean and neighbouring regions, plate 11, figures h-k.
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