Mimachlamys spinicostata, Dijkstra & Beu, 2018

Dijkstra, Henk H. & Beu, Alan G., 2018, Living Scallops of Australia and Adjacent Waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae), Records of the Australian Museum (Rec. Aust. Mus.) 70 (2), pp. 113-330 : 293-294

Mimachlamys spinicostata sp. nov.

Figs 94, 95D–E,G, 96A–B,F–G, 100E

Mimachlamys australis (Sowerby) .–Cotton, 1961: 105, fig. 91; Lamprell & Whitehead, 1992: [22], pl. 9, fig. 55; Slack- Smith & Bryce, 2004: 237 (as Mimachlamys ? australis ) [misidentification as Pecten australis G. B. Sowerby II, 1842 , = Mimachlamys asperrima ( Lamarck, 1819) ].

Chlamys australis (Sowerby) .–Abbott & Dance, 1982: 309, fig.; Wells & Bryce, 1985: 158, pl. 60, fig. 583; Wells, Slack-Smith & Bryce, 2000: 42 (misidentification).

Chlamys (Mimachlamys) australis (Sowerby) .– Rombouts, 1991: 27, pl. 10, fig. 4, pl. 28, figs 6–6a (misidentification).

Mimachlamys sp. nov.?; Beu & Darragh, 2001: 145, figs 52A, E.

Holotype (pr) AM C.073505, Western Australia, Shark Bay , 26°07'S 113°25'E, leg. Mrs B. M. Bannear. Paratypes (17) (pr + v) in AM, WAM and ZMA : 1 (pr), same lot as holotype, AM C.476729, illustrated; 2 (pr), Eastern group of Abrolhos Islands , Middle Channel, alive, WAM S13892 ; 3 (pr + v), AM C.097574; 2 (v) Shark Bay , Dirk Hartog Island, 25°45'S 113°03'E, dead, AM C.094526; 4 (pr), Shark Bay , 25°37'S 113°14'E, alive, 16.7–16.8 m, WAM S13893 –96 ; 5 (pr), Shark Bay , 20 m, alive on muddy sand, ZMA Moll. 409008 .

Additional material examined. WESTERN AUSTRALIA: Rottnest Shelf, 25°17.96' S 112°59.13'E, dead, 100 m (2 v, WAM S12527 ); Abrolhos Islands , dead (1 v, WAM S12556 );Abrolhos Islands ,outside Wallabi Group, 28°25'S 113°33' E, dead (1 pr, C.094528).

Description. Shell up to c. 120 mm high, most specimens smaller, to c. 90 mm; moderately inflated, almost equally convex, equivalve, slightly inequilateral, anterior auricles much larger and longer than posterior ones, umbonal angle c. 90°; uniform orange, red, yellow, purple, brown, some specimens with pale maculations in early growth stage.

Both valves sculptured with c. 20 almost evenly spaced, delicately squamous, rounded primary radial plicae, almost equal in prominence; each plica flanked by a secondary spinous riblet, subdivided in late growth stage; 3–4 further narrow secondary spinous riblets in radial interspaces. Auricles delicately sculptured with numerous, closely spaced, spinous radial riblets; anterior auricle of right valve with c. 5 squamous radial costae. Interior more deeply furrowed than in all similar species, but internal rib carinae weak, short, present only around ventral margin. Byssal notch deep, byssal fasciole moderately broad. Functional ctenolium well-developed, with c. 6 teeth. Resilial and dorsal teeth moderately prominent. Covered with sponges in life.

Dimensions. Illustrated specimens: holotype, AM C.073505, rv: H 98.8, L 103.5 mm; lv: H 99.6, L 102.7 mm; D 38.0 mm; paratype, AM C.476729, rv: H 88.7, L 86.3 mm; lv: H 87.9, L 86.2, D 35.1 mm .

Discussion. Mimachlamys spinicostata sp. nov. has generally been known in the literature as Mimachlamys australis (Sowerby) (Cotton, 1961; Lamprell & Whitehead, 1992) or Chlamys australis (Abbott & Dance, 1982; Wells & Bryce, 1985; Rombouts, 1991), but Beu & Darragh (2001: 145), following the advice of T. R. Waller, correctly placed P. australis for the first time in the synonymy of Mimachlamys asperrima ( Lamarck, 1819) , although with a query. The type material of both species is indeed indistinguishable. Beu & Darragh (2001) compared Mimachlamys spinicostata sp. nov. only with the temperate Australian species M.

.

B.

.

G

nov

.

(sp

scabricostata spinicostata nearly circular inflated, sculpture sculpture spinose fine

(

)

,

Reeve

.

M

Mimachlamys 120 mm

.

high

c

to elongate moderately equally convex solid radial fine radial coarse ribs,

20

radial rounded closely spaced throughout developed strongly more monochromatic gloriosa ) ribs.

,

M

( asperrima

)

Lamarck

Mimachlamys scabricostata . 80 high c mm elongate, inflated moderately equally convex solid radial sculpture fine sculpture coarse radial ribs 20 radial, rounded throughout spaced c (widely 5. lamellae spaced and fine spinose closely developed weakly polychromatic Mimachlamys

: circular sculpture in

Australia occurring gloriosa Mimachlamys mm c 120 high. elongate to nearly inflated, moderately equally convex solid coarser radial slightly coarse radial sculpture – radial ribs 20, 22 rounded widely spaced lamellae developed weakly polychromatic species

Mimachlamys

asperrima circular nearly, inflated convex than

rv solid the distinguishing larger.

sp.

nov

Mimachlamys

high

c.

mm

100

to elongate moderately slightly more

lv

moderately to thin fine sculpture radial fine radial sculpture ribs

24 –

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22

radial angular to rounded fine closely spaced spinose throughout developed strongly polychromatic

spinicostata

lv rv lv

8

Table

Characters.

.

III) M and

Sowerby

characters size shape convexity thickness shell anterior auricle anterior auricle

macrosculpture sculpture rib secondary riblets colour asperrima , but not with two closely related tropical congeneric species that are not recorded as fossils: M. scabricostata from the northwestern region of Australia and the more widely distributed species Mimachlamys gloriosa (Reeve, 1853) from the northeastern region of Australia and the Indo-West Pacific. Characters distinguishing these species are listed in Table 8.

Habitat. Living in the littoral to sublittoral zones on soft bottoms.

Distribution. Mainly from Shark Bay, Western Australia, southwards to the Abrolhos Islands . Present specimens alive at 16.7– 20 m.

Etymology. The specific epithet (Latin, “spiniger”— spinous; “costatus”—with ribs; adjective) refers to the delicate spinous sculpture on the ribs of this species.