“Genus Macromckenziea new genus
Derivation of name – For Kenneth G. McKenzie, in recognition of his contributions to our knowledge of the Cypridacea.
Type species – Macrocypris siliquosa Brady, 1887.
Species included – Listed by original binomen:
Macrocypris siliquosa Brady 1887; Holocene, eastern Atlantic Ocean.
Macrocypris australiana Neale, 1975; Cretaceous, Australia.
Macromckenziea glacierae n. sp.; Holocene, Drake Passage and Weddell Sea.
Macromckenziea gregalis n. sp; Holocene, south of Tasmania
Macrocypris linguistica Bonaduce, Masoli, and Pugliese, 1977; Plio-Pleistocene to Holocene, Mediterranean region.
Macrocypris porcelanica Whatley and Downing, 1983; Miocene, Australia.
Macromckenziea swansoni n. sp.; Holocene, Tasman Sea.
Macromckenziea sp. 2; Holocene, southwestern Atlantic Ocean.
Macromckenziea sp. 3; Holocene, Drake Passage.
Macromckenziea sp. 4; Holocene, Mozambique Channel.
Macromckenziea sp. 5; Holocene, Weddell Sea.
Macromckenziea sp. 6; Holocene, Tasman Sea.
Macromckenziea sp. 7; Holocene, Mozambique Channel.
Macromckenziea sp. 19; Holocene, Drake Passage.
Geologic range – Cretaceous to Holocene.
Geographic distribution – Atlantic, Indian, and Southern oceans; known composite live depth range 97 to 3111 m, dead from 95 to 3829 m.
Diagnosis—Carapace smooth, thick-walled, small to medium-sized, often cream to light tan in color, sometimes with a visible layer of brown chitinous endocuticle lining the inner margin, selvage, and interior of valves. Carapace shape elongate-oblong, asymmetrical; right valve subquadrate to subhemispherical in lateral view; anterior margin broadly rounded; dorsal margin straight to gently arching; posterior margin truncate or rounded ending in nearly right-angled posteroventral angle; ventral margin nearly straight to gently sinuate. Carapace elongate-ovate in dorsal view with very slight anterior and posterior taper; sides nearly straight, parallel or gently curving; greatest thickness located medially; lines of dorsal and ventral overlap gently sinuate, not exaggerated. Hinge normal for the family, thick and easily seen. Zone of concrescence narrow, vestibules open, radial pore canals mostly short and straight, no dentiform corner. Adductor muscle scar pattern relatively large with numerous discrete scars, occupying as much as one quarter of the height; within the lower group of adductor scars the upper and posterior scars often are arranged compactly in a single curved line, with the anteroventral scars being segregated as a separate spot; the result being a scar pattern with possible homologies to Bairdiidae.
Antennule robust, thick, tapering, with nearly equant podomeres and thick, short setae; podomeres II and III flexibly articulated. Antenna compact, thick-proportioned, tightly curled, with numerous, thick, long, clawlike terminal setae; very long sensory aesthetascs on podomere II; 4 or 5 rather long swimming setae on podomere III; anterodistal setae of podomere IV very long. Podomeres I and II of maxillule palp completely fused without suture or with very faint, partial, vestigial suture; the anterodistal seta of podomere I may remain separate or may migrate distally to join the three setae of podomere II.
Palp of male fifth limb forms a robust right-angled hook on right side, somewhat more recurved on left, with ventral seta, two slender pegs, and sensory seta but with no dorsal seta. Palp of female fifth limb slender; either the mediodistal or ventrodistal seta may be the longest. Sixth limb small, with the two distal setae equal or nearly equal in length. Seventh limb small, with rather short cleaning seta, one distal seta much longer than the other. Furca may be similar to that of Macrocypris, or it may be vestigial, lacking the terminal seta and the distal portions of the cylindrical rods, with the proximal regions fused into a single, very small, inflexible shaft or nub terminated by two pairs of tiny proximal setae. Male hemipenis roundedsubtriangular in lateral outline, with anterior segment very small; copulatory rod short and straight or long and coiled. Zenker's organ with large, elongate bulb and short muscular segment; proximal part of vas deferens greatly enlarged, coiled into three or four tight coils.
Affinities—Some species of Macromckenziea are easily confused with Argilloecia and related genera, which have very similar carapace shape and overlap. They may be distinguished externally by the greater sinuosity of the dorsal and ventral overlap, by the muscle scar pattern, and by the macrocypridid rather than argilloeciine pores and setae. Some species of Abyssocypris, Bythocypris, and Krithe also show striking resemblances in external carapace morphology to Macromckenziea. Some life habit or adaptation common to the deep-sea representatives of these unrelated lineages may be responsible for this pronounced evolutionary convergence.
In soft-part characters, Macromckenziea is closest to Macrocypris. There may be at least two species-groups within the genus, the siliquosa-group and the glacierae-group, as shown by the existence of both a normal and a reduced furca and by the two different kinds of hemipenis. Alternatively, two or more different stocks of Macrocyprididae may have independently adopted this small, robust, oblong carapace shape, just as so many other deep-sea podocopids have done. In the latter case, the similarities would be due to convergence, and the genus would be polyphyletic. Not enough species with good soft parts are available yet to distinguish between these possibilities.
When both carapace and soft-part characters vary independently within a taxon, contradictory interpretations may be possible, depending on which set of characters is given more weight. The generic classification proposed here groups all species with similar carapaces into Macromckenziea, even though this produces heterogeneity in some soft-part characters. It has the practical advantage of being applicable to fossils and, therefore, potentially testable as an evolutionary hypothesis The type species, Mk. Siliquosa, is regarded as morphologically typical, and Mk. lingustica appears to be very closely related to it. Mk. glacierae, Mk. gregalis, Mk. porcelanica, and perhaps Mk. swansoni represent a second species-group. Several additional species in open nomenclature show the potential diversity of this new genus, and Mk. australiana demonstrates its antiquity.
Remarks – Kenneth G. McKenzie also suspected that Mk. lingustica and Mk. siliquosa might need to be classified together in a new genus (personal communication, letter of 18 May 1979).” (Maddocks 1990, p.48-50)
