Variation of the Molluscan Genus Verconella with
Descriptions of New Recent Species.
[Read before the Auckland Institute, 24th November, 1925; received by Editor, 11th December, 1925; issued separately, 8th February, 1927.]
For the bulk of the material dealt with in this paper, the writer's thanks are due to the captains and crews of the trawling vessels operating from Auckland and Wellington respectively. Captain Ormes of the S.T. “Futurist,” Wellington, and Mr. H. Hamilton of the Dominion Museum, were responsible for the addition to our fauna of the most interesting and handsome of the new species. Since the initial discovery, Captain Ormes has systematically collected many fine lots of material for the Dominion Museum.
It gives the writer much pleasure to associate with this new Verconella the name of its discoverer. The writer is also much indebted to Dr. J. A. Thomson for permission to describe this species, and also to Professor R. Speight for loan of valuable material from the Canterbury Museum.
Most of the Northern material was collected alive, but usually the animal was in an advanced state of decay before the specimens were received, consequently preservation of the soft parts was not possible. The opercula, however, were secured in most cases, and have proved very valuable for morphological discrimination between specimens showing variable shell characters.
Verconella Iredale, Proc. Mal. Soc. 11, p. 175, 1914.
Type: Fusus dilatatus, Q. & G.
Siphonalia, admitted by Suter and others to the Australasian fauna, has been shown by Iredale (1915, pp. 463–465) to be misapplied. Siphonalia is a Japanese genus of the Buccinidae while Verconella belongs to the family Chrysodomidae (Finlay, 1924, p. 501). The species now classed as Verconella have been greatly confused. Hedley (1920, p. 54) has shown that the New Zealand deep water shell ascribed to Megalatractus maximus (Tryon) by Suter is really the true dilatata of Quoy and Gaimard, while the shallow-water and littoral species usually recorded as dilatata must bear the name adusta of Philippi.
As so much confusion has centered around the recent records of the Verconella species, a thorough revision of the Tertiary species is essential before any attempt at geological range can be made. Finlay (1924, p. 501) has stated that neither the Recent dilatata nor adusta really occurs in Awamoan (Miocene) horizons, the records referring to new species of Verconella. Probably all the Miocene records refer to ancestral species distinct from Recent Shells.
(1) Identity of Species Discussed.
|Adopted name.||Suter's name (Man. N.Z. Moll.)|
|Verconella dilatata (Q. & G.)||— Megalatractus maximus (Tryon)|
|Verconella mandarina (Duclos)||— Siphonalia mandarina (Duclos) in part|
|Verconella adusta (Philippi)||— Siphonalia dilatata (Q. & G.)|
A. Dilatata (typical) group.
Confined to deep water. Comparatively thin shell. Operculum horny inside, with a white callus along outer margin of muscle-scar (Fig. 1). Protoconch of three and a half to four convex whorls, always brown (Fig. 8).
B. Adusta group.
Littoral to comparatively deep water. Heavy shell. Opercullum horny inside, always minus the white callus (Fig. 6). Protoconch of two and a half to three whorls, only slightly convex and always white (Fig. 10).
Opercula of Verconella (all¾ natural size.).
Fig. 1.—Verconella dilatata (Q. & G.) of sp. 1435.
Fig. 2.—Verconella dilatata var. cuvieriana n. subsp. (of holotype).
Fig. 3.—Verconella elongata n. sp. (of holotype).
Fig. 4.—Verconella ormesi n. sp. (of holotype)
Fig. 5.—Verconella mandarina (Duclos) (of f. 8, pl. C.).
Fig. 6.—Verconella adusta (Philippi).
Fig. 7.—Verconella adusta var. mandarinoides n. subsp. (of holotype). Protoconchs (all × 4)
Fig. 8.—dilatata (Q. & G.).
Fig. 9.—ormesi n. sp.
Fig. 10.—adusta (Philippi).
(3) Types of Specific & Individual Variation.
1. dilatata (Q. & G.)
Gradual change from typical form to thinner and proportionately narrower shell as depth increases (See table). Individual variation in strength of peripheral keel.
2. dilatata, cuvieriana, n. subsp.
3. dilatata, rotunda n. subsp.
Divergent forms not accounted for by gradual depth-variation. Due probaby to specialization through isolation from main stock. Discriminating characters constant but not sufficiently distinct to warrant full specific rank.
4. elongata, n. sp.
Origin as Nos. 2 and 3 but sufficiently distinct from No. 1 to warrant full specific distinction.
5. ormesi, n. sp.
Quite distinct from all four above, but probably it and dilatata sprang from a common ancestor in the early Tertiary.
6. mandarina (Duclos).
Characters constant. Typical from the rocky littoral of southern New Zealand.
7. adusta (Philippi).
Typical from rocky littoral of northern New Zealand. Shell thinner and less nodulous from deep water.
8. adusta, mandarinoides, n. subp.
Typical in sandy and deep water northern localities. Occasionally intermediate forms (discussed below) indicate this form as a species in the making which can conveniently be given subspecific rank.
(4) Suggested Ancestry of Species.
Verconella dilatata (Q. & G.).
The original figure is obviously that of a juvenile, showing a very short canal. The type was dredged in 25 fathoms at the Bay of
Islands. A specimen, considered a typical adult, is here figured (Fig. 18) and compared with a typical 50 fathom shell, while following is a table showing the gradual change in proportion (diameter compared with height) as the depth increases. These shells compared from extreme depths also show differences in colour, weight and relative lengths of canal and spire, but as the variation is gradual bathymetrically all forms are connected in an unbroken series and it is impossible to separate the deep water shell even as a subspecies.
Typical 25 Fathom Shell.
Shell large, solid, canal short, slightly curved, widely open. Aperture + canal 0.365 times greater than height of spire (Sp. 1433). Inside of aperture smooth. Sculpture consisting of numerous very fine spiral lirae alternating with slightly stronger spiral riblets. Whorls nine and a half sharply angled at periphery with three stronger spiral ribs forming carina which is produced into horizontally compressed projecting nodules. The average specimens (Figs. 18, 20) have one of the spirals of the carina much the stronger but in occasional specimens all three ribs are of equal strength (Fig. 21), colour buff, interstices of riblets varying from light to darker reddish-brown with occasional axial streaks of same colour. Inside of aperture, canal and parietal wall porcellaneous white. Inner margin of outer lip showing small dark blotches caused by interstitial colour bands of exterior showing through callus of thin edge of lip.
Height 149 mm.; diameter 72 mm.; weight 2.529 ozs. Cab. No. 1433.
This form is common in the Hauraki Gulf, being representative of the 20–25 fathom area, and has been observed by the writer from Hen and Chicken Islands to Mayor Island in the Bay of Plenty.
An extremely large example recorded by Miss Mestayer (1924) from Farewell Spit, Nelson, is also quite typical. The dimensions were given as 257 mm. × 98 mm. but the exact measurements prove to be 210 mm. × 100 mm.
40–50 Fathom Shell.
Shell larger, thinner than typical species, coloured uniformly buff, without darker bands or blotches on outer lip. Whorls nine and a half, canal proportionately longer, not so open. Aperture + canal 0.492 times greater than height of spire (sp. 1435). Outer lip more dilated. Inside of aperture faintly lirate.
Height 167 mm.; diameter 79 mm.; weight 2.073 ozs.
Specimen figured (Fig. 19) from off Whakatane in 40–50 fathoms, in collection of Dr. C. E. R. Bucknill. (H. 159 mm.; D. 73 mm.)
Operculum (Fig. 1 of shell sp. 1435) is identical with that of shallow-water form; horny with nucleus terminal. Inside with a white callus along outer margin of muscle-scar. Outlines convex, pointed above. Heavy pad directly above, nucleus on inside.
100 Fathom Shell.
The Canterbury Museum specimen (Fig. 22) from west of Cape Runaway in 105 fath., measures 122 mm. × 50 mm., but as it is
Fig. 11.—Verconella dilatata var. rotunda n. subsp. (holotype).
Fig. 12.—Verconella dilatata var. rotunda n. subsp. (paratype).
Fig. 13.—Verconella dilatata var. cuvieriana n. subsp. (holotype).
Fig. 14—Verconella dilatata var. cuvieriana n. subsp. (paratype).
Fig. 15.—Verconella ormesi n. sp. (holotype).
Fig. 16—Verconella ormesi n. sp. (paratype).
Fig. 17.—Verconella ormesi n. sp. (paratype).
Fig. 18.—Verconella dilatata (Q. & G.) (25 fath. typical).
Fig. 19.—Verconella dilatata (Q. & G.) (40–50 fath.)
Fig. 20.—Verconella dilatata (Q. & G.) 18–20 fath. Whangarei
Fig. 21.—Verconella dilatata (Q. & G.) sp. 1431, 18–20 fath. Heads
Fig. 22.—Verconella dilatata (Q. & G.) (105 fath.)
Fig. 23.—Verconella elongata n. sp. (holotype)
Fig. 24.—Verconella elongata n. sp. (paratype).
Fig. 25.—Verconella adusta × adusta var. mandarinoides n. subsp. (hybrid).
Fig. 26.—Verconella adusta (Phil.ppi) 20 fath. Hauraki Gulf.
Fig. 27.—Verconella adusta (Philippi) 36–40 fath. Cuvier Island.
Fig. 28—Verconella adusta (Philippi) 30 fath. off Whakatane.
Fig. 29.—Verconella adusta (Philippi) 10 fath. off Tryphena, Gt Barrier Island.
Fig. 30—Verconella adusta (Philippi) littoral, Takapuna, Hauraki Gulf.
Fig. 31.—Verconella adusta var. mandarinoides n. subsp. (holotype).
Fig. 32.—Verconella adusta var. mandarinoides n. subsp. littoral, Mt. Maunganui
Fig. 33.—Verconella mandarina (Duclos) littoral, Wellington Harbour.
minus the adult lip is not included below in bathymetric table. The peripheral keel is not so sharp—nor are the nodules as prominent as in shallower-water forms, but a series from depths intermediate between 50 and 100 fath. would no doubt show the same gradual variation as observed in the 18–50 fath. series.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Species||Height in mm.||Diameter in mm.||Proportions Diam. into Height||Depth in fathoms||Locality||Cabinet No.|
|"||143||71 5||2||18-20||Whangarei Heads||1431|
|"||146||72||2·027||20-25||Off Cape Colville||1432|
|"||205 + 3 for protoconch||100||2·08||27-30||Mayor Id.||1434|
|"||164||76 5||2·143||40-50||Off Whakatane||1436|
|"||210 + 5 for protoconch||100||2·15||Cast up on beach||Farewell Spit||D.M.M. 1307|
|cuvieriana n. sub. sp.||150||67||2·238||38-40||Off Cuvier Id.||1438|
|"||136||59||2·305||38-40||Off Cuvier Id.||1442|
|dilatata rotunda N. sub. sp.||150||72||2·083||25-30||Off Whakatane||1439|
|elongata n. sp.||134||55||2·436||19-20||Nr. Whale Id. off Whakatane||1440|
|"||129||53||2·434||19||¼ mile off Whale Island Bay of Plenty||1441|
New Species and Sub-species.
Verconella dilatata var. cuvieriana n. subsp. (Figs. 13, 14.)
Differs from typical species in being proportionately narrower (see bathymetric table) and stronger. Peripheral nodules strong but
blunt, very little compressed and not connected by sharp carina as in true dilatata. Periphery angled. Shoulder slightly concave. Adult lip not dilated. Colour buff; interstices of spiral sculpture obscurely lined with light brown. Aperture, interior of canal and parietal wall porcellaneous white. Margin of outer lip showing small dark-brown blotches caused by interstitial colour lines of exterior showing through callus. Protoconch damaged in both specimens.
Operculum (Fig. 2) horny, terminal nucleus inside with whitish marginal callus typical of dilatata. Differing from that of typical species in flattened upper outer slope, forming an angle of 52° with axis and also in the nuclear pad of the inside which is much less prominent.
Height 136 mm.; diameter 59 mm.; (holotype) (Fig. 13).
Height 150 mm.; diameter 67 mm.; (paratype) (Fig. 14).
Holotype and one paratype in Author's collection, Auckland.
Habitat: off Cuvier Island, Bay of Plenty, in 38–40 fath.
The slightly changed operculum proves morphological divergence indicated by shell characters.
Verconella dilatata var. rotunda n. subsp. (Figs. 11, 12).
Differs from the typical species in having the whorls more rounded, the periphery only slightly angled, the carina composed of several ribs of equal strength produced into squarish nodules, and the spire proportionately shorter. Outer lip of aperture dilated and marked with colour-blotches as in typical species. Colour-markings absent from 40–50 fathom shell. Operculum, protoconch, and number of whorls same as those of typical species.
Height 150 mm.; diameter 72 mm. (holotype) (Fig. 11).
Holotype and one paratype in Author's collection, Auckland.
Habitat: off Whakatane, Bay of Plenty, in 25–30 fathoms. (Type) also from 40–50 fath. off Whakatane.
This specialised form is the Eastern Bay of Plenty equivalent to the 20–25 fath. typical dilatata of the Hauraki Gulf and North.
So far, rotunda has been observed only from off Whakatane. Charts of the Bay of Plenty show a shallow-water connection of about eight fathoms between Matata and Rurima Rocks.
V. dilatata and its allies are never found in less than eighteen fathoms, so this shallow-water arm forms a natural division and barrier to the dispersal of the inshore fauna. Thus through partial isolation, east of the barrier, this new form is diverging from the ancestral type. As its differentiating characters are confined to the shell, the operculum not reflecting any morphological change, this form is indicated as a species in the making which can conveniently be classed as a sub-species.
No intermediate forms have been observed, and the differences in shell characters are readily distinguishable at sight. Occasionally
rotunda ranges down to 40–50 fathoms, a specimen being trawled alive together with the deep-water form of dilatata which, however, is directly related to the inshore typical dilatata from west of the barrier.
Verconella elongata n. sp. (Figs. 23, 24.)
Differs from dilatata in being proportionately much narrower with shoulder descending at a much sharper angle, canal straighter, outer lip not dilated and minus colour-blotches. Operculum distinct.
Shell large, solid, canal long, almost straight, narrowly open. Whorls nine. Protoconch of three and a half whorls, shaped as in dilatata. Height of spire and strength of peripheral nodules variable. Outer lip sinuous at shoulder, not dilated, lirate within, minus marginal colour-blotches, shoulder straight sharply descending, forming an angle of 30°-32° with vertical axis of shell (40°-50° at outer lip), in dilatata the angle is about 45° (55° at outer lip). Sculptured with numerous very fine spiral lirae alternating with stronger spiral riblets. Colour buff with the riblets light reddish-brown. Inside aperture and canal white, parietal wall whitish with light brown of body-whorl showing through. Operculum (Fig. 3) differing from that of dilatata in the flattened upper outer slope which forms an angle of 52° with axis. It is very close to the operculum of dilatata cuvieriana but in that species the nuclear pad of the inside is much less prominent than in dilatata and elongata.
Height 129 mm.; diameter 53 mm.; (holotype) (Fig. 23).
Height 134 mm.; diameter 55 mm.; (paratype) (Fig. 24).
Habitat: Quarter of a mile off Whale Island, Bay of Plenty, in 19 fathoms. (Type) near Whale Island in 19–20 fathoms.
As in the case of the preceding subspecies of dilatata the same factor of isolation from main stock seem to have caused the divergence of still another form, so distinct from dilatata that full specific distinction is warranted. This species has been obtained only from the vicinity of Whale Island, off Whakatane, in 19–20 fathoms. The shallow-water arm stretching from Matata to Rurima Rocks, mentioned above, is no doubt the direct cause of the divergence, the inshore Whakatane colonies being thus isolated from those west of the barrier.
Verconella ormesi n. sp. (Figs. 15, 16, 17.)
Shell very large, thin, canal short, slightly curved and widely open, spire tall. Aperture + canal 0.971 times greater than height of spire (holotype). Whorls eleven. Protoconch (Fig. 9) of four convex whorls, first four or five post-nuclear whorls axially costate and slightly keeled, succeeding whorls rounded, slightly appressed towards suture. Sculpture similar to that of dilatata consisting of numerous very fine spiral striae alternating with stronger spiral riblets. Aperture faintly lirate within. Outer lip thin, not dilated, slightly flexuous. Inner lip spreading as a thin callus across parietal wall and inner edge of columella. Occasional aged specimens with
thickened callus separated by groove from parietal wall. Colour uniformly pale buff, inside of aperture and canal porcellaneous white. Parietal callus whitish sometimes stained buff or brownish. The whole shell sometimes covered with a very thin, ochreus brown epidermis worn off in most specimens: dilatata never has an epidermis. In a few specimens peripheral angle reaches last whorl, but none has been observed with the axial ribs descending lower than the fifth post-nuclear whorl. Operculum (Fig. 4) horny with terminal nucleus, inside with whitish marginal callus typical of dilatata group. Differing from that of dilatata in the flattened upper outer slope forming an angle of about 52° with axis, and also in absence of a defined nuclear pad in the inside.
Height 201 mm.; diameter 75 mm.; (holotype) weight 1.818 ozs. (Fig. 15.)
Height 163 mm.; diameter 65 mm.;
Height 133 mm.; diameter 54 mm.; (paratype.) (Fig. 16.)
Type in Dominion Museum, Wellington.
A number of specimens trawled in 50–60 fathoms off Cape Campbell, Marlborough.
Key to Species.
mandarina. Shell large, solid, whorls rounded, sculptured with very strong regularly spaced primary ribs and pairs of very fine interstitial riblets. Early whorls showing faint axial foliations absent from adult whorls. Canal short. Characters constant.
adusta var. mandarinoides. Shell very large, solid, but not heavy, whorls by nodulous keel. Sculptured with numerous spiral chords of varying strengths, and a variable number of fine interstitial riblets. Canal short. Details of sculpture variable, shape fairly constant. Operculum differing slightly in shape from that of mandarina.
adusta mandarinoides. Shell very large, solid, but not heavy, whorls rounded, sculpture rather fine consisting of crowded uneven spiral chords. Early whorls slightly angled, with a few axial foliations. Canal long-Operculum almost identical with that of adusta.
Verconella mandarina (Duclos).
As the location of the type of this species does not seem to be known and no definite locality was given for it at the time of description, a figure is provided in order to fix and represent the characters of the species. The figured specimen was obtained alive on the littoral shore in Wellington Harbour, and its distinctive characters are given in above key. Dimensions 90 mm. × 41 mm. (Fig. 33). Operculum (Fig. 5). The distribution of typical mandarina is now restricted to the South Island and southern shores of the North Island of New Zealand. A recent specimen in the Canterbury Museum from Wanganui represents the most northerly locality for the typical species known to the writer.
Marshall and Murdoch (1920) in their valuable paper on Tertiary rocks near Wanganui suggested that during the early Pliocene Cook
First line of second paragraph under Group B should read adusta, Shell large, solid, heavy, Whorls sharply angled at periphery To face page 556
Strait must have been closed and a continuous beach must have extended from Kahurangi Point to the Wanganui area. This would effectively account for the occurrence of this and many other species of southern origin now found in the Wellington district.
Mandarina which is typical of the rocky littoral of the South is replaced in similar stations in northern New Zealand by the nodulous-angled adusta. In northern sandy and deep-water localities, a mandarina-like form has developed which, however, can be traced by the unequal inheritance of nodules and peripheral keel in some specimens to northern adusta.
In the light of modern evolutionary conceptions, it now becomes difficult to define a species, many apparently distinct types being bridged by the occasional occurrence of intermediate forms when bathymetric and littoral series from a variety of formations are brought together. As the extremes, however, represent the evolutionary forces at work, it is best to recognize extreme variation from the named type when comparatively stable as of sub-specific rank, being really species in the formation which ultimately with the combing out process of natural selection would probably become comparatively fixed forms or species.
The Northern mandarina-like shell, obviously derived from adusta, is therefore quite distinct from southern typical mandarina, to which species it bears only superficial resemblance; it is accordingly described below as a new sub-species, adusta-mandarinoides, none of the names attributed to the mandarina synonymy being applicable to the northern shell.
Environmental changes in this group evidently take considerable time to develop. In the Hauraki Gulf, mandarinoides is unknown, typical adusta ranging from the rocky litoral (Fig. 30) down to the sandy and muddy 20 fathom depths (Fig. 26). From off Cuvier Island in 36–40 fathoms, slightly modified forms of adusta (Fig. 27) are found, always with the axial sculpture and periphery angle fairly prominent. From Mercury Islands in 40–45 fathoms down to Whakatane in 40–50 fathoms, however, typical mandarinoides (Fig. 31) is mostly found. Only one specimen, referrable to adusta by the slightly angled periphery, was obtained from off Whakatane in about 30 fathoms (Fig. 28). In the Tauranga littoral mandarinoides is the common form (Fig. 32, 135 mm. × 64 mm.) which is found at certain periods breeding at the rocky Beacon Reef inside Tauranga Harbour. The Bay of Plenty being for the most part sandy, probably the advent of mandarinoides to rocky surroundings is of comparatively recent date, sufficient time not having elapsed to bring adaptive forces into play.
It seems quite evident that mandarinoides is the result of slowly-moving adaptive forces rather than that of spontaneous steps or mutations. These acquired changes, due to environment, appear to become transmittable, and an individual is not sufficiently plastic to be able, during its lifetime, to adapt or revert perceptibly to suit changing conditions. Consequently the association of adusta with
rocky shores and mandarinoides with sandy and deep-water locations in the north is not quite a hard and fast rule.
Probably hybridization also takes a part where the extreme types are brought into close proximity through the agency of the variable formations of the habitat. A specimen dredged with several adusta in ten fathom at Tryphena Bay, Great Barrier Island, appears to be a hybrid between adusta and adusta mandarinoides (Fig. 25).
Verconella adusta var. mandarinoides n. subsp. (Figs. 31, 32.)
Shell large, solid, canal long, slightly curved, rather open. Protoconch of two and a half to three whorls. Whorls ten. Body-whorl and sometimes penultimate covex slightly appressed towards suture. Upper post nuclear whorls only showing traces of axial foliations and peripheral keel. Sculpture rather fine consisting of crowded uneven spiral chords. Outer lip flexuous, not dilated, crenulated by spiral sculpture. Inner lip spreading as a callus over parietal wall and down inner edge of canal. Colour reddish-brown, the spirals darker. Inside of aperture, canal and parietal wall white. Operculum very similar to that of typical adusta, but with the nucleus less prominent (Fig. 7).
Height, 162 mm.; breadth 72 mm.; (holotype) (Fig. 6).
Height, 154 mm.; breadth 70 mm.; (paratype).
Holotype and one paratype in author's collection, Auckland.
Habitat: off Whakatane, Bay of Plenty in 40–50 fathoms.
Type: off Mercury Islands in 40–45 fathoms: Mount Maunganui, Bay of Plenty (littoral) (Fig. 32).
Finlay, H. J. 1924. The Molluscan Fauna of Target Gully. Part 1. Trans. N.Z. Inst., vol. 55, pp. 495–516.
Hedley, C. 1920. On Siphonalia Dilatata of Suter's Manual, N.Z. Journ. Sci. & Tech., vol. 3, p. 54.
Iredale, T. 1915. A commentary on Suter's Manual of N.Z. Mollusea, Trans. N.Z. Inst., vol. 47, pp. 417–97.
Marshall, P., & Murdoch, R., 1920. Tertiary Rocks near Wanganui, Trans. N.Z. Inst., vol. 52, p. 118.