Diadumene neozelanica

Description 4

A common anemone.
Habitat
Grows outwards or downwards from the substrate. Often associated with mussels in the shade on wharf piles, and sides of rocks near the low water mark. So seen for example in Wellington harbour, but not on the southern Cook strait coast where mussels are also absent.

Pedal disc
Firmly attached, wider than column (sometimes very much wider, seemingly stretched over the rocks). Can move from place to place.

Column
Smooth sided, with white and coloured stripes from top to bottom, with a distinct "neck" at the top. The usually orange stripes may alternatively be pink, yellow or transparent white. The neck is the same colour as the stripes. When the anemone is partially contracted the neck may no longer be visible, but the tentacles may still protrude. When contracted the column often has horizontal wrinkle lines. The neck is constricted in a collar at the top of the main column, then tends to flare out at the top. When fully extended the collar is less pronounced.
Can extrude white stinging "acontia" threads through "cinclides" in the column wall if disturbed. Up to 50mm diameter and 80mm tall when fully extended.

Oral disc
Edge ruffled into lobes, and the disc is often not visible due to the tentacles curled above it. The disc is a dark version of the stripes in colour, with a very bright, ridged, orange mouth and throat. The disc is up to 60mm diameter.

Tentacles
Numerous fine, 15 to 20mm long tentacles giving feathery appearance. The tentacles are described as 'the same colour as the column' by Parry, but as usually 'a deep, rich brown' by Cook, they seem to vary from almost white to dark brown. Additionally there may be 12 much larger 'catch' tentacles (up to 60mm long) on the inner whorl, these may appear darker when contracted, or transparent when stretch out.
Appears to be a filter feeder on plankton.

Distribution
Endemic, throughout NZ.



Edited version of Records of the Canterbury Museum, Vol 6, No 2, p138-8, Aug 1952
Article: The Actiniaria of New Zealand - a check-list of recorded and new species, a review of the literature, and a key to the commoner forms Part 2
By G. Parry. :

Genus DIADUMENE Stephenson, 1920
Diadumenidae with well-developed basal disc. Column smooth, divisible into scapus and capitulum which are separated from one another by a collar round the upper margin of the scapus. Scapus with cinclides. Margin of capitulum tentaculate. Sometimes the collar smooths away when the body is fully extended. No distinct sphincter. Tentacles long, numerous, more or less regularly arranged, not or imperfectly retractile. Some or all of the inner tentacles typically thicker than the other tentacles, and form catch-tentacles, containing, among other nematocysts, atrichs and holotrichs. In some individuals, however, these special tentacles may be absent. Outer tentacles sometimes with macrobasic amastigophors. Siphonoglyphs and directive mesenteries variable in number in connection with asexual reproduction. Six or a few more perfect mesenteries. Mesenteries more numerous above than below. Retractors diffuse, more or less restricted. Parietobasilar and basilar muscles weak. Perfect mesenteries and the stronger imperfect ones, fertile. Acontia well-developed, with basitrichs and microbasic p-mastigophors. Cnidom:—spirocysts, basitrichs, atrichs, holotrichs, microbasic p-mastigophors, and microbasic and macrobasic amastigophors.

Diadumene neozelanica Carlgren, 1924
The anatomy of this species has been described very fully by Carlgren, from the Mortensen collection, but there has been no account, to date, of the living animal, and its environment.

The base is very firmly adherent, and only detached with some difficulty. The epithelium of the base is very thin and easily torn. Generally it is a little wider than the column, but in some cases may be very much wider, the animal being stretched over the substratum, to such an extent that the animal seems unable to expand in the normal way. The base is very mobile, and the animals tend to move about aquaria by means of its muscular activity. The column is about as broad as high—sometimes more elongated when the animal is fully expanded—and is usually wider at the basal end. The scapus is striped longitudinally with white and orange, in most cases. Its epithelium is thin and delicate, even when contracted. It is smooth when the animal is fully expanded; very delicately wrinkled with transverse and longitudinal striations when contracted. The cinclides are numerous, and are arranged in rings from the region of the collar, where the scapus and capitulum meet, to the base. They are placed one above the other, always on the white stripes of the scapus. The collar between scapus and capitulum is prominent, although it is less so in fully expanded animals. The capitulum is trumpet shaped, expanding suddenly below the tentacles, to form an undulated margin. It has the same colour as the coloured stripes of the scapus—it may be orange, pink, yellow, or transparent white. It is paler towards the collar, deepening towards the margin. The skin is even more delicate than that of the scapus. During the daylight hours, the animal is usually only partly expanded, the capitulum being retracted into the scapus, with the tentacles just protruding. At night, or in a dim light, there is full expansion of both parts of the column so that the anemone may almost treble its size.
The tentacles are very fine and fairly long, and so numerous that they give the appearance of a fine feathery ruffle round the top of the capitulum. The edge of the disc is generally folded into 5-6 lobes. An inner ring of twelve catch-tentacles, immediately distinguishes this species from the genus Metridium. The tentacles of this inner ring are of the same colour as the others (though if they are contracted they look much darker)—that is, they are the same as the colour of the column. They are much stouter and longer than the other tentacles and carry a special armature of nematocysts. They may extend widely beyond the animal and have been observed to sweep slowly about in the water.
The disc is the same colour as the rest of the animal, though perhaps the colour may be a little more intense. It is not often visible, usually being covered, more or less, by the tentacles. The peristome is raised a little above the surrounding disc. The actinopharynx is longitudinally ridged, the ridges being very brilliant in colour and conspicuous. Size varies greatly, probably with age. Expansion alters the size and shape perhaps more in this species than in any other. For a fully expanded specimen (in a dim light)—width of base 5 cm., height of column 8 cm., width of crown 6 cm., length of outer fine tentacles 1.5-2 cm, length of catch-tentacles up to 6 cm.
Nothing is known of the reproduction of this species, other than that it has non-yolky eggs, and hence, presumably, direct development. The British species, D.cincta may reproduce by asexual fission, but this has never been observed in D. neozelanica. The evidence in its favour, however, is that it is a gregarious species, and that groups of individuals of varying size, and the same colour variety, are often found centred round one small area.
The anemone is found more or less commensal with the common mussel, Mytilus edulis. In mussel beds it is common along with tube worms (Pomatoceros sp.) and acorn barnacles. The reason for this commensalism seems merely that all these animals require the same ecological conditions. In all the places where I have found it, there is one common condition that there is an almost continual current of sea water, rushing back and forth with the tide. Normally, they are exposed only by the low water springs, and then usually for a short time. However, they are able to withstand considerable exposure, as I once found a group at Governor's Bay (Lyttelton Harbour), which were exposed to the mid-day summer sun for some hours, and became dry and hard to the touch. These seemed to survive quite well. In common with the other animals living in the same habitat, the anemone feeds microphagously from the plankton carried by the sea water. Although I have been unable to see ciliary currents on the disc and tentacles, I have been quite unable to feed this species macrophagously, but in natural conditions it will catch small planktonic crustaceans. Its gut never contains the shells of crabs etc., like other species of actinians. Collected from Heathcote Estuary (causeway at MacCormack's Bay and Monck's Bay); Governor's Bay, Lyttelton Harbour, on rocky shore; on piles at the end of a breakwater, Lyttelton Inner Harbour; on exposed reefs on the eastern side of Bank's Peninsula. Further north, I have found it at Tauranga, and on wharf piles at Devonport, Auckland Harbour. Garlgren reports it from Slipper Island, and Kaipara.



Edited description from Videnskabelige Meddelelser by Dansk naturhistorisk Forening i København, vol 76, pp 239-245

Diagnosis. Column smooth. Collar very distinct in contracted state of the column. Margin somewhat undulated. Tentacles 160 to about 200 (or more) cylindrical, the inner considerably longer than the outer. Tentacles distributed over the greater part of the oral disc.

Colour?

Dimensions in preserved, rather contracted state: Largest specimen from Kaipara: length 2 cm, breadth 1.3 cm, that from Slipper Island, length: 1.5 cm, diameter of the column a short distance from the pedal disc 0.6 — 0.8 cm, diameter of the oral disc 0.7 cm, length of the inner tentacles about 0.3 cm. Smallest specimen : height of the column 0.7 cm, breadth of the pedal disc 0.5 cm.

Occurrence. Slipper Island, low water, together with Thoe vagrans. Kaipara, on conglomerates of sand.

Exterior aspect. The pedal disc is well developed, of almost the same breadth as the oral disc. The column is smooth with indistinct longitudinal furrows, which are more distinct and more numerous above the collar. In all specimens there is namely a perspicuous collar at some distance from the tentacles as in Metridium. Whether this collar is formed by a contraction of the pennons in the lower part of the body, resulting in a small invagination of the upper part of the column in the lower, or the collar is visible also in not contracted specimens, it is difficult to decide in preserved specimens. The circumstance, that in two very expended and elongated specimens there was a low, but rather distinct wall in the same place as in the other more contracted specimen, possibly speaks for the presence of a real collar. Above the collar the column is broader towards the tentacles at the same time as showing a tendency to be lobed. The cinclides are not visible in contracted state of the animal, but I have observed them in sections as well in the vicinity of the oral part of the actinopharynx, and at the basal disc as a!so in the collar region. Thus they are probably scattered. The tentacles are very numerous, I counted in the largest specimen about 160 tentacles. They are more cylindrical than conical, the inner tentacles considerably longer than the outer, one part of which are very small. Almost the whole disc is provided with tentacles.

Remarks. It is possible that this species is identical with Metridium canum Stuckey 1914 p. 134 from the Kermadec Islands, but the description of this species given by Stuckey is so imperfect and short, that it is impossible to decide its place. Among other things Stuckey does not mention any collar.

(ed. there is a very extensive scientific description that followed, but detail omitted here)

References 4

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Synonyms

  • Diadumene neozeelandica
  • Diadumene neozelandica
  • Diadumene novaezelandicus

Sources and Credits

  1. (c) Tony Wills, some rights reserved (CC BY-SA), uploaded by Tony Wills
  2. (c) Avenue, some rights reserved (CC BY-SA), http://commons.wikimedia.org/wiki/File:Anemones_on_rocks_at_low_tide,_Karekare.jpg
  3. (c) Tony Wills, all rights reserved, uploaded by Tony Wills
  4. (c) Tony Wills, some rights reserved (CC BY-SA)

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