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Mimetridium cryptum

Description 4

Cadet Hand in 1960 described this new species that up until then had been assigned the name Metridium canum by Parry (1951,52), Ralph & Yaldwyn (1956), Batham (1956), Grimstone (1958). The original Metridium canum of Stuckey (1914) and Carlgren (1949) is a separate species.

Habitat
Usually partially buried in muddy sand, with numerous shells, pebbles present.

Column
Divided into the main column (scapus) and neck (capitulum) separated by a collar which disappears when the anemone is fully extended. The neck narrows then flares out into a lobed oral disk.
Colour light grey-green, sometimes khaki (light browny yellow). Colour fades at about mid column down to white at the base.

Oral disc
Up to six undulating lobes in large specimens.
Colour about the same grey-green as the capitulum. White or cream coloured lips, heavily ribbed, usually rises slightly above the oral disk.

Tentacles
Inner most slightly longer than outer, up to 2.5cm long. Numerous, fine, forming a frilly crown.
Colour about the same as the neck (grey-green), with no markings. Translucent when extended.

Distribution


Edited version of Tuatara: Volume 6, Issue 2, December 1956
Seafloor Animals from the Region of Portobello Marine Biological Station, Otago Harbour
By Patricia M. Ralph and J. C. Yaldwyn

Metridium canum (Stucky). The plumose anemone. Up to 15cm with a well developed adherent base but often so deeply buried in sand or mud that it does not appear to be attached. Column soft and thin-walled and colour merges from a dull grey-green at the mouth end to almost white at the base. Disc same colour as upper part of column. Tentacles very numerous and tapering to a point so that the animal appears to have a ‘ruff’ about the mouth. The animals prefer a dim light and only about 2 to 3cm appear above the surface of the mud, and when covered with water the extended disc and tentacles appear almost flush with the surface. When exposed and contracted at low tide they appear as conical humps. Rare.


edited version of Transactions of the Royal Society of New Zealand : Zoology, Volume 1, Issue 4, 15 July 1961
Two New Acontiate New Zealand Sea Anemones
By Cadet Hand

Description (see PI. 1 and Fig. 1).

Base. Generally circular in outline, adherent and with well developed basilar muscles present. When the anemone is well elongated the base may be twice, or even more than twice, the diameter of the scapus (see PI. 1, E). The base is used in active burrowing when this species is freed upon a sandy or muddy substrate, and the anemone sometimes actively creeps about on its base in aquaria. The colour of the base in freshly collected specimens is a creamy white, apparently due to a lack both of intrinsic pigment and of symbiotic algal cells. In expanded individuals the base becomes transparent.

Column. Divisible into a scapus and capitulum which are separated by a collar (see PI. 1, G). In expansion the collar disappears and the column becomes very elongate (see PI. 1, D, which is the same anemone as PI. 1, G). In attached animals the scapus is nearly the same diameter throughout except near the base, where it flares towards the limbus. In extreme extension the scapus becomes nearly transparent and its diameter may be only about one-sixth of its length; commonly it tapers gently from the flared base to the collar or collar region. Above the collar the capitulum narrows and then expands again to meet the lobed and widely spread tentaculate margin of the oral disc. The capitulum is slightly thinner and is more transparent than the scapus. In full extension the capitulum is only about one quarter or one-fifth the length of the scapus. The minimal diameter of the capitulum may be less than one half that of the scapus, or in other poses the diameter of both may be nearly the same. In freshly collected specimens the colour of the capitulum and upper half of the scapus is a light grey-green, sometimes khaki, resulting from the presence of symbiotic algae in the endoderm. This colour fades gradually at about the mid-scapus to the white of the base. Specimens kept for months in daylight illuminated aquaria gradually become nearly the same grey-green throughout due apparently to a spread of algae to the more basal tissues. The difference in coloration of the upper and lower parts of a freshly collected specimen is indicated in Plate IE. In the field only the upper third or half of the scapus extends above the sand or mud in which the anemone dwells, and it is only in this upper, more illuminated, part that the algae seem to thrive (PI. 1, A). The scapus and proximal capitulum show 48 lines throughout their length which correspond with the 48 mesenteries present in these regions. The upper capitulum shows many more lines, up to and probably more than 384, corresponding to the many additional mesenteries present at the margin. Cinclides are present throughout the scapus, occurring most abundantly in the endocoels, of the upper half of the scapus. The cinclides are perforate and in longitudinal sections of the column can be seen to occur as breaks in the mesogloea with both the ectoderm and endoderm becoming thinner and tapering to the actual pore. In life the cinclides of an expanded specimen can be seen as' sometimes opaque but usually transparent minute specks. Acontia are ' readily emitted, through the cinclides. The cinclides are not arranged in rings, and, being relatively scarce in the exocoels, give the impression of being in longitudinal rows.

Cinclides do not occur in the capitulum.

Oral Disc. Wider than the column when expanded and folded into about six undulating lobes in large specimens (PI. 1, B). There is little tentacle-free area around the mouth. In the tentacle-free area numerous pairs of lines representing the mesenterial insertions show through the rather transparent tissues. Colour of the disc about the same grey-green as the capitulum and upper scapus. The white or cream coloured lips of the actinopharynx are heavily ribbed and the two siphonoglyphs can usually be seen. The number of ribs on the lips vary, there being about 24 in small specimens to about 48 in large ones. The lips usually are raised slightly above the level of the disc.

Tentacles. Regularly hexamerous in arrangement, with five to seven or eight cycles present. As far as can be determined the number of tentacles corresponds exactly to the number of mesenteries. A medium sized specimen (10 cm long by 3 cm diameter) had 384 mesenteries at the margin and apparently the same number of tentacles. Larger specimens appear to have more mesenteries and correspondingly more tentacles. The inner tentacles are longer than the younger, outermost ones, although most tentacles are of about the same length. On a large anemone an individual tentacle may be as much as 2.5 cm long, and all tentacles are gently tapered throughout their length. The tentacles are translucent when extended and of about the same colour as the capitulum and upper scapus. No special pigments, bands, bars or other markings occur on the tentacles. The very numerous fine tentacles and the lobed disc give the crown a rather frilly appearance (PI. 1, B-E). As individual tentacles contract they sometimes appear to show a darker central area surrounded by a translucent outer layer. This appearance seems to result from the symbiotic algae present in the tentacular endoderm.

Size. The sizes of some small to medium specimens are indicated in Plate 1, which is reproduced at life-size. In the field small specimens whose length is barely 2 cm have been encountered as have very large specimens capable of expanding to at least 30 cm long. One large specimen in the preserved condition had the following measurements: 13 cm tall, 7 cm diameter base, 8 cm diameter mid-column, 9 cm diameter crown, 4.5 cm diameter at collar.

Localities and Habitat. This species is locally abundant near the Portobello Marine Biological Station in Otago Harbour. There is a large colony living in the shade of a beached hulk on Quarantine Island (also known as St. Martin’s Island) and individuals can be seen beneath the wharves at Port Chalmers. Other specimens have been collected at Weller’s Rocks and isolated individuals have been seen, or collected from various other localities. Within the intertidal zone the species is quite rare except in shaded situations such as under wharves or alongside the hulk mentioned above, although occasional isolated individuals may be seen in completely unshaded positions. This anemone occurs from about the level of the low water of neap tides well into the subtidal. The most numerous population noted to date occurs between about the low water level of neap tides down to that of spring tides in the shade of the old hulk on Quarantine Island. The substrate in which the species lives is usually a muddy sand with rather numerous bivalve shells, pebbles and small stones present. It is to these latter items that the anemones attach, although occasional individuals, especially the smaller ones, seem not to be attached. In their natural habitat they usually live partially buried in the substrate, although some individuals, particularly smallish ones, may be found hanging from the underside of the old hulk. The base of the anemone may be attached from a few to 15 cm or more beneath the surface, depending upon the size of the individual, and only the upper third or half of the animal is to be seen above the surface of the substrate.

Type Locality. Otago Harbour, N.Z.

References 4

Note any thumbnails in this section are only to indicate what that reference shows while this page is being built. They have not yet been verified, don't assume they are correct examples.

Synonyms:

  • The Metridium canum described by Parry (1951,52), Ralph & Yaldwyn (1956), Batham (1956), Grimstone (1958).

Sources and Credits

  1. (c) Tony Wills, some rights reserved (CC BY), uploaded by Tony Wills
  2. (c) Hexacorallians of the World, some rights reserved (CC BY-NC-SA), http://hercules.kgs.ku.edu/hexacoral/anemone2/images/03301_03350/03323.jpg
  3. (c) Hexacorallians of the World, some rights reserved (CC BY-NC-SA), http://hercules.kgs.ku.edu/hexacoral/anemone2/images/03301_03350/03321.jpg
  4. (c) Tony Wills, some rights reserved (CC BY-SA)

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