SEA-STARS AND SEA-URCHINS.
At low-water, turning over stones and looking into rock-crevices, we
are sure to come across members of the _Echinodermata_--the creatures
with tough and rough or spiny coverings, popularly known as Star-fish
and Sea-urchins. There are many forms of these to be found on the
British coasts, though some of them are peculiar to deep water, and not
likely to fall in our way, unless it be their dead bodies washed up to
our part of the shore. But we can obtain a fair knowledge of the class
to which they belong, from the specimens we can find living their lives
in our own littoral zone. Here, hunched up into an almost globular form
under this drooping mass of leathery wrack, is the common Five-fingers,
Cross-fish, or Star-fish (_Uraster rubens_). Turning him on his back we
see the reason for the contracted condition of his five rays: in the
hollow thus formed he holds no less than three specimens of the Purple
or Dog Winkle. Why? He is a glutton, and is eating those three poor
mollusks at one sitting.
Not many years ago we all believed literally the tales that were told
of the Star-fish swallowing oysters as large or larger than itself. It
was well known that they caused havoc to oyster and mussel beds, and
that seemed the most likely way in which the valuable bivalve would
be destroyed. Some went so far as to assert that Five-fingers waited
his opportunity to catch the oyster gaping, and then slipped in one of
his fingers, and so prevented the shell closing. It was left to the
imagination to picture that same finger hooking out the native and
swallowing it in the approved fashion--off the shell.
The Uraster’s mouth is small, and the integuments tough and not capable
of great distention; but its stomach is a most accommodating organ,
though a very delicate one, and when the Star has come upon food too
large to pass through the mouth to the stomach, the stomach passes
through the mouth to the food. It surrounds the victim with its fine
membrane, pours out its gastric juice, and having reduced it to a fluid
condition, re-absorbs the whole, and returns to its natural position
inside the Star. That is a wonderful process, but it is quite a common
one, and you will certainly catch the animal in the act before you have
long been shore-hunting.
This is probably the way in which the securely boxed up oyster falls a
victim to Five-fingers. The oyster’s powerful adductor muscles keep the
valves closed, and appear to defy any burglariously-disposed creature
of its own size; but Five-fingers’ gastric juice is a penetrating
solvent which paralyzes the muscles and kills the oyster. The elastic
hinge then opens the shell automatically, and allows Five-fingers to
make an unresisted entrance, and a short end of the oyster.
As we have shaken off the dog-winkles, the Star-fish takes in his
stomach for safety, and we are enabled to have a look at his exterior.
When we say that he has five rays proceeding from a common centre, we
have said well-nigh all that is to be said about his form. But the
minutiæ of the organs disposed over those rays, and within them--for
their interiors form part of the general body-cavity--requires much
describing and explaining. The creature has no legs, yet he moves
with considerable celerity in any one direction as easily as another,
and inequalities of surface present no difficulties to him. And yet
the five rays, from their stiffness, are practically useless for this
purpose; but on the under surface of these rays are hundreds of pliable
and active little suckers, worked by hydraulic power, and it is all one
to them whether they have to walk on rock, weed, or glass, up or down,
across the floor, or under the ceiling.
Looking at the underside of this Star, we find that each of the rays is
deeply channelled along its centre. Only the true Stars have got this
channel; the Sand-stars and Brittle-stars have not, neither have they
got the wonderful suckers; but along each side of the channel, under
each of Five-fingers’ arms, there are two rows of soft filaments that
bend and wave in any direction, and that end each in a little knob
containing a tiny limy plate. By means of this little plate each knob
is converted into a sucker, similar to those by which trades-people
suspend their goods from the surface of their plate-glass shop-fronts,
but worked by water instead of air. There are hundreds of these to
each ray, and all act in unison, so that real progress is made when
Five-fingers’ olfactory sense informs the sucker-feet of the direction
in which food may be sought.
Ah, you say, has it a nose? No, it has not; but experiments have shown
that the entire underside is sensitive to odours. At the tip of each
ray there is a spot that is ordinarily spoken of as its eye, but it has
no true eye, though these spots are sensitive to light. Its mouth is in
the centre of its under surface, and opens directly into the stomach,
which has branches running into each of the rays. The vent for the
undigested particles of food and for waste, is on the upper surface.
Near the junction of two of the rays on the upper surface will be seen
a round stony knob, which is sometimes taken for the creature’s eye.
This is not a very wild shot at its purpose, though it is entirely a
wrong one, for as placed it certainly does suggest some such function.
Its real office could not suggest itself to any person unacquainted
with the internal economy of the Star-fish. Looked at through a lens,
it will be found to have a number of minute pores in its surface.
Strange as it may seem that the Star-fish should require such a
convenience, this is really a filter. Scientific men honour it with
the important-sounding name of the “madreporiform plate,” because
its tubes resemble somewhat those of the madrepore coral. I have
already referred to the hydraulic system by which the sucker-feet are
distended and worked, and this is the “intake” of the supply, as a
water-company would call it. Within these is a tube, running near to
the creature’s mouth on its lower surface, and connecting with a ring
of tube that surrounds the mouth, and sends out a branch to each of the
five rays. To this branch-pipe all the sucker-feet in a particular ray
are connected, and the pressure can be so regulated as to alternately
distend the sucker-feet, or to leave them partly empty and flaccid.
Upon one occasion, when I was describing these arrangements of the
Stars to a jocular friend, he said the idea of having a big mouth
that let in water freely, and a number of minute mouths that let it
in slowly, reminded him of the poet Cowper’s whim in making a large
aperture for his big hares to pass through, and a small one for the
little hares. He thought the mouth would have served both purposes; but
as I pointed out to him, the water that the Star takes in involuntarily
with its food goes into the stomach, where the food is retained and the
water strained off by the mouth again. This water would contain grains
of sand, vegetable _débris_, and other impurities, which would clog the
delicate tubes and spoil a beautiful piece of mechanism. The water that
percolates through the minute pores of the stony plate must be pure,
and free from all extraneous matter, so that the special supply-pipe
is a necessity. The scientific appellation of the sucker-feet is
_pedicels_ or _ambulacral feet_.
We must not omit to mention organs of another sort that occur in
plenty among the sucker-feet, and for many years presented a puzzle to
naturalists, who long regarded them as parasites--something foreign
to the Star-fish. They are now understood to be pedicels that have
been specialised to adapt them for particular functions. They consist
of slender flexible stalks, ending in an enlarged head of three claws
which normally converge to a point, but they are for ever opening and
shutting and taking hold of something. They are analogous to those
curious bird’s-head organs on some of the zoophytes, to which attention
has already been directed. Their function is to take hold of seaweeds
and other substances, until the suckers can be got to work; also to
keep the sucker-feet clean by removing all matter tending to clog them
and impede their efficient working.
The upper side of a common Star-fish is covered with rough or spiny
plates, and bosses of carbonate of lime secreted by the creatures, and
these take definite patterns in different species.
The Common Star-fish (_Uraster rubens_) is well-known for its rough
orange-coloured exterior, and its profusion, in some seasons, upon
certain parts of the coast. It swarms on oyster and mussel beds,
and causes considerable annoyance to fishermen, who find it taking
possession of the bait on their lines, and so keeping off the fishers’
rightful prey.
There is a less common but prettier species, the Spiny Star (_Uraster
glacialis_), you may find among the rocks at low-water. It is much
larger than the common Cross-fish, and in proportion the rays are
longer, their sides more parallel, the upper side more distinctly
spiny, and the colour a glaucous green, with variations towards violet.
It is more angular-looking than the common species.
Another species is the Eyed Cribella (_Cribella oculata_), which has an
upper surface quite free from spines or roughnesses, and of a purple
colour.
These Stars go through a remarkable metamorphosis. In the year 1835,
Sars, the celebrated naturalist, discovered a peculiar creature about
an inch in length, to which he gave the name, _Bipinnaria asterigera_,
and classed it among the Jelly-fishes. Nine years later, however, some
further observations caused him to reconsider this view, and to regard
the creature as more probably the larva of a Star-fish; and in the
course of a few years this opinion was confirmed by the researches of
Messrs. Koren and Danielssen.
The Sun Star (_Solaster papposa_) is really a glorious creature, with a
broad central cushion of rich crimson, from which radiate from twelve
to fifteen arms of the same colour, but with a band of lighter tint at
their base. The upper surface is covered with a network of slightly
raised lines, upon which are threaded, as it were, a great number of
little cushions, supporting erect brushes of spines. It may be found at
low-water, but is more frequently obtained from trammels set in deeper
water, and from the fishermen’s lines. It is sometimes nearly a foot
across from tip to tip of opposite rays.
[Illustration: SUN STAR.]
In the bottom right-hand corner of the plate on page 93, will be seen
a figure of the Gibbous Starlet (_Asterina gibbosa_), in which it
will be seen that the figure of the Common Star has been considerably
modified by the partial filling up of the angles between the rays,
so that the body appears to be more extensive than the rays. This
pretty species--it is represented natural size--is fairly plentiful in
rock-pools where there is sand and a vigorous growth of coralline and
fine weeds. In such pools it is not easily seen, owing to the manner in
which it harmonises with its surroundings. It is covered with a short
“pile” of spines, of a greenish-grey tint, with an indefinite shade of
brown. It is cushion-shaped; and the underside is channelled from the
five points to the central mouth. These channels are bordered with a
row of spines on each side, to protect the double range of sucker-feet
within.
[Illustration:
PURPLE-TIPPED URCHIN. FEATHER-STAR. STARLET.
]
In the same pools, among the rubbish at the bottom, under stones at
low-water, and climbing about corallines and weeds, we shall be sure to
find in plenty a little Brittle-star (_Ophiocoma neglecta_), of very
attenuated proportions, and not exceeding an inch across, if you can
get it to keep still whilst you measure it. It is exceedingly active,
and all its tiny rays bend and wriggle at the same time.
The Brittle-stars pass to the other extreme from the Starlet, in
modifying the five-rayed plan of the Common Star. Here the creature
runs almost entirely into the five writhing arms, which leave but
little material for the circular trunk, which looks, in truth, as
though five active worms had simultaneously seized a minute button by
its edge.
There are several other species of Brittle-star to be found between
tide-marks, but they all share, more or less, the peculiarity which
gives them the popular name. They are so “touchy” that you need
scarcely do more than look at them to cause them to voluntarily snap
off a part or whole of a ray, or several rays--and they commonly throw
off the lot, if they commence self-mutilation. The amputated members
are replaced by new growths, if the Star lives; for sometimes this
act of renunciation of limbs that offend, is but a prelude to the
extinction of vitality in the trunk.
[Illustration: GRANULATE BRITTLE-STAR.]
In the illustration here given of the Granulate Brittle-star, it will
be seen that the rays do not merge imperceptibly into the trunk, but
are attached to it by a kind of dovetail joint on the upper side.
Below, the arms, at their termination, form a ring, within which is the
mouth, whilst the trunk acts as a roof above the mouth, and overhanging
all round. The rays are composed of a series of joints, which allow
free lateral action, or wriggling, but not much vertically. Each of
these joints consists of four little plates, one each above and below,
and one on each side. The side plates bear each from five to ten stiff
and granular spines of varying length; and short tentacles come out
beside the lower plates. These tentacles are not sucker-feet, like
those of Five-fingers, but rigid, hooked processes; and there are no
_pedicellariæ_ with their snapping jaws. The mouth is a very extensive
opening, but its area is largely occupied by the five jaws, the free
ends of which extend upwards far into the body cavity, and are covered
with rows of long, close-set teeth. These teeth, on the five jaws
being brought together, must form a wonderfully efficient masticatory
apparatus.
One of the commoner forms of these Brittle-stars is the Granulate
Brittle-star (_Ophiocoma granulata_), represented in part in our
illustration. I have seen crab-pots brought in with this species
thickly coating the bottoms inside, and attached to well-nigh every
bar; there must have been thousands in each “pot.”
An allied species that is more plentiful as an inhabitant of the
littoral zone, is the Red Brittle-star (_Ophiothrix rosula_), which
will be found sprawling over the under surfaces of big stones at
low-water, in company with the Broad-claw Crab. Of this species Edward
Forbes truly remarks:--
“Of all our native Brittle-stars, this is the most common and the most
variable. It is also one of the handsomest, presenting every variety of
variegation, and the most splendid displays of vivid hues, arranged in
beautiful patterns. Not often do we find two specimens coloured alike.
It varies also in the length of the ray-spines, the spinuousness of the
disk, and the relative proportions of rays and disk; and in some places
it grows to a much greater size than in others. It is the most brittle
of all Brittle-stars, separating itself into pieces with wonderful
quickness and ease. Touch it, and it flings away an arm; hold it, and
in a moment not an arm remains attached to the body.”
Another species, the Long-armed Brittle-star (_Ophiocoma brachiata_),
has the rays about twenty times the diameter of the disk, each
consisting of three or four hundred joints; so that if one reckons
up the four plates that go to make one joint, then adds to these the
eight to ten spines on each joint, and multiplies the first total by
say three hundred and fifty (the number of joints), and this second
total by five (the number of rays), one gets a grand total of seventy
thousand pieces, constituting merely the external covering of the rays
of this small creature--leaving entirely out of the reckoning the
internal bony framework upon which these are placed.
These Brittle-stars go through a peculiar stage of existence, prior to
their assumption of rays. When summer is verging upon autumn, their
minute larval forms may be gathered in a fine muslin net, from the
surface of the sea. Gosse has given a description of this stage with
admirable brevity. He says:--
“A painter’s long easel affords the only object with which to compare
the little creature; for it consists of four long, slender, calcareous
rods, arranged two in front and two behind, with connecting pieces
going across in a peculiar manner, and meeting at the top in a slender
head. On this shelly, fragile, and most delicate framework, as on a
skeleton, are placed the soft parts of the animal, a clear gelatinous
flesh, forming a sort of semi-oval tunic around it, from the summit
to the middle; but thence downward the rods, individually, are merely
encased in the flesh, without mutual connection. The interior of the
body displays a large cavity, into which a sort of mouth ever and anon
admits a gulp of water. Delicate cilia cover the whole integument, and
are particularly large and strong on the flesh of the projecting rods.
“The appearance of this most singular animal is very beautiful; its
colour pellucid-white, except the summit of the apical knob, and the
extremities of the greater rods, which are of a lovely rose-colour. It
swims in an upright position, with a calm and deliberate progression.
The specimens which I have seen were not more than one-fortieth of an
inch in length.
“From this form the Brittle-star is developed, but in a manner
unparalleled in any other class of animals. The exterior figure is not
gradually changed, but the star is constructed within a particular part
of the body of the larva, ‘like a picture upon its canvas, or a piece
of embroidery in its frame, and then takes up into itself the digestive
organs of the larva.’ The plane of the future Star-fish is not even the
plane of the larva, but one quite independent of, and oblique to it.
Strange to tell, the young Star does not absorb into itself the body of
the larva, which has acted as a nidus for it, but throws it off as so
much useless lumber--flesh, rods, and all!”
Prof. A. Agassiz, however, would have taken exception to that last
sentence, for he declared that “the whole larva and all its appendages
are gradually drawn into the body, and appropriated.”
In the plate on page 93 there are two figures besides the Starlet--the
Feather-star and a Sea-urchin. The Feather-star (_Comatula rosacea_)
is really a deep-water form, but it has been taken occasionally within
the littoral zone, and may occur there in the experience of the reader.
It is undoubtedly the most beautiful of the entire group, so far as
British waters are concerned, and it possesses a special interest
for us, as being the only British representative of the Stone-lilies
or Encrinites that so abounded in Palæozoic times that their remains
make up whole strata, but of which, until the deep-sea explorations
of recent years, no living European species was known. But the
Feather-star, as shown in our illustration, had been long known, for
in several localities round Britain and Ireland it came up abundantly
in the dredge, yet no one suspected it was closely related to the
Encrinites.
In the year 1823 Mr. J. Vaughan Thompson, when dredging in the Cove of
Cork, brought up a tiny creature less than an inch in length, but which
might have been one of these Encrinites, into which life and mobility
had been infused. The discovery was hailed with joy by naturalists,
and the little stranger was named _Pentacrinus europæus_. Thirteen
years later Thompson came to the conclusion that his _Pentacrinus_ was
only the larval form of _Comatula_; and in 1840 Edward Forbes, Robert
Ball, and C. Wyville Thomson were dredging in Dublin Bay, when the
dredge brought up specimens of the so-called _Pentacrinus_ in a more
advanced stage than had been seen hitherto, and behold, some of these
underwent the final change in their early history under their eyes: the
Feather-star left its stalk and floated off, a true _Comatula_. Sir C.
Wyville Thomson has given this interesting account of its progress from
the egg condition:--
“The young escapes from the egg a pear-shaped free animalcule, swimming
and gyrating rapidly through the water, large end foremost, by four
transverse bands of cilia, and by a tail-like tuft of long cilia,
which it uses somewhat in the style of a screw propeller. On one side
of the body there is a large oval mouth, richly ciliated, and a short
curved stomach. After swimming freely in this form for several days,
a network of calcareous plates begins to appear, at length making a
closed chamber in the wide end of the pear, and extending as a sort
of stalk to the narrow end. The stalk now lengthens, and the creature
loses its symmetrical form; it attaches itself to a stone or seaweed,
and from the free, wide extremity, there springs a little circlet of
branches--the arms of the second stage.”
On turning again to the illustration (page 93), it will be seen that
the Rosy Feather-star, to give it the full title, is possessed of
ten rays, or rather five rays each forking into two, and that these
branches are _pinnate_, or feathered with little appendages which
contain the ova. The ordinary organs are all contained in the central
body, and do not extend into the rays as in Five-fingers.
The remaining figure in that plate is the Purple-tipped Sea-urchin
(_Echinus miliaris_), which is a well-known inhabitant of rock-pools.
It is enclosed in a stone box, which is a miracle of design, for
although there is no elasticity about it, and it cannot be stretched,
it yet serves the growing Urchin for years, and never cramps him. There
is never any necessity for throwing it off, as the crabs and lobsters
have to do repeatedly with _their_ suits of armour. The nearest
parallel to it in nature is the human skull, which although consisting
only of a few pieces, enlarges in a similar manner to accommodate the
growing brain.
It is remarkable how, in the whole sub-kingdom Echinodermata, all the
wonderful variety displayed by the many species is found compatible
with rigid loyalty to the dominating “number” principle: in these
animals everything is governed by the number five. With a few
exceptions, the rays are in fives, or multiples of that number; so are
the jaws, the boundaries of the plates, and other details, as may be
seen in any of the Stars to which we have alluded.
In the Sea-urchins we get an advance in that direction, for its stone
box is built up of nearly six hundred five-sided[2] plates of lime,
securely attached to each other by their edges, and fitting with such
beautiful accuracy, that there is not the ghost of a crevice from base
to crown of this wonderful cupola.
[2] Dr. Andrew Wilson, in his “Glimpses of Nature,” impresses upon
his readers this “pentarchy” in the building of an _Echinus_, but
curiously describes the plates as being _six_-sided. He evidently had
none but living specimens to refer to when he thus wrote. It is only in
a specimen from which the spines and skin have been carefully cleaned
that the form of the plates can be seen.
But if there are no crevices there are many apertures--over five
thousand of them in a full-grown _Echinus esculentus_. Forbes, many
years ago, calculated there were 3,720 in a _moderate-sized_ specimen;
and his figures, though used in all the books since his day, do not
appear to have been checked. But I have counted the pores in what
I should describe as a moderate-sized individual, _i.e._, one that
measured, when denuded of its spines, twelve inches in circumference,
and find no less than 4,800. The calculation is as follows: ten
bands, each consisting of eighty rows of six holes (10 × 80 = 800 × 6
= 4,800). The specimens that the crabbers take out of their crab-pots,
and smash against the rocks, are commonly much larger than this. It
always grieves me to see such wonderful structures destroyed in that
fashion.
The five thousand pores are in pairs, each pair giving rise to one
_pedicel_ or sucker-foot, like those we described in the Five-fingers.
The ten bands of pores are also arranged in pairs, the bands forming
a pair being separated by about five rows of spines, and each pair
of bands being separated from the next by twenty (4 × 5) rows of
spines. These intervening spines are borne on two series of long, yet
still five-sided, plates; the number of spines to each, in a growing
specimen, varying; but from counting many of these I should suppose a
fully-grown plate, from the middle of a series, would support twenty
spines; at the top and bottom of the series, however, there are only
two or three spines to each plate. These spines are not mere rigid
outgrowths like the prickles on a chestnut bur; they are beautifully
finished pieces of mechanism, with considerable latitude for movement
in any direction. Although only about five-eighths of an inch in
length, each is a beautiful column in alabaster, tapering slightly to
the top, and decorated from near the base with a series of thirty (6 ×
5) parallel rounded ridges. The bottom of this spine is hollowed out
and polished perfectly, to enable it to move freely on the polished
knob upon which it fits. These knobs are the bosses left on the shell
when the spines have been cleaned off; the spines being held to them
and moved by a circular band of muscular tissue.
If we look at the underside of the Urchin we shall find the mouth
occupying the centre, with five polished white teeth protruding.
Although these are not much to look at from outside, they form a
large and complicated structure within, which goes by the name of the
“Lantern of Aristotle,” because the famous Stagyrite appropriately
compared its shape to a lantern. Within we find a set of organs
similar to those described in connection with Five-fingers, much of
the space being occupied with the water-vascular system by which the
enormous number of sucker-feet are worked. The Urchin also possesses
a great number of pedicellariæ which keep the upper parts of the
huge sphere clean, by passing any particles of dirt from one to the
other, until they are passed off altogether. The madreporiform plate
is situate right at the summit of the edifice, near the five eyes and
the vent. As its specific name suggests, this urchin is edible; it is
boiled like an egg.
The Purple-tipped Urchin (_Echinus miliaris_) is depressed in form,
and its outline would represent an oval from which one-fourth had been
cut away, whilst _E. esculentus_ would represent a circle from which
about one-sixth had been abstracted. The skin of _E. esculentus_,
when the spines are removed, is reddish; that of _E. miliaris_, a
dusky greenish-grey. _Miliaris_ is common in rock-pools and about the
rocks at low-water; but _esculentus_ is found in deeper water, though,
from the frequency with which it is brought in by the crabbers for
destruction, rather than throw it overboard where they find it, and
from its empty house being rolled in by the waves, it is a fairly
common object of the shore.
There is a rarer shore species, called the Purple Urchin
(_Strongylocentrus lividus_), which excavates circular holes in the
rocks large enough to house itself, spines and all. This is more
plentiful in Ireland than on the English coasts; and it is remarkable
not only for its excavating propensities, but also because it sheds its
thick purple-spines annually, and produces a new crop.
[Illustration:
SIPUNCULUS. SEA-CUCUMBER.
]
Closely allied to the Sea-stars and Sea-urchins are the Sea-cucumbers,
of which we have a number of native species, though many of them
belong too exclusively to the deeper waters to be mentioned here.
Several of the genus _Cucumaria_, however, may be met among the rocks,
at low-water, on our southern coasts. One of these is represented in
the accompanying plate, protruding from a crevice in the rock. It
is the Sea-cucumber (_Cucumaria pentactes_), a species that requires
a fair pair of eyes to detect it. Certainly, when seen for the first
time, unless the finder had previously read about Sea-cucumbers,
it would never strike him as being a relation of the Sea-stars and
Urchins. There are no spines, no limy plates; instead, the body is soft
and molluscous, so that it can progress by its alternate extension
and contraction. But a careful scrutiny of the appendages encircling
the mouth might awaken suspicion, for there are ten branching rays,
and then it might be noted that the body has five distinct angles,
and that these angles are pierced with pores not unlike those of the
Urchins, through which protrude sucker-feet. This, he would consider,
constituted a very strong case in favour of their relationship to the
Echinoderms; and in this conclusion he would be in agreement with
the scientific men, who have, however, also taken the Sea-cucumber’s
internal arrangement into consideration. Another point which suggests
affinity with the Sea-stars--especially with the Brittle section--is
their trick when suffering from want of food or lack of oxygen in the
water surrounding them, of throwing off portions of their body, and
thus increasing their chances of life by their reduction of the area or
bulk that has to be fed or refreshed. The animated Cucumber not only
throws off its rays for such reasons, but also its mouth and dental
apparatus, and its intestines and ovaries are turned out, and only an
empty hollow bag remains. Should its prospects brighten through the
access of food and the oxygenating of its surroundings, it will, in the
course of a few months, reproduce these sacrificed organs, and make a
fresh start with a new lease of life. This is a close connection of
the tropical Beche de Mer, of which the Malays make Trepang, a very
important item in their trade with China, by whom it is used as a
choice article of food.
The creature to the left of the Sea-cucumber, on page 103, is the
Dotted Siphon-worm (_Sipunculus punctatissima_), formerly included
with the Sea-cucumbers, but now relegated by the systematist to the
biological lumber-room, whose door is labelled “Vermes,” that limbo
to which all sorts of creatures are sent who cannot be satisfactorily
classified, in the hope that future discoveries may make their
affinities more clear. The Siphon-worm has a cylindrical proboscis that
is almost as long as its body, and a wreath of simple tentacles around
the mouth.