A history of the British hydroid zoophytes. By Thomas Hincks.

About: The article was published on 1868-01-01 and is currently open access. It has received 87 citations till now. The article focuses on the topics: Hydroid (zoology).

Summary

RATE OF GROWTH. PHOSPHORESCENCE.

• All the evidence the authors possess on the point seems to show that the development of the fixed Hydroida proceeds rapidly.
• The following illustration of the enormous rate at which some of the Hydroids multiply is from M'Cracly: "I have observed the medusas (of Tubularia cristata) fully grown and casting their larva; as early as March 10th, and as late as September 13th, during all which time thousands of larv;u arc.
• The large, arborescent masses of the stouter kinds of Sertularia, Halecium, Eudendrium, &c. must be the growth of several seasons.

The common

• Obelia geniculata, which may be met with on every coast, is a phosphorescent species, and, if agitated soon after its removal from the sea, will furnish a fine display of " living stars.".
• This is recognized in the absence of many fine species of Hydroida which occur on the southern and western coasts, as well as in the presence of a few northern forms that are not found elsewhere, and the prevalence of others which become rare in warmer districts.
• The British Hydroida are all marine, with the exception of Hydra (a truly fluviatile form) and Cordylophom (which is an inhabitant of fresh water here, but elseAvhere is met with in waters more or less saline) .
• Many species manifest a preference for certain zones of the space included between tide-marks, and are only found within very definite limits.

Catalogue of

• North American Acalephee/ by Alexander Agassiz ; while the well-known journal,, the ' Archiv fur Naturgeschichte/ contains a critical review of the Coelenterate literature of each year by Prof.
• The characters on which the dichotomous division is INTRODUCTION.
• Calycles not constricted at the base and perfectly sessile CUSPIDELLA.
• If the reproductive bodies are absent, the student must treat it as a single genus, and identify his zoophyte by a reference to the specific descriptions.

CLASSIFICATION.

• It would be a fruitless labour to give any detailed account of the earlier systems of classification, which have now only an antiquarian interest.
• The accumulation of facts has proceeded steadily since that period ; but the correct interpretation of them and the elaboration of a really philosophical classification are amongst the latest results of research.
• And these elements are variously manifested and combined in the Hydroid group.
• There has been considerable diversity of opinion as to the true position of the small number of medusan * forms that are developed directly from the ovum without the intervention of any fixed Hydroid stock.
• At certain points of the Hydroid series, the apparent dissimilarity is much less marked ; and a colony of Hydr actinia or Podocoryne very plainly betrays its affinity to Velella or Physalia.

INTRODUCTION.

• The Calycophorida and Physophorida I should also rank as suborders,, and unite in the single order Siphonophora.
• In classifying the Hydroida and constructing the generic groups, respect must be had, as emphatically pointed out by Allman*, to both the nutritive and reproductive elements.
• The trophosomes of two species may agree very closely in character, while the gonozooids are widely dissimilar, and vice versa.
• In the large and beautiful family Campanulariidae, all the generic groups, with a single exception, are founded on characters supplied by the gonosome alone; and many similar cases might be cited.
• This is remarkably the case in the * A. Agassiz (in bis ' Cat. of North American Acalcphae, 1865) expresses his belief that at a more advanced stage these gonozooids would exhibit differencesand will not allow that " medusae generically identical " are " developed from Hydroids generically distinct.".

CLAVA MULTICORNIS.

• O the creeping filiform base, white, rose-, or flesh-coloured, with numerous tentacles; GONOPHORES round, hanging in many-pedicled clusters immediately behind the lower tentacles.
• AFTER much consideration I venture to assign Forskal's name to the common Clava of their coasts, with scattered polypites.
• In C. squamata the polypites are closely massed together, and form colonies on the fronds of the Fucus, the larger of Avhich measure about half an inch across.
• The gonophores hang in large bunches below the posterior tentacles, and form a massive and conspicuous collar.
• The polypites are more delicately formed and want the broad expansion towards the upper part of the body; they taper gradually, and not very markedly, downwards.

CLAVID^E.

• Allman found the clusters of gonophores scattered in all the zooids of the colony which he examined.
• The polypites, too, were attenuated, and of a delicate rose-colour.
• Der. Tubus, a tube, and Clava, the name of a Hydroicl genus.
• Allmaii has remarked, an affinity between it and Cordylopliora.

CLAVLD^E.

• Ycited; tentacles numerous, scattered over the whole of the club-shaped head; GONOPHORES in mulberry-likemasses, borne on very short stems, which are situated in openings in the creeping base (rudimentary tubes}.
• Stems short, rooted by a filiform stolon, bearing the polypites on their summits ; the ccenosarc invested by a polypary ; polypites claviform, with scattered filiform tentacles.
• The passages or tubes thus formed are covered in above, not by a solid wall, but by a chitinous network, which stretches across them a little below the free serrated edges of the lamellae.
• WE have had conflicting accounts of this zoophyte from authors, their discrepancies being due to the fact of their having observed it in different stages of growth.the authors.the authors.

PODOCOHYNID^E.

• P. carnea is furnished with the curious spiral appendages first described by Wright as occurring on Hydr actinia echinata.
• WE require further information before anything can be said with certainty of this extraordinary form.the authors.the authors.
• Sir John Dalyell's figure of Coryna glandulosa (Rem. An. vol. ii. pi. xxi.) is an admirable representation of this species.
• GONOPHORES borne at the base of the tentacles over the lower half of the body, spherical, shortly stalked.
• THE size of the polypites is the point that first attracts attention in this species.

COBYNIDJE.

• This is the common Syncoryne along the north-eastern coast.
• The tentacles are sometimes reduced by absorption to mere papillae ; sometimes they disappear altogether; and in some cases the whole head vanishes, and the stem is surmounted by a single gonozooid, or occasionally by two.
• The heads of the polypites had in almost all cases disappeared, and each stalk bore near its extremity one or two ovate medusiform bodies attached by a short peduncle (Plate X. fig.

GONOZOOIDS

• Stems simple and very short, rising from a creeping filiform stolon, the whole invested by a polypary ; polypites borne on the summit of the stems, with a single verticil of capitate tentacula round the base of the proboscis.
• Filippi J would regard this difference as specific ; but of his own specimens, while a large proportion had six arms, 15 per cent, had seven.
• I have already pointed out the close resemblance which there is between the reproductive zooid of Clavatella and the alimentary polypite.
• At times they are greatly elongated and attenuated, and present the appearance of most delicate milk-white threads*.

ARUM, Vigurs.

• Polypites solitary, cylindrical, terminating above in a conical proboscis, springing from an adherent base, which is clothed with a chitinous polypary ; tentacles very small, capitate, covering the greater portion of the body.
• Colour; the ADHERENT BASE massive, of a dark horncolour, sending out a few tubular and root-like prolongations.
• Gonophores developed from the body of the polypite below the tentacles, or from the stem, containing fixed sporosacs the female simple, the male consisting of several chambers arranged in moniliform series.
• E. rameum occurs near the North Cape, as well as abundantly on their own shores, and ranges to the Mediterranean.

EUDENDRIIDyE.

• Deep water, on shells, stones, &c. ; widely distributed.
• Reproductive bodies, which, hoAvever, were wholly absent from their larger brethren in the cave " (A. M. N.) .
• Salicornaria farciminoides &c., not uncommon ; near Polperro, Cornwall (T. H.).
• The polypites bearing the reproductive buds are not confined to any particular portion of the zoophyte, but are irregularly distributed.

His variety corymbifera is probably

• Torquay, on rocks between tide-marks; Ilfracombe; Swanage, Dorset (T. H.).
• On the undersides of stones and the roots of Laminariae at Tynemouth and Cullercoats, occasionally (J. A.) : Largo (T. S.W.) : under stones, and on Laminariaroots, Filey Brigg, very common (T. H.).
• STEMS erect, simple or bifurcate, more or less dilated and cup-shaped above, from g to \ inch in height; POLYP IT E small, club-shaped, white, partially retractile into the upper part of the tube ; tentacles from 4-1 2, according to age; GONOPHORES pedicellate, borne on the stems at various heights.
• The gonozooid at the time of detachment has only two arms fully developed ; but two more are present in a very rudimentary state, or soon bud from the two smaller marginal tubercles.

PERIGON1MUS PALLIATUS.

• The polypary of this species is extremely delicate, yielding like a mere skin to the movement of the polyp ites.
• Found in a Pecten-shell dredged from the Firth of Forth, near Inch Keith (T. S.W.).

GENERIC CHARACTER. Stems very short (rudimentary),

• The gonophores spring from branches terminating above in a shallow cup, which exactly resemble those that support the polypites.
• As the two zoophytes perfectly agree in other characters, it is probable that this slight discrepancy between the descriptions merely points to a difference in the condition of the specimens examined.
• On the Bimer Rock, near North Queensferry, and on Inch Garvie, Firth of Forth (T. S. W.): Firth of Forth, " attached to other zoophytes and seaweeds near low water, spring tides" (G. J. A.): Whitby, Yorkshire; Torbay and Salcombe, South Devon, dredged on other zoophytes, not uncommon (T. H.).
• Stem branched, rooted by a filiform stolon, the whole ccenosarc invested by a polypary ; pohjpites fusiform, with a single wreath of filiform tentacles round the base of a conical proboscis ; gonophores developed from the branches and originating free zooids.

THECAPHORA.

• In another the species are arborescent and sometimes of considerable size, their tree-like tufts presenting the most lovely shapes, the branches laden with the hyaline calycles (variously formed and adorned) and with the vase-like capsules, and the whole structure exhibiting an indescribable delicacy of texture and gracefulness of habit.
• I have therefore retained Clytia, which was assigned by its author to such species, for the first section, and Campanularia for the third*.
• Umbrella (at the time of liberation] depressed and disk-like ; manubrium short and quadrate ; radiating canals 4 ; 'marginal tentacles numerous (increasing in number with age) , prolonged at the base and projecting inwards ; lithocysts 8, two in each interradial space, borne on the inner side of eight of the tentacles near the base, also known as Gonozooid.

I

• Have noticed a little orange-colour at the base of the manubrium.
• The pedicels of the terminal calycles are of unusual length, ringed at the top and bottom and smooth between.
• "The most common and characteristic zoophyte (next to Tubularia indivisa, perhaps) of their shores.
• IT is difficult to settle the synonymy of this species, as the descriptions of the older authors are wanting in minuteness and precision, and several kindred forms have been confounded under the Linnean name dichotoma.
• The main stem is a bundle of delicate tubes closely adherent to one another, and gives off branches at short intervals; those on the lower portion are thick and compound, those above becoming gradually more slender, until towards the extremity of the shoot they are perfectly simple.

1G7

• On the red algoe chiefly (Delesseria sanguined &c.), near low-water mark and in moderate depths ; not common.
• Pegwell Bay, near Ramsgate (R. S. Boswell) : Old Head CAMPANULAllIIU.E.
• On pedicles, which are more or less annulated at the top and bottom,, patent, and arranged in whorls at regular intervals ; GONOTHECVE flask-shaped, smooth, with a narrow neck, and very shortly stalked.

THE term "

• Equisetiform" which Ellis has applied to this species, gives an admirable idea of the mode in which the pedicels are disposed on the stem and branches.
• In amazing profusion it spreads over a considerable portion of the littoral zone, now half buried in the mud beneath the loose stones, now covering with its delicate forests the sides of the tidal pools filled with the most pellucid of water.
• The authors cease to be surprised at its abundance when they examine the reproductive capsules *, which are of enormous size, as compared with the calycles, and often crowded on the shoots, each one containing a large number of planules.
• On the underside of stones, between tide-marks, and on other zoophytes &c., from inshore to the coralline region; common.

t/

• The capsules are three or four times as large as the hydrothecse.
• The male capsules form rows on the branches, partly overlapping one another.
• The branches divide and subdivide dichotomously ; and at certain seasons the pinnules thus formed bear the capsules, profusely, in rows.
• This species seems to be less abundant than the preceding, though very widely distributed in deep water.

Hebrides (A.M. N.).

• [There is a specimen from Algoa Bay in Mr. Busk's " PIIEASANT'S-TAIL CORALLINE," Eflis, Corall. 14, pi. viii.
• THE stem of this very handsome species (the " Palma marina" of old Barrelier*, the "PheasantVtail" of Ellis) * 1714.
• On the back of it, " at nearly equal distances, are formed little regular arch-like risings, which are compressed and hollowed a little in the middle.".
• They are formed by the occasional divergence of a portion of the tubes from the ascending line of the stem, and are, in fact, arrested branches.
• The pinnae in perfect specimens usually clothe a large proportion of the stem, a small section only towards the base being naked.

Sidmouth, on

• Cornwall, also known as Rhytiphlcea (Miss Cutler).
• The tentacles are more or less extensile, and bear n formidable armature in the shape of numerous thread-cells, which arc grouped together on small prominences or 310 HYDRIDES.
• Worms and larvae, Entomostraca, and even minute fishes constitute the food of the Hydra and these are seized by the long, flexible arms, and probably paralyzed by the threads which are darted forth from the numerous batteries of thread-cells covering their surface.
• At certain seasons, and especially towards autumn, true reproductive organs are developed, the spermary and ovary being usually present on the same individual, but borne on different regions of the body.
• In a paper presented to the Royal Academy of Turin, so recently as 1865, this author has proposed the above name for a Mediterranean Hydroid, which is nothing more or less than a very ordinary member of the old and well-known genus Coryne.

Figures

Fig. 13.

Fig. 27.

Fig. 44.

Fig. 45.

Fig. 5.

TABLE I. ATHECATA.

Fig. 11.

Fig. 23.

Fig. 29.

Fig. 41.

Fig. 22.

Fig. 28.

Fig. 36.

TABLE II. THECAPHORA.

Fig. 38.

Fig. 32.

Fig. 1.

Fig. 18.

Fig. 24.kind of network. The calycles are exceedingly minute, and of equal width throughout, till within a short distance of the base, when they are abruptly rounded off; they are of a somewhat dense corneous texture, and preserve their shape well when

Fig. 26.

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BRITISH
HYDEOID
ZOOPHYTES,
VOL.
I.