STAUROMEDUSAE UK
An online guide to the Stalked jellyfish (Stauromedusae) found
around the coastal waters of the United Kingdom and Ireland.
Includes notes on their identification, and where and how to find them.
HALICLYSTUS AT SCARBOROUGH.
JOHN IRVING, M.D., Scarborough,
The unexpected has happened, and another marine record for the Yorkshire coast is added to our lists. It is an important one, for Haliclystus octoradiatus nominally belongs to the South. In the final paragraph of a short article on Lucernaria campanulata {Naturalist, July, 1913), I mentioned the absence of Zostera grass as a reason why Haliclystus, the common lucernarian of the English Channel, was not found at Scarborough.
That statement holds good no longer, for since July, many young
Haliclystus octoradiatus.
Fig. 1.— Diagram (aboral view): (C) colleto-cystophores, (G) genital bands.
Fig. 2.— Diagram (oral view): (C) colleto-cystophores, (M) mouth.
Fig. 3. — Diagram of end of stomodaeum.
Fig. 4. — Diagram of section of colleto-cystophore.
forms, adhering to Red Ceramium, have appeared in two distinct South Bay areas. Not a single adult, however, has been discovered. The natural inference is that adults are, or have been, in the vicinity, probably at some lower level where Zostera may be hidden, and that, subsequent to spawning, their progeny have been driven shorewards into sunnier and warmer tidal sand pools containing appropriate weeds for anchorage. Ceramium is often associated with Zostera, and in this connection the young of Haliclystus. initially, may be more at home on slender Ceramium filaments than on broad Zostera blades.
Messrs. Walmsley and Wilson, of the Marine Laboratory, found young specimens of Haliclystus on Ceramium in Robin Hood's Bay, during August, and report the capture of an adult Lucernaria on Ulva by dredge.
Very few specimens of Lucernaria campanulata continue in evidence at Scarborough, and these have lost the white egg masses which were so conspicuous in May. Unfortunately the process of spawning and hatching was not seen, but as the result young lucernarians are now abundant in the same region, invariably, as their parents were, attached to Halidrys siliquosa.
It is curious that the young of Lucernaria, and the young of Haliclystus, whose habits are to all intents and purposes the same, and whose food supply is identical, should exhibit well marked preference for dissimilar weeds so that, without examining the animals, one can positively determine the species by the weed which supports it. What instinct causes Lucernaria to select Halidrys, and Haliclystus, Ceramium? Is
there some inherent colour sense that guides aright? Both species are carnivorous, hence the plants chosen are simply protective supports, not food. Why Haliclystus in later life should transfer itself from red Ceramium to green Zostera is a colour problem. One thing is certain, the tints, varying from green to red and brown, which characterize the young, harmonise perfectly with a Ceramium environment, and render detection improbable, save in good light to a trained eye.
Two diagrams, based on photo-micrographs, of a very young Haliclystus, 3/16 inch (4.8mm) in diameter when fully expanded, afford details for comparison with sketches of Lucernaria given in the July Naturalist. The creature had been under observation, in a glass cell containing sea-water, for some weeks, and as it had fixed its disc to the centre of the glass bottom it provided an unusual object for microscopic study. Its essential movements corresponded precisely with those of Lucernaria, confirming the impression that lucernarians are much more akin to actinozoa than to medusae. An anaesthetic, sufficiently powerful to suspend movement and sensation without causing an organism to alter its life-like appearance, is useful in elucidating anatomical detail. Chloretone, 5 grains, in an ounce of distilled, or cold boiled water, answers best. If the dose administered is neither too large, nor too prolonged, delicate creatures, when transferred to fresh sea-water, soon recover from its effect. Chloretone, too, may be employed advantageously in heavier dose, as a preliminary to preservation with formalin, to ensure specimens being fixed permanently in a natural condition for Museum purposes. Under microscopic observation, the selected Haliclystus, covered with a minimum of sea-water, was given clear chloretone solution through a pipette, drop by drop, until the whole surface of its bell, and all its tentacles, were at rest. Suddenly a final, but unlooked for, movement shot out the gullet, or stomodaeum, in an upward direction, just as some marine worms, under similar circumstances, extrude their probosces as a protest against physic. The mouth was but the puckerings of an inverted muscular tube, which, when everted, ceased to be. Thus transformed it was a straight cylinder, exhibiting four longitudinal muscle bands, whose upper extremity, when brought into focus (Fig. 3), was a circle divided into quadrants by two septa crossed at right angles. The length of this cylinder was equal to half the diameter of the expanded bell mouth. In the first issue of the Jersey Marine Journal (November, 1893), the late James Hornell had an illustrated article on Haliclystus in which he, a most careful student, erroneously assumed the mouth of this animal to be square and fixed. It is not square but irregularly rugose, appearing more or less angular owing to four equidistant muscles pulling downwards from opposite points of insertion. Motility of mouth and eversion of stomodaeum are in accord with phenomena seen in actinozoa.
Haliclystus octoradiatus is easily distinguished by the presence of eight colleto-cystophores, which are non-existent in Lucernaria. The peculiar situation and shape of these organs are noteworthy. They are placed on the outer surface of the bell, just below, and in the centre of, the bay margins. Each penetrates its pedicle to the inner wall nearly at right angles to the tentacular processes. Seen from without (aboral, Fig. 1), the organ is a large oval, supporting a diminutive capitate tentacle. Viewed from within (oral, Fig. 2), it is globose with a projecting nipple. When the bell is fully closed, by the concerted action of all the tentacles, these eight colleto-cystophores assume the perpendicular, form a circular body-guard of sentinels, and, their short capitate nipples being charged with nematocysts, serve, presumably, to defend the organism against alien invasion while the general army of tentacles are otherwise engaged. To regard them as vestigial, like the human appendix, as some writers do, seems incredible considering their size, equipment, and anatomical disposition.
Genital bands in Haliclystus form eight separate rows occupying tentacular radii; in Lucernaria they are in pairs situated in alternate bays. In Haliclystus the clusters of tentacles are spread out, whereas in Lucernaria they are close set claw-like tufts.
