Ophiothrix Fragilis Research Articles

Localization of catecholamines in the nervous system of a starfish, asterias rubens, and of a brittlestar, ophiothrix fragilis

a 1. 1. A histochemical study was made of the distribution of catecholamines in the nervous systems of a starfish and a brittlestar. 2. 2. Dopamine- and noradrenaline-containing neurones were confined to the ectoneural system. The amine containing neurones appear to serve an internuncial role. Amines were not observed in any non-nervous tissue. 3. 3. In the starfish, the amine-containing neurones are probably involved in tube-foot coordination.

Ophiuroids feeding on Phytoplankton

RECENTLY, Nagabhushanam and Colman1 have described carrion-eating by some species of ophiuroids including Ophiocomina nigra (Abild.) and Ophiothrix fragilis (Abild.), from observations both in the laboratory and in the sea, a phenomenon which has been recorded previously2,3. The two species mentioned as well as Ophiopholis aculeata (L.) have, however, been reported to feed on a wide range of food from seston and plankton to bottom invertebrates2,3. In particular, Ophiothrix fragilis and Ophiopholis aculeata are considered to be mainly suspension feeders4,5 (using strong ciliary currents6 in catching detritus), being also facultatively carnivorous. Of the species mentioned, Ophiocomina is anatomically well adapted for a carnivorous habit3. Nevertheless, all the species mentioned are considered to feed in essentially the same way2,3.

Carrion-Eating by Ophiuroids

OPHIUTROIDS are known1,2 to eat a wide range of food, including phytoplankton, zooplankton, polychaetes and detritus; carrion-eating can now be added to the list, for it has recently been observed in this laboratory on the part of Ophiocomina nigra (Abild.), Ophiothrix fragilis(Abild.), Ophiura texturata Lam. and O. abilda Forbes. In aquaria these brittle-stars were seen to eat on one occasion a dead lesser weever (Trachinus viper C. and V.), and on another a small dead cephalopod (Sepiola atlantica d'Orb.). Each ophiuroid's stomach was scarcely everted at all while feeding, but the long tube-feet round the mouth made strong tugging movements, breaking off small pieces from the prey which were later found in the ophiuroid's stomach.

A photographic survey of certain areas of sea floor near Plymouth

An improved underwater photographic apparatus has been used to take further series of photographs of the sea bottom near Plymouth. The photographs in the present series are each ¼ m.2 in area instead of 1 m.2, and at this scale definition is much better.Photographs of the bottom in the Rame Mud area showed ripple marks but no living epifaunal animals. In an area south of the Rame Mud, on a muddy sand and gravel bottom and in a similar area 6 miles south of Looe, dense populations of the brittle-star, Ophiothrix fragilis were photographed. In the area south of Looe this type of population (density more than 100 individuals per m.2) ha s been photographed on three different occasions in 1950–1. In a similar but still denser Ophiothrix population found ¾ mile north-west of Eddystone, there were about 340 individuals per m.2, and this aggregation was apparently of long standing, since exceptionally large dredge hauls of Ophiothrix were taken there in the last decade of the nineteenth century. It is suggested that the food supply for these populations, in the form of suspended material, is brought to them largely by the tidal streams and that the crowded beds are in localities where this is likely to happen.

Occurrence of young Ophiothrix fragilis within the Genital Bursa of the Adult

IT has been recorded by Mortensen1,2,3 that young specimens of the ophiuroids Ophiothrix fragilis Abildgaard, O. triglochis M. and Tr. and Ophiactis Kroyeri Ltk. are sometimes to be found clinging to the arm spines of the adults. The occurrence of the young individuals on the adults does not, in Mortensen's opinion, indicate a viviparous habit in these ophiuroids since one, at least, namely O. fragilis, is known to have pelagic larvae ; rather, it is “quite by chance that the young ones, after their metamorphosis from the pelagic larvae, happen to settle down on adult specimens in places where these latter occur in good numbers”2.

The Development of Ophiothrix fragilis

The principal points which have been brought out in this paper may be summarised as follows : (1) The early development of Ophiothrix fragilis varies with the condition of the egg at the moment of fertilisation, and the development of the unripe egg resembles in certain features that of Ophiura brevis. (2) The cœlom originates as a single vesicle from the apex of the archenteron, and this appears to be true for all classes of Echinoderms. (3) The segmentation of the cœlom proceeds along the same lines as those already elucidated for Asteroidea and Echinoidea, viz. into three somites on each side, but the middle somite on the right side is not shifted dorsally as it is in Asteroidea and Echinoidea. This somite occasionally assumes a five-lobed form, proving beyond doubt that it is a right antimere of the water-vascular system. (4) The left hydrocœle is budded from the anterior division of the left cœlom, not from the posterior division as Bury supposed (5), and its persistent connection with the left anterior cœlom constitutes the stone-caual; this opens into the hydrocœle between lobes 1 and 2, as in Asteroidea, not between lobes 4 and 5 as Bury asserted. (5) The metamorphosis is initiated by a preponderant growth of the organs of the left side, which affects the larval arms and the sides of the œsophagus, aud which not only carries the hydrocœle round the œsophagus but also the madreporic pore and the left anterior cœlom, so that these come to be near the right hydrocœle. (6) The perihæmal system of canals originates as a series of five hollow evaginations, the cavities being small and the walls thick. The first Originates from the left anterior cœlom, the other four from the left posterior cœlom. From their walls originate the motor ganglion cells and in all probability the ventral inter-vertebral muscles. (7) The left posterior cœlom gives rise to a dorsal and a ventral horn, which eventually meet, causing it to assume a ring-shape. From it five evaginations give rise to the arm rudiments and the first of these comes to overlie hydrocœle lobe No. 2. (8) A peri-oral cœlom closely surrounding the adult œsophagus originates from the left posterior cœlom. (9) A series of epineural ridges, the tops of which grow out so as to form arch-like folds, are formed inter-radially alternating with the primary tentacles. By the union of adjacent arches the basal portions of the tentacles are covered, exactly as occurs in. the Echinoid larva. (10) The adult œsophagus is formed from the left inner portion of the larval one: its covering is made of the adoral ciliated baud, chiefly of the left half thereof, which grows pari passu with the left hydrocœle. The outer part of the larval œsophagus opens out in consequence of the shrinkage of the forehead to form an atrium into which the primary hydrocœle lobes project. (11) The larval intestine slowly diminishes in size and degenerates, this process being accompanied by a vacuolisation of its cells. The larval stomach becomes pushed over to the right--a process which leads to the same result as the moving of the larval mouth to the left in Holothuroidea, or the formation of the adult mouth on the left in Asteroidea and Echinoidea. (12) The primitive germ-cells originate from the left posterior cœlom covering the stone-canal. In conclusion, I have to express my thanks, first to the University of Cambridge and to the British Association, who granted me the use of their tables at Plymouth; next to Dr. E. J. Allen, Director of the Marine Biological Laboratory at Plymouth, who in the most whole-hearted and generous manner placed the resources of the laboratory at my disposal; then to my friend and colleague, Mr. J. Simpson, B.Sc., Demonstrator of Zoology in McGill University, to whoso skill I owe a large proportion of the drawings which illustrate this paper; and lastly to my wife, who also assisted with the more complicated drawings, with the text-figures, and with the general revision of the text.

Some points in the development of ophiothrix fragilis

The subject of which the present communication is a brief preliminary account has occupied by attention during the last five years, and a full account will be published shortly. Meanwhile, a brief outline of the main results is given here. Ophiothrix fragilis is one of the commonest species of British Ophiuroidea. Especially in the neighbourhood of Plymouth, where the material for this research was obtained, this species is found in immense swarms, so that, on certain kinds of bottom, hundreds of individuals are brought up with each haul of the dredge. During the months of June and July it spawns, and on which it lives is full of its larvæ in all stages of development.