Ol~I MYZOSTOMA GOPALAI SPECIES NOVA FROM THE MADRAS HARBOUR. BY M. K. SUBRAMANIAN. (-From the Department of Zoo ogy, UMversity of Madras, Madras.) Received April 16, 1938. (Communicated by Professor R. Gopala Aiyar.) VERY recently I had an opportunity to collect laIge numbers of Myzostomes from a common Crinoid Trofliornetra encrinus Clark (1921, 1932), from the Kadras Harbour. This elongated Myzostornid appears to be distantly related to M. rotundum Graft, M. abundans Graft, M. elegans Graft (1883, 1884), M. evermanni McClendon (1907) and M. polycvclus Atkins (1927), but is very distinct from all the above to justify in my opinion the creation of a new species, Myzostoma gopalai to receive it. This form commonly occurs attached to the ventral surface of the arms of the Crinoid. In freshly collected Tropiometra they have never been observed on the disc or near the mouth, but if the Myzostomes are distuibed they have a tendency to hide themselves in the spaces between the aims. The number of Myzostornes found on a single Crinoid varies from 1-6, how- ever, several Crinoids were found without these ectoparasites. The body of the animal is of almost uniform thickness, but gradually thins out towards the margins. In the attached condition the dorsal surface is convex and the ventral concave. The pharynx in the majority of the specimens is extended and contractions of this structure could be observed with the naked eye. When the Myzostcrnes are picked out and put in a dish of sea-water they always lie on their dolsal surface with the sides of the body directed upwards. If two or more individuals lie close together they have a tendency to stick by means of their suckers and all of them rolling together to form a ball-like mass. The large specimens carry young Myzo- stomes of various sizes, but more than one young has not been observed on any of the specimens. The colour of the animal is highly variable. It has a yellowish-orange ground eolour on which is superimposed a brown one. The yellowish orange occurs as irregular diamond-shaped areas in the middle line, with strands to the margins, in between which are (Plate XXVII, Fig. 1) the five brownish- orange bands. The first, fourth and last of these of either side a.re united 270 01z Myzostoma gopalai Species Nooa from t/ze zlladras Hat'our 271 in the median line while the second and third are separated by diamond- shaped areas in the middle line. This is the typical colouration and is of a protective nature since the Ciinoid arm has alternating bands of a]mcst similar colours. But specimens which are yellowish orange or completely brownish also occur. Moreover the width and disposition of the bands show great variation. The ventral surface is yellowish. As most workers have up till now examined only preseived material, an attempt was made to narcotize the animal with a view to detelmine the bast method of preserving all the details. Magnesium chloiide and menthol do not induce the Myzostomes to expand, and later preservation of animals so treated, in alcohol or formalin does not show the cirri properly. The body in such cases becomes rolled up. Narcotization under a coverslip with varying grades of alcohol is fortuitous and it appears to me that the best method is to kill the animal with Bouin or corrosive acetic while kept under pressure between two slides. The margin and the cirri are the most difficult to preserve with clarity. Among various fixatives I find corrosive acetic the best. Specimens were mounted between two slides and were irrigated with corrosive acetic. The first touch of the fixative leads to violent contraction, but if the slides are kept together by pressure a toler- ably decent preservation is obtained. After ten minutes the animal is slowly removed from the slide with a brush and kept in a small dish of the fixative for another twenty minutes. This treatment renders the animal whitish making it possible to photograph it on a black background and also to study accurately the disposition and structure of the parapodia, suckeIs, etc., under reflected light. In the living animal and in one mounted after clearing there is a transparent marginal zone free of alimentary canal prolongations which is not seen when the animal is presezved in formalin or alcohol. The hook and manubrium could not be made out in preserved material. I am giving below a table in which measurements of the various diagnostic characters from 10 living specimens of one day's collection are given. The length and breadth of the animal in an expanded condition under a coverstip were measured with the aid of a binocular, while the cirri were measured in a similar condition under the low power of the microscope. The other measurements were taken while the animals were in a watch glass of water. All measurements were initially taken with an eye-piece micro- meter and were later .converted into millimetres. The measurements of the cirri are given in microns. The body of the animal is oblong (Plate XXVIJ, Fig. 2) and seems to grow to a maximum length of 8 mm. The maximum width observed is about 272 M. K. Subramanlam TABLE. Table of Measurements of the Various Diagnostic Characters. Specimen Number 8 9 10 Length of animal 2.26 2.78 4.70 5,66 5.92 6.26 6.26 6.44 6,70 7- 74 ram. Width of animal 1.74 2.00 3 -22 3.04 3.40 2.50 4.69 4.00 3.80 4.80 ,, Length of pharynx 2.18 2.78 2.52 Width of pharynx 0.26 0.34 0.52 to 0.56 Vidth of clear margin Nil. Nil. 0,17 0.26 0.17 0.17 0.30 0.26 0.26 0.17 ,, to to 0.47 0.20 Width of white streak 0.17 0.26 0,20 0.26 0.34 0.26 0.26 0.26 0.26 in the mid ventral to to to to to to to to to ,, line 0.26 0.35 0.34 0.34 0.43 0.34 0.34 0.34 0.34 Length of parapodia 0.12 0.26 0.43 0.34 0.30 0.26 0.44 0.43 0.44 0.30 ,, A.--Base B.--Tip 0.09 0.17 0.17 0.26 0.17 0.17 0.26 0.17 0.26 0.20 ,, Width of parapodia 0.17 0.30 0.34 0 -43 0.30 0.26 0.44 0.44 0.44 0.34 ,, A.--Base B .--Joint 0.09 0.13 0.17 0.26 0.17 0.17 0.26 0.26 0.26 0.26 ,, C.--Tip 0.05 0.09 0.12 0.12 0.17 0 -13 0-17 0.17 0.17 0.20 ,, Distance of para- 0.47 0.52 0.96 1.31 1.13 1.13 1.29 1.14 1.13 1-29 ,, podia from margin )iameter of suckers 0.09 0.09 0.17 0,12 0.17 0.17 0.17 0.17 0.13 0.26 ,, Distance of suckers 0.17 0.13 0.26 0.17 0.34 0.26 0.26 0.30 0.35 0.44 ,, from margin Distance of cloaca 0.34 0.43 0.69 1.04 0.78 0.70 0.70 1.15 0.78 0.87 ,, from hind margin ~umber of cirri 20 48 54 94 84 84 96 94 70 136 ,, Length of cirri in i~ 50 8 10 2O 2O 44 44 50 22 44 to to to to to to to to to 90 180 100 100 174 174 150 174 215 Width of cirri in/~ 50 22 44 44 44 44 to to to to to 90 132 132 88 132 5 mm. The anterior and posterior ends of the animal in the living condition are rounded and inconspicuous notches are seen at the anterior end. But, On Myzostoma gopatal Species Nova from l/le Madras Har3our 273 if the animal is pressed between two slides during fixation, in order to expand the pharynx, there appear at the anterior and posterior ends notches which vary in shape very greatly. Yet, it has been found possible to fix the animal in as life-like a condition as possible. The dorsal surface of the animal is smooth and without crests, ridges, papillae or warts. If the animal is irritated five projections on each side of the dorsal surface, corresponding to the parapodia could be made out. This peculiarity is seen in some preserved material also, but to my mind this seems to have no significance at all. In some preserved material wart- like projections were observed on the dorsal surface, but they lacked regu- larity in arrangement and occurrence and being absent in living material appear to b~ ouly results of the physiological reaction of the animal at the time of preservation. The margin of the body is transparent in the living animal and bears 20-136 cirri (Fig. 3). In the youngest specimens observed there are only FIG. 3. Ventral view of the animal showing the parapodia, suckers, male papillae, etc. • 15, twenty cirri, ten on each side. These are almost as long as the longest cirri in the largest of the specimens. They are distributed along the margin at almost equal distances, and all of them are of equal length and shape. When the animal grows older, other cirri make their appearance between these ten primary ones.