WMemoirs of the Museum of Comparative Zodlogy AT HARVARD COLLEGE. Vout. XXXIX. No. 2. REPORTS ON THE SCIENTIFIC RESULTS OF THE EXPEDITION TO THE TROPICAL PACIFIC, IN CHARGE OF ALEXANDER AGASSIZ, BY THE U. S. FISH COMMISSION STEAMER “ALBATROSS,” FROM AUGUST, 1899, to MARCH, 1900, COMMANDER JEFFERSON F. MOSER, U. S. N., COM- MANDING.
XV.
ECHINI.
ECHINONEUS AND MICROPETALON. By A. M. WESTERGREN. WITH THIRTY-ONE PLATES. (PublishedbypermissionofGeorceM.Bowers,U.S.CommissionerofFishandFisheries.] CAMBRIDGE, U. S. A.: Printed for the Museum. Aveust, 1911.
CONTENTS.
REPORTS ON THE SCIENTIFIC RESULTS OF THE EXPEDITION TO THE TROPI- CAL PACIFIC, in charge of ALEXANDER AGassiz, by the U. S. Fish Commission Steamer **Albatross,” from August, 1899, to March, 1900, Commander Jerrerson F. Moser, U.S. N., Commanding. XV. Ecuint: Ecutnonitus anp Micropetaton. By A. M. WESTERGREN. With 34 pp. and 31 Plates.
TABLE OF CONTENTS. INTRODUCTORY NOTE ECHINONEUS CYCLOSTOMUS Lesxke THEOUTLINEOFTHEAMBITUS.Plates4,5 DEVELOPMENTOFTHECORONALPLATES.Plates6,7,13 ORALANDANALSYSTEMS.Plate15 THEABACTINALSYSTEM.Plate14 THESPHAERIDIA.Plates16,17 ARRANGEMENTOFTHETUBERCLESANDSCROBICULARCIRCLES.Bia24,25 THEPEDICELLARIAE.Plates18-23;Plate26,figs.16-19,30,31;Plate27,oe12,pee23,24, 35,36,43,44 THESPICULESOFTHETUBE-FEET."Plate28,“Ass=4. THE PERIPODIA. Plate 28, figs. 15-24 : THE spINEs. Plate 26, figs. 1-15, 20-29; Plate 27, Fes, 1- il, 14-29, 25-34, 37- 42 THE LANTERN AND AURICLES. Plate 11, figs. 1, 2, 7, 8; Plate 12 . . : THEALIMENTARYCANAL.Plates8-10;Plate11,figs.8,9 MICROPETALON PURPUREUM A. Aaassiz ano H. L. Cuarx. Plates 29-31 . LIST OF SPECIMENS SYNONYMICAL LIST PLATES.
41 At 46 47 49 50 51 53 57 58 59 60 61 63 65 66
TROPICAL PACIFIC ECHINI.
ECHINONEUS AND MICROPETALON.
INTRODUCTORY NOTE.
Av the time of his death Mr. Agassiz had in view the publication of a Report on the genus Echinonéus, the illustrations for which I had worked upon, first in 1903 and later in 1908, until their completion in August, 1910. The material in the collections in the Museum of Comparative Zodlogy at my disposal for study and for the preparation of the illustrations was excellent there being no less than two hundred and forty-four specimens of which one hundred and sixty were alcoholic, and the remainder dry bare tests. They range in size from a length of about three millimetres up to nearly forty. They come from different localities in the West Indies, the Pacific and East Indian regions. Besides the above Dr. Richard Rathbun of the U. 8. National Museum had the kindness to send for comparison two perfect adult specimens in alcohol, collected during U. 8. Eclipse Expedition of 1889 to West Africa, which though labeled Ascension Is.,? were probably obtained at Barbados. As a result of the examination of this material, Mr. Agassiz had reached the conclusion that it represents a single species, for which cyclostomus Leske (1778), seems to be the earliest available name. Linne’s name ovalis (1753) would have been preferable but unfortunately was used prior to 1758. From Mr. Agassiz’s paper ‘“‘On the existence of teeth and of a lantern in the genus Echinonéus Van Phels” (Amer. Journ. Sci., November, 1909, ser. 4, 28, p. 490-492, pl. 2) I quote:— “This is perhaps one of the most interesting recent discoveries in the domain of echinology, considering the relationship hitherto recognized of Echinonéus to the Atelostomata. The presence of teeth would transfer them to the vicinity of such types of the exocycla Gnathostomata as Holectypus, Discoidea, Pygaster (Echinoconide) and more remotely to the Conoclypide. * * * “Young specimens of Echinonéus * * * and but slightly larger than those
42 TROPICAL PACIFIC ECHINI.
in which teeth were observed, have no teeth or lantern * * * and nothing is left of them * * * so that in the older and adult stages of Echinonéus its relationship to the Spatangoids is in no way modified. * * + “Tt is interesting to note that this dentate stage of Echinonéus should connect the embryonic Spatangoids with the early stages of Clypeastroids and of the Echinoconide, while the toothed Pygastroides of Lovén connects it with some of the Echinoconide; both Echinonéus and Pygastroides are West Indian genera.
“The presence or absence of auricles, teeth and pyramids forms the basis of Zittel’s classification of the irregular Echini into Gnathostomata and Atelostomata. The position of the anal system on the actinal surface close to the actinostome is a very modern feature: its gradual passage from an anal system enclosed within the calycinal system as in Pygaster, where it is outside of the abactinal system, can be traced towards the ambitus to the ambitus and finally to an actinal position.
“In some of the Holectypide the jaws are greatly reduced in size and solidity and their importance much lessened, and in others the Jaws have entirely disappeared, the perignathic girdle having become rudimentary. In the Echinometrade the auricular girdle is most highly developed. In the Holectypide we find primitive irregular Echini as well as types which have persisted to the present day. In the Discoidea and Galerites the ambulacral processes and teeth are absent; in the auricular girdle the processes become low. In the Clypeastroids there are neither braces nor compass, the jaws move horizontally, and finally in the Atelostomata the girdle and jaws are completely absent. We may imagine the process of resorption of the lantern of Echinonéus to have gone through some such succession.”
The specimens upon which Mr. Agassiz based the above remarks were collected by Dr. H. L. Clark who has kindly supplied the following notes:— ~ Echinonéus occurs at Port Antonio, Jamaica, only in the sand-flat within the reef on the north and west sides of Litchfield Point. Search in similar habitats in the vicinity of Port Antonio, both in 1897 and in 1909, failed to reveal a single specimen.
“On this sand-flat, which is more or less covered by a feeble growth of short eel-grass, are numerous fragments of coral-rock, ranging from a few inches to two or three feet in diameter. These fragments are more or less imbedded in the sand and it is under them that Echinonéus occurs, commonly in company with Brissus unicolor Klein. As a rule, both these species are completely buried