MYTILOPHILUS-PACIFICAE-N-G, N-SP - A NEW MYTILID ENDOCOMMENSAL CILIATE (SCUTICOCILIATIDA)

Autor: John R. Dolan, Gregory A. Antipa
Přispěvatelé: Laboratoire d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
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TRANSACTIONS OF THE AMERICAN MICROSCOPICAL SOCIETY
TRANSACTIONS OF THE AMERICAN MICROSCOPICAL SOCIETY, 1985, 104 (4), pp.360-368. ⟨10.2307/3226489⟩
Popis: Mytilophilus pacificae n. g., n. sp. is described as an endocommensal scuticociliate found on the foot and mantle of the Pacific coastal mussel Mytilus californianus. M. pacificae is distinctive in its buccal apparatus which, while pleuronematine in organization, is dominated by the third membranelle. The third membranelle is a characteristic of the genus and distinguishes M. pacificae from other pleuronematine scuticociliates. The general size, body form, dense ciliation, and nuclear configuration are reminiscent of Peniculistoma mytili, which probably occupies a similar ecological niche in the bay mussel Mytilus edulis. Based on the strong correlation of characters of general morphology, buccal structure and habitat with P. mytili, M. pacificae is placed within the Family Peniculistomatidae. The close correspondence between these two organisms and their respective host species suggests that investigation of possible Mytilophilus-Peniculistoma-host interrelationships may provide instructive data for our understanding of speciation events and ciliate evolution. The general morphology, buccal structure, and occurrence of a new pleuronematine scuticociliate, Mytilophilus pacificae n. g., n. sp., are described. M. pacificae is a large ciliate found on the foot and mantle of Mytilus californianus Conrad, a common littoral mussel of the Northeast Pacific Basin. The new species shares a suite of morphological characters, including size, shape, ciliation pattern, and nuclear configuration with Peniculistoma mytili (De Morgan, 1925) Jankowski, a ciliate found in the circumtemperate littoral mussel Mytilus edulis L. (see Beers, 1959; Fenchel, 1965; Kidder, 1933; Raabe, 1949). The new ciliate's marked similarity in morphology and habitat to the relatively well-known P. mytili may explain its past anonymity. However, silver-stained specimens of M. pacificae demonstrate its unique buccal structure, which distinguishes it from P. mytili and all other known ciliates. Thus, we have erected a new genus Mytilophilus n. g., with a single included new species, M. pacificae n. sp., for this unique scuticociliate.3 1 We acknowledge the assistance of Ms. M. H. Marks and Mr. G. Haughee for collecting mytilids during a part of this investigation and Dr. E. B. Small who participated in some of the early observations. We are grateful especially to Ms. Sharon Antipa who suggested the initial site of discovery, Pigeon Point. This investigation was supported, in part, by N.S.F. Grant DEB 78-03550 awarded to G.A.A. 2 Present address: Marine-Estuarine-Environmental Science Program, % Zoology Department, University of Maryland, College Park, Maryland 20742, U.S.A. 3 The generic name Mytilophilus first appeared in Corliss' text on the ciliated protozoa as a nomen nudum in anticipation of the present publication. See his discussion of such treatments (pp. 207, 209 in Corliss, 1979). TRANS. AM. MICROSC. Soc., 104(4): 360-368. 1985. ? Copyright, 1985, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.192 on Wed, 24 Aug 2016 04:54:13 UTC All use subject to http://about.jstor.org/terms VOL. 104, NO. 4, OCTOBER 1985 MATERIALS AND METHODS Host Collection and Examination Individuals of Mytilus californianus were collected during low tides from large, well-established mussel beds at several locations between Pigeon Point, California and Astoria, Oregon. Mussels were pried open to allow for the insertion of a Pasteur pipette filled with filtered seawater. The seawater was squirted vigorously into the mantle cavity with attention to washing off the fleshy parts of the mantle and foot. The rinse fluid was collected in a Syracuse dish, and, after 2-3 repetitions, ciliates were removed individually by micropipette. We have not made a systematic investigation of the autecology of this organism, but Mytilophilus pacificae was recovered from greater than 80% of the specimens at most localities examined; the numbers of individuals found within each mussel appeared to vary significantly. Cytological Techniques and Mensurations Live specimens were examined and photographed with the aid of phasecontrast and differential interference-contrast optics (Zeiss). Two methods of silver impregnation were used: the AgNOs method of Chatton & Lwoff (see Corliss, 1953) and the Protargol method of Bodian (see Kirby, 1950). Ciliate depth, length, width and number of kinetal rows were determined for 25 similarly oriented, Protargol-stained specimens from each of two locations. Length and depth were measured with a calibrated ocular micrometer at 400x for both living and Protargol-stained organisms. Width was determined by focusing through the ciliate and counting the 2-Am units of the fine focusing knob of the microscope. The manufacturer's calibration was verified to be accurate by tests on a stack of coverslips which had been measured with a die-maker's micrometer gauge and engraved on each side to allow for visualization. Due to the extremely dense ciliation of this organism, the number of kinetal rows could only be counted on selected specimens with great difficulty. Therefore, in order to achieve an accurate and unbiased estimate, the following sampling protocol was devised. Since the organism is approximately elliptical in median transverse section, the perimeter of each ellipse was calculated using the width and depth measurements achieved (see above). Two quadrants were selected, each 6 um wide, one just above the nucleus on the right side and the other just below the nucleus on the left side. The mean number of kinetal rows in the two quadrants was extrapolated to give the total number of kinetal rows around the ciliate. Standard counts made on each of two extraordinarily well-stained and oriented specimens fell within the range of kinetal rows calculated for the 25 specimens from that locality and within 5% of the computed values for these two specimens.
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