UC San Diego Bulletin of the Scripps Institution of Oceanography Title Review of the Deep-Sea Fish Family Platytroctidae (Pisces: Salmoniformes) Permalink https://escholarship.org/uc/item/35v4k0ks Authors Matsui, Tetsuo Rosenblatt, Richard H Publication Date 1987 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Bulletin of the Scripps Institution of Oceanography Volume 26 Review of the Deep-Sea Fish Family Platytroctidae (Pisces: Salmoniformes) Tetsuo Matsui and Richard H . Rosenblatt UNIVERSITY OF CALIFORNIA PRESS Berkeley•Los Angeles•London BULLETIN OF THE SCRIPPS INSTITUTION OF OCEANOGRAPHY OF THE UNIVERSITY OF CALIFORNIA LA JOLLA, CALIFORNIA Advisory Editors: Charles S. Cox, Abraham Fleminger (Acting Chair for Volume 26), Gerald L. Kooyman, and Richard H. Rosenblatt (Chairman) Vol ume 26 Approved for Publication June 6, 1984 UNIVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES CALIFORNIA UNIVERSITY OF CALIFORNIA PRESS, LTD. LONDON, ENGLAND ISBN: 0-520-09708-4 LIBRARY OF CONGRESS CATALOG CARD NUMBER: 86-25088 COPYRIGHT c 1987 BY THE REGENTS OF THE UNIVERSITY OF CALIFORNIA PRINTED IN THE UNITED STATES OF AMERICA Library of Congress Cataloging-in-Publication Data Matsui, Tetsuo. Review of the deep-sea fish family Platytroctidae (Pisces: Salmoniformes). (Bulletin of the Scripps Institution of Oceanography, University of California, San Diego ; v. 26) Bibliography: p. 1. Platytroctidae—Classification. 2. Platytroctidae. 3. Fishes—Classification. I. Rosenblatt, Richard H. II. Title. III. Series. QL638.P63M38 1987 597 .55 86-25088 ISBN 0-520-09708-4 (pbk. : alk. paper) CONTENTS ABSTRACT 1 INTRODUCTION 3 Taxonomic history 3 Methods 5 Abbreviations 5 Acknowledgments 6 MORPHOLOGICAL CHARACTERS 7 Shoulder organ 7 Photophores 11 Dentition 13 Modified lateral line scales 15 Subcutaneous canals and pores 16 Cephalic lateral line canals 18 Circumorbital bones 19 Vertebrae and median fin supports 20 RELATIONSHIPS 23 Outgroup comparison of the opercular series 24 Phylogenetic hypothesis 25 VERTICAL DISTRIBUTION 29 EVOLUTION AND DISTRIBUTION 31 General distribution 31 Eastern Pacific 31 Indo-West Pacific 34 Southern Ocean 35 Atlantic Ocean 36 Mouth and body size and the evolution and distribution of 37 platytroctids Summary and discussion 39 KEY TO THE FAMILY 41 TAXONOMY 49 Persparsia 49 P. kopua 49 Paraholtbyrnia 52 P. cyanocephala 52 Holtbyrnia 54 H. innesi 58 H. macrops 59 H. latifrons 60 H. laticauda 61 H. conocephala 61 H. sp 62 H. anomala 62 H. rostrata 63 H. intermedia 64 Sagamichthys 65 S. schnakenbecki 67 S. abei 68 S. gracilis 69 Searsia 71 S. koefoedi 71 Mirorictus 74 M. taningi 74 Tragularius n. gen 77 T. perforates 79 T. bythios n. sp 81 T. crassus 82 T. mesalirus n. sp 83 Pellisolus 85 P. facilis 86 P. eubranchus n. sp 87 P. longirostris 89 Maulisia 90 (Subgenus) Maulisia 90 M. (M.)mauli 91 M. (M.) argipalla 92 (Subgenus) Aphanichthys n93 M. (A.) microlepis 94 M. (A.) acuticeps 95 M. (A.) isaacsi n. sp 95 Normichthys 97 N. operosus 98 N. yahganorum 99 Searsioides 100 S. multispinus 101 S. calvala 102 Platytroctes 102 P. apus 104 P. m i r u s 106 Barbantus 106 B. curvifrons 108 B. parini 110 B. elongatus 110 B. aequipinnis n. sp 111 LITERATURE 117 CITED FIGURES 129 1 ABSTRACT The salmoniform fish family Platytroctidae (= Searsidae) was last revised by Parr (1960) and then included 17 species in 12 genera. Since Parr’s revision, 20 nominal species and 2 genera have been introduced. This rapid increase in new taxa, a number of which are poorly diagnosed and described, has left the taxonomy in an unsatisfactory condition. As a result of our study, 5 species and 2 genera are synonymized. We recognize 37 species (5 new) in 13 genera (1 new). A key to the family is presented and each genus is diagnosed and described, with a synopsis for each species. Besides the sac beneath the cleithrum that contains luminous fluid (shoulder organ), platytroctids are clearly set apart from other alepocephaloids by a number of synapomorphies including the presence of a subcutaneous canal system, a unique arrangement of the anterior predorsal spines, and the configuration of the caudal skeletal complex. Intrafamilial relationships were determined by use of a number of characters, including nature of photophores, presence or absence of a cleithral spine, fin position, shape and configuration of supraorbital and infraorbitals, path of cephalic lateral line canals, and dentition and jaw structure. Subfamilies are not recognized, but lines of relationship between the genera may be discerned. The deeper-living genera (bathypelagic) form a natural group and are regarded as the more advanced. They differ from the shallower-living (mesopelagic) genera in having a spinous cleithral symphysis, and are more compressed, with considerable nonmuscular tissue along the dorsal margin of the body. The platytroctids and alepocephalids are viewed as having had a common ancestor, which perhaps was closest to the Bathyprionidae among living forms. The course of platytroctid evolution is viewed as involv- ing movement from mesopelagic to bathypelagic depths, with many of the morphological changes being reductional. Persparsia is regarded as the most primitive and generalized genus. Most platytroctid distributions are in the form of relatively narrow bands along the highly productive equatorial waters and the western side of continents. More oceanic records are primarily in areas of high-relief bottom, such as ridges and fracture zones, and near oceanic islands. Records of the generalized genera Persparsia and Paraholtbyrnia are from areas where temperatures at mesopelagic depths are relatively high—up to 12◦C. However, the remaining mesopelagic genera are mostly distributed meridionally in colder waters of the eastern boundaries of the Atlantic and Pacific. They tend to be rare toward the tropics. The more advanced genera predominate at low latitudes. The generalized eastern boundary forms are typically provincial in distribution. In contrast, four of the more advanced equatorial forms are circumglobal. However, none of them extends south of 24◦S, and two, Platytroctes apus and Searsia koefoedi, have never been taken in the South Atlantic. Both species show geographic variation, with the eastern Pacific and Atlantic populations more similar to each other than to the Indo-Pacific population. From this and other evidence, we suggest that the former Panama seaway may have provided a passage for deep-water as well as shallow-water fishes. 3 INTRODUCTION The family now known as the Platytroctidae was separated from the Alepocephalidae by Parr (1951) on the basis of the presence of a sac containing luminous fluid beneath the cleithrum and opening through a black tube supported by a modified scale. Although it has been referred to almost exclusively as the family Searsidae (or Searsiidae) since then, the family name Platytroctidae Roule 1916 has priority (Sazonov 1980). The family has been the subject of a series of papers by Parr, culminating in his 1960 revision that included 17 species in 12 genera. In subsequent works, 1 species, Per sparsia taningi, was synonymized, and 2 genera, Paraholtbyrnia Krefft 1967 and Searsioides Sazonov 1977, and 20 nominal species have been introduced (Krefft 1967b, 1970, 1980; Lavenberg 1965a, 1965b; Sazonov 1976a, 1977, 1978; Sazonov and Golovan 1976; Sazonov and Trunov 1978; and Matsui and Rosenblatt 1979). The rapid increase in taxa, some only poorly diagnosed, has left the taxonomy of platytroctids in an unsatisfactory state. As a result of our study, 13 genera (1 new) and 37 species (5 new) are recognized. Mentodus is placed in the synonymy of Holtbyrnia, and Platytroctegen is included in Platytroctes. Some of the taxa previously placed in Mentodus are placed in a new genus, Tragularius. Maulisia is further split into subgenera, one of which, Aphanichthys, is new. We include Holtbyrnia problematica in the synonymy of H. macrops, H. kulikovi in the synonymy of H. innesi, H. ophiocephala in the synonymy of Sagamichthys schnakenbecki, and Normichthys campbelli in the synonymy of Mirorictus taningi. We consider the holotype of Bathytroctes melanocephalus not to be a platytroctid, and agree with Krefft (1980) that the name should no longer be used in Holtbyrnia. Each genus is diagnosed and discussed, and in addition to detailed description of the new forms a synopsis of each species of the Platytroctidae is given. All the genera and most of the species are figured, a key to the species is given, and the relationships within the family and the distributions are discussed. Taxonomic History Roule (1916; Sazonov 1980 incorrectly cites Roule 1919) considered the presence of the shoulder organ and the openings in the caudal peduncle of Platytroctes apus sufficiently significant to warrant the placement of P. apus in a monotypic family, the Platytroctidae. But, except for Koefoed (1927), the new family was not recognized by others until Parr (1951) included it as one of 3 subfamilies in a new family, the Searsidae. The family Searsidae (or its variant Searsiidae) was used by subsequent authors until Sazonov (1980) pointed out that Platytroctidae was the oldest name for the taxon. The first two platytroctids were collected by the Challenger Expedition and described by Gunther¨ (1878) as Platytroctes apus and Bathytroctes rostratus. The supposed diagnostic characters of B. rostratus—i.e., maxilla reaching behind the orbit and the presence of projections on the premaxilla—could apply to a large number of platytroctids and, although for the following 50 years most platytroctids were referred to B. rostratus,Parr (1951, 1960) concluded that Mentodus rostratus (= Holtbyrnia rostrata) has been collected just once, in spite of its lengthy synonymy. The name, however, appears in the synonymy of Searsia koefoediy Persparsia kopua, and Sagamichthys abei. Other records of B. rostratus (e.g., Koehler 1896; Holt and Byrne 1908; Zugmayer 1911; Murray and Hjort 1912) are in our opinion not accompanied by sufficient descriptions to allow their allocation to any species. 4 Bathytroctes melanocephalus Vaillant 1888, which was placed in Holtbyrnia by Parr (1951), also has a complicated history.