FAMILY ECHENEIDAE — LACHNER 75 



cephalic migration, probably through use, which brought about a 

 modification of certain cranial bones. This modification was mainly 

 a process of a flattening and widening of the bones to form a cranial 

 table for the disk. 



The possible relationship of the echeneids to a number of compara- 

 tively diverse families has been suggested, owing to their superficial 

 external appearances or to their habits or to their comparatively 

 similar osteolog3^ Among these are the Rachycentridae, Carangidae, 

 Pomatomidae, the seriolid pilotfish Naucrates, and the centrolophid, 

 Palinurichthys. A distant relationship with gobioid and blennioid 

 stocks also has been suggested. Their derivation from some perciform 

 stock is generally agreed upon. Two families are recognized, the 

 living Echeneidae, comprising two distinct subfamilies with a total 

 of eight species, and the monotypic fossil Opisthomyzonidae. 



Although only two species are knowTi from the Marshall and 

 Marianas islands, four additional species and possibly a fifth, Remora 

 australis, occur in Oceania. All seven are included in the key. The 

 two species reported from the study area, Echeneis naucrates and 

 Remora remora, have a variety of hosts, but other species of echeneids 

 have more restricted if not specific hosts: for example, Remora 

 brachyptera and Remora osteochir are found almost always on sword- 

 fish, sailfish, and marlin; Remorina albescens is almost always found 

 on manta rays; and Remora australis, only on cetaceans. All disk- 

 fishes occurring in Oceania have a worldwide distribution in the warm 

 seas. In several species, only minor infraspecific differentiation 

 occurs between Atlantic and Indo-Pacific oceanic populations. 



KEY TO THE SPECIES OF ECHENEIDAE FROM OCEANIA 



la. Caudal fin in the young lanceolate, the middle rays produced in a long 

 filament; almost truncate in the adults, with longer outer rays on the 

 lobes; pectoral fins acute in the adults; anal fin base long, anal rays 29 

 to 41; lower jaw produced in a flap; body slender, elongate, usually with 

 a dark lateral horizontal stripe ; pelvic fins narrowly adnate to abdomen ; 

 disk smaller; vertebrae 30 or 40. (Echeneiinae.) 

 2a. Disk laminae numerous, 18 to 27; body elongate, species attaining a 

 large size, over 2 feet in length; vertebrae 30. (Sharksucker.) 



Echeneis naucrates Linnaeus 



26. Disk laminae fewer, 9 to 11; body elongate, very slender; size smaller, 



usually less than 18 inches in length; vertebrae 40; plate 131, 



B. (Slender suckerfish.) Phtheirichthys lineatus (Menzies)2° 



16. Caudal fin in young forked, transforming to a more or less emarginate or 



truncate fin in adults; pectoral fins rounded; anal fin base short; anal 



rays 18 to 28; lower jaw not produced in a flap; body stout, short; 



horizontal stripe wanting; pelvic fins broadly adnate to abdomen in all 



species except Remorina albescens; disk larger; vertebrae 26 or 27. 



(Remorinae.) 



'OEcheneis lineata Menzies, Trans. Linn. Soc. London, vol. 1, p. 187, pi. 17, fig. 1, 1791 (type locality, 

 tropical Pacific Ocean). 



