チゴダラ属の二種の比較

抄録

In December of 1951 the writers published a description of a previously unknown species of the morid genus Physiculus, P. jordani (BOHLKE and MEAD, 1951: 27). The description was based on a single specimen trawled by the U. S. Fish Commission Steamer “Albatross” off Suruga Bay, Japan. In March of the following year Dr. Toshiji KAMOHARA of Kochi University described P. inbarbatum as new (KAMOHARA, 1952: 94), designating as types three specimens obtained from the Mimase market (Kochi City, Shikoku). Since these two nominal species appeared to be strikingly similar in many respects, a direct comparison of the type material seemed desirable. This comparison was effected through the kind cooperation of Dr. KAMOHARA, who made available to us not only his types but also several specimens subsequently collected from the type locality.
Specimens of P. jordani and P. inbarbatum are similar in the absence of the mandibular barbel, in the extremely slender caudal peduncle, in color pattern and in many other general features. In several meristic and morphometric characters, however, the type of P. jordani differs significantly from those of P. inbarbatum. Counts and proportional measurements of the specimens at hand are recorded in Table 1. It is immediately apparent that our specimen has a greater number of dorsal and anal rays, a slightly longer and broader head, a longer snout, a wider interorbital space and more posteriorly placed pectoral and ventral fins than has Dr. KAMOHARA'S material.
We cannot, therefore, assign P. inbarbatum a place in the synonymy of P. jordani, although it seems improbable that two closely related and morphologically similar populations could have evolved and maintained their identity while living together in waters off Shikoku and southern Honshu.
A third form apparently closely related to these two is Physiculus edelmanni (BRAUER, 1906: 274, pl. 12: 6, from the Indian Ocean off the coast of Africa. Counts and measurements of this species, taken from BRAUER'S type description, are also included in the table. In many respects the specimens of P. inbarbatum appear to be intermediate between P. jordani, as originally understood, and P. edelmanni. A biometric study of the members of this complex based on material from various localities and depths may demonstrate the existence of but a single widespread and highly variable species. However, since available representatives of the three forms are in several respects at variance with one another the three nominal species must tentatively be considered distinct.