THE COMPLETE LARVAL DEVELOPMENT OF THE WEST INDIAN HERMIT CRAB PETROCHIRUS DIOGENES (L.) (DECAPODA, DIOGENIDAE) REARED IN THE LABORATOR yl ANTHONY J. PROVENZANO, JR. Institute of Marine Sciences, University of Miami ABSTRACT The complete zoeal development and the early post-larval development was followed in the laboratory. Description and illustrations of five zoeal stages and the glaucothoe are presented. There may be five or six zoeal stages in the larval development of P. diogenes, the number depending in part upon temperature. The zoeal stages and glaucothoe were compared in detail with those known of other species of diogenid and coenobitid hermit crabs and the systematic significance of a number of morphological features was evaluated. Ridges and grooves on the zoeal carapace of Petrochirus have not been reported for any other hermit larvae and may be unique to the genus, but other zoeal features considered to be "generic" in signifi- cance are shared with Dardanus. The glaucothoe described in a previous paper by this author and attributed to Petrochirus is shown to have been erroneously identified. Starved stage-I larvae were not able to survive to molt at any of five temperatures used, but survival was longer at 20° C than at lower or higher temperatures. At 10° C, and ] 5° C, larvae provided with Artemia nauplii as food were also unable to molt, and died in approximately the same time as starved siblings. At 20° C, 25° C, and 30° C, fed larvae were able to molt and to continue growth. Viable glaucothoes were not obtained at 20° C, but a few specimens reaching the terminal molt died in the process of becoming glaucothoes. At 25° C, glaucothoes were obtained after five and six zoeal stages. At 30° C, nearly all specimens reaching glaucothoe did so after only five zoeal stages. At all temperatures, the first zoeal stage had a longer mean duration than did the stages immediately following, but duration increased again in the last zoeal stages and reached a maximum in the glaucothoe, becoming less again at the crab stages. Explanations for these differences are offered. Total duration of the zoeal phase of development was approximately 50 days at 20° C and approximately 25 days at the higher temperatures used. Since the glaucothoe also is planktonic for much of its existence, the total potential planktonic life of this species may vary from 31-43 days at 30°, 37-50 days at 25°, and 72-84 days at 20" C. INTRODUCTION The last decade has seen a sudden increase in laboratory studies on the larval development of decapod crustaceans, and more information 1 Contribution No. 867 from the Institute of Marine Sciences, University of Miami. This work was supported by grant No. GB-4305 from the National Science Foundation and grant No. GM-1I244 from the Institute of General Medical Sciences, U. S. Department of Health, Education and Welfare. 144 Bulletin of Marine Science [18(1) concerning the development of hermit crabs has been gathered during this period than in all the years preceding. The tropical western Atlantic contains a relatively rich pagurid fauna, the two major families, Diogenidae and Paguridae, being represented by well over 100 species, at least 10 per cent of which are still undescribed (Provenzano, unpublished data). Until 1962, no larval histories were known for any of the tropical western Atlantic hermit crabs and very few in other parts of the world had been studied. The tropical hermit crab family Diogenidae is represented in the western Atlantic by about 40 species. The only descriptions of known diogenid larvae and glaucothoes of this faunal region published as of the present writing are those for Calcinus tibicen (all stages, Provenzano, 1962a), Paguristes sericeus (all stages, Rice & Provenzano, 1965), and the glau- cothoes of Dardanus venosus and D. insignis (Provenzano, 1963a, 1963b). Additional species of western Atlantic diogenids (Clibanarius, three species; Calcinus verrilli; Cancellus spongicola; Dardanus venosus and six species of Paguristes) have been reared at this laboratory but the results are not yet ready for publication. The genus Petrochirus is composed of only three Recent species, P. pustulatus (H. Milne-Edwards, 1848), which occurs off West Africa, P. californiensis Bouvier, 1895, from the tropical eastern Pacific faunal region, and P. diogenes (L.) of the western Atlantic. The West African species is much less similar to the American forms than the latter are to each other. Toula (1911) described a fossil pagurid which he referred to the Recent West Indian species of Petrochirus, but Rathbun (1918), noting that it appeared to have the right chela of P. californiensis and the left chela of P. bahamensis (= P. diogenes), considered Toula's form as a distinct species, possibly ancestral to the Recent American forms. No larval forms of this genus have been described previously, although Provenzano (1963b) attributed specimens of a large glaucothoe to Pet- rochirus diogenes, erroneously, as is now evident (see discussion which follows). Petrochirus diogenes (L.), the correct name of which was established by Holthuis (1959: 151-152) is known from Cape Hatteras, North Car- olina (Williams, 1965) south through the West Indies (including even the northern Gulf of Mexico [Hulings, 1961; Pounds, 1961]) to southern Brazil (Alves Coelho, 1964). Its large size and frequent occurrence in Queen Conch shells (Strombus gigas) make it a conspicuous element of the shallow-water fauna of this region. The purpose of the present paper is to present an account of the complete lOeal development and the glaucothoe of Petrochirus diogenes as discovered from laboratory rearings, to summarize the morphological features of the 1968] Provenzano: Larval Development of Petrochirus 145 zoeae and glaucothoes of the Diogenidae as presently known, and to make available some limited ecological data derived from the rearing experiments. ACKNOWLEDGMENTS The female hermit crab which yielded the larvae described herein was coUected by the RjV HERNANCORTEZ,research vessel of the Florida State Board of Conservation, Division of Salt Water Fisheries. I am indebted to the staff of the State Board of Conservation Marine Laboratory at St. Petersburg, especially to Mr. William G. Lyons, and to the crew of the HERNANCORTEZfor their efforts to obtain this specimen for me and for keeping it alive after capture until it could be transferred to Miami. The success of the rearing experiments was largely due to the special efforts of C. Edith Marks who took care of the larvae daily from the time of hatching through metamorphosis, assisted at times by Mr. Talbot Mur- ray and Mr. Koesoebiono. I am especially grateful to Miss Barbara Stolen who did the necessary dissections and made all the illustrations. The financial support for the work came from research grant No. GB-1405 from the National Science Foundation and from grant No. GM-11244 from the National Institutes of Health, U. S. Department of Health, Education and Welfare. METHODS On 2 August, 1966 an ovigerous Petrochirus diogenes (shield length 14 mm, total carapace length 31 mm) was taken in a trawl by the RjV HERNANCORTEZat "hourglass station D" off the west coast of Florida (27°37'N, 83°58'W) at about 55 meters depth (180 feet). The bottom temperature at the station was 210 C. Two days later she was ashore at St. Petersburg in aerated sea water, and after being transported to Miami on 5 August she was placed in running sea water which fluctuated between 29-300 C from that date until hatching, which occurred on 14 August. Eggs examined on 6 August were very early in development with no differentiation of the embryo apparent under 60 X magnification, indicating that the eggs probably were laid not earlier than one or two days im- mediately preceding capture of the female. At the time of hatching, the sea water in the aquarium was at 29° C, and approximately 500 larvae were collected and placed into water of similar temperature. After isolation of the larvae into compartmented trays (as described in prior publications of this author and others) the trays were then placed at various temperatures. Some larvae were kept in mass culture at room temperature. Some isolated larvae were starved to deter- mine survival time at various temperatures, but most others were fed with Artemia nauplii daily or every second day, depending on temperature. All larvae except those at "room temperature" were kept in non-illu- 146 Bulletin of Marine Science [18(1 ) minated, controlled-temperature cabinets (BOD boxes or converted refrig- erators). Hence the larvae were reared essentially in the dark with exposure to normal lighting daily for one to two hours only. Larvae reared at room temperature were subjected to diurnal light variation, but were not permitted to receive direct sunlight. The lowest and most stable temperature used was 10° C, variations being less than plus or minus 0.2° C during the short duration of the experiment. Other larvae were maintained at approximately 5° C intervals which for convenience are hereafter termed 15° C, 20°, 25" and 30° C. In fact the variation at each of these tempera- tures above 10° C was considerable as revealed by recording thermometers. Thus the "15° C" actually varied between 13.5-14.5° C during the rela- tively short duration of that experiment. The "20° C" box varied from 19.5-21.5° C, during the time larvae were kept therein. The "25° C" or room temperature varied most of all, ranging from 27-26° during the first two weeks, dropping to about 25° during the third week. Because of factors not relevant to the experiment, room temperature dropped to about 20-21 ° during the fourth week, then returned to about 25° after the fourth week.