STUDIES ON THE WESTERN ATLANTIC ARROW STENORHYNCH0US ( BRACHYURA, MAJIDAE) I. LARVAL CHARACTERS OF TWO AND COMPARISON WITH OTHER LARVAE OF INACHINAE 1) BY

WON TACK YANG School of Marine and Atmospheric Science,University of Miami, Florida, U.S.A.

ABSTRACT

The larvae of two populations, presumably both belonging to the western Atlantic majid crab, seticornis (Herbst) were reared in the laboratory, and described and illustrated. Larvae obtained from the shallow water population differ from the larvae obtained from the deep water population. The marked larval character differences suggest that there are two species involved in the present nominal species of "". The larval characters of Stenorhynchus are discussed and compared with those of other members of the subfamily Inachinae.

INTRODUCTION

The of the Atlantic populations of the majid "arrow " Stenorhyn- chus has been confused and controversial for over a century. Rathbun ( 1925 ) stabilized the taxonomy of this genus by selecting Stenorhynchus seticornis (Herbst, 1788) as the type species and synonymizing all other Atlantic species within it. As a result of her synonymy, S. Jeticonzis would appear to have both a wide geographic and vertical distribution. The present study of characters of laboratory reared larvae suggests that the western Atlantic populations are composed of two distinct species; a shallow water form herein referred to S. JeticoJ'llis and a deep water form known, for the time being, as Stenol'h)'nchlls sp. The larvae of several European crabs have been described in the genus Stenorhyiichus. Stuxberg ( 1874) described the zoea of what he indicated as Stenorhynchu.v rOJtratUJ (Linn6), but did not illustrate it. Cano ( 1893 ) in his Oxyrhyncha development study illustrated the zoeae and megalopae of "Stenorhyn- chums phalängium" ( Fabr. ) . The larvae described and illustrated by Cano and referred to Stenorhynchtls have completely different features from the larvae of true Steno??h y?achar.ras described in the present paper. Lo Bianco ( 1901 ) illustrated a megalopa attributed to S. phä!cmgi1l1n. Lebour ( 1927 ), Gurney ( 1938 ) and

1) Contribution from the Rosenstiel School of Marine and Atmospheric Science, University of Miami. This work was supported by Public Health Research Grant GM-11244. 158

Bourdillon-Casanova (1960) showed that all these Stenorhynchu.r records are probably based on rostrata (L. ) . The present work deals with the complete larval development to the first crab stage, of S. seticornis, and the first zoeal stage of Stenorh)'nchllJ sp. In addition, the larvae of these two species of Stenorh)'nchtls are compared with the larvae of other genera of the Inachinae. The characters of the adult form show marked differences and the nomenclature and systematic status of adult populations in the western Atlantic will be dealt with in the second part of the present series. The author is grateful to Drs. L. B. Holthuis, A. J. Provenzano, Jr., and Gilbert L. Voss for their advice and encouragement during the course of this study. Dr. Patsy McLaughlin kindly helped in final revision of the manuscript.

MATERIALSAND METHODS

The ovigerous females of the shallow water Stenorhpachu?? seticornis studied here were collected from Bear Cut, Biscayne Bay, Florida during 1962-1966. The habitat depth was usually less than 2 meters, and females were kept in running sea-water aquaria until the larvae hatched. Larvae were reared at room tempera- ture ( 17°-29° C) in individual compartments of plastic tackle boxes in approxi- mately 50 ml of filtered seawater from Biscayne Bay. The salinity of the bay water used ranged between 32 and Newly hatched Artemirt were given as food and the culture water was changed daily. An ovigerous female of Stenorhynchus sp. was collected at R/V "Gerda" station G-624 on June 29, 1965. Because this female was collected from con- siderable depth (gear depth 216-234 meters), it was necessary to conduct the research under refrigeration (7° C). However, within several days after capture this female discarded her eggs. Approximately 30 eggs were collected and placed on shakers in 15 C and 25° C. The eggs in 15 C water failed to hatch but the five eggs in 25° C water hatched into prezoeae. One individual prezoea developed into a well-formed first zoea, the only stage obtained. Additional prezoeae were later obtained from a female from the R/V "Pillsbury" Panama-Colombia cruise in 1966 (Cruise No. 6607, Station P-330) and the prezoeal characters verified. Culture techniques and illustration methods are as reported in earlier works (Yang, 1968-1971). The preserved female of S..reticoryai.r has been deposited in the museum of the School of Marine and Atmospheric Science of the University of Miami (UMML 32-2859). The female of Stenos?hy?achu_r sp. will be deposited in the National Museum of Natural History, Washington, D. C.

DESCRIPTION

Stenorhynchus seticornis (Herbst, 1788) - First Zoea (fig. 1). Size: Carapace length 0.75 mm. The carapace (fig. 1 A-C) has only a dorsal spine; both the rostral and the