Nematocysts of stages in the life cycle of Stomolophus meleagris, with keys to scyphistomae and ephyrae of some western Atlantic Scyphozoa DALE R. CALDER Department of Invertebrate Zoology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ont., Canada M5S 2C6 Received July 28, 1982 CALDER, D. R. 1983. Nematocysts of stages in the life cycle of Stomolophus rneleagris, with keys to scyphistomae and ephyrae of some western Atlantic Scyphozoa. Can. J. Zool. 61: 1185-1 192. Nematocysts were examined in the planula, scyphistoma, ephyra, and medusa stages of the rhizostome scyphozoan Stomolophus meleagris from South Carolina, U. S . A. Two categories of nematocysts , holotrichous isorhizas and heterotrichous microbasic euryteles, were present in all four stages. Holotrichous isorhizas were of one morphological type (a-isorhizas) in the planula, ephyra, and medusa, and two types (a-isorhizas and a-isorhizas) in the scyphistoma. Several distinct varieties of heterotrichous microbasic euryteles were observed. Those of the planula were all small (5.7-7.0 X 3.9-4.8 pm), those of the scyphistoma and ephyra were either small (5.7-8.4 X 3.8-5.9 pm) or medium (7.5-9.8 x 6.0-7.6 pm), and those of the medusa were small (6.4-10.1 x 4.5-6.5 pm), medium-large (10.5-12.6 x 7.3-9.Opm), or large (13.2-17.8 x 8.0- 10.3 pm). The cnidom is compared with that of other scyphozoans, and identification keys to the scyphistomae and ephyrae of temperate western Atlantic semaeostome and rhizostome Scyphozoa are presented. CALDER, D. R. 1983. Nematocysts of stages in the life cycle of Stomolophus meleagris, with keys to scyphistomae and ephyrae of some western Atlantic Scyphozoa. Can. J. Zool. 61: 1185- 1192. Les nCmatocystes ont Cti examines chez les stad~s planula, scyphistome, iphyrule et miduse du scyphozoaire rhizostomien Stomolophus meleagris de Caroline du Sud aux Etats-Unis. Deux types de nimatocystes, des isorhizes holotriches et des eurytkles microbasiques hCtCrotriches se retrouvent chez les quatre stades. Les isorhizes holotriches sont d'un seul type (a-isorhize) chez la lame planula, 1'Cphyrule et la meduse et de deux types (a-isorhize et a-isorhize) chez le scyphistome. Plusieurs variCtCs distinctes d'eurytkles microbasiques hitirotriches ont CtC observies: les eurytkles de la planula sont tous de petite taille (5,7-7,O X 3,9-4,8 pm), ceux du scyphistome et de l'ephyrule sont petits (5,7-8,4 x 3,8-5,9 pm) ou moyens (7,5-9,8 X 6,O-7,6 pm) et ceux de la mCduse sont petits (6,4- 10,l X 4,5-6,5 pm), moyennement gros (10,5- 12,6 X 7,3-9,O pm) ou gros (13,2-17,8 x 8,O-10,3 pm). Le cnidome de cette esp?ce est comparC a celui d'autres scyphozoaires; on trouvera ici une clC d'identification des scyphistomes et des Cphyrules des scyphozoaires ~Crniostomiens et rhizostomiens de 1'Atlantique Ouest . [Traduit par le journal] Introduction Nematocysts, characteristic of the phylum Cnidaria, are remarkably complex intracellular secretion products (Mariscal 1974) consisting of a coiled tube within a double-walled capsule. Based largely on the morphol- ogy of the discharged tube, over 25 categories of nematocysts have been recognized (Weill 1934a, 1934b;Mariscal 1974). Over half of these categories are restricted to the class Hydrozoa and only three, holotrichous isorhizas, heterotrichous anisorhizas, and heterotrichous microbasic euryteles, have been observed in the class Scyphozoa (Calder 1974). None of these three is unique to scyphozoans. Nematocyst differences were even found from one stage to another in the life history' of many species, particularly between the divergent pol ypoid and medusoid forms. However, the cnidom was typically constant for a given stage of a species. The nematocyst complement has not been docu- mented for the majority of cnidarian species, despite its potential systematic value. This investigation was undertaken to characterize the cnidom of the planula, scyphistoma, ephyra, and medusa stages of Stomol- ophus meleagris, one of the most common scyphozoans along the southeastern and Gulf coasts of the United States (Calder 1982). The value and limitations-of nematocysts in cnidarian Materials and methods systematics were discussed in detail by Weill (1934a, 19346). ~~~~d on a comprehensive study of more than Nematocysts were examined in formalin-preserved plan- ulae, scyphistomae, newly liberated ephyrae, and mature loo species' Weill found that groups recognized. as medusae of Stomolophus meleagris. Medusae were collected distinct on the basis of anatomical and embryological a5 km of the entrance of Murrells Inlet, South evidence were likewise distinct in their nematocyst carolina, U . ~ . ~ . , on 15 luly 1981. planulae, scyphistomae, ~haracteristics- Yet, Weill found that genera and and ephyrae were obtained from laboratory cultures sometimes species could often be distinguished by established by isolating planulae from these medusae (Calder differences in the nematocyst complement or cnidom. 1982). Additional planulae were obtained from medusae of S.