11 June 1992 PROC. BIOL. SOC. WASH. 105(2), 1992, pp. 275-298 NAUPLII AND COPEPODIDS OF THE CYCLOPOID COPEPOD DIOITHONA OCULATA (FARRAN, 1913) (OITHONIDAE) FROM A MANGROVE CAY IN BELIZE Frank D. Ferrari and Julie W. Ambler Abstract.—Som\\e^, appendage segments and armament elements of 6 nau- pliar and 6 copepodid stages are described for Dioithona oculata (Farran, 1913) from Belize. Dioithona oculata were cultured on Isochrysis galbana from egg through naupliar stage 5 with some individuals growing as far as copepodid stage 3; copepodid stages were collected from daytime swarms. At 31°C, de- velopment time from 50% Nl to 50% N5 was 3.8 days. New information about morphological development is described for appendage segments and arma- ment elements. Modified setae are present only on copepodids and are found on exopods of the mandible and maxillule, the endopod of swimming leg 4, and on the caudal ramus. The naupliar antennule is 2-segmented and the number of setae on this appendage is reduced from nauplius 6 to copepodid I. Development of ramal segments for swimming legs follows the common pattern for copepods with identical patterns for legs 1 and 2. The pattern of addition of setae and spines is identical for swimming legs 2 and 3. A study of formation homology for swimming leg 3 suggests that new segments form proximally to the distal-most segment of each ramus; new armament elements usually appear first at the proximal edge of the distal-most segment and sub- sequently become incorporated onto the next newly formed segment at the next molt. Oithonid copepods are among the nu- discuss homologies of several appendages merically dominant copepod species in and their armament. many estuarine, coastal, and oceanic eco- Dioithona oculata is a tropical cyclopoid systems (Marshall 1949, Marlowe & Miller copepod with a circumglobal distribution in 1975, Peterson et al. 1979, Lonsdale 1981, neritic areas (Nishida 1985). During the day, Turner & Dagg 1983, Ambler et al. 1985, D. oculata often forms swarms, composed Roman etal. 1985, Paffenhoferet al. 1987). of copepodid stages, in coral reef and man- Some developmental stages of oithonid spe- grove habitats (Emery 1968, Hamner & cies have been described for nine species Cariton 1979, Ueda et al. 1983, Ambler et belonging to Oithona and one species of al. 1991). Along mangrove shores of cays Dioithona (Table 1). No descriptions are off Belize, swarms of D. oculata among available for the remaining oithonid genera, mangrove roots disperse at sunset to open Paroithona and Limnoithona. From our water 3-5 m away, adjacent to shore. Before studies of swarms of D. oculata, we describe dawn the copepodids move back under the changes in the exoskeletal morphology for mangroves to form swarms during the day all naupliar and copepodid stages, present (Ambler et al. 1991). Females produce egg molting rates for naupliar stages, compare sacs at night, and approximately 24 hours our findings to developmental information later, nauplii hatch to join the plankton in known for other cyclopoid copepods, and the water adjacent to the mangroves (Am- \ 276 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Table 1.—Sources of information about develop- Table 1.—Continued. ment of cyclopod copepods. Notodelphyidae Oithonidae Doroixys uncinata Canu(1892) Dioithona rigida Ramamohana Rao (1958) Doropygus seclusus Dudley (1966) [as Oithona] Nolodelphys affinis Dudley (1966) Oithona atlantica Gibbons & Ogilvie (1933) Pachypygus gibber Hipeau-Jacquotte (1978) [as O. spiniroslris] Pygodelphys aquitonaris Dudley (1966) O. brevicornis Goswami (1975) Scolecodes huntsmani Dudley (1966) O. davisae Uchima(1979)[asa brevicornis] O. nana Haq(1965) [as Oilhoni- na] bier et al. 1990). Nauplii remain in the O. nana Murphy (1923) O. oligohalina Fonseca & Almeida Pra- plankton until they molt to the first cope- do(1979) podid stage (CI); CI's migrate horizontally O. ovalis Fanta(1976) to swarms among mangrove roots. Two O. similis Gibbons & Ogilvie (1933) other oithonid species are present with D. [as O. helgolandica] oculata in the plankton at night. O.fonsecae O. hebesl Goswami (1975) [O. hebes is neotropical] is found in tropical Atlantic lagoonal waters (Ferrari & Bowman 1980), and O. nana has Ascidicolidae a tropical oceanic and nearshore distribu- Ascidicola rosea Illg& Dudley (1980) Enterocola fulgens Canu(1892) tion (Nishida 1985). E. ferlilis Illg& Dudley (1980) E. laliceps Illg& Dudley (1980) Methods Enteropsis capilulatus Illg& Dudley (1980) Haplosaccus elongatus Ooishi (1980) Copepodid stages of Z). oculata were sort- Haplostoma alhicatum Ooishi(1980) ed from preserved swarm samples collected Haplostomella distincta Ooishi (1980) at Twin Cays, Belize (le^SO'N, SS'OS'W), H. oceanica Ooishi (1980) in May 1985, June 1988, and July 1990. Zanclopus cephalodisci Caiman (1908) Nauplii were cultured from eggs hatched Cyclopidae from dropped egg sacs of females isolated Acanthacyctops viridus Lucks (1927) [as Cyclops] from swarm samples collected in February Allocyclops sihaticus Rocha & Bjomberg [in litt.] and May 1989. Nauplii were kept in several Apocyclops dengizicus Valderhaug & Kewalra- 500 ml (February) or 50 ml (May) beakers mani (1979) of ambient seawater which were suspended Bryocyclops caroti Bjornberg(1984) with a styrofoam float in a water-bath cool- Cyclops sirenuus Gumey(1932) er, and fed a chrysomonad, Isochrysis gal- Diacyclops bicuspidatus Amores-Serrano (1978) [as Cyclops] bana. Temperatures varied from 20-25''C Ectocyclops rubescens Carvallio(1971) in February and 30-31°C in May. In Feb- Eucyclops serrulatus Auvray & Dussart (1966) ruary, 12-80 nauplii from several beakers Graeteriella unisetigera Lescher-Moutoue (1973) were collected daily; during May, 30-70 Halicyclops negleclus Candeias(1966) nauplii were collected from a 50 ml beaker Macrocyclops albidus Defaye(1984) Mesocyclops edax Amores-Serrano (1978) in 8-12 hr intervals. Specimens were fixed Speocyclops racovitzai Lescher-Moutoue (1966) with 2.0% formaldehyde, preserved in 0.5% Cyclopinidae propylene phenoxytol/4.5% proplylene gly- Cyclopina tongifera Goswami (1977) col/95.0% water, cleared in steps through 50.0% lactic acid/50.0% water to 100% lac- Lemaeidae tic acid, and stained by adding a solution Lamprogtena chinensis Kuang(1962) Lernaea cyprinacea Grabda(1963) of chlorazol black E dissolved in 70.0% eth- anol/30.0% water. VOLUME 105, NUMBER 2 277 Table 2. —Development of Dioithona oculata nauplii reared in laboratory from May 18, 1989 experiment. Time from egg hatching to 50% of stage i (T50), instar duration (T), coefficient of determination (R2) for linear regression of angular transformed percent stage versus time. In parentheses is probability of rejecting Ho: Slope = 0, Slope, and Intercept, n = number of points in regression. Stage n Ts„ (hours) T (hours) R' Slope Inlercepl Nl 4 24.00 10.93 0.959 0.225 -4.62 (0.0206) N2 3 34.93 34.89 1.000 0.125 -3.57 (0.0105) N3 8 69.82 25.00 0.901 0.0274 -1.13 (0.0003) N4 8 94.82 21.22 0.744 0.0250 -1.59 (0.0059) N5 8 116.04 0.767 0.0167 -1.15 " (0.0043) Depending upon their availability, up to the percent molted to the next stage, was 30 specimens of each stage were measured used to meet the assumption of constant to determine body length; caudal rami were variance. Time was calculated from time included in body length measurements of zero (May 18, 0400) when females produce copepodids. From 3 to 10 specimens of each egg sacs (see Ambler et al. 1990). stage were dissected; the number depended Naupliar stages are abbreviated Nl to N6; upon the degree of difficulty in determining copepodid stages CI to CVI; male = m, fe- structural morphology or variability of an male = f Appendages are A1 = antennule; appendage. Results consist of brief descrip- A2 = antenna; Mn = mandible; Mxl = tions of changes in each appendage for each maxillule; Mx2 = maxilla; Mxp = maxil- developmental stage. The ventral view of liped; swimming legs = legs 1^; posterior nauplii or lateral view of copepodids are to these are two simple appendages = legs shown for each developmental stage, and 5 and 6; caudal ramus = CR. Appendage the appropriate appendages are illustrated. segments are named following Boxshall Descriptions of appendage segments or their (1985) with exopods = Re; endopods = Ri; armament elements are not repeated if they medial lobes of a segment = li. Armament have not changed from the previous stage. elements of appendages are spines and setae Dense setules on a seta or spine are indi- which are distinguished by apparent degree cated in illustrations only over a short sec- of flexibility (Dudley 1966); medial, ter- tion of a seta and are not repeated for similar minal and lateral elements are si, st and se. elements. Homology of appendages, their segments Developmental times for naupliar stages and elements in different developmental were determined from the experiment start- stages usually was established by position ed on May 18, 1989. The time when 50% and occasionally by morphology. For a few of the nauplii had molted to a particular appendages, homology by formation was stage was determined from linear regression determined if the developing appendage or of the angular transformation (Sokal & Rohlf element of a succeeding stage was visible 1969) of percent stage as a function of time. within the skeleton of the preceding stage. Developmental times were calculated as a difference of times between two successive Results stages for 50% of the specimens to molt. The angular transformation for each stage, For experiments in February and May which is the arcsine of the square root of 1989, D. oculata was reared from Nl 278 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Table 3. —Length range (mm), number of somites or pairs. CI CR (Fig. 4B) length 1.6 x width, complexes [two or more fused somites] (S + C), ap- I lateral, 1 dorsal, 4 terminal setae; medial- pendage buds and number of swimming legs (SI) on most terminal seta with thick base and re- stages of Dioilhona oculaia.