33 TANE (1967) 13: 33 - 42 THE EARLY STAGES OF SOME NEW ZEALAND SHORE BARNACLES. by B. A. Foster* INTRODUCTION Barnacle larvae or nauplii are distinguished from the larval stages of other Crustacea by the possession of the peculiar fronto-lateral horns of the carapace. During the life cycle there are six naupliar stages, which are followed by the cypris stage which actively seeks suitable settling sites for permanent attachment and metamorphosis into the adult. Barnacle nauplii are mostly identified for description by rearing them in isolation from the first nauplius stage, which can be readily hatched from the ripe ovigerous lamellae which are the deposited egg masses in the mantle cavity of the parent and there develop to the first nauplius stage within the egg membrane. Difficulty can be experienced in successfully rearing plankton larvae about which very little is known of their environ• mental and food requirements. Some success has been achieved by using plunge-jar systems (Bassindale, 1936) or more sophisticated circulating sea water apparatus (Wisely, 1960). In most cases the nauplii must be fed, usually on cultures of phytoplanktonic algae. There is evidence that there are specific algal preferences for the various species of barnacles (Moyse, 1963). If the optimum of food species can be found then reason• able success in larval development can be achieved, e. g. cyprids of Elminius modestus can be reared from just hatched nauplii in six days on a diet of Skeletonema costatum whereas relatively fewer cyprids can be obtained on a diet of Phaeodactylum closterium in at least ten days. Alternatively, barnacle nauplii may be captured from the plankton and size frequency distributions used to indicate the stages present (e. g. Knight-Jones and Waugh, 1949 ), although such a procedure is of limited use when more than one barnacle species has unknown larvae in the plankton at the same time. The naupliar stages of European barnacles have been described by various authors (Bassindale, 1936; Pyefinch, 1949; Jones and Crisp, 1953; Norris and Crisp, 1953; Moyes, 1961; Crisp, 1962), and preliminary investigations of the life history of seven barnacle species from South Africa have been made by Sandison (1951). The life histories of New Zealand barnacles have received scant attention: Batham (1946) has described the larvae of Pollicipes spinosus, which do not feed, and Knight- Jones and Waugh (1949) have described the stages of Elminius modestus from specimens that have become established in European waters. The larval stages of most New Zealand barnacles still await description. This paper does not describe the life histories, but on the basis of observation of early stage nauplii of seven known species out• lines what may be useful characters for the identification of barnacle 'Department of Zoology, University of Auckland Present Address: Marine Science Laboratories, Henai Bridge, Anglesey, U. K. 34 FIG. 1 Nauplii of Elminius plicatus: I, the first stage nauplius; II, the second stage nauplius; a, the entire nauplius from dorsal and ventral aspects for nauplii I and II respectively; b, the antennule; c, the antenna; d, the mandible; e, the abdominal and caudal process of nauplius II. 35 nauplii from the plankton. THE EARLY NAUPLII When mature ovigerous lamellae are extracted from the adult and placed in fresh sea water the first stage nauplii (nauplii I) readily hatch and become active. The pronounced positive phototaxis of barnacle nauplii conveniently aggregates the nauplii in regions of maximum light intensity, and samples can then be withdrawn and transferred to further containers or preserved. Within a few hours the first moult occurs to yield the second stage nauplii (nauplii II). The requirements for continued growth and moult• ing then become more exacting and no stage III nauplii were obtained. The nauplii were preserved in 70% ethyl alcohol or 5% formalin in sea water, and then examined on a covered glass slide with the aid of a binocular and a compound microscope. Nauplius I The first nauplius (Fig. I) carries three pairs of limbs - the antennules, antennae, and mandibles - all of which have unfeathered setae. The fronto- lateral horns are projected in a latero-posterior direction, and the caudal. appendage is short. The frontal filaments are usually inconspicuous. The first nauplius is a locomotory stage and thought not to feed (Pyefinch, 1949) and moults within a few hours. Interspecific differences of stage I nauplii are hard to find, and no readily ascertainable characters can be suggested. The labrum is nearly always inconspicuous. A size difference occurs (Table I), but the ranges of sizes are not mutually exclusive. Stage I nauplii may make up some temporary part of inshore plankton, but as the moult occurs within a few hours they are probably of less importance in the offshore plankton. Live nauplii could be retained until metamorphosis, when slightly better chances of identification prevail. Table I. Dimensions of stage I nauplii of six barnacle species. Species Carapace width Total length Length/width m. m. m. m. C. brunnea 0. 12 0. 27 2. 25 C. columna 0. 10 0. 23 2. 30 T. purpurascens 0. 15 0. 33 2. 20 E. plicatus 0. 16 0. 35 2. 19 E. modestus Q. 12 0. 25 2. 08 B. vestitus 0. 17 0. 30 1. 76 Nauplius II The second nauplius (Fig. 2) differs from the first stage in its greater size, 36 Balanus vestitus FIG. 2 Outlines of the carapace and labrum of stage II barnacle nauplii; all drawn to the same scale. 37 the more forwardly swept fronto-lateral horns, the sometimes appearance of the frontal filaments, the extension of the caudal spine on the carapace (Fig. 1, He), the pronounced labrum, and the increased setation of the antennules, antennae and mandibles. The limb setae may or may not be feathered. Outline drawings of the stage II nauplii of seven barnacle species are given in Fig. 2. These drawings are from the ventral surfaces and show the shape of the labrum. A number of setation formulae have been devised to summarize the setation characteristics of each limb of each stage of each species (Bassindale, 1936; Jones and Crisp, 1954; and Newman, 1965). However, the procedure of checking the number and nature of the setae of the nauplii from a plankton sample makes such a scheme of little practical value. The setation, which always increases from one stage to the next, is a develop• mental as well as a specific feature, and is useful mainly for separating stages within the species. The nature of the spine armature and relative proportions of the abdominal process of nauplii can be used to separate many of the stages (e. g. Knight- Jones and Waugh, 1949); these characters might be useful for interspecific distinction as well. Sandison (1951) found that "... no one character can be used to determine both species and stage in nauplii. A consideration must be made firstly of the carapace shape, the form of the labrum and of the caudal appendages to indicate the species, and secondly of the size of the nauplius and the setation formula to deter• mine the stage". Table 2. Dimensions of stage II nauplii of seven barnacle species. Species Carapace width Total length Length/width m. m. m. m. C. brunnea 0. 19 0. 35 1. 89 C. columna 0. 17 0. 30 1. 76 T. purpurascens 0. 20 0. 47 2. 37 E. plicatus 0. 20 0. 49 2. 50 E. modestus 0. 15 0. 36 2. 36 B. trigonus 0. 19 0. 37 2. 00 B. vestitus 0. 20 0. 55 2. 75 On consideration of the characters shown in Fig. 2 a distinction can be made between the Chthamalidae (Chamaesipho) and the Balanidae (Balanus, Tetraclita and Elminius). The squarish carapace (with a ratio of total length to carapace width of less than two) and the almost single labrum with two pronounced teeth on the distal border separates the genus Chamaesipho. The presence of the toothed labrum has been demonstrated for Octomeris angulosa and Chthamalus dentata by Sandison (1951) and for Chthamalus stellatus by Bassindale (1936); but neither worker has suggested that this may be a family characteristic. PIG. 3 The percentage of adult barnacle populations at Leigh with mature (shaded) and immature (unshaded) larvae as ovigerous lamellae within the mantle cavity. Samplings arranged in quarter monthly periods. Blocks below the axis indicate populations sampled but no lamellae found. 39 The two species of Chamaesipho are not easily distinguished except on the basis of size, C. brunnea being the larger. This closely parallels the similarity of the adults where the distinction is one of size and a number of minor considerations of mouthparts and cirral setation. Jones and Crisp (1954) distinguish Elminius modestus and Balanus improvisus primarily by the labrum which in the former species "the middle lobe protrudes by a distance greater than one third of its width; this is not true for any other known species of Balanus". Although Jones and Crisp suggest this as a generic characteristic, Elminius plicatus (Fig. 1) does not show a protruding middle lobe of the labrum. The genera Elminius and Tetraclita differ from Balanus by the straighter anterior margin of the carapace and the more forwardly swept fronto-lateral horns. E. modestus may be separated from E. plicatus and T. purpurascens by the protruding middle lobe of the labrum. The carapace of E. plicatus is more of a "thistle" shape than the slender "wine-glass" shape of that of T. purpur• ascens but otherwise these two species are very similar. Both species of Balanus in Fig. 2 show a rounded anterior margin of the carapace, and laterally directed fronto-lateral horns. Bassindale (1936, p. 69) recognized the similarity of the nauplii of the species of Balanus.