Atlas of Crustacean Larvae

18. Facetotecta

18 general: The Facetotecta (or enigmatic y-larvae) have been found in the plankton in many seas. Adult stages of the facetotectans are still unknown in situ. Their larval development consists of at least five naupliar instars and a cypridoid (y-cypris) larva (Itô 1990; Grygier 1996; Kolbasov and Høeg 2003). The naupliar head shield and the carapace of the y-cyprid have a surface pattern of reticulated cuticular ridges, forming plates. Itô (1985) proposed the new genus Hansenocaris for his 3 new species, described on the basis of their respective y-cyprids. Currently, the facetotectans encompass 7 species, established on the basis of y-cypris morphology and assigned to a single genus, Hansenocaris (Itô 1990; Kolbasov et al. 2007), but their number will have to be very significantly extended (Glenner et al. 2008). An additional 4 species of Hansenocaris were described on the basis of naupliar stages (Belmonte 2005), but these are dubious, because they were not established on a full naupliar series (five instars), and the corresponding (following) y-cyprids are unknown. The y-cyprid metamorphoses into a slug-like stage, called the ypsigon (Glenner et al. 2008). The morphology of both the y-cyprid and the ypsigon strongly indicates that adult stages are advanced parasites in still-to-be-identified hosts. The life cycle includes at least five free-swimming naupliar stages, a y-cypris larva, and a slug-like ypsigon that is probably a juvenile . Larval stages are free living; adults are unknown and are probably parasites. larval types Nauplius and Y-Cypris: Only lecithotrophic forms have been reared through all stages. The nauplius stage is called a y-nauplius. The y-nauplii (fig. 18.1) are planktotrophic or lecithotrophic . All stages are semitransparent, with a pigmented nauplius eye and, in feeding forms, a brownish gut colored by food particles (fig. 18.1A–D). The y-cyprid is always nonfeeding . Its carapace is univalved and does not cover the whole body of the larva (fig. 18.2). The y-cyprid is the last larval stage and probably serves for infestation of a host. morphology Y-Nauplius: The naupliar body consists of a cephalic anterior part, covered by the head shield, and a posteriorly projecting hindbody (fig. 18.1F, J, M–O). Cuticular ridges divide the head shield and hindbody into numerous dorsal polygonal plates, which are all arranged in a symmetrical pattern (fig. 18.1I–L). Some dorsal plates of the head shield have symmetrical pores and setae (fig. 18.1L). The dorsocaudal organ (fig. 18.1L), which has a round knob shape, lies posteriorly on the dorsal side of the hindbody. The hindbody terminates in a conspicuous spine, and a pair of smaller ventral spines represents the furcal rudiment (fig. 18.1F, N, O). A pair of pores projects a little anteriorly to the labrum (fig. 18.1E). The prominent labrum consists of a big proximal rounded part and a smaller distal elongated part (fig. 18.1E, H, G, M, N). Three pairs of naupliar appendages surround the labrum (fig. 18.1E, F, H, N, O). The uniramous antennules consist of a basal portion, with several circular annulations, and an elongated distal portion that bears setae. The biramous antennae and mandibles bear setae and gnathobases on the inner margins. The area behind the mandibles may bear the setiform maxillulary rudiments, and more posteriorly the ventral surface is ornamented by several closely spaced, quite prominent ridges armed with minute denticles (fig. 18.1M–O). Y-Cypris: The y-cyprid has a univalved carapace that only partially covers the larval body (fig. 18.2A–E). The carapace resembles an inverted boat, but with elongated sharp posterior ends (fig. 18.2A, B). Long longitudinal cuticular ridges may ornament the carapace (fig. 18.2A–E), and its surface also bears numerous pores, forming a symmetrical pattern (fig. 18.2D, E). Five pairs of lattice organs (without a pore field) are grouped around big unpaired anterior (lattice organs 1 and 2) and posterior (lattice organs 3–5) pores (fig. 18.2E). Paired compound eyes lie anteriorly in the body (fig. 18.2A). A complex of structures—including the antennules, labrum, paraocular processes, post-ocular filamentary tufts, and two pairs of rudiments of antennae and mandibles—is situated ventrally Jens T. Høeg Benny K. K. Chan Gregory A. Kolbasov Mark J. Grygier Jens T. Høeg, Benny K. K. Chan, Gregory A. Kolbasov, and Mark J. Grygier Facetotecta Facetotecta 101 under the compound eyes (fig. 18.2C, F). The...