Atlas of Crustacean Larvae

48. Caridea

general: Carideans are commonly called shrimps or prawns (as are dendrobranchiates). They are the largest group of the shrimp-like Decapoda, with an estimated 3,438 extant species, partitioned among 389 genera, 36 families, and 16 superfamilies (Holthuis 1993; Bracken et al. 2009a; De Grave et al. 2009; Fransen and De Grave 2009; De Grave and Fransen 2011). Carideans differ from dendrobranchiate shrimps in various characters: the pleuron of the second abdominal somite overlaps those of the first and the third somites; the first pereopods are usually chelate, the second pereopods are always chelate, and the third pereopods are never chelate; the gill structure is lamellar (phyllobranch); and the fertilized eggs are incubated by the female and remain attached to the pleopods. Caridean shrimps occur in all aquatic habitats on the planet, from the deep sea (including hydrothermal vents) to shallow tropical and subtropical marine waters and freshwater systems. Species of the genus Merguia (Hippolytidae) are even considered semiterrestrial (Abele 1970; S. Gilchrist et al. 1983). Freshwater caridean shrimps account for approximately one quarter of all described Caridea (De Grave et al. 2008). Among freshwater families, the two most speciose are the nearly exclusively freshwater Atyidae and the Palaemonidae, which also have brackish water and marine representatives (De Grave et al. 2008). The majority of caridean shrimps are free living, but they commonly establish associations with other organisms (Bauer 2004). The life cycle consists of a zoea, a decapodid (not always clearly distinguishable), a juvenile, and an adult phase. Larval stages are free living, except for the zoeae and decapodid of the genus Dugastella (Cuesta et al. 2006; Huguet et al. 2011). larval types Zoea: Caridean shrimps are characterized by a series of planktonic shrimp-like larval stages, each of which is called a zoea. The number of zoeal stages can be as few as 1 or 2 (e.g., many freshwater Palaemonidae and Atyidae) or as many as 11 (e.g., the Rhynchocinetidae) or 13 (e.g., the Pandalidae). These stages are often designated ZI, ZII, ZIII, and so forth. The number of zoeal stages can also vary within a species, due to environmental characteristics. Decapodid: The post-zoeal stage (usually called a decapodid ) is very similar to the juvenile stages, with setose natatory pleopods on the abdominal somites. Decapodids show a general resemblance to the adult, although some larval characters are retained. The transition between the zoeal and decapodid phase is a gradual morphological change, and thus is not truly metamorphic. Post-Larva: The post-larva is a decapodid in which the zoeal pereopodal exopods are reduced. In the juvenile, they are lost completely (Anger 2001). morphology Zoea: While there is no concise definition that would apply to the whole group, several characters are generally applicable (Gurney 1942; D. Williamson 1982a; Haynes 1985). The carapace has a rostrum or rostral spine that is directed forward (although it may be absent), is styliform, and usually does not have teeth or spines in ZI. The presence or absence of certain spines on the carapace is useful for distinguishing among families and for identifying one or more stages (fig. 48.1C). All zoeae have a pair of compound eyes, which are almost always sessile in the first stage and stalked in subsequent stages (with the peduncle having a variable relative length); a nauplius eye is never seen. In early zoeal stages, the antennules have an unsegmented peduncle that later becomes three-segmented. The antennae are biramous, the antennal exopods (scaphocerites) are usually segmented in ZI, and the unsegmented endopods bear one long apical seta (fig. 48.1G). This seta may be fused with the endopod to form a long spine; there may also be a small spine or another seta. The mandibles are usually asymmetrical and possess an incisor, a molar region, and a lacinia mobilis. The maxillules always have coxal and basial endites and an endopod; reduced exopods are present in some species (fig. 48.1I). The maxillae always have coxal and basial endites, 48 Guillermo Guerao José A. Cuesta Guillermo Guerao and José A. Cuesta Caridea Caridea 251 an endopod, and an exopod (the scaphognathite) (fig. 48.1 J). Three pairs of maxillipeds are functional upon hatching. The maxillipeds are biramous and bear natatory setae on the exopods . Maxillipeds 2 and 3 have an endopod that is longer than that of maxilliped 1 (fig. 48.1K–M); the number of natatory setae on the exopod of each maxilliped is helpful for distinguishing zoea I of different shrimp species at...