Atlas of Crustacean Larvae

32. Fossil Malacostracan Larvae

32 general: Mesozoic limestones—especially the Jurassic lithographic limestones of southern Germany (including the well-known Solnhofen deposits), but also the Cretaceous limestones of Lebanon and Brazil—are the only fossil lagerstätten that have yielded fossil malacostracan larvae to date. In the Solnhofen lithographic limestones, fossil palinurid larvae are extremely abundant and are known from thousands of specimens ; stomatopod larvae are also known from the Solnhofen deposits. larval types Phyllosoma Larvae: Larvae of the Achelata (phyllosoma larvae ; see chapter 51) are the most common among the fossil malacostracan larvae. This is quite astonishing, as these larvae appear to be very fragile. From the lithographic limestones of southern Germany, five different types of phyllosoma larvae can be distinguished. Type A (†Phalangites priscus; fig. 32.1E) is known from seven successive stages (Polz 1972), and type B (†Palpipes cursor; fig. 32.1D) is known from eight stages (Polz 1973). These two larval types are known from thousands of specimens and are most likely the early developmental stages of the 2 co-occurring species of †Palinurina: †P. longipes, and †P. tenera (Polz 1987; J. Haug et al. 2011b). Larva type C (†”Dolichopus ” tener; fig. 32.1A–C) is much rarer, but here, too, several successive instars can be identified (Polz 1987). Type C could represent the larval stage of the supposed scyllarid †Cancrinos claviger (Polz 1996; J. Haug et al. 2009a, 2011b). Larva type D was described from a single specimen (Polz 1995), but comparable specimens are present in different collections (fig. 32.1F, G; pers. obs.). A description of a fifth type of phyllosoma larva was based on a single ill-preserved specimen and might be a representative of Scyllaridae sensu stricto (J. Haug et al. 2009a). Additionally, puerulus stages (the megalopa/decapodid of the Palinurida) are expected to be present in the Solnhofen lithographic limestones (Polz 1995), but they have not been identified as such with certainty. The lithographic limestones from Lebanon are similar to those of southern Germany in many of their faunal components . Therefore it was not surprising that in 2009 the first phyllosoma larva from these deposits was reported (Pasini and Garassino 2009). In addition, these authors pointed out that more specimens are present in other collections, an observation that we can confirm (a second specimen was depicted by J. Haug et al. 2011b). Isolated stalked compound eyes in a phosphatic Orstentype preservation from limestone concretions from the Cretaceous Santana Formation of Brazil were described by G. Tanaka et al. (2009). These were also interpreted as fragments of phyllosoma larvae. Zoea and Decapodid Larvae: Other fossil decapod larvae are extremely rare. Two specimens from the Santana Formation represent the only definitive fossil report of crab zoea larvae (Maisey and de Carvalho 1995). Fragmentary specimens from the Solnhofen lithographic limestones may also represent decapod zoea larvae (fig. 32.2K; J. Haug et al. 2011b), but their systematic affinities remain uncertain until better-preserved specimens are found. Possible megalopa/decapodid stages of the eryonid †Cycleryon propinquus may be represented by specimens that are usually identified as †”Knebelia schuberti” (Garassino and Schweigert 2006; J. Haug et al. 2011b). Stomatopod Larvae: In addition to decapod larvae, larval stages of the Stomatopoda were found in the Solnhofen lithographic limestones. A large larva, possibly representing a new species, was reported by J. Haug et al. (2008) as the first definitive fossil stomatopod larva (fig. 32.2A–C). Two different larval stages of another stomatopod, †Spinosculda ehrlichi, are known (fig. 32.2D–I) (J. Haug et al. 2009b, 2010c). A small, rather poorly preserved specimen might be a larva of †Sculda pennata, the most common stomatopod in the Solnhofen deposits (fig. 32.2J; J. Haug et al. 2010c). morphology: Only certain morphological aspects will be explained in this section, as the Mesozoic larvae are very similar to their extant relatives in their general morphology. Joachim T. Haug Shane Ahyong Carolin Haug Joachim T. Haug, Shane Ahyong, and Carolin Haug Fossil Malacostracan Larvae Fossil Malacostracan Larvae 177 Phyllosoma Larvae: In the phyllosoma larvae, the antennules , antennae, and eyes are often preserved in their far anterior position (fig. 32.1A). The head shield, however, is usually not preserved, probably because most of these fossils are exuviae (but see the reconstruction in fig. 32.1C, based on a larva with a preserved shield). The phyllosoma larvae in general possess a very small pleon, except for larva D, which has a quite large pleon (fig. 32.1F). The fossil eyes of supposed phyllosoma larvae from the Santana Formation...