Larvae of two species of Trizocheles (Decapoda: Anomura: Paguroidea: Pylochelidae: Trizochelinae), description of the adult of one, and preliminary implications of development on pylochelid phylogeny Author Mclaughlin, Patsy A. Author Lemaitre, Rafael text Zootaxa 2008 1911 52 68 journal article 10.5281/zenodo.184552 8eb92ccd-80d7-4381-bee3-7616ef59d4b1 1175-5326 184552 Trizocheles vaubanae n. sp. Material examined. 3 specimens , cl (including rostrum) approximately 1.8–2.0 mm (carapaces damaged); two dissected. All specimens hatched from single ovigerous female at time of preservation. Female (sl = 4.2 mm ), EBISCO stn DW 2606, 19º36.0’S , 158º42.0’E , 442–443 m , 18 Oct 2005 (MNHN-Pg 7776). Description. Yolk granules present. Carapace . Globoid, lacking spines and setae, posterior margins rounded; rostrum approximately 0.2 of carapace length, quite slender, directed downward. Eyes . Stalked, corneas large. Antennule ( Fig. 3 a). Biramous; protopod elongate, unsegmented; endopod shorter than exopod, naked; exopod with 2 short terminal setae and 2 or 3 aesthetascs, 1 long aesthetasc on inner margin. Antenna ( Fig. 3 b). Biramous; protopod with spine at endopodal junction and larger spine at scaphocerite junction; endopod overreaching tip of distolateral spine of scaphocerite. Scaphocerite with 7 moderately long setae and 1 very short seta proximally on inner margin, upper margin with 2 or 3 setae; distolateral spine subdistal in origin, prominent, simple, lateral margin with or without small spine-like protuberance at midlength. Mandible ( Fig. 3 c). Subquadrate with large, unsegmented, naked palp. Maxillule ( Fig. 3 d). Bilobed bud. Maxilla ( Fig. 3 e). Well developed, with bilobed coxal and basial endites, endopod and scaphognathite, all lacking setae. First maxilliped ( Fig. 3 f). Protopod unsegmented; exopod unsegmented, elongate, 4 slightly evaginated setae visible distally beneath cuticle; endopod short, unsegmented. Second maxilliped ( Fig. 3 g). Protopod unsegmented; exopod unsegmented, elongate, 4 slightly evaginated setae visible distally beneath cuticle; endopod approximately 0.3 length of exopod, unsegmented. Third maxilliped ( Fig. 3 h). Protopod unsegmented; exopod unsegmented, elongate, naked; endopod slight shorter than exopod, unsegmented, naked. Chelipeds ( Fig. 4 a). Dactyl clearly defined, but still fused to palm, longer than fixed finger; segments all unarmed and lacking setae. Pereopods 2 and 3 ( Fig. 4 b, c). Dactyls short, stout, terminal claws apparent; all segments unarmed and lacking setae. Pereopods 4 and 5 ( Fig. 4 d, e). Dactyls developed but still fused to propodi. Pleon ( Fig. 4 f). Six-segmented, with telson clearly separated; pleomeres 1–4 and 6 unarmed, pleomere 5 with pair of moderately long posterolateral spines; biramous pleopod buds present on pleomeres 2–5; pleomere 6 with biramous uropods, lacking setae. Telson ( Fig. 4 f, g). Moderately long; terminal margin with narrow V-shaped median cleft and 8 + 8 processes, all articulated, 3–8 each with fringe of marginal setae, fourth process longest. FIGURE 3. Metazoea of Trizocheles vaubanae n. sp. a, antennule; b, antenna; c, mandible; d, maxillule; e, maxilla; f, first maxilliped, g, second maxilliped; h, third maxilliped. Scale: 0.25 mm. Remarks. In advanced development, morphological characters appearing in later zoeal stages are shifted backward or compressed into first and second stages. However when compression of morphological features unites with elimination and/or shortening of durations of stages, a highly advanced larva results ( Gore 1985 ). Development in Trizocheles is clearly quite advanced and also lecithotrophic as it is in Pomatocheles and Pylocheles . As previously noted, all of the larvae of Trizocheles are believed to have hatched prematurely as the females were preserved. The variation in development of the appendages seen in the several dissected specimens of T. s. spinosus indicated that the embryos were not all at the same level of development when they hatched. Whether this disparity resulted from differences in initial egg deposition or from irregularities in the embryonic molt cycles among individuals can not be determined from the material available. As the present larval descriptions are based on prematurely hatched specimens, some of the larval differences seen between the two species simply may be variations in developmental levels. However, metazoeae of these two species of Trizocheles are readily distinguished from one another by the structure of the antennae, which is consistent for each species. In T. s. spinosus , the subdistal lateral spine of the scaphocerite is prominently bifid, but it is simple in T. vaubanae n. sp. Although the development of the uropodal endopods was greater in the latter species, both species appeared to be near the end of their embryonic molt cycles and would hatch either as megalopae or in the last zoeal stage before metamorphosis.