Complete development and comparative morphology of larval Thenus orientalis and Thenus sp. (Decapoda: Scyllaridae) reared in the laboratory

Abstract

Newly hatched phyllosomas of 2 species of Thenus, T. orientalis and Thenus sp., were successfully reared to the juvenile stage under laboratory conditions. Separate cultures of phyllosomas of T. orientalis were fed on 4 food regimes consisting of fresh flesh of Donax brazieri, frozen flesh of D. brazieri, frozen gonad of Perna canaliculus, and nauplii of Artemia. Phyllosomas of Thenus sp. were fed only on fresh flesh of D. brazieri. For rearing both species, water temperature was maintained at 27.0 ± 0.5°C. All phyllosomas of the 2 species of Thenus fed on fresh flesh of D. brazieri developed through 4 phyllosomal instars, equivalent in development to the 4 larval stages of T. orientalis previously described from planktonic material. The morphology of these 2 species of Thenus at the phyllosomal and nisto stages were compared. The mean number of paired exopodal setae on pereiopods and the total body length of the phyllosomas differed between the two species which were fed fresh flesh of D. brazieri. Phyllosomas of T. orientalis fed on frozen food (D. brazieri or P. canaliculus) showed poor survival, prolonged duration of instars, and poor molt increments. Furthermore, approximately 50% of these phyllosomas developed an extra instar (fifth instar) before metamorphosing to the nisto stage. One diagnostic character, the ornamentation of the anterolateral margin of the antennule, was consistent throughout all cultures of both species and identified the larvae of each species. In all instars of T. orientalis, there was a short terminal spine on the anterolateral margin of the antennule, whereas in Thenus sp. a short seta was present in this position. However, no morphological differences were found to distinguish between the nistos of the two species.