Abstract
In this report, I review the taxonomic history, body adaptations, ecology, and reproduction of the infraorders Axiidea (ghost shrimps) and Gebiidea (mud lobsters). Known until recently as the “Thalassinidea,” modern classification divided Axiidea into six families and Gebiidea into five. Ghost shrimps are characterized by having the first and second pereiopod chelate and a soft and delicate body, whereas mud lobsters possess the first pereiopod chelate or subchelate and second pereiopod subchelate or simple with a hard and heavily calcified body. Among the main body adaptations of these organisms are distinguished: (i) carapace laterally compressed, (ii) pleon longer than the cephalothorax in ghost shrimps but usually shorter in mud lobsters, and (iii) anterior feet thrown directly forward. Current accounting of axiideans and gebiideans reaches around 781 and 240 extant species, respectively, with major number of species in Callianassidae and Upogebiidae within of each clade. Male reproductive system involves paired testes linked to the vas deferens that open in gonopores on the ventral coxal segment of the fifth pereiopod. In females, the reproductive system is composed of paired and colored ovaries, one ovary shorter than another, and a pair of short and translucent oviducts linking each ovary to the gonopore, this latter located on the ventral coxal of the third pereiopod. When present in males, the first pleopod is sexually dimorphic. Most ghost shrimps show distinct sexual dimorphism in body size and the major cheliped which become them in a promising group for growth studies. Hypertrophied chelipeds in males are often used to defend galleries against invasion from other shrimps from the same or opposite sex or during the intense male-to-male competition for sexual partners. Knowledge about sexual systems of these species remains limited; however, available information suggests that hermaphroditism might be commonly present in axiideans and gebiideans. Regarding mating systems, all species of ghost shrimp and mud lobster with solitary habits and remarkable sexual dimorphism in the major cheliped are expected to be polygamous. Finally, considerable variability among Axiidea and Gebiidea species in fecundity and egg size may indicate important differences in the reproductive strategy and may also reflect a latitudinal trend as observed in other decapods.
Highlights
The first cladistic analysis of Thalassinidea was conducted by Poore [6]
Males of most ghost shrimps and mud lobsters can be identified by the absence/presence and morphology of the first pleopod
26 species are gonochoristic; 2 males are hermaphrodites, and 10 species present intersexed specimens (Table 3). Considering this information and given that reproductive biology has been studied in only a small proportion of the 781 ghost shrimps and 240 mud lobsters, it can be concluded that hermaphroditism might not be unusual in these organisms
Summary
The term “Thalassinoides” is introduced for the first time into subsection Macrura (reptant) by the zoologist Latreille [1], including in it the genera Gebia Leach, 1816; Thalassina Latreille, 1806; Callianassa Leach, 1814; and Axius Leach, 1815. She stated that infraorder Thalassinidea was the only group of Reptantia impossible to define precisely and so introduced the term (French) “Thalassinacea.” De Saint Laurent [5] argued that in “Thalassinacea,” relationship between the epistome and the carapace varied notably from one family to another, the number of chelate pereopods (sometimes one and sometimes two); an appendix interna was not always present From these observations, she proposed the separation of “Thalassinacea” into infraorders Axiidea and Gebiidea, transferring the families Axiidae and Callianassidae for the former infraorder and Laomediidae; Upogebiidae Borradaile, 1903; and Thalassinidea for the latter infraorder [5]. Taxonomy of old name Thalassinidea follows being very controversial among carcinologists from the “American school” and opinions of Sakai, in what concerns to the correct use of the names Axiidea and Gebiidea versus Callianassidea and Thalassinidea [19, 20]
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