Fabia Dana 1851

Fabia Dana, 1851

Type species. Fabia subquadrata Dana, 1851, by monotypy. Gender feminine.

Diagnosis. Female (after Campos 1996). Carapace widening posteriorly, broader than long, with 2 longitudinal sulci arising from upper margin of orbit, extending as far as gastric region. Third maxilliped obliquely placed on buccal cavity; ischium, merus indistinguishably fused; palp slender, 3 articles; propodus subtrapezoidal, subequal to or longer than carpus; dactylus digitiform, sublunated, inserting in angular notch placed in middle third on inner margin of propodus; exopod slender 2-segmented flagellum. Abdomen with 6 somites, telson well separated.

Male (after Campos 1996). Carapace dorsally convex, surface smooth shiny, porcelain-like. Anterolateral carapace margin with fringe of setae extending to hepatic region; longitudinal sulci present, ill-defined or absent in some cases. Third maxilliped similar to female. Abdomen with 2 or more somites fused, demarcation line sometimes visible.

Distribution. Western Atlantic: Florida, USA to Mar de Plata, Argentina; Eastern Pacific; Alaska, U.S.A. to Magdalena Bay, Baja California Sur, Mexico, San Felipe, Baja California (Gulf of California) and Málaga, Colombia (Campos 1996, Campos & Manning 1998).

Hosts (Campos 1996). Mollusca-Bivalva: Arcidae (Anadara Gray, 1847); Carditidae (Cyclocardia Conrad, 1867), Donacidae (Donax Linnaeus, 1758), Glycimeridae (Panopea Ménard, 1807), Hiatellidae (Hiatella Bosc, 1801), Myidae (Crypotomya Conrad, 1849); Mytilidae (Modiolus Lamark, 1799, Mytilus Linnaeus, 1758); Phodalidae (Barnea Risso, 1826, Parapholas Conrad, 1848); Semelidae (Semele Schumacher, 1817) Tellinidae (Tellina Linnaeus, 1758); Veneridae (Leukoma Römer, 1857, Tapes Megerle von Mühlfeld, 1811, Tivela Link, 1807).

Sexual dimorphism of species of Fabia Dana, 1851. The species of Fabia are sexually dimorphic and both sexes are remarkably different in shape and size. Adult males are small (5 mm or less), with a hard, convex and porcelain-like carapace with the antero-lateral margin fringed with setae that extend to the hepatic region, and abdomen with two or more abdominal somites fused, although the suture line is sometimes observed between two fused somites (Figs. 4A, B, E; 5A, C). The most significant difference between the subadult male (pre-hard stage) and the adult males (hard stage) is the absence, in the former phase, of swimming setae on the meri, carpi and propodi of P3–P4, which are long and plumose in the adult phase. The female, like males, undergo a pre-hard and hard stage, but moult through several additional post-hard stages. The external morphology of both sexes is almost identical in the pre-hard and hard stages. Females with a masculine appearance can only be separated from males by the absence of gonopods and the presence of gonopores on thoracic sternite five. Females undergo several key morphological changes during the post-hard stages: the carapace become soft, fragile, with two dorsal sulci on the carapace and absence of traces of setae on its anterolateral margin, the abdomen gradually widens until it almost cover the entire sternal surface of the cephalothorax, and the P2–P5 became slender and feeble, losing the long and plumose swimming setae on P3–P4 (Fig 1; 2A; 3A, B). The P3 of adult females are asymmetrical in length and shape, while male and pre-hard and hard female always have symmetrical P2–P5. Pearse (1966) provided a detailed description of the stages of development of F. subquadrata and detailed remarks of its life history and ontogeny.