Monogenea is a class of ectoparasitic flatworms on the skin, gills, or fins of fish. Microcotylidae is a family of polyopisthocotylean monogeneans parasitising only marine fishes. This work describes and taxonomically determines a microcotylid polyopisthocotylean monogenean in an important fish in Saudi aquaculture.

During the period from January 2014 to the end of July 2014, a total of 21 fishes belongingto two species of the family Ephippidae (Platax teira and P. orbicularis) were captured fromIraqi marine waters, northwest Arab Gulf. The study revealed the existence of one species ofmonogenean, Sprostoniella multitestis from gills of both fish species. The record of S.multitestis in the present study is considered as the first record in the Iraqi territorial waters ofthe Arab Gulf and both P. teira and P. orbicularis are new host records for this parasite in theArab Gulf.

The present study deals with a monogenean parasite infecting, some marine fish through light and scan electron microscopy. It revealed that the percentage of infection was 48% (14 out of 50 fish), 28% (14 out of 50 fish), 22% (11 out of 50 fish) and 16% (8 out of 50 fish) in Diplodus noct, Gerres oyena, Lethrinus elongates and Siganus revulatus, respectively. The present work recorded Paranaella diplodae (Polyopisthocotylea; Microcotylidae; Monogenea) as a new species collected from the investigated fish gills. They are lanculate flukes, the haptor is not distinguished from the body proper approximately 1/3 of the whole body length. The surface topography of the parasite bears small pits and conspicuous transverse folds and richly supplied with papillae-like unicellate sensory ending. The opisthohaptor is typical of Microcotylidae. The clamp structure and the haptoral tegument are similar to the rest of the body

A ultraestrutura da glândula de Mehlis de Metamicrocotyla macracantha, parasita de brânquia coletado de Mugil liza do Rio de Janeiro, Brasil, foi estudado através da microscopia eletrônica de transmissão. A glândula de Mehlis consiste de dois tipos de células secretoras, S1 e S2, cada uma produzindo um corpo secretor diferente. Os corpos S1 são esféricos, em forma de lamelas e observados em diferentes estágios de desenvolvimentos no citoplasma dessas células. Os corpos S2 são esféricos a ovais com conteúdos densos, apresentando uma estrutura cristalina. O citoplasma das células da glândula de Mehlis apresenta também ribossmas livres, retículo endoplasmático granular e complexo de Golgi, organelas características de células secretoras.

The ultrastructure of Mehlis' gland of Metamicrocotyla macracantha, a gill parasite collected from Mugil liza from Rio de Janeiro, Brazil, was studied by transmission electron microscopy. The Mehlis' gland consists of two types of secretory cells, S1 and S2, each producing a different secretory body. The S1 bodies are spherical, lamellae-like and were observed in different stages of development in the cytoplasm of these cells. The S2 bodies are spherical to ovoid with dense content, showing a crystalline structure. The cytoplasm of Mehlis' gland cells contains also free ribosomes, granular endoplasmatic reticulum and Golgi complex, characteristic organelles of secretory cells. | A ultraestrutura da glândula de Mehlis de Metamicrocotyla macracantha, parasita de brânquia coletado de Mugil liza do Rio de Janeiro, Brasil, foi estudado através da microscopia eletrônica de transmissão. A glândula de Mehlis consiste de dois tipos de células secretoras, S1 e S2, cada uma produzindo um corpo secretor diferente. Os corpos S1 são esféricos, em forma de lamelas e observados em diferentes estágios de desenvolvimentos no citoplasma dessas células. Os corpos S2 são esféricos a ovais com conteúdos densos, apresentando uma estrutura cristalina. O citoplasma das células da glândula de Mehlis apresenta também ribossmas livres, retículo endoplasmático granular e complexo de Golgi, organelas características de células secretoras.