Redescription of the rare amphipod crustacean Pseudaeginella montoucheti (Quitete, 1971) from Brazil

Abstract Pseudaeginella montoucheti (Quitete, 1971) is redescribed based on newly collected specimens from red and brown algae and tubiculous polychaete colony that were obtained from shallow waters at Tamboretes Archipelago, Balneário Barra do Sul and Sepultura Beach, Bombinhas, Santa Catarina State, Brazil. Of 10 species of Pseudaeginella so far reported, Pseudaeginella montoucheti is closest to Pseudaeginella sanctipauli Laubitz, 1995, but differs from the latter by having more numerous body spines including ventro-lateral ones over gills on pereonites 3 and 4, and the antenna 1 length measuring half body length. An identification key for Pseudaeginella species and a checklist of Caprellidea occurring along the Brazilian coasts are also presented.

Gnathopod 2 inserted in the pereonite 2 at 2/5 from anterior margin (Fig. 1A); coxa vestigial; basis 1.3 times of pereonite 2 length, with a spiny projection near antero-distal corner; ischium rectangular; merus rounded; carpus triangular and provided with scarce simple setae; propodus oval, ratio between width: length = 0.57, inner margin provided with 1 stout setae proximally, 3 triangular projections medially and distally and numerous setae: few simple setae on the outer margin; dactylus shorter than palm and slightly curved with a row of setulae alongside the inner margin (Fig. 2D).
Abdomen with a pair of lateral lobes and dorsal lobe with a pair of dorsal setae (Fig. 4F).
Intraspecific variation. In adult males and females including those collected by Quitete (Quitete, 1971a) in Pernambuco State, the number of articles in the flagellum of antenna 1 varies from 5 to 7 during growth. The size reduction of the mid-dorsal projections on pereonites 3 and 5 mentioned by this author was only found among specimens studied by her. Setal formula for terminal article of mandibular palp can be 1-5-1 or 1-6-1. The body spination is rather constant among individuals summing up 30 spines in males.
Remarks. Takeuchi (1993) proposed a classification with four families, Caprellidae, Caprogammaridae, Paracercopidae, and Phtisicidae for the Amphipoda Caprellidea (Cyamidae excluded) based on the cladistic analysis. Fallotritella and Pseudaeginella were set under the Caprellidae. At the same time, Laubitz (1993) proposed a classification with eight families, Caprellidae, Caprellinoididae, Caprogammaridae, Cyamidae, Paracercopidae, Pariambidae, Phtisicidae and Protellidae. In her classification system, Fallotritella and Pseudaeginella were included in Caprellinoididae which is considered to be more related to Paracercopidae and Phtisicidae than to Caprellidae.
The above treatment of Fallotritella and Pseudaeginella performed by Takeuchi (1993) was followed by Myers and Lowry (2003) and Vassilenko (2006). In the higher classification system of Myers and Lowry (2003) based on cladistic analysis of corophiid amphipods, Caprellidae, Caprogammaridae and Cyamidae are included among the Caprelloidea. The Caprellidae of Myers and Lowry (2003) is composed of two subfamilies, Caprellinae and Phtisicidae. Fallotritella and Pseudaeginella with ca. 50 genera constitute the Caprellinae under the Caprellidae (Myers and Lowry 2003). Vassilenko (2006) reviewed the recent studies dealing her support to Takeuchi's (1993) treatment more than to Laubitz (1993) Quitete (1971a). The suggestion of synonymy of these two genus, i.e., Pseudaeginella and Fallotritella was mentioned under remarks of Pseudaeginella by McCain (1968). The lack of reference materials of Pseudaeginella tristanensis (Stebbing, 1888), the type species of Pseudaeginella, has been led to the presumption towards absence of pereopods 3 and 4 in Pseudaeginella. At the same time, F. biscaynensis was recorded to possess 1-articulate pereopods 3 and 4 in the generic description for Fallotritella. He also noted that, in case of presence of pereopods 3 and 4 in the two known species of Pseudaeginella, Fallotritella would fall as junior synonym of Pseudaeginella (see McCain 1968, p. 100). Almost 30 years later, Laubitz (1995) examined individuals of Pseudaeginella tristanensis collected from Amsterdam Islands in the southern Indian Ocean and reported the synonymy of these two genera based on the presence of minute pereopods 3 and 4 on these specimens.
Pseudaeginella montoucheti (Quitete, 1971) is a tiny caprellidean that measures less than 3.5 mm in body length (see Fig. 1). Within this genus, P. montoucheti is the second spiniest species (total of 30 spines on the head and pereonites 1-7 of males) and only surpassed by P. sanctipauli that has a total of 33 spines on body surface. In the drawing of P. montoucheti from Pernambuco State performed by Quitete (1971a) the following body projections are missing in male: a pair of dorsal projections instead of one dorsal spine medially on pereonite 5 and ventro-lateral projections over the insertion of pereopod 5 and 6 on pereonite 5 and 6, respectively. In spite of the wide distribution, P. montoucheti showed a relatively low intraspecific variation in its external morphology.
Of 10 species of Pseudaeginella, the closest species to P. montoucheti can be considered P. sanctipauli that was described from St. Paul and Amsterdam Islands, South Indian Ocean (Laubitz 1995), since both are the spiniest species within the genus. On the other hand, Pseudaeginella montoucheti can be distinguished from P. sanctipauli by the spinier body, antenna 1 length equals half body in males, and presence of ventrolateral spines over gills on pereonites 3 and 4.
A key to the species of Pseudaeginella is presented below; it was mainly based on the characteristics of body somites because these can be observed without dissections of mouthparts.    Fig. 6D)