The Morphological Radiation of Setae in the Cladocera (Crustacea) and Their Potential for Morphogenesis

Abstract

The present review seeks to demonstrate the presence of an inherent biological tendency for the modification of form in cladoceran setae. We present a comparative description of the setal equipment of the cladoceran antenna I, antenna II, maxilla I, maxilla II, each thoracic limb, the carapace valves, and the postabdomen. We revealed significant differences between planktonic and benthic species of the Cladocera. Also our analysis stresses the great differences between the "daphniid" line (Daphniidae + Moinidae) and the "chydorid" line (all other families) of the order Anomopoda.Comments on cladoceran limb evolution are made, and some general conclusions concerning the major tendencies of setal evolutionary transformations are drawn. The morphological range of homologous structures in different species is generally wide, from an undifferentiated seta to either its disappearance or to enlargement, heavy chitinization, and specialization. Special issues, such as parallelisms, oligomerization, asymmetry, abnormalities, and conjugated morphogenesis are discussed. It is assumed that, having been originated, if not eliminated, these modifications either find some adaptive use in the process of radiation at the next level -adaptive radiation -or restrict the niches of specialized groups, or just remain ecologically neutral and then give rise to a series of similar species.

Leydigia (Neoleydigia) cf. striata Birabén, 1939 (Crustacea: Cladocera: Chydoridae) from Colombia and its differentiation from L. (N.) cf. ipojucae (Brehm, 1938)

“…These specimens were deposited at the Museo de Colecciones Biológicas at the Universidad del Atlántico (UARC), Colombia. For explanation of the system of seta numeration on the thoracic limbs see Smirnov and Kotov (2010). Description.…”

Peculiarities of Immature Individuals Developing from Both Resting and Subitaneous Eggs of Polyphemus pediculus (Cladocera, Onychopoda)

“…The number of setae on the first of the four segments of the ventral branch, or endopod, of Ant II (Smirnov & Kotov, 2010) is one less than in other stages of immature individuals, and in adult females (table III). The second of the three segments of the dorsal branch, or exopod (Smirnov & Kotov, 2010), bears one seta and a large, sabre-like thorn ( fig. 2a).…”

“…The size of the apical setae of the swimming antennae has increased most markedly, by 50 to 73%. At the same time, changes in the size of the basal segment (Smirnov & Kotov, 2010) and especially the branches of Ant II, are insignificant. Morphological transformations of immature individuals proceed gradually and bear a stable character (table III).…”

Endemism in the Cladocera (Crustacea: Branchiopoda) of Southern Africa

“…For the system of seta enumeration, see previous papers (Kotov, 2007a(Kotov, , 2007b(Kotov, , 2009Bekker et al, 2012). The homologies of different limb parts of the Anomopoda are explained in Smirnov and Kotov (2010). Drawings and photographs of A. capensis are by KVD and of E. freyi n.sp.…”