DEVELOPMENTAL PATTERNS AND HYPOTHESES OF HOMOLOGY IN THE ANTENNULES OF THECOSTRACAN-NAUPLIUS LARVAE (CRUSTACEA)

Antennular development is summarized for non-brooded nauplius larvae o f the Ascothoracida (families Lauridae and Petrarcidae) and for select ed nauplii of the Facetotecta. In the Cirripedia Thoracica, nauplii of the Lepadomorpha and Scalpellomorpha/Sessilia are shown to differ in their patterns of antennular setal addition and division into articles , and one or two possible apomorphies for each group are identified. S everal variations of the scalpellomorphan/sessilian pattern are outlin ed. These data on the Ascothoracida, Facetotecta, and Cirripedia provi de the basis for modifying an earlier proposal of structural homologie s among the naupliar antennules of thecostracan maxillopodans. 'Virtua l' articles (ones that are never completely free) are invoked to accou nt for setae that 'jump' across article boundaries at molts and for su pposedly homologous setae found on adjacent articles in different taxa . The identities of the preaxial setae in the Cirripedia are ambiguous and force consideration of two models for that group and for the thec ostracan antennular Bauplan; the latter may have included up to 11 or 12 articles, more than the previously supposed 8 or 9. The scoring of characters used in an earlier cladistic study of thecostracan and othe r maxillopodan taxa is not seriously affected. A comparison with the C ambrian maxillopodan Bredocaris suggests that division of the antennul e into discrete articles in extant thecostracans is an apomorphic stat e and that yet one more apical article once existed in the maxillopoda n antennule.