Male genital organs in the eulittoral meiofaunal polychaete Stygocapitella subterranea (Annelida, Parergodrilidae): ultrastructure, functional and phylogenetic significance

Abstract

The marine interstitial polychaete Stygocapitella subterranea is characterized by aberrant morphological and biological traits resembling those of clitellates and Hrabeiella periglandulata, a terrestrial polychaete species. Although clearly related to the terrestrial Parergodrilus heideri, there are distinct diVerences in their morphology. An ultrastructural study of the male genital organs was undertaken to look for common apomorphic features in Parergodrilidae, to Wnd structural evidence for clarifying their reproductive biology and mode of sperm transfer. Finally it should be elucidated whether a supposed sistergroup relationship of Parergodrilidae and Orbiniidae based on molecular evidence can be supported by morphological characters as well. In S. subterranea the male organs consist of an unpaired seminal vesicle, a pair of sperm ducts and two large tube-like prostate glands. These glands constitute the distal parts of the gonoducts and open ventrally on a small genital papilla in chaetiger 9. True copulatory organs or organs for storage of mature sperm are lacking. The seminal vesicle is a coelomic cavity composed of two apposed coelomic linings supplied with blood spaces. The testes are found ventrally. The prostate glands are covered by a single layer of muscle Wbres running in a longitudinal/ spiral direction along the gland. There are no signs of spermatophore formation in any part of the male system. Since females always carry sperm, pseudocopulation can be excluded and the likelihood of either direct transfer of sperm or hypodermic injection is discussed. The structure of genital organs reveals similarities to those of P. heideri. Gonochorism, paired seminal vesicles and two pairs of male gonoducts opening in chaetigers 9 and 10 with a distal glandular part most likely belong to the ground pattern of Parergodrilidae. The observations conWrm that consistencies with either clitellates or H. periglandulata are the result of convergent evolutionary events. On the other hand, the relationship of Parergodrilidae to an orbiniid/ questid clade receives support from the present data.

Phylogeny of Annelida (Lophotrochozoa): total-evidence analysis of morphology and six genes

“…The sister-group relationship between Parergodrilidae and Orbiniidae- Questa is strongly supported by all analyses [ 8 , 24 ]; both groups share gonoducts with a distal glandular part [ 25 ]. No closer orbiniid-spionidan relationships [ 26 ] have been recovered by the present analyses. Also Apistobranchus consistently grouped with OPC in the taxon-exclusion analyses.…”

Nerves innervating copulatory organs show common FMRFamide, FVRIamide, MIP and serotonin immunoreactivity patterns across Dinophilidae (Annelida) indicating their conserved role in copulatory behaviour

“…The suggested closely related Lobatocerebridae (Martín-Duran et al, unpublished) or Orbiniida [52] likewise have external fertilization except for Parergodrilidae (within Orbiniida), which have internal fertilization. However, they seem to lack true copulatory organs [53,54]. Remarkably, three more distantly related meiofaunal annelids have independently evolved somewhat similar, mostly medioventral, to some extend protrusible, muscular unpaired internal copulatory organs: Microphthalmus aberrans (Webster & Benedict, 1887) [55] is furthermore the only species within its genus possessing an unpaired (slightly offcentered to the right) copulatory organ, supporting its independent origin within the group.…”

Male reproductive system in the Italian newt Lissotriton italicus (Peracca 1898) (Amphibia, Urodela): ultrastructural and morphological study with description of spermiogenesis, spermatozoon and spermatophore

“…Knowledge of testes, eVerent ducts, spermiogenesis and spermatozoal morphology and ultrastructure is indispensable for the study of reproductive biology and is of value for reconstruction of phylogenetic relationships in many animal taxa (Purschke and Jördens 2007;Longo and Trovato 2008;Tavares-Bastos et al 2008;Tourmente et al 2008) and in particular for all amphibians taxa (Baker 1965;Wake 1968Wake , 1970Williams et al 1984;Zalisko et al 1984;Brizzi et al 1992;Lee and Jamieson 1993;Selmi et al 1997Selmi et al , 1999Jamieson 2003a, b, 2006).…”