The Vas Deferens of the Spanish Lobster,Scyllarus chacei

Summary

The male reproductive tract of Scyllarus chacei consists of paired testes and vasa deferentia that conduct sperm containing spermatophores to the genital pores at the base of each fifth walking leg. The testis is joined to the vas deferens which can be divided into four regions: (1) the anterior vas deferens can be further divided into three regions. It is highly convoluted and is the region in which the sperm become encapsulated in ovoid spermatophores of approximately 100 sperm as well as produces seminal fluids. (2) The middle vas deferens is the primary site of sperm storage and adds to seminal fluids which formed in the anterior region. (3) The posterior region is highly muscularized and may serve for limited sperm storage. (4) The most distal portion is the ejaculatory duct which is highly muscularized for extruding the spermatophoric mass for transfer to the female. A final seminar product is added here.     

The effects of predation and unionid burrowing on bivalve communities in a Laurentian Great Lake coastal wetland

Unionid (Mollusca: Unionidae) densities have declined dramatically throughout the Laurentian Great Lakes after the introduction of dreissenid mussels (Mollusca: Dreissenidae). Recent surveys in some Great Lake coastal wetlands have found abundant unionid populations, but the factors that reduce zebra mussels on unionids in these habitats are not well understood. In 2001–2002, we tested effects of predation and unionid burrowing on corbiculids, sphaeriids and dreissenids in a Great Lake coastal wetland in western Lake Erie. In one experiment, we reduced access by molluscivores using exclosures with two mesh sizes (1.3 cm × 1.3 cm; 5 cm × 10 cm) and sampled bivalves after 15 months. Small mesh exclosures had higher numbers of dreissenids, Corbicula fluminea and sphaeriids (54.9, 3.8, 22.6 individuals/m², respectively) than large mesh exclosures (0.0, 1.13, 0.13 individuals/m², respectively) or open controls (0.3, 1.0, 0.1 individuals/m², respectively). Numbers of dreissenids on C. fluminea were higher in small mesh exclosures (3.8 dreissenids/Corbicula) than in large mesh exclosures (0.1 dreissenids/Corbicula) or cageless controls (0␣dreissenids/Corbicula). In a second experiment, we held two species of live unionids (Leptodea fragilis, Quadrula quadrula) and immobile Pyganodon grandis shells in exclosures (2.5 cm × 2.5 cm mesh) with either 5 cm, 10 cm, or 20 cm deep sediments and sampled bivalves after 2 months. There were fewer dreissenids on L. fragilis than P. grandis shells, but there was no difference in the number of dreissenids on Q. quadrula and P. grandis shells. Numbers of attached dreissenids were higher inside (189–494 dreissenids/unionid) than outside (8–11 dreissenids/unionid) exclosures, and densities of sphaeriid and C. fluminea clams were also higher inside (21.8, 4.7 individuals/m², respectively) than outside (0.4, 0.9 individuals/m², respectively) exclosures. Numbers of attached dreissenids were higher on unionids that could burrow below the sediments (20 cm depth) than unionids in shallow sediments (5 cm depth) for unexplained reasons. Our data suggest that molluscivores can play a pivotal role in limiting numbers of bivalves including dreissenids in coastal wetlands.     

Anatomy and reproduction of viviparous Pisidium (Parapisidium) reticulatum Kuiper, 1966: Implications for the phylogeny of Sphaeriidae (Mollusca: Bivalvia: Heterodonta)

The pea clams Sphaeriidae represent a major molluscan freshwater radiation with cosmopolitan distribution in all kinds of lotic and lentic habitats. Their phylogenetic relationships are still controversial, with comprehensive taxonomic sampling and examination of morphological characters still challenging. Here, based on rare and rediscovered original material, we study in detail the anatomy and aspects of brood protection of the African Pisidium reticulatum Kuiper, 1966. Representing the monotypic subgenus Parapisidium Kuiper, 1966, this species is characterized by its peculiar combination of shell and anatomical features of potentially high phylogenetic relevance. While similar to other congeners in several anatomical characters (e.g. reduction of inhalant siphon and descending lamella of outer demibranch, simplified structure of intestine coil and nephridium), P. reticulatum differs from other Pisidium species in retaining both pairs of retractor muscles of the inhalant siphon, and particularly in its peculiar mode of brooding. The yolky eggs are relatively large (160–170 μm in diameter) and are incubated in the gill, albeit in the absence of the formation of brood pouches. During later stages of incubation the larvae are surrounded by large cells similar to nourishing cells in other sphaeriids and probably with similar function. This unique combination of reproductive features is hypothesized to represent an intermediate stage between the typical ovoviviparity of Euperidae and euviviparity (i.e. nourishment by the parent animal) as found exclusively in Sphaeriidae, the latter being characterized by the possession of closed brood pouches. Phylogenetic analyses based on a comprehensive set of morphological characters reveal Parapisidium as the most basal lineage within a clade Pisidium. Evaluating the phylogenetic reconstructions based also on available molecular data for Sphaeriidae, we discuss alternative scenaria of (parallel) evolution of brood pouches and viviparity in this group.     

Moitessier's pea clam Pisidium moitessierianum (Bivalvia,Sphaeriidae): a cryptogenic mollusc in the Great Lakes

Pisidium moitessierianum Paladilhe, 1866, a small pea clam native to Europe, was identified for the first time from the lower Great Lakes basin based on an examination of historical collections of Pisidium performed by V. Sterki in 1894 and 1903 and new material collected during 1997 and 1998. During recent surveys, P. moitessierianum individuals were found in the St. Clair River delta, Lake St. Clair and western Lake Erie, but were not detected in the Detroit River or western Lake Ontario. Pisidium moitessierianum was collected on sand, silty sand and mud substrata from water depths ranging between 0.6 and 5.4 m. Populations occurred at an average density of 51 ind. m^–2 and included juveniles and adults. All individuals were less than 2.0 mm in length. We examined the structure of the umbos and hinge, surface sculpture and shape of the shell, and the anatomy of gills, mantle and nephridia in populations from the lower Great Lakes and Ukrainian inland basins (Dnieper River and Lake Beloye). The results indicated that the Great Lakes' pea clams match European specimens of P. moitessierianum in these conchological and anatomical characteristics. As with other nonindigenous sphaeriids in the Great Lakes, P. moitessierianum was likely introduced through shipping activities into the Great Lakes, possibly as early as the 1890s.     

Anatomical evidence of close affinity between endemic species of Pisidium (Bivalvia, Sphaeriidae) from some ancient lakes, and the widely distributed taxa

Anatomical characters of three endemic taxa from the Balkan lakes Ohrid and Prespa and one species from Lake Baikal were studied and compared with those of the widely distributed species of Pisidium . A close affinity of Pisidium edlaueri Kuiper 1960 from Ohrid and Pisidium maasseni Kuiper 1987 from Prespa to the Holarctic Pisidium nitidum Jenyns 1832 was confirmed; Pisidium raddei Dybowski 1902 from Baikal is anatomically identical to the Boreo-alpine Pisidium conventus Clessin 1877. Similarity in anatomical characters between the Ohridan subspecies Pisidium subtruncatum recalvum Kuiper 1960 and the nominal subspecies was also shown. These findings are compared with the situation in other ancient lakes. The similarity in some shell characters between the nonrelated taxa inhabiting these lakes is interpreted as being the result of convergent evolution.