Morphology and Systematics of the Nemertean Pseudocarcinonemertes homari (Hoplonemertea:Mortostilifera) from the American Lobster, Homarus americanus

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Abstract
Our study of the morphology and systematics of the nemertean Pseudocarcinonemertes homari Fleming and Gibson, 1981 is based on specimens removed from the damaged egg masses of American lobsters, Homarus americanus, caught in the type locality at Grand Manan, N.B., in the Bay of Fundy and nearby Passamaquoddy Bay. Morphological characteristics and measurements of males, females, and developmental stages, obtained through examination of live and preserved nemerteans plus stained histological sections, revealed differences and provided additional indications of variability in measurements of taxonomic characters when compared with the original description. Specifically, female nemerteans are longer and slightly wider than males; the rhynchodael opening is subterminal; sensory bristles occur lateral to the rhynchodael and anal openings; cephalic furrows are observable on living specimens; the combined stylet–basis length is longer than reported and stylet length appears a stable character; the bulbous or sacculate foregut joins to a distinct pyloric tube; ova are large, 260 × 251 μm in length and width; and larvae retained in the membranous brood sac lack anterior and posterior cirri or tufts. Comparison of characters that define Pseudocarcinonemertes and differentiate it from Carcinonemertes with those defining free-living hoplonemerteans strongly supports its removal from the family Carcinonemertidae to the family Tetrastemmatidae.