**1. Introduction**

Marine shelled gastropods follow, in general, three types of larval development: (1) direct, in which embryo development is completed in the egg capsule and the juvenile is ready

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to commence its benthic life immediately after hatching. (2) Lecithotrophic development in which, after hatching, the larva spends from a few minutes to several days as a veliger without feeding or growing. (3) Planktotrophic development, in which the larva hatches as a veliger and spends a few days to several months in the planktonic mode of life during which it feeds and grows [1]. In all cases, a larval shell is formed which is called protoconch.

The size of fossilized early protoconches suggests that feeding (planktotrophic) embryos first appeared at the transition from the Cambrian era to the Ordovician as Ordovician protoconches were smaller than Cambrian ones indicating smaller Ordovician eggs and offspring. It is believed that planktotrophy would prolongate their escape from benthic predators and that an increasing nutrient supply and availability of photoautotrophic plankton in the world oceans of that period have facilitated both planktotrophy and suspension feeding [2]. The eventual loss of planktotrophy in the Pliocene has been documented in some taxa of Conoidea (*Raphitoma*, *Bela*) and is believed to be irreversible [3]. The same phenomenon has occurred in the families such as Cerithiidae (*Bittium*), Turritellidae (*Turritella*), Rissoidae (*Rissoa*, *Pusillina*), and Nassariidae (*Nassarius*) [4, 5].

Planktotrophic mode of life with long-living planktonic larvae is considered advantageous in the dispersal of the larvae as they may drift considerable distances with the currents [6, 7]. In addition, it has been demonstrated that the switch in some conoidean taxa from the planktotrophic to the non-planktotrophic development has increased their adaptive radiation, especially in polar or insular region, or in groups with narrow bathymetric distribution [3, 7]. In the case of *Oenopota elongata* Bogdanov, 1989, and in the polar genus or bathyal Indo-Pacific genus *Bathytoma* Harris & Burrows, 1891, the loss of planktotrophy actually preceded adaptive radiation [8–11].

Within the Neogastropoda, Conoidea is a diverse superfamily of venomous and exclusively marine gastropods which harbors more than 300 genera, 4000 known species, and an estimated number of over 12,000 existing species [3, 12, 13]. Due to the species richness and the extensive homoplasy among shell's features and the anterior alimentary system, they have resisted repeated attempts to be permanently classified with those attempts to be hindered primarily by the absence of a stable phylogenetic framework. Rather recently, DNA analysis provided an updated classification and divided the superfamily of Conoidea into 13 families [14–16]. Among them, the position of Raphitomidae is not sufficiently secured as a clade of Conoidea and for that reason there has been an on-going attempt to clarify the phylogeny of its Mediterranean members through a greater number of taxonomic data [17, 18]. These later publications have taken into account the pioneering works of Thorson [19, 20], concerning the relationship between the morphology of the protoconch and the type of the larval development in Caenogastropoda, e.g., the dichotomy "multispiral protoconch/planktotrophic development" and "paucispiral protoconch/lecithotrophic development" that has been widely accepted [6, 21]. Although some authors have used this dichotomy to divide species into planktotrophic genera and non-planktotrophic ones [3, 22, 23], it has been clearly demonstrated that such a division based exclusively on the morphology of the protoconch produces artificially separated polyphyletic taxa of otherwise distinct genera of closely related species. A separation, for instance, between the genus *Raphitoma* (with multispiral protoconch) and the genus *Philbertia* (with a paucispiral protoconch) is inconsistent and, therefore, must be rejected [17]. Nevertheless, this planktotrophic or lecithotrophic mode of larval life as reflected in the morphology of its protoconch comprises a useful basis for distinguishing different species in several genera in Prosobranchia and Opisthobranchia Mollusca [24–29].

Under the weight of the above unsettled situation, the aim of this study was to aid the classification of the Mediterranean *Raphitoma* species by presenting new material from the Hellenic seas, demonstrating them in detailed descriptions and coming up with new ideas on the protoconch issue. More specifically, our objective was to put to test the hypothesis that protoconch poecilogony exists within a species population, with lecithotrophic larvae being produced from fewer and larger eggs, while planktotrophic ones from more and smaller eggs that result merely by additional cleavages of the maternal stem cells.
