Abstract
To the memory of William Ronald Sendall Sternaspid polychaetes are common and often abundant in soft bottoms in the world oceans. Some authors suggest that only one species should be recognized, whereas others regard a few species as widely distributed in many seas and variable depths from the low intertidal to about 4400 m. There are some problems with species delineation and the distinctive ventro-caudal shield has been disregarded or barely used for identifying species. In order to clarify these issues, the ventral shield is evaluated in specimens from the same locality and its diagnostic potential is confirmed. On this basis, a revision of Sternaspis Otto, 1821 (Polychaeta: Sternaspidae) is presented based upon type materials, or material collected from type localities. The sternaspid body, introvert hooks and shield show three distinct patterns, two genera have seven abdominal segments and tapered introvert hooks, and one genus has eight abdominal segments and spatulate introvert hooks. The ventro-caudal shield has three different patterns: stiff with ribs, and sometimes concentric lines, stiff with feebly-defined ribs but no concentric lines, and soft with firmly adhered sediment particles. Sternaspis is restricted to include species with seven abdominal segments, falcate introvert hooks, and stiff shields, often exhibiting radial ribs, concentric lines or both. Sternaspis includes, besides the type species, Sternaspis thalassemoides Otto, 1821 from the Mediterranean Sea, Sternaspis affinis Stimpson, 1864 from the Northeastern Pacific, Sternaspis africana Augener, 1918, stat. n. from Western Africa, Sternaspis andamanensis sp. n. from the Andaman Sea, Sternaspis costata von Marenzeller, 1879 from Japan, Sternaspis fossor Stimpson, 1853 from the Northwestern Atlantic, Sternaspis islandica Malmgren, 1867 from Iceland, Sternaspis maior Chamberlin, 1919 from the Gulf of California, Sternaspis princeps Selenka, 1885 from New Zealand, Sternaspis rietschi Caullery, 1944 from abyssal depths around Indonesia, Sternaspis scutata (Ranzani, 1817) from the Mediterranean Sea, Sternaspis spinosa Sluiter, 1882 from Indonesia, and Sternaspis thorsoni sp. n. from the Iranian Gulf. Two genera are newly proposed to incorporate the remaining species: Caulleryaspis and Petersenaspis. Caulleryaspis gen. n. is defined by the presence of falcate introvert hooks, seven abdominal segments, and soft shields with sediment particles firmly adhered on them; it includes two species: Caulleryaspis gudmundssoni sp. n. from Iceland and Caulleryaspis laevis (Caullery, 1944) comb. n. from Indonesia. Petersenaspis gen. n. is defined by the presence of spatulate introvert hooks, eight abdominal segments, and stiff shields with poorly defined ribs but no concentric line; it includes Petersenaspis capillata (Nonato, 1966) from Brazil and Petersenaspis palpallatoci sp. n. from the Philippines. Neotypes are proposed for eight species: Sternaspis thalassemoides, Sternaspis affinis, Sternaspis africana, Sternaspis costata, Sternaspis fossor, Sternaspis maior, Sternaspis scutata and Sternaspis spinosa, to stabilize these species-group names, and a lectotype is designated for Sternaspis laevis which is transferred to Caulleryaspis gen. n. The geographic range of most species appears to be much smaller than previously indicated, and for some species additional material in good condition is needed to clarify their distributions. Keys to genera and to all species are also included.
Highlights
The peculiar, peanut-shaped sternaspid polychaetes have been known since the eighteenth century because they are common in shallow water sandy bottoms
The anterior abdomen has some segments without chaetae in the adult stage, whereas the posterior abdomen carries the ventro-caudal shield, its associated marginal chaetae, and two dorsal groups of branchial filaments, usually arranged in discrete branchial plates
Some species have filamentous papillae associated with the branchiae, or abundant sediment attached to the ventro-caudal shield area, both of which can make the peg chaetae difficult to locate
Summary
The peculiar, peanut-shaped sternaspid polychaetes have been known since the eighteenth century because they are common in shallow water sandy bottoms. The sternaspids are capable of invaginating some anterior segments including the first three chaetigers, which often carry falcate hooks (Fig. 1A) This eversible body region is followed by another one with no chaetae in the adult stage, often carrying two fleshy ventral outgrowths, the gonopodial lobes or genital papillae, over its anterior margin. This allowed us to propose emendations and redescriptions for species, and provide good illustrations In this contribution, we first studied the morphological variation of the ventro-caudal shield in different sized specimens of a single species from the same locality and validated its usage as a diagnostic feature. We first studied the morphological variation of the ventro-caudal shield in different sized specimens of a single species from the same locality and validated its usage as a diagnostic feature On this basis, three genera are recognized and two are newly proposed. We include a key for all species on the basis of the form of the ventrocaudal shield plus other morphological features
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