Sagaminopteron nigropunctatum

sympatric Sagaminopteron nigropunctatum View in CoL and S.

ornatum are 11.0% divergent. Geographically isolated sister species such as S. leah and S. quadrispinosum are 9.3–9.9% divergent, whereas S. michaeli and S.

tigrinum are 10.2% divergent. In contrast, allopatric conspecific Hawai’ian and Philippine specimens of Gastropteron minutum are 3.2% divergent. Widely separated specimens of some apparent conspecifics exhibit some intriguing patterns of divergence. A Red Sea specimen of Sagaminopteron nigropunctatum is 8.8% different to a specimen of what has been considered the same species from the Philippines. Three western Pacific specimens of S. psychedelicum from Australia, Papua New Guinea and the Philippines are 1.1–1.4% divergent to each other, whereas the specimen from Madagascar is 11.1–12.3% divergent to the western Pacific specimens. The data for both S. nigropunctatum and S. psychedelicum strongly suggest that the Red Sea and western Indian Ocean specimens of these species represent distinct cryptic species and are in need of more detailed study. The western Pacific and western Indian Ocean specimens of S. tigrinum are strongly divergent (12.3%). In fact, S. michaeli is more similar to the western Indian Ocean specimen of S. tigrinum (8.1%) than the two S. tigrinum specimens are related to each other. It appears that the species listed as S. brunneomarginatum by Anthes et al. (2008) represents a distinct taxon from the specimen identified as S. brunneomarginatum and sequenced in this study as these two taxa are 14.8% divergent in their COI sequences and 10.5% divergent from its closest relative, S. tigrinum . The identity of this taxon remains questionable and no voucher specimens exist.

RELATIONSHIPS BETWEEN MORPHOLOGY AND MOLECULAR PHYLOGENY

Much of the comparative anatomy and phylogenetic relationships based on morphological characters were presented by Gosliner (1989). In that study, four genera were distinguished: Gastropteron , Enotepteron , Sagaminopteron and Siphopteron with Gastropteron and Enotepteron as sister taxa and with Sagaminopteron and Siphopteron as sister taxa. Anthes et al. (2008) found a similar arrangement of taxa but did not include any species of Enotepteron in their molecular analysis. In their study, S. pohnpei nested with species of Sagaminopteron rather than with species of Siphopteron . In this study, we find a similar result with both S. pohnpei and S. multimaculatum nesting within Sagaminopteron and have placed these taxa within this genus. No suitably preserved specimens of Enotepteron were available to include in the molecular analysis and the specimen initially identified as Enotepteron sp. is nested within Siphopteron , as clade 2, and was likely misidentified. This species is the sister to the remainder of Siphopteron , but was not observed alive.

Three of the four genera of Gastropteridae recognized by Gosliner (1989) were studied here. Of those, only Sagaminopteron is strongly supported as monophyletic, while Gastropteron and Siphopteron are not. Nevertheless, they have morphological synapomorphies that support their continued use until more robust phylogenies are developed. Gosliner (1989) noted that species of Gastropteron had a synapomorphy of possessing a triangular thickening on the inner lateral tooth that is also present in G. multo and G. minutum , described here ( Figs 3C, 6C, indicated by arrow). The same is true for Siphopteron . While we transferred Sagaminopteron pohnpei together with its sister taxon, S. multimaculatum to Sagaminopteron , the remaining species of Siphopteron all have a complex penis and narrow, triangular inner lateral teeth with a reduced number of denticles, attributes that are considered to be synapomorphies in the morphological phylogeny of Gosliner (1989).

While the monophyly of Gastropteron and Siphopteron was not supported, the various well-supported clades recovered in our molecular phylogeny have strong morphological correlates. In Gastropteron , the strongly supported subclade that includes G. multo and G. bicornutum , both sister taxa have a pair of posterior flagella, whereas in the strongly supported subclade of G. minutum and G. rubrum have only a single flagellum. Unfortunately, molecular data are not available for other species of Gastropteron to ascertain, for example, whether the Indo-Pacific G. minutum is indeed most closely related to the Atlantic G. rubrum or whether other taxa from different geographical regions are more closely related to these two taxa. Inclusion of these taxa in the future is necessary for further testing the monophyly of Gastropteron , which was not supported in this study.

In Sagaminopteron View in CoL , the clade that includes S. ornatum View in CoL , S. nigropunctatum View in CoL and S. psychedelicum View in CoL all have a simple penis and inner lateral teeth with two large cusps ( Tokioka & Baba, 1964; Gosliner, 1989), while S. pohnpei View in CoL and S. multimaculatum View in CoL have a more complex penis with a secondary duct and have an inner lateral tooth with many elongate denticles ( Gosliner, 1989; this study). Only when S. pohnpei View in CoL and S. multimaculatum View in CoL are added to Sagaminopteron View in CoL , is the monophyly of this genus strongly supported.

The three clades of Siphoptero n recovered here also have some unifying morphological features. In the first well-supported clade of Siphopteron View in CoL ( Fig. 23, clade 1) that includes, S. tigrinum View in CoL , S. michaeli View in CoL and S. brunneomarginatum View in CoL , the inner radular teeth have a weakly developed masticatory margin with a series of small denticles. The penial papilla of S. tigrinum View in CoL and S. michaeli View in CoL have cuticular spines, whereas the penis of their sister species, S. brunneomarginatum View in CoL , lacks spines. The strongly supported large clade 3 that includes S. nakakatuwa View in CoL , S. flavolineatum View in CoL , S. vermiculum View in CoL , S. sp. 1, S. sp. 2, S. nigromarginatum View in CoL , S. dumbo View in CoL , S. quadrispinosum View in CoL , S. leah View in CoL and S. makisig View in CoL , the radula has an inner tooth with two large, triangular denticles. These are the only species of Siphopteron View in CoL with this form of dentition. In the well-supported subclade of clade 3 that includes S. quadrispinosum View in CoL , S. leah View in CoL and S. makisig View in CoL , the penis is complex with a few large basal cuticular spines on the penial papilla that has spirally arranged spines or tubercles and a cuticular stylet present on a secondary papilla. In the remaining species in the second subclade of clade 3, there are multiple rows of cuticular spines associated with the penis and the penial papilla is not elongate with a series of spirally arranged spines. The anatomy of S. sp. CASIZ 181575 (clade 2) that is the sister taxon to the remain- der of Siphopteron View in CoL remains unstudied.