Philinopsis buntot Gosliner, 2015

Gosliner, Terrence, 2015, Three New Species of Aglajid Cephalaspidean Mollusks from the Tropical Indo-Pacific of the Verde Island Passage, Proceedings of the California Academy of Sciences 62 (6), pp. 191-205 : 192-197

Philinopsis buntot Gosliner , sp. nov.

Figures 1C–E , 2A , 3, 4.

MATERIAL EXAMINED.— HOLOTYPE: PNM 41060 , 5 m depth, subsampled for molecular study, Anilao Harbor , Mabini, Batangas Province, Luzon, Philippines, 13.75994°S, 120.83036°E, 30 April 2011, E. Jessup . PARATYPE: CASIZ, 185780, one specimen, 5 m depth, Anilao Harbor , Mabini, Batangas Province, Luzon, Philippines, 13.75994°S, 120.83036°E, 24 May 2011 , T. M. Goslin- er. CASIZ 185942 , one specimen, dissected, 7 m depth, Cemetery Beach , Tingloy, Batangas Province, Luzon, Philippines, 13.68433°S, 120.82993°E, 19 May 2011 , T. M. Gosliner . CASIZ 185777 , two specimens, 7 m depth, Cemetery Beach , Tingloy, Batangas Province, Luzon, Philippines, 13.68433°S, 120.82993°E, 19 May 2011 , T. M. Gosliner .

GEOGRAPHICAL DISTRIBUTION.— Thus far, known only from southern Luzon Island, Philippines.

ETYMOLOGY.— The name “buntot ” is the Tagalog word for tail, referring to the distinctive posterior appendage of this species.

NATURAL HISTORY.— This species is found crawling on clean sand where it is nocturnally active. It has not been observed diurnally and may remain buried in the sand during the day.

DESCRIPTION.— External morphology: The living animals are 7 to 12 mm in length and 3–6 mm wide. The general body color of the living animal ( Figs. 1C–E ) is translucent white with varying amounts of reticulated brown pigment on the dorsal surface. In specimens with sparse brown pigment patches of opaque white may also be present. The brown pigment frequently surrounds small yellow spots on the dorsal surface. Larger yellow spots are evident along the margins of the cephalic and posterior shields and on the margins of the parapodia.

Living animals are elongate, and relatively slender. The anterior end of the cephalic shield is blunt and quadrangular. The cephalic shield is roughly rectangular and terminates posteriorly with a rounded edge. No upturned papilla was observed on the end of the cephalic shield. The posteri- or shield is slightly rounded anteriorly and terminates in a medial elongate, digitiform posterior projection that is well-elevated from the base of the shield. This appendage is rounded at the apex and is often held upright in actively crawling individuals. The posterior end of the posterior shield is much lower that the area with the projection and two relatively flat lateral posterior lobes are short and simply rounded. The parapodia are relatively short, leaving most of the cephalic and posterior shields visible. The gill is simply plicate consisting of 12 primary folds and is situated ventrally on the right posterior end of the animal.

Shell ( Fig. 2A ): The shell is relatively thickly calcified and consists of a narrow band that occupies the posterior extreme of the animal. There is a membranous periostracum that is slightly more extensive anteriorly than the calcified portion. The area at the base of the shell near the protoconch is more thickly calcified that the rest of the shell.

Digestive system: The buccal mass is large, highly muscularized and slightly elongate posteriorly and occupies the body cavity for the entire length of the cephalic shield. The buccal bulb entirely lacks any vestige of a radula. There is a large ventral oral gland and a smaller dorsal oral gland. At the posterior end of the buccal mass, near the junction with the crop, is a pair of elongate salivary glands. The crop is large and saccate, wider than the buccal bulb. The crop narrows posteriorly and enters the digestive gland. The intestine emerges from the right side of the digestive gland and terminates near the posterior end of the body near the base of the gill.

Central Nervous System (Fig. 3A): The circumesophageal nerve ring consists of paired cerebral, pedal and pleural ganglia and a single supraintestinal ganglion on the right side. The cerebral and pedal commissures are both elongate with well-separated respective ganglia. Immediately adjacent and posterior to the right pleural ganglion is the supraintestinal ganglion. From its posterior end is the right branch of the visceral loop and the osphradial nerve. The two lateral branches

REMARKS.— The presence of a quadrangular anterior end of the body, a posterior lobe of the cephalic shield, a large muscular bulb, the single branch of the hermaphroditic duct to the albumen and membrane glands, a bilobed mucous gland are all characteristics of species of Philinopsis ( Rudman, 1972a) . Philinopsis buntot lacks the elevated posterior extension of the cephalic shield but has all the other characteristics of Philinopsis . The anatomy of P. buntot differs significatntly from other described members of the genus. The most obvious morphological attribute that distinguishes P. buntot is the presence of the elongate posteromedial appendage on the posterior shield. The penis is also similar to that described for P. falciphallus Gosliner, 2011 and P. coronata Goslin- er, 2011. These two species also have a oblong prostate that is connected to the penial sac by means of a thin duct. In all three species, the penial papilla is armed with spines, whereas no other species of Philinopsis are known to have an armed penis. In P. falciphallus , the base of the penis has a series of spines and a large chitinous sickle-shaped spine near the apex, whereas P. coronata has a ring of spines around the apex of the penial papilla and a ring of larger spines at the base of the penial papilla with a second ring of larger spines above the penial papilla. The arrangement of spines along the margins of the two penial papilla lobes and spines along a basal collar in P. buntot is unique to this species.

In his review of Philinopsis, Rudman (1972a) indicated there were two distinct groups of species. Members of the first group are characterized by having a large quadrangular head, a bulbous buccal mass and a specialized penis with a basal elongate penial papilla and a short prostate (Marcus and Marcus 1967: fig. 12) or a simple penis in P. depicta (Renier, 1807) ( Gosliner 1980) . Members of the second group of species have a rounded head with an elevated bulbous region (that resembles the front end of a Boeing 747) with prominent eyes visible at the base of the bulb, an elongate, tubular buccal bulb and a simple penis.

In the molecular study by Camacho-García et al. (2014) ( Fig. 7 ), these two groups are largely upheld, but two additional groups of taxa being included in the same clade as the taxa with a tubular buccal bulb. Philinopsis orientalis (Baba, 1949) and P. petra (Marcus and Marcus, 1976) are sister to the clade of species with the tubular buccal mass. Philinopsis coronata Gosliner, 2011 , together with P. buntot (as P. sp. CASIZ 185779), is sister to the remainder of the members of this clade. Philinopsis falciphallus , which has very similar morphology to P. buntot and P. coronata , surprisingly nests with Aglaja regiscorona Bertsch, 1972 , and several species of Chelidonura . This relationship requires additional study as the COI mitochondrial gene was not able to be amplified for P. falciphallus . The morphological distinctions of P. buntot , P. coronata and P. falciphallus are discussed above, but the molecular data suggesting a sister species relationship between P. buntot and P. coronata is consistent with their morphological similarity.

Figures

FIGURE 1. Living animals A–B. Philinopsis aliciae sp. nov., holotype, PNM 41061, Mabini, Philippines. C. Philinopsis buntot sp. nov., holotype, PNM 41060, Mabini, Philippines, ventral view showing markings on foot. D. Philinopsis buntotparatype, CASIZ 185942, Tingloy, Philippines. E. Chelidonura alexisi sp. nov., holotype, PNM 41062, Mabini, Philippines.

FIGURE 2. Shells.A. Philinopsis buntot. sp. nov., paratype, CASIZ 185942, Tingloy, Philippines. B. Philinopsis aliciae sp. nov., holotype, PNM 41061, Mabini, Philippines. C. Chelidonura alexisi sp. nov., holotype, PNM 41062, Mabini, Philippines.

FIGURE 7. Bayesian maximum credibility tree showing all taxa included for the analysis of the combined H3, 16S, and COI sequence alignments (after Camacho et al. 2014). Posterior probabilities areindicated above each branch (for the analysis without COI third positions on the left, and for the analysis with COI third positions on the right) and bootstrap values areindicated below each branch. Branch lengths are also shown here indicating the proportion of substitutions. Species names are color-coded according to their range, blue forIndo-Pacific, red for Atlantic and green for Eastern Pacific. The phylogenetic positions of Philinopsis buntot sp. nov. and Chelidonura alexisi sp. nov. are indicated by arrows on the tree.