Phyllodesmium acanthorhinum, Elizabeth Moore & Terrence Gosliner, 2014

Elizabeth Moore & Terrence Gosliner, 2014, Additions to the Genus Phyllodesmium, with a Phylogenetic Analysis and its Implications to the Evolution of Symbiosis, The Veliger 51 (4), pp. 237-251 : 238-242

Phyllodesmium acanthorhinum n. sp.

(Figures 1 A; 2 A; 4 A, B; 5 A, B; 8 A)

Phyllodesmium spec. Wägele et. al, 2006: 38,

figure 5 I.

Phyllodesmium spec. 6 Gosliner et. al, 2008: 389,

bottom photo.

Material examined

Holotype: California Academy of Sciences, CASIZ 0 99093, 3 – 4 m depth, near Onna Village, Horseshoe Cliffs, Okinawa, Ryukyu Islands, Japan, 1 July 1994, R. F. Bolland .

Paratypes: Three specimens, two dissected, CASIZ 104702, 3 – 4 m depth, near Onna Village, Horseshoe Cliffs, Okinawa, Ryukyu Islands, Japan, 8 July 1994, R. F. Bolland .

Geographic range

This species is known from the Horseshoe Cliffs, Okinawa, Ryukyu Islands, Japan (this study) and

Table 2

Character states present in species of Phyllodesmium and outgroups G. quadricolor and F. japonicus .

Lizard Island, Great Barrier Reef, Australia (Wa¨gele et al., 2006).

Etymology

This species was named after the spiny appearance of the papillae on the surface of the rhinophores.

Natural history

Specimens were all found in shallow water on vertical walls with miscellaneous red algae. The wall where specimen 0 99093 was found was near a bottom covered with a live, stony coral reef, whereas the others were found in a rocky cut near shore. The diet of this species is still unknown.

Description

Color and external morphology: The living animals are elongate, with edges of the foot extending laterally just beyond the mantle. They range in length from 17 to 28 mm for living animals studied. Preserved specimens examined ( CASIZ 104702 include three specimens, two of which were dissected and are later referred to as 104702 a and 104702 b) were 14 mm ( CASIZ 104702 a), 8 mm ( CASIZ 104702 b), and 8 mm ( CASIZ 099093).

The anterior portion of the foot margin is broad with short, blunt angular foot corners while the posterior end is tapered to a point.

The body of the living animal, including the rhinophores, oral tentacles, and foot is predominantly transparent with opaque white markings on the dorsum. These markings vary and can appear as white specks or as distinct white lines creating a network along the dorsum and head (Figure 1 A). The anterior margin of the foot is white in some specimens, extending to the angular foot corners. The viscera and gonad are readily visible through the mantle tissue.

The cerata are elongate and cylindrical, with larger cerata near the medial region of the dorsum. The digestive gland is undulating and undivided within the cerata and is cream or yellow colored near the body leading to red, and then yellow at the apex of each ceras. The cerata are primarily transparent, with slight blue coloration near the tips and have a cnidosac without nematocysts. The ceratal arrangement consists of arches and rows, with arches forming in the anterior ceratal groups ( Figure 8 A). The precardiac cerata are grouped into one arch on each side of the body containing 6–7 cerata. The genital aperture is located between the arms of the precardiac arch on the right side of the animal. The renal opening is situated in the interhepatic space, slightly toward the posterior between the precardiac arch and the first postcardiac arch on the right side. The postcardiac cerata are grouped on both sides into arches containing 5–6 cerata in the first two arches, and 4–5 cerata in the third arch. The anal papilla is located within the first postcardiac arch on the right side. The fourth postcardiac group appears as a partial arch in some animals and as a row in others containing 3–4 cerata. One or two additional postcardiac ceratal groups appear as rows containing 2–3 cerata.

The rhinophores are conical in shape and are roughly half as long as the oral tentacles. In addition, there are numerous, yellow-cream–colored tubercles on the entire surface of the rhinophores that lead to a yellow-cream, pointed tip. The oral tentacles are smooth, and taper from the anterior edge of the head to pointed apices. They are transparent or slightly bluish basally, leading to white or yellow-cream tips.

Reproductive wystem ( Figure 2 A): The large gonad occupies the posterior portion of all specimens. As in most mature animals of this group, the female gland mass is large and consists predominantly of the mucous gland with smaller albumen and membrane glands. The large, looped ampulla branches to the oviduct and the prostatic portion of the vas deferens. The oviduct connects to the S-shaped receptaculum seminis. A second branch extends from near the base of the receptaculum and joins the female gland mass near the albumen gland. The second branch of the ampulla connects to the vas deferens. The proximal portion is prostatic with the prostate being highly convoluted and prominent, with a short, conical-shaped penial bulb.

Buccal armature: The jaws are thin and coriaceous. There are four to seven knobby denticles situated along the masticatory border of each jaw ( Figure 4 A, B). The radulae have a formula of 33 × 0.1.0 for specimen 104702 b and 34 × 0.1.0 for specimen 0 99093 (specimen 104702 a had a radular formula of 19 × 0.1.0; however, this may be an incomplete radula). The teeth are triangular in shape leading to a pointed and slightly curved primary cusp. The rib on the ventral side of each tooth extends from the posterior of the tooth to the apex of the cusp in some specimens and in others stops slightly short of the apex. Denticulation extends along the margin from the base of the tooth nearly to the apex. The number of denticles varies between specimens. Specimen 104702 a has 19–28 denticles ( Figure 5 A), 104702 b has 19–22 denticles ( Figure 5 B), and 0 99093 has 25–28 denticles per radular tooth. The denticles vary in appearance and can be triangular and broad, with well-separated points or slightly elongated with closely spaced denticles that reach slightly under the edge of the tooth ( Figure 5 A, B). The denticles at the base of the tooth are generally more defined, where denticles near the apex of the cusp are fused together in some specimens.

Remarks: Of the previously described species of Phyllodesmium , there are only two, Phyllodesmium horridum (Macnae, 1954) , and Phyllodesmium opalescens Rudman, 1991 , that have undivided digestive tissue within the cerata. Rudman (1981, 1991) described P.

horridum as pale translucent, which is notably different from the predominantly transparent mantle of P. acanthorhinum . The digestive gland undulates noticeably, without nodulation, in cerata of P. acanthorhinum , compared to the straight and sometimes nodulose digestive gland in cerata of P. horridum . In addition, P. horridum and P. opalescens have smooth rhinophores, unlike the rhinophores of P. acanthorhinum , which are covered in papillae. The body and cerata of P. opalescens are superficially similar to P. acanthorhinum in coloration and transparency, but the digestive gland within the cerata of P. opalescens is generally straight, with little or no undulation. Also, the opaque white markings along the dorsum of P. opalescens are individual diamond- or teardrop-shaped spots running the length of the dorsum. Phyllodesmium acanthorhinum has many white flecks, or thin lines creating a network along the dorsum. The reproductive system of P. acanthorhinum also differs from the drawings of P. opalescens and P. horridum shown by Rudman (1981, 1991). The prostate is highly convoluted compared to that of P. horridum , and the receptaculum seminis is notably S-shaped in contrast to the teardrop-shaped structure in P. opalescens . Also worth noting in these papers is the incorrect labeling of the receptaculum seminis as a bursa copulatrix. The structure is found a good distance from the genital opening and is connected to the female gland by the oviduct in these animals, indicating it should be described as a receptaculum seminis.