Phyllodesmium pinnatum, Moore, Elizabeth & Gosliner, Terrence, 2009

Moore, Elizabeth & Gosliner, Terrence, 2009, Three new species of Phyllodesmium Ehrenberg (Gastropoda: Nudibranchia: Aeolidoidea), and a revised phylogenetic analysis, Zootaxa 2201, pp. 30-48 : 37-39

Phyllodesmium pinnatum n. sp.

( Figures 1 B, 2D,E, 3B, 5C,D, 6B, 7)

Synonymy. Phyllodesmium sp.1 Gosliner, Behrens & Valdés, 2008: 385.

Material examined. Holotype: CASIZ 103710, not dissected, 0–34m depth, Devil’s Point, Maricaban Island, Batangas Province, Luzon Island, Philippines, 24 Feb 1995, T.M. Gosliner. Paratype: CASIZ 179101, dissected, 0–34m depth, Devil’s Point, Maricaban Island, Batangas Province, Luzon Island, Philippines, 24 Feb 1995, T.M. Gosliner. Paratype: CASIZ 110371, poorly preserved, molecular sample taken from foot, 0– 22m depth, Arthur’s Rock, Batangas Province, Luzon Island, Philippines, 22 Apr 1997, T.M. Gosliner.

Geographic range. This species is known only from Batangas Province, Luzon Island, Philippines (this study).

Etymology. The species is named after the digitate projections present on the cerata of these animals.

Natural history. Unknown. Based on the external appearance, and the location within the phylogeny, this species is likely associated with xeniid corals.

Description. Color and external morphology. Living animals ( Fig. 1 B) are elongate, with edges of the foot extending laterally only as far as the edge of the mantle. The three preserved specimens are 7mm (CASIZ 110371), 11mm (CASIZ 103710), and 12mm (CASIZ 179101) in length. The anterior portion of the foot margin is wider than the rest of the foot, with slightly angular foot corners. The posterior end of the foot tapers to a point. The body of the living animal, including dorsum and foot, is predominantly gray in color with faint, white, oval-shaped markings on the central part of the dorsum. The cerata, oral tentacles, and rhinophores are a slightly darker, brownish-gray color compared with the color of the dorsum. The viscera and gonad are not readily visible through the mantle tissue, but branches of the digestive diverticula can be seen through the epidermis of most cerata. Zooxanthellae are present in the digestive tissue of large cerata (near the dorsum) ( Fig. 2 D), but less so in the small, laterally located cerata. Zooxanthellae also appear to be located outside the digestive tissue near the epithelial surface of each ceras. The cerata are elongate and paddle-shaped, flattened dorso-ventrally, with larger cerata near the medial region of the dorsum. Each ceras has numerous, digitate projections that concentrate near but are not exclusive to, the margins of the flattened ceras. The digestive gland has noticeable secondary ( Fig. 2 D), and probably tertiary, branches within the cerata. The digestive gland extends into, and continues to branch within, the ceratal projections. The digestive gland appears slightly lighter in color than the brownish-gray of the cerata, making it just visible near the epidermal surface of each ceras. Phyllodesmium pinnatum does not appear to have the obvious, non-functional cnidosac that is characteristic of this genus ( Fig. 2 E). The ceratal arrangement consists of arches and rows, with arches forming in the anterior ceratal groups ( Figure 3 B). The precardiac cerata are grouped into one arch on each side of the body containing 11–12 cerata. The genital aperture is located between the arms of the precardiac arch, near the ventral most cerata, on the right side of the animal. The genital aperture has two openings, one for the male and female reproductive organs separately. 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 9–10 cerata in the first arch, and 7–8 cerata in the second arch. The anal papilla is located between two cerata, in the first postcardiac arch on the right side. The third postcardiac group appears as a partial arch and contains 4–5 cerata. Two additional postcardiac ceratal groups appear as rows containing 4 and 2 cerata respectively (the most posterior cerata are extremely tiny and have few digitate projections). The rhinophores are cylindrical in shape, with very subtle bumps or wrinkles. The rhinophores are slightly longer than the oral tentacles. The oral tentacles are smooth and taper from the anterior edge of the head to pointed apices.

Reproductive System ( Figure 7 ). Large quantities of gonad fill the posterior portion of the dissected specimen. 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 ampulla is small relative to the other reproductive structures and has one main curve before branching to the oviduct and the prostatic portion of the vas deferens. The oviduct connects to a large, nodulose receptaculum seminis. A second duct extends from near the base of the receptaculum and joins the female gland mass near the albumen gland. The proximal portion of the vas deferens (where the second branch of the ampulla connects) is prostatic, with the prostate being highly convoluted and large, with a short, conical-shaped, unarmed penial bulb.

Buccal Armature. The jaws are thin and coriaceous. There are eight to nine denticles situated along the masticatory border of each jaw. The largest denticles are elongate, and taper to smaller, more triangular denticles along the border of the jaw ( Figure 5 C, D). The radula has a formula of 25 x 0.1.0. The teeth ( Figure 6 B) are triangular in shape leading to a pointed primary cusp. Denticulation extends along the margin from the base of the tooth nearly to the apex. The number of denticles varies from 34–36 on each tooth. The denticles are slightly elongated, triangular in shape, and are well separated along the majority of the margin of the cusp. The denticles at the base of the tooth are generally more defined, and denticles near the apex of the cusp are often fused together or fused with the margin of the cusp.

Remarks. Of the described species of Phyllodesmium there are six species, P. crypticum , P. hyalinum , P. lembehensis , P. lizardensis , P. koehleri , and now P. tuberculatum with obvious nodules on the external portions of the cerata. None of these species have finger-like projections on their cerata that closely resemble those on P. pinnatum , and they all contain a non-functional cnidosac in each ceras, which P. pinnatum appears to lack. In addition, the cerata of P. pinnatum are noticeably fewer than those of P. hyalinum , with only single rowed arches in the precardiac and first three postcardiac arches. Also, the denticulation along the margin of the radular teeth varies between the two. Phyllodesmium hyalinum has up to 56 denticles per tooth, and P. pinnatum has only 34–36 denticles. When comparing P. pinnatum with P. crypticum , the jaws of P. pinnatum have large, distinctive denticles where P. crypticum has jagged, coarse denticles. The reproductive systems are also noticeably different, where Phyllodesmium crypticum has a large, convoluted ampulla and small receptaculum seminis, while P. pinnatum has a greatly reduced, curved ampulla and a prominent, nodulose receptaculum seminis. Despite being externally very dissimilar, Phyllodesmium lizardensis and P. lembehensis can also be distinguished from P. pinnatum by their increased number of radular teeth. Phyllodesmium lizardensis is reported to have 40 denticles on the radula and P. l e m b e h e n s i s has 35 compared to only 25 observed in P. pinnatum . When comparing P. pinnatum with P. tuberculatum , the reproductive system of P. tuberculatum has a large and prominent ampulla and small receptaculum seminis. In addition to the noticeably different appearance, P. tuberculatum also has a slightly more elongate prostate, which further differentiates it from P. pinnatum .

Figures

FIGURE 1. Living animals A. Phyllodesmium tuberculatum n. sp. B. Phyllodesmium pinnatum n. sp. C. Phyllodesmium karenae n. sp.

FIGURE 3. Lateral view of preserved specimens showing ceratal arrangement A. Phyllodesmium tuberculatum n. sp. (CASIZ 106547). B. Phyllodesmium pinnatum n. sp. (CASIZ 179101). C. Phyllodesmium karenae n. sp. (CASIZ 177313). Scale bars represent preserved specimen length.

FIGURE 7. Reproductive system of Phyllodesmium pinnatum n. sp. Abbreviations: am ― ampulla, rs ― receptaculum seminis, od ― oviduct, vd ― vas deferens, p ― penial papilla, pr ― prostate, al ― albumen gland, mu ― mucous gland, me ― membrane gland.

FIGURE 2. A. Phyllodesmium tuberculatum n. sp., micrograph of ceras showing secondary branching. B. Phyllodesmium tuberculatum n. sp., ceratal ducts with zooxanthellae shown by arrows. C. Phyllodesmium tuberculatum n. sp., ceratal apex showing cnidosac devoid of nematocysts, c ― cnidosac. D. Phyllodesmium pinnatum n. sp., micrograph of ceras showing secondary branching, zooxanthellae shown by arrows. E. Phyllodesmium pinnatum n. sp., ceratal apex showing absence of cnidosac. F. Phyllodesmium karenae n. sp., ceratal apex showing undivided digestive gland duct and absence of cnidosac.

FIGURE 5. A. and B. Jaw plate and masticatory denticles of Phyllodesmium tuberculatum n. sp. (CASIZ 106547). C. and D. Jaw plate and masticatory border of Phyllodesmium pinnatum n. sp. (CASIZ 179101). E. and F. Jaw plate and masticatory denticles of Phyllodesmium karenae n. sp. (CASIZ 177313).

FIGURE 6. A. Radular cusps and denticles of Phyllodesmium tuberculatum n. sp. (CASIZ 106547) B. Radular cusps and denticles of Phyllodesmium pinnatum n. sp. (CASIZ 179101) C. and D. Radular cusps and denticles of Phyllodesmium karenae n. sp. (CASIZ 177313, note the ventral denticle near the apex of each cusp).