Phyllodesmium undulatum Moore & Gosliner, 2014, n. sp.

Phyllodesmium undulatum n. sp.

(Figures 1B; 2B; 4C, D; 5C, D; 8B)

Phyllodesmium sp. 4 Gosliner et al, 2008: 389, top three photos. Material examined

Holotype: California Academy of Sciences, CASIZ 177171, not dissected, 14 m depth, Waterfall Bay, Pulau Tioman, Malaysia, 4 October 2007, T. M. Gosliner.

Paratypes: CASIZ 105746, 0–17 m depth, Sepok, Maricaban Island, Batangas Province, Luzon, Philippines, 24 February 1995, T.M. Gosliner.CASIZ 115810, 12 m depth, beneath Tengan pier 14 km west of Ikei-shima, Okinawa, Ryukyu Islands, Japan, 25 June 1995, R. F. Bolland.CASIZ 176717, 14 m depth, Waterfall Bay, Pulau Tioman, Malaysia, 4 October 2007, T. M. Gosliner.

Geographic range

Known from Sepok, on Maricaban Island off southern Luzon, Philippines, near Ikei-shima in the Ryukyu Islands, Japan, and Waterfall Bay, Pulau Tioman, Malaysia (present study). There is one photograph of this species from Manado, Indonesia, taken by Pauline Fiene in 1991, but there are no specimens available from this region.

Etymology

This species is named in recognition of the extensively undulating digestive duct within the cerata.

Natural history

Specimens are often found crawling on a red gorgonian octocoral in the genus Acabaria. This is likely the prey of this species, but actual feeding has not been observed.

Description

Color and external morphology: Living animals are very elongate with the mantle extending laterally just beyond the narrow foot. Preserved specimens are 15 mm (CASIZ105746), 18 mm (CASIZ115810), and 45 mm (CASIZ176717) in length. The length of specimen 115801 when living was 46 mm. The anterior portion of the foot margin is broad with moderately tentacular foot corners.

The body of the living animal is predominantly transparent, with viscera and gonads visible through the mantle and foot. A single thin, opaque white line follows the entire length of the animal middorsally between the rhinophores and along the dorsum. The anterior foot corners have a cream-yellow line extending from the lateral sides of the head to the tips of the tentacular processes (Figure 1B).

The cerata are generally transparent with the exception of a slight blue color near the tips followed by yellow at the terminus of each ceras. They are cylindrical and contain extensively undulating and undivided digestive tissue. The digestive gland within each ceras is a cream-yellow color near the dorsum, turns slightly pink just before the blue portion of the ceras, and turns cream-yellow again at the tip of the ceras. The cerata contain distinctive but nonfunctional cnidosacs at the distal ends. The longest and widest cerata are near the median region of the dorsum, with newly developing cerata at the edge of the mantle. The ceratal arrangement consists of arches and rows, with anteriormost groups forming arches and posteriormost groups forming rows (Figure 8B). One specimen (CASIZ115810) was missing all cerata, but the raised basal groupings appear consistent with the other specimens. The precardiac and first postcardiac arches both contain 7–11 cerata, with the largest animal (CASIZ176717) having ceratal groups containing the most cerata, and the smallest animal (CASIZ105746) with the least. The genital aperture is located just anterior to the precardiac arch on the right side. The renal pore is in the interhepatic space between the precardiac and first postcardiac arches on the right side, slightly closer to the postcardiac group of cerata. The anal papilla is directly under the first postcardiac arch on the right side. The second postcardiac ceratal arch contains 6–11 cerata, followed by 5–10 cerata in the third postcardiac arch. The fourth postcardiac ceratal group contains 5–7 cerata and is an incomplete arch, while the fifth and sixth postcardiac groups each contain 2–3 cerata in rows (specimen number 105746 had only one ceras in the fourth, fifth, and sixth postcardiac ceratal groups, but this was suspected to be due to prior injury). Specimen number 176717, being the largest specimen, had a seventh postcardiac ceratal row containing three cerata. The oral tentacles and rhinophores are smooth, and taper to pointed apices. The rhinophores are extended in length, as long as the oral tentacles in preserved specimens, and both are generally transparent with variable blue and/or yellow bands. Two specimens (CASIZ105746 and 176717) have only yellow on the rhinophores, whereas the other has a hint of blue midway up each rhinophore. The oral tentacles and rhinophores terminate in broadly yellow tips for all specimens.

Reproductive system (Figure 2B): All three dissected specimens were mature, with well-developed female glands consisting mostly of mucous gland. The albumen and membrane glands were completely developed but smaller in comparison. A large, looped ampulla branches to the oviduct and the prostatic portion of the vas deferens. The oviduct joins a nodulose receptaculum seminis, and a second branch extends from the base of the receptaculum to join the mucous gland near the albumen gland. The second branch of the ampulla connects to the vas deferens with the proximal portion being prostatic. The moderately sized prostate is slightly convoluted in two specimens (CASIZ115810 and 176717) and totally straight in the other (CASIZ105746), leading to a small, conical-shaped penial bulb in both specimens. The genital aperture has two openings, one each for the male and female genital systems (Figure 2B).

Buccal armature: The jaws are thin and coriaceous with undeveloped, possibly vestigial, bumps on the masticatory border. These are not denticulate, but noticeable in both specimens (Figure 4C, D). The radulae have formulae 17 × 0.1.0 for specimen 105746 and 22 × 0.1.0 for specimen 115810. The radular teeth are triangular in shape leading to long, slightly curved, primary cusps in one specimen (105746; Figure 5C) and blunt, short primary cusps in the other (115810; Figure 5D). The latter specimen appears to have an abnormality in the length of the primary cusp, or this may have been caused by severe wear on the teeth. The rib on the ventral side of each tooth extends from the posterior of the tooth to the point of curvature on the primary cusp in specimen 105746. In the specimen with the blunt, short primary cusp, the ventral rib extends nearly to the apex. Denticulation extends along the margin of each tooth, starting at the base of the tooth and ending at the curvature of the primary cusp in one specimen, and nearly to the apex of the cusp in the other. The denticles numbered 12–14 in specimen 105746 and 10–14 in specimen 115810. The denticles are elongate and pointed, reaching slightly underneath the ventral portion of the tooth in specimen 105746, and appear shorter and more blunt in specimen 115810. This further indicates increased wear on the teeth in the latter specimen.

Remarks: Of the previously described species of Phyllodesmium, only P. opalescens, P. horridum, and P. acanthorhinum have undivided digestive tissue within the cerata. However, in 1991, Rudman noted the presence of nodules or buds on the digestive gland in P. horridum, which are not seen in P. opalescens or in the new species, P. undulatum and P. acanthorhinum. In addition, the predominantly transparent mantle and cerata of P. undulatum varies noticeably from the translucent and pale appearance of the mantle in P.

horridum. When compared to P. opalescens, P. undulatum differs noticeably in a number of ways. Externally, the digestive tissue within the cerata of P. undulatum undulates unmistakably whereas in P. opalescens the tissue is relatively straight. Also, the opaque white line down the dorsum of P. undulatum is different from the distinctive white diamonds or teardrop-shaped patches down the dorsum of P. opalescens. The jaw structure of P. opalescens includes large, blunt denticles (Rudman, 1991), whereas the jaw of P. undulatum has no obvious denticles. The reproductive system of P. opalescens and P. undulatum also differ, as P. undulatum has a nodulose receptaculum seminis and a moderate, predominantly straight prostate. Phyllodesmium opalescens has a smooth receptaculum seminis and a prominent, highly convoluted prostate. When externally comparing P. undulatum and P. acanthorhinum, they can be easily distinguished by the papillate rhinophores in P. acanthorhinum compared with the smooth rhinophores in P. undulatum, and by the single white line down the dorsum of P. undulatum and the network or flecked pattern on the dorsum of P. acanthorhinum. Additionally, P. undulatum has elongate angular foot corners, whereas those of P. acanthorhinum are short and blunt. Their reproductive systems also vary. Phyllodesmium undulatum has a nodulose receptaculum seminis and a straight, moderately sized prostate, whereas P. acanthorhinum has an S-shaped receptaculum seminis and prominent, convoluted prostate. The jaw morphology is definitive based on the absence of masticatory denticles in P. undulatum and 4–7 knobby denticles in P. acanthorhinum.