Asteronotus markaensis Donohoo & Gosliner 2020, sp. nov.
Creators: name: Donohoo, Samantha A.
name: Gosliner, Terrence M.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Nudibranchia
Discodorididae
Asteronotus
Asteronotus markaensis

description: Asteronotus markaensis sp. nov.
(Figs. 2A, 3, 4A, 5A)
urn:lsid:zoobank.org:act: 1645B16B-8D63-43A6-B108-CA4DC468BB64
Asteronotus sp.— Gosliner et al. 2015: page 182, top right photograph. Gosliner et al. 2018: page 102, bottom left photograph.
Type material. Holotype: CASIZ 192316 A, one specimen, dissected, foot subsampled for molecular analyses, Marka Island, 18.22668° N 41.31740° E, Red Sea, Saudi Arabia, 7.9m depth, 06 March 2013, T. M. Gosliner. Paratypes: CASIZ 192316 B, one specimen. Marka Island, 18.22668° N 41.31740° E, Red Sea, Saudi Arabia, 7.9m depth, 06 March 2013, T. M. Gosliner.
Type locality. Marka Island, Saudi Arabia, Red Sea.
External morphology. The living animals (Fig. 2A) are oval in shape, range in length between 10–20 mm, and are found under foliose sponges on reef flats between 8– 9m. The body color is medium to dark grey with scattered dark flecking predominantly along the edge of the mantle. The underside of the mantle is tan with a few scattered dark flecks concentrated near the oral tentacles. Light grey tubercles are arranged in irregular groups across the mantle and may also have opaque white spotting along the tips. The gill surrounds the anus and has eight dark grey bipinnate branchial leaves with opaque white spotting along the rachises. The gill pocket contains eight distinct lobes with gentle crenulations that are similar in color to the rest of the body. The rhinophores are perfoliate with 6–10 grey lamellae. The foot is broad, anteriorly notched, and tan in color with scattered dark flecking along the dorsal side. An elongate, digitiform oral tentacle is found laterally on either side of the labial region and mouth.
Internal anatomy. Buccal mass and radula. The buccal mass is muscular and anteriorly connects to a thin labial cuticle which is devoid of armature or rodlets. The radula (Fig. 3A) is composed of predominantly smooth hamate teeth and the radular formula is 44 × 23.0. 23 in the holotype CASIZ 192316A. The inner lateral four to five teeth (Fig. 3B) are short with a broad base and a curved cusp. Some of the inner teeth have a single triangular denticle along the outer side of the primary cusp. The middle lateral teeth (Fig. 3C) are larger and more elongate than the inner teeth with a smooth, narrow cusp. The outer lateral teeth (Fig. 3D) are also larger and elongate, but have a much shorter, rounder smooth cusp than the middle laterals.
Reproductive System. From a narrow preampullary duct, the convoluted ampulla expands before folding and narrowing into the vas deferens and a short oviduct (Fig. 4A). The vas deferens enter an irregular, wide prostate that abruptly narrows distally before elongating into a muscular, ejaculatory portion connected to the penis which enters the common genital atrium shared with the vagina. A narrow, elongate vagina enters a bursa copulatrix that is smaller than the prostate. A short duct connects near the base of the bursa to an elongate receptaculum seminis. The uterine duct also connects to the base of the receptaculum and enters the female gland mass. A sessile elongate nodular accessory gland enters the common genital atrium between the penis and the vagina. Within the base of the accessory gland is a semi-elongate strongly curved accessory spine with a wide base (Fig. 5A).
Etymology. This species is named Asteronotus markaensis after the type locality Jazirat Marka or Marka Island, which is found in the Saudi Arabian Red Sea.
Geographical distribution. Known only from the Saudi Arabian Red Sea.
Remarks. In our molecular phylogeny, Asteronotus markaensis is part of a clade of cryptic species that includes A. spongicolus (Fig. 2B) and A. mimeticus (Fig. 2C). Asteronotus markaensis is sister to A. mimeticus and closely related to A. spongicolus. All three are to some extent externally similar; however, our ABGD and bPTP analyses reveal that there is a strong genetic divergence of 12.92% in the COI gene between A. markaensis and A. mimeticus; as well as a minimum divergence of 13.01% between A. markaensis and A. spongicolus. These high genetic differences combined with key differences in the internal morphology support A. markaensis as a distinct species. Externally, A. markaensis is a medium to dark grey with numerous irregular groups of light grey tubercles that cover the entire body; whereas, A. mimeticus body coloration is grey, brown, or yellow and either entirely smooth or it may have a few groups of tubercles and elongated papillae (Gosliner & Valdés 2002, figs. 1A–D). The body coloration of Asteronotus spongicolus is green or brown with scattered spots a central line of light pigment along the body and is either entirely smooth or with very few tubercles (Gosliner & Valdés 2002, figs. 1E–F). Gosliner and Valdés (2002) described the variability of color and texture in the tropical A. mimeticus and A. spongicolus as a reflection of the variability in sponge prey species potentially due to their wide geographical distribution. Asteronotus mimeticus is found throughout the western Pacific Ocean, while A. spongicolus is widespread throughout both the Indian and western Pacific oceans including the Red Sea. This type of color and prey variation may also occur in the newly described A. markaensis from the Red Sea; however, additional specimens are required to confirm whether this variability is present.
The radular teeth are similar in shape between A. markaensis, A. mimeticus, and A. spongicolus; but the presence of denticles and the shape of the outermost tooth vary. In A. markaensis, some of the inner five lateral teeth have a single triangular denticle on either side of the cusp, while most of the A. mimeticus specimens studied in Gosliner and Valdés (2002) had no denticles; however, one specimen of A. mimeticus from Papua New Guinea had one to two triangular denticles on the outer edge of the cusp on the innermost 14 teeth (Gosliner & Valdés 2002, figs. 4C–D). In contrast, the innermost teeth of A. spongicolus have one to two denticles along the inner cusp, followed by an additional seven teeth having one to two denticles along the outer cusp (Gosliner & Valdés 2002, figs. 7A–B). In all A. mimeticus specimens studied the outermost tooth is reduced to an ovoid plate (Gosliner & Valdés 2002, fig. 7D), while the outermost tooth in A. spongicolus is reduced to a quadrangular plate (Gosliner & Valdés 2002, figs. 3D, 4B, 4D), but in A. markaensis the outermost tooth is simply a reduced version of the rest of the outer lateral teeth and is narrow and elongate.
The reproductive system of A. markaensis has a large irregular prostate with a smaller bursa copulatrix and a smaller elongate receptaculum seminis; whereas A. mimeticus has a large bursa copulatrix, a smaller rounded receptaculum seminis, and a smaller prostate (Gosliner & Valdés 2002, fig. 5), while A. spongicolus has a large receptaculum seminis, a slightly smaller bursa copulatrix, and a small wide prostate (Gosliner & Valdés, 2002, fig. 8). Furthermore, the accessory gland in A. markaensis is sessile, rounded and elongate with a shorter, strongly curved accessory spine; whereas, the accessory gland in A. spongicolus is more irregular with a similarly curved accessory spine; however, the base is much broader and the cusp more narrow (Gosliner & Valdés 2002, fig. 6C). In contrast to A. markaensis and A. spongicolus the accessory gland in A. mimeticus is more regular in shape with an elongate, slightly curved accessory spine (Gosliner & Valdés 2002, figs. 6A–B).
description: Published as part of Donohoo, Samantha A. & Gosliner, Terrence M., 2020, A tale of two genera: the revival of Hoplodoris (Nudibranchia: Discodorididae) with the description of new species of Hoplodoris and Asteronotus, pp. 1-37 in Zootaxa 4890 (1) on pages 9-11, DOI: 10.11646/zootaxa.4890.1.1, http://zenodo.org/record/4301483