Research Article |
Corresponding author: Ellen E. Strong ( stronge@si.edu ) Academic editor: Eike Neubert
© 2021 Ellen E. Strong, Boris I. Sirenko, James H. McLean.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation:
Strong EE, Sirenko BI, McLean JH (2021) The only species of Mohnia Friele, 1879 (Caenogastropoda, Buccinoidea, Buccinidae) in the North Pacific represents an unrecognized new genus of Newtoniellidae (Triphoroidea). ZooKeys 1055: 69-87. https://doi.org/10.3897/zookeys.1055.68911
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Mohnia kurilana Dall, 1913 was described more than 100 years ago from deep waters off the Kuril Islands and remains exceedingly rare in museum collections. Originally placed in the carnivorous neogastropod family Buccinidae, fragmentary soft parts from the type lot and from several specimens belonging to allied species collected in the Aleutian Islands in the 1990s have allowed anatomical investigations for the first time. These have revealed the presence of a paucispiral operculum with an eccentric nucleus, foot with a deep propodial pedal gland and metapodial pedal gland, taenioglossate radula, short acrembolic proboscis, well-developed mid-esophageal gland, glandular prostate, and the absence of a penis; the nervous system is epiathroid with a long supra-esophageal connective and numerous statoconia in the statocysts. Analysis of the gut contents revealed abundant halichondriid sponge spicules. This evidence indicates a placement in the Triphoroidea, a diverse superfamily of specialized spongivores. Mohnia kurilana is transferred to the Newtoniellidae and placed in the new genus Pseudomohnia gen. nov. Pseudomohnia rogerclarki sp. nov. is established for a new species from the Aleutian Islands characterized by its narrowly turreted shell and distinctive multicuspid rachidian. A lectotype is designated for Mohnia kurilana.
Anatomy, radula morphology, shell morphology, systematics
Mohnia kurilana Dall, 1913 was described more than 100 years ago from deep waters off the Kuril Islands in the northwestern Pacific (Figs
Comparative material has remained exceedingly rare. Dried soft parts from the type lot of Mohnia kurilana, as well as several specimens belonging to allied species collected in the Aleutian Islands in the 1990s, have enabled anatomical investigations for the first time, which allow its affinities to be reassessed.
Shell morphology of Pseudomohnia gen. nov. A, B Pseudomohnia kurilana (Dall, 1913) comb. nov A lectotype,
Anatomical investigations of Mohnia kurilana were based on dried soft parts in the type lot,
Specimens were dissected under a Leica MZ 16.5 stereo microscope with camera lucida and stained with toluidine blue to enhance contrast. Radulae were tissue digested overnight in 100 µl of ATL lysis buffer (Qiagen, Inc.) containing ~ 50 µg of Proteinase-K, then sonicated and rinsed in de-ionized water (
The classification used here follows
Repositories:
Anatomical investigations revealed the presence of a paucispiral operculum with an eccentric nucleus, foot with a deep propodial pedal gland and deep medial cleft bearing the opening of a metapodial pedal gland, short acrembolic proboscis, taenioglossate radula, well-developed mid-esophageal gland, glandular prostate, epiathroid nervous system with a long supra-esophageal connective, and numerous statoconia in the statocysts. The stomach and intestine contained abundant sponge spicules. This evidence indicates a placement in the Triphoroidea, a diverse superfamily specialized to feed on sponges, and to the Newtoniellidae in particular, a family distributed predominantly in cold, deep marine waters and frequently characterized by their dextral shell and taenioglossate radula (
Superfamily TRIPHOROIDEA Gray, 1847
Newtoniellidae gen. nov. pro “Mohnia” kurilana Dall, 1913: Sirenko, Kantor and Gulbin 2013: 156.
Mohnia kurilana Dall, 1913, here designated (Fig.
Shell dextral, thin, whitish in color, ~ 15–20 mm in adult shell length; whorls convex, suture deeply impressed, growth indeterminate. Protoconch large, multispiral, nucleus smooth, cancellate sculpture on subsequent whorls, transition to teleoconch gradual or indistinct. Teleoconch with spiral sculpture of fine cords and axial threads, often diminishing on body whorl and on base. Axis slightly gyrate, pervious; columellar plait lacking. Anterior canal short, slightly recurved. Operculum paucispiral with eccentric nucleus. Radula taenioglossate with small, concave rachidian, robust bicuspid lateral teeth, and slender marginal teeth with cylindrical shafts. Foot with deep propodial pedal gland and with metapodial pedal gland opening to deep medial cleft. Acrembolic proboscis short, salivary glands acinous, mid-esophageal gland well developed. Penis lacking. Nervous system epiathroid with long supra-esophageal connective.
In reference to the superficial similarity of the shell and its original placement in the genus Mohnia Friele, 1879 (Neogastropoda, Buccinoidea).
Known only from the Kuril and Aleutian Islands (Fig.
The unique combination of shell and radula characters displayed by Pseudomohnia are unknown in the family and cannot be confused with any other genus. The recognition of Mohnia kurilana as representing a new genus of Newtoniellidae had already been noted by
As documented in a number of newtoniellids, the presence of a large, ribbed protoconch with a gradual or indistinct transition between protoconch and teleoconch, despite being multispiral, points to a non-planktotrophic and intra-capsular mode of larval development (e.g.,
Little is known of the anatomy of newtoniellids, but that of Pseudomohnia compares favorably with
Mohnia kurilana
Dall, 1913: 503;
Mohnia kurilana:
Lectotype. Kuril Islands • 13.40 mm in length; off Simushir Island; 46°42'N, 151°45'E; 229 fm [~ 419 m]; 24 June 1906; USFC steamer Albatross stn 4803;
Kuril Islands • 1 spm; near Iturup Island; 44°47.7'N, 148°55.5'E; 660 m; 27 July 1984; R/V Odyssey; B Sirenko leg.;
Shell. Shell broadly turreted, spire angle ca. 42°, ~ 14 mm in adult shell length, consisting of approximately six, thin, convex whorls, separated by deeply impressed suture (Fig.
Protoconch and operculum morphology of Pseudomohnia gen. nov. A, B, E Pseudomohnia kurilana (Dall, 1913) comb. nov. Lectotype,
Operculum
[Lectotype]. Operculum thin, corneous, honey in color, thinning toward edges; paucispiral, nucleus eccentric, occupying ca. 31% of operculum length (Fig.
Radula
[Lectotype]. Radula taenioglossate (Fig.
Radula morphology and gut contents of Pseudomohnia kurilana (Dall, 1913) comb. nov., lectotype,
Anatomy
[Lectotype]. Foot elongate oval. Propodium large, triangular, presumably with deep, propodial groove (Fig.
Anatomy of Pseudomohnia gen. nov. A Pseudomohnia kurilana (Dall, 1913) comb. nov., lectotype,
Head with broad, muscular snout and long, tapering cephalic tentacles. Eyes conspicuous, on prominent ocular peduncles at outer bases of tentacles. Mantle edge smooth, with short siphon at left. Columellar muscle long, extending roughly one whorl to the level of mid-stomach. Mantle cavity one-half whorl in length. Mantle roof partially adhering to head and neck, not well preserved. Details of osphradium not readily observable. Ctenidium long, extending from siphon to base of mantle cavity. Hypobranchial gland well developed at left of rectum, releasing abundant mucus upon rehydration. Rectum broad, filled with sponge spicules, terminating in non-papillate anus well back from mantle edge. Pallial gonoduct presenting thin, non-glandular, open furrow below rectum. Penis lacking. Pericardial complex behind rear of mantle cavity compressed owing to retraction; details not observable. Bordered just behind by intestine.
Proboscis acrembolic, short. Jaws large, robust, dorsally flanking mouth. Buccal mass large with large odontophore occupying posterior two-thirds of buccal cavity behind jaws when retracted. Odontophore flattened, elongate, projecting upward from ventral posterior buccal mass, with flattened anterior end projecting against buccal roof behind jaws. Long, narrow, glandular subradular organ projecting between jaws from antero-ventral surface of odontophore. Moderately long radular ribbon emerging mid-ventrally near posterior end, embedded within acinous salivary glands posteriorly enclosing posterior buccal mass, and extending alongside anterior esophagus. Rather narrow mid-esophagus forming mid-esophageal gland with broad, glandular septae almost completely occluding lumen.
Stomach extending to ~ 1.5 whorls back from mantle edge, forming elongate chamber ~ 0.5 whorl in length, lying along left side of whorl ventrally surrounded by digestive gland. Stomach chamber broader posteriorly, narrowing anteriorly, filled with sponge spicules (Fig.
Known only from the Kuril Islands (Fig.
The original description stated that the type material was dredged by the U.S. Bureau of Fisheries steamer Albatross in 229 fathoms (~ 419 m) off the Kuril Islands. The original, handwritten accession ledger at the
Only limited morphological observations were possible given the size and condition of the dried soft parts but agree well with those obtained for Pseudomohnia sp. (see below). Although undeveloped, the pallial gonoduct appears to lack accessory sperm storage pouches (
Analysis of the gut contents revealed the common occurrence of large (297 × 14 µm mean length × width) along with skinnier oxeas (248 × 6 µm) (Fig.
Holotype. Aleutian Islands • 17.53 mm in length; Near Islands, north of Attu Island; 53°5.55'N, 173°43.46'E; 114 m; 4 August 1997; R/V Dominator stn 23-971-218; RN Clark leg.;
Aleutian Islands • 2 spms; Near Islands, north of Attu Island; 53°5.55'N, 173°43.46'E; 114 m; 4 August 1997; R/V Dominator stn 23-971-218; RN Clark leg.;
Shell. Shell narrowly turreted, spire angle ca. 30°, ~ 18 mm in adult shell length, consisting of approximately eight, thin, convex whorls, separated by deeply impressed suture (Fig.
Operculum
[Holotype]. Operculum thin, corneous, honey in color, thinning toward edges; paucispiral, nucleus eccentric, occupying ca. 38% of operculum length (Fig.
Radula
[Holotype and
Radula and jaw morphology of Pseudomohnia rogerclarki sp. nov., holotype,
Anatomy
[Holotype and
In honor of Roger N Clark, Associate in Malacology at the
Known only from the Aleutian Islands (Fig.
This species differs from Pseudomohnia kurilana in having constricted and elevated early whorls with an early angulation that is somewhat variable among available specimens. The shell is more turreted, with a narrower spire angle, and the operculum has a slightly larger nucleus. The radula is distinguished by the multicuspid rachidian and a greater number of cusps on the marginal teeth.
A radula preparation showing the distinctive multicuspid rachidian that was photographed in July 2006 could not be located in the collections of the
Aleutian Islands • 2 spms; Rat Islands, southwest of Amchitka Island; 51°27.70'N, 178°35.0'E; 384 m; 27 July 1997; R/V Dominator stn 23-971-181; RN Clark leg.;
Shell
[
Operculum
[
Radula
[
Anatomy
[
Head with short, broad, muscular snout and long, tapering cephalic tentacles (Fig.
Proboscis acrembolic. Introvert rather short, muscular, oral tube not cuticularized. Jaws large, robust, surrounding anterior end of odontophore (Fig.
Nervous system epiathroid. Circum-esophageal nerve ring surrounding anterior esophagus (Fig.
Known only from the Aleutian Islands (Fig.
Given the absence of accessory sperm storage pouches in the pallial gonoduct (
The disposition of the remnants of the shell from
To the extent that comparisons are possible, the anatomy of Pseudomohnia sp. agrees well with that of P. kurilana. The most conspicuous differences between the two concern details of the anterior alimentary system; specifically, the salivary glands appeared more irregular, the snout longer, the radular sac shorter, the mid-esophageal gland less developed, and the length of the introvert shorter in P. kurilana. The length of the introvert is known to vary within the family (
In triphoroideans, the plesiomorphic taenioglossate condition has yielded an impressive diversity in tooth number and morphology possibly reflecting the diversity of their sponge hosts (e.g.,
As noted by
While showing some affinity to species currently classified in the Laeocochlidinae, the morphology of the radula and shell of Pseudomohnia presents many unique features previously undocumented in newtoniellids (
This collaboration began as part of Jim McLean’s ‘Northeast Pacific Shelled Gastropods’ project (https://doi.org/10.11646/zoosymposia.13.1). We are grateful to Lindsey Groves (