Gastropoda: Lottiidae

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Rre VENUS (]ap, Jour, Malac.) VoL 52, No. 3 (1993): t93-209

･J- 2e9flZes ISfKyayoiacmea (-V a -r 7N VV"-}J' )if l tc) a)ee-k･･-U j51 as51>･X!

k7? *Ziiav ･ ISgl k}pt.M

( wi, i( 1< re k\)

Anatomy and Systematic Position of Yayoiacmea, a New Genus

``Coelisella" for Japanese Tiny Limpet oyamai Habe, 1955 (Gastropoda: Lottiidae)

Takenori SAsAKI and Takashi OKuTANI

(Tokyo University of Fisheries, 4-5-7 Konan, Minato-ku, Tokyo 108)

" Abstract: The investigations on shell and anatomical characters on Colliselta" Qyamai Habe, 1955 revealed that it should be placed in the subfamily Patelloidinae of the Lottiidae and need a new genus, Ydyoiacmea. Of systematic characters of the new genus, the radula teeth morphology is unique among the known members of the family.

Introduction

It is extremely difficult to determine the systematic position of a simple limpet solely by shell morphology. Yityoiacmea qyamai (Habe, 1955), the type species of the new genus established here, has been allocated in the genus Collisetla ( =Lottia) of the subfamily Lottii- nae among the family Lottiidae, but the redula, the most important basis for generic alloca- tion, has never been investigated. In addition, nothing was known about the anatomy of

this species, and unfortunately likewise for other related taxa. Ybyoiacmea oyamai has been by no means well-known species in Japanese lottiid limpets "Minutes even since it was described. This species was first described by Habe (1955) in of Conchological Club of Southern California" with a brief note. As the above-mentioned publication was recognized as nomenclaturally valid (Habe, personal communication), and "This thus Habe's statement in two lines, is the smallest acmaeid species in Japan, with

the white, solid, conic shell, on the surface of which radiates reddish rays'', is warranted as the original description. The identity of this species had stayed rather ambiguous until Inaba and Oyama (1977) illustrated the holotype specimen, with a note on dimension, deposi-

tory and type locality. The present study provides the detailed description of the shell and soft part morphology with the discussion on the systematic position of this species. It also offers additional in- stances for anatomical and ecological importance in the limpet systematics.

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Materials and Methods

Materials used for the description were collected by the first author from Banda, Tateyama Bay, Boso Peninsula at a depth of 1 rn during June 1 to 4, 1992. Specimens in National Science Museum Tokyo (NSMT) and some private shell collections were also exarnined for

assembling the data for geographic distribution. Specimens taken alive was relaxed with mag-

nesium chloride, and external anatomy and the body coloration were observed. After fixation, twelve specimens were dissected for internal anatomy under a binocular microscope. Radulae were treated with cool KOH solution for 12 hours and observed with S.E.M. Broken

shell fragments were also observed with S.E.M. for shell structure. Three specimens were

sectioned in 10 ptm thick and then stained with hematoxylin and eosin to observe and recon-

struct some detai]ed structures.

Systematics Family LoTTiiDAE Gray, 1840

The shell is eomposed of four to six shell layers of different structure. The central area is consistently radial crossed-lamellar, the exterior is spherulitic prismatic, the area outside the myostracum is predominated by concentric crossed-]amellar, and foliated structure is absent. The radula has three pairs of mineralized lateral teeth, and less than two pairs of

ehitinous marginal teeth. Remarks: This family had been integrated into the family Acmaeidae (e.g. Habe, 19S5; Fretter and Graham, l962; PondeT and Creese, 1980; Lindberg, 1981a; Nakamura, 1986), but it was recently separated again and re-defined by Lindberg (1986).

Subfamily Patelloidinae Chapman and Gabriel, 1923

The shell consists of four shell layers. The exterior (M+2 layer) are spherulitic prismatic, the intermediate area (M+1 layer) is concentric crossed-lamellar, muscle scar (myostracum) is prismatic, and the central area (M-1 layer) is radial crossed-lamellar in structure (Fig. 1). The radula has zero or two pairs of marginal teeth on both sides of three pairs of lateral teeth.Remarks:

This subfamily was originally a full family established by Chapman and Gabriel (1923), but it has been customary for long period to include all lottiid taxa in the Acmaeidae. It was re-defined as a subfamily by Lindberg and Vermeij (1985) based on shell structure. '

Yinyoiacmea n. gen.

The shell is small patelliform without radial sculpture. Pallial tentacles are shert and sparse. The gill is flap-like bipectinate ctenidium without secondary gill on the pallial groove. A vestigial pair of osphradia is aligned sagittally within the nuchal cavity. The radula consists of three pairs of lateral teeth of equal size with the formula O.3.0.3.0; the innermost and middle teeth arranged obliquely, while the middle and outermost teeth are fused laterally.

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Sasaki & Okutani: New Limpet GenusYliyoiacmea 19S

Fig.1. Ybyoiacmea oyamai; scanning electron micrographs of shell structure. tryi,itfftrtf'Ia)dilimaittoag-uetuSts4E' a. Spherulitic prismatic structure of M+2 layer. Scale= 10 itin. IM.l re inde{M+2 fi ) b. Crossed-lamellar structure of M+1 layer. Scale=25 ptm. tkl"ofirela+ (M+1 e)

± c. Crossed-lamellar structure of M-1 layer. Scale=20 ptm, zk!-kdieeis (.M.1E) d. Myostra ¢ um (M) and adjacent two layers (M+1, M-1), Scale = 20 "m. RX ASIit"tpt CM ee) tL h'oitLk.za

The licker has no lamellate sculpture. The intestine turns in 4 loops. 7ype species: ColliseUa oyamai Habe, 1955 Etymology: Yayoi is an elegant and classic word for March and comesfTOMJapanesestand-

ard name of this limpet.

Ybyoiaemea oyamai (Habe, 1955) (Figs, 1-18)

CoUiseUa eyamai Habe, 1955, p. 3; Takahashi and Okamoto, 1969, p, 27, pl. 1, fig. 8; Nakamura, 1986, p. 39. Collisella (ConoicZacmea) ayamai: Inaba and Oyama, 1977, p. 93, pl. VI, fig. 2. CottiseUa nakamigawai: Oyama, 1963, Collisella (2), figs. 1-2. SheU: The shell is small, moderately thick, and patelliform of medium height with elongate oval aperture. The apex is dorsally pointed and situated at about anterior two-fifths of the shell length, and the protoconch is always detached off. The anterior slope is almost straight, the posterior slope is straight to slightly convex, and the lateral slope is straight. In some

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Fig. 2.Yayoiacmea oyamai; Banda, Tateyama Boso Peninsula. 6.9x5.2x3.8 mm. VHd7litii'"-ffi.Bay,fi1'il[1i･EaFH,re

pm ctn

Fig. 3-4. YZiyoiacmea ayamai. 1' 1 i A O' h'it fi' t 3. Dorsal view, shetl and mantle removed. eSlfigMSWMi 4. Ventral view, Telaxed and shell removed. W(tst'/tiSMstlin' a, anus; a", auricle; ct, cephalic tentacle; ctn, ctenidinm; dg, digestive gland; e, eye; f, foot; i, intestine; il, inner lip; j, jaw; lk, left kidney; mm, mantle margin; nc, nilchal cavity; ol, outer lip; olp, eral lappet; pc, pericardium; pf, pallial fold;pm, pallial muscle; pt, palliar tentac]e; rep, right excretory pore; rk, right kidney; sm, shell muscle; st, stomach; ve, ventricle.

specimens the apertural margin is slightly convex in lateral view, otherwise straight. TheandThe

exterior is radiated with pink to reddish brown streaks which are variable in number

in width on white background, and sculptured by weak concentric growth Iines only.

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197 Sasaki & Okutani: New Limpet Genus Ybyoiacmea

9epnppn

SPO

"c' 1 ] h -i-h'"'ab'( Figs. 5-6. Ybyoiacmea ayamai. t 5. Nuchal cavity and anterior part of visceral mass. I,E-:ISeVEre t IJil wadi/1 a'ISO) Mnygy Ipt1 6. Buccal region, cut open. whG'[SOfl4'irjl'xl a, anus; ae, anterior esophagus; apn, anterior pallial nerve; au, auricle; ba, diges- bulbous aorta; bm, buccal mass; buc, buccal cavity; ctn, ctenidium; dg, leftexcre- tive gland; esg, esophageal gland; g, gonad; i, intestine; j, jaw; lep, tory pore; lk, left kidney; os, esphradium; pc, pericardium; ppn, posterior pallial nerve; rep, left excretory pore; rk, right kidney; sbo, subesophageal- osphradial connective; sd, salivary duct; sg, salivary gland; sm, shell muscle; spo, supraesophageal-osphradial connective; st, stomach; ve, ventricle; yn, visceral

nerve.

interior margin is spotted by maculations that correspond to the exterior color pattern and disappear gradually toward the center. The interior from the intermediate to the central area is shinning white and is so translucent that exterior radiation is seen through. The muscle to variable extent. scar is distinctly shining, and the central area is sometimes stained in brown Eivternal anatomy: The mantle which covers whole dorsal area of the body is pigmented in light green except the marginal area. Dorsal part of the mantle margin is pale and slightly fringed in brown. The shell muscle is horseshoe-shaped and subdivided into approximately curve 14 segments. The pallial muscle hanging over the nuchal cavity roof makes a gradual over the head (Fig. 3). The foot covers about 70CVb of the body length. The mantle margin have a row of very only when short, sparse but somewhat thick pallial tentacles which are barely observable from slightly inner fully extended. They are arranged alternatively by smaller one arisen region of the mantle margin and by relatively longer one projected from the edge, and only is light likethe each base of the latter has a white spot (Fig. 4). The pallial grooye green

mantle, but other ventral area is pale. The mouth is surrounded by outer lip and then extended oral lappet. The cephalic tenta- buccal mass is seen through cles bear the pit-like eye which is pigmented in black inside. The the snout in red, but its color is faded away soon after fixation. The nuchal cavity is shallow and occupies 25glb of the body length. The ctenidium

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ab ic aw

''' '/'

li/t mc

pw pc pp7

sd sd lic srm... lsg

rsg op 9 10

Figs. 7-10.Ybyoiacmea oyamai. t'yt/i-tfi'･eff( 7. Jaw. ua4S( 8, Buccal cartilage, rTl-itlj･ 9. Licker. 10. Saliyary gland. etaHM ab, anterior band; aw, anterior wing; lc, lateral cartilage; lic, licker; lsg, left salivary gland; mc, main cartilage; pc, posterior cartilage; pp, posterier projection ; ps, posterior wing; rsg, right salivary gland; sd, salivary duct; srm, subradula membrane.

Fig. 11.Yb]oiacmea oyamai: Scanning electron of radula.Scale=50pm. g , N - -r ft. i 1 )lf' )v if a) ts,l iFk a) Fa r- pm ittst !i P.micrographs

originated from the posterior wall of the cavity is bipectinate, flap-like, and very flexible in living condition. A pair of osphradia is yestigial and aligned sagittally on the nuchal cavity floor c]ose to the anterior end.of the shell muscle (Fig. 5). The anus and both kidnies

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ilt

olt

rnlt

iip

olp

rc /

Fig. 12. Ybyoiacmea ayamai: Strucrure and growth process of radula. ft'Hi7xt ff ,J- tiv' ( eD ts G- a) re ia- t JV hk j.A-i{ bp, basal plate; ilp, innermost lateral plate; ilt, innermost lateral teeth; Lic, licker; mlp, middle lateral plate; m[t, middle lateral teeth; olp, outermost lateral plate; olt, outermost lateral teeth; rc, radula caecum; rm, radula membrane; rs, radula sac; srm, subradula membrane.

open into the cavity on the right front of the visceral mass. Digestive system: The buccal cavity is dorsally covered with the jaw which is connected by muscles with buccal cartilage and oral tube. The posterior wing of the jaw widely extends laterally, and the anterior wing is smaller and rounded (Fig. 7). The anterior band is narrow without median teeth. The posterior projection which directly covers the functional area of

the radula reaches the posterior end of the posterior wing. The radula is fixed on the odontophore by muscles which are attached to broad and semicircular subradula mernbranes. The licker is situated in fTont of the first radula segment, and almost rectangular with no lamellate sculpture (Fig. 9). The radula teeth consist of three pairs of lateral teeth (Fig. 11). The innermost lateral tooth is situated on the frontal part of radula segment, and the cusp is blunt and weakly curved backward. The middle lateral tooth lies obliquely against the innermost tooth, and the cusp is a little narrower than the innermost tooth and also blunt. The outermost tooth is almost the same width as the middle tooth and also blunt. The middle and outermost

teeth are entirely fused. The boundary between the two teeth is barely visible on the posterior

side but completely undistinguishable anteriorly due to mineralization, so that they look like

a single bicuspid tooth. The radula segment is wider than long. The anterior margin of the basal plate is slightly concave with acutely pointed corner in the outer half, but a part of innermost lateral plate is pushed out over the inner half. The posterior margin is convex, and the inner and outer

margins are straight.

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The basal plate has three lateral plates which are surrounded by chitinous ridges cor- responding to the basal attachment of lateral teeth (Fig. 12), The innermost lateral plate is the largest of the three, and elongated posteriorly with projection. The inner margin is almost straight but only posterior part is concave; the outer margin is slightly sigmoid. The middle lateral plate is narrow, broadened posteriorly, and curved inward. The outermost lateral plate is somewhat oval, well reunded, and posteriorly narrowed. The lateral teeth are mineralized and stained in brown in the process of the radula forma- tion (Fig. 12). At the initial stage, transparent chitinous processes arise on each lateral plate, gradually become brown from the tip of the teeth, and finally the whole teeth are strength-

ened by minerals except for the base.

The buccal mass contains a pairs of cartilages which are made up of three portions, the rnain, lateral, and posterior cartilage (Fig. 8). The main cartilage is well expanded and anteriorly narrowed, and the right and left ones are medianly connected by connective tissue. The lateral cartilage is triangular, thin, and overlies the main cartilage. The posterior cartilage is slightly projected backward and completely fused as a part of main one. The beginning of the buccal cavity is marked by outer Iip and a narrow groove of inner

lip. The buccal cavity swells laterally over the anterior half of the subradula membrane,

and at the end of it the radula is separated by esophageal valve and enclosed by the radula sac. The anterior esophagus is stTaight at first, then gradually turns left and extends laterally at the posterior region (Fig. 6). Dorsal part of anterior esophagus has two thick dorsal folds between which the dorsal food channel is formed, and the ventral part is weakly ridged by two ventral folds.

The anterior esophagus is accompanied by two pairs of accessory glands, viz. the esophageal and salivary glands (Fig. 6). The esophageal glands are depressed dorso-ventrally and extended to the mid-esophagus. The salivary glands are situated along postere-lateral sides of the buccal mass, elongated, and cotton-like in appearance. The right gland is more elongate than the left one (Fig. 10) and its posterior half clings to the pleuro-visceral connectiye, but does not extend to pass through the visceral nerve loop. Mid-esophagus is moderately developed, the ventral and dorsal folds are enclosed by many corrugated lateral folds. The posterior esophagus is marked by sudden constriction on the mid-esophagus, and sculptured internally by several longitudinal folds. The dorsal folds which lie over the ventral fold in the anterior esophagus begin to get under the ventral fold by twisting counterclockwise in the mid-esophagus, and totally inverted in the posterior esophagus. The stomach is inflated, C-shaped sac situated near the dorsal surface (Fig. 13). It sud- denly directs ventralward and leads to the intestine which loops in four times. The first

loop of the intestine tapers and proceeds forward under the stomach, then comes up to the dorsal surface and runs posteriorly again in contact with the margin of the st6mach. The second loop extends toward the frontal region of the visceral mass, and turns posteriorly to the left at a level little lower than the rectum and stomach. The third loop goes down and curves at the bottom of visceral mass across the posterior esophagus and the pyrolic part of the stornach, The fourth loop appears on the dorsal surface again, and encircles

the stomach. The rectum terminates as the anus opens in the anterior right corner of the visceral mass.

The radula sac is of medium length (Fig. 14). After separated from the buccal mass,

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rltp

Figs, 13-14. YZTyoiacmea oyamai. 1'uif"htfi'irffi 13. Cenfiguration of digestive tract. ?liilicljO"tlW 'piEN=IXoesIW 14. Configuration of radula sac, leop; mes, mid-esophagus; 11p, lst loop of intestine; 21p,2nd 3tp, 3rd loop; 41p, 4th loop; pes, posterior esephagus; st, stomach.

' half the first loop of it extends posteriorly, passing between the stomach and postenor of the intestine. In the center of the body, it turns anteriorly and upsets to show the bottom

behind of radula membrane. It runs along the anterior part of the ribbon, and ends just

the buccal mass as the radula caecum.

Circutatory system: The pericardium is situated on the anterior left corner between visceral mass and the shell muscle (Fig. 5). The auricle is small and triangular, and has connection anteriorly with several pores from efferent pallial vessel, capillary vessels ef nuchal cavity roof and efferent ctenidial vessel, and posteriorly with ventricle through a single slit. The

ventricle is also triangular but elongated and situated along both lateral walls of the pericardi-

um. The right and corners of the ventricle are firrnly attached to the pericardial posterior ' ' wall, but the left corner is free therefrom with a small proJection. The bulbous aorta lies beneath the ventricle which is connected with it by a long slit, penetrates the pericardium,

and leads anteriorly to the anterior aorta toward the buccal region and posteriorly to the aorta does not through posterior aorta that branches to the visceral mass. The anterior pass visceral nerve loop. The renopericardial canal extends from the right anterior corner of the

pericardium to the kidney. iixcretory system: There are two kidneys of extremely unequal in size on each side of the one, rectum (Fig. 5). The left kidney is much more reduced in size compared with the right The right kidney and encloses the rectum within. The left excretory pore proJects forwards. extends dorsally, touching the fourth loop of the intestine and shell muscle, and also spreads over a large ventral area of visceral mass. The right excretory pore which also serves as gonopore protrudes as a duct toward the outsides of the nuchal cavity. IVervous system: The nervous system is of hypoathroid type (Fig. 15). The cerebral ganglia are laterally attached to the snoutal wall at the base of cephaiic tentacles and connected

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Fig. 15.Ybyoiacmea oyamai: Central nervous system. -Vg ･tii-t ff"Vtf'(a)i1iHs'. IeKkapn, anterior palliat nerve; bc, buccal commissure; bg, buccal ganglion; cc, cerebral comrnissure; cg, cerebral ganglion; Lbc, labial-buccal connective; [g, labial ganglion; on, optic nerve; pbc, pleural-subesophageal connective; pc, pedal cord; pg, pedal ganglion; pdc, pedal-cerebral connective; plc, pleural-cerebral connective; p]g, pleural ganglion; ppc, pleural- supraesophageal connective; ppn, pesterior pallial nerve; sbg, subesophageal ganglion; sbo, subesophageal-osphradial connective; spg, supTaesophageal ganglion; st, statocyst; tn, tentacular nerve; vg, visceral ganglion; vn, visceral nerve.

with each other by a thick cerebral commissure and with labial, pleural and pedal ganglia by connectives, respectively. The labial ganglia are embedded in the ventral protractor muscles of buccal mass and give off a slender connective to the buccal ganglia along the anterior margin of lateral buccal cartilages. The buccal ganglia are situated between anterior esophagus and radula sac, approaches posteriorly, and ultimately joined by a short buccal cemmis- sure. Fine nerves from cerebral ganglion innervate tentacle, eye and outer lip. The labial

ganglia send several nerves to ventral buccal region, and the buccal to dorsal buccal .reglon. ganglia

The floor of the body cavity posterior to the buccal mass is the most concentrated area of various ganglia. The pedal ganglia are largest of all ganglia, very clo$e to each other, continuous with pleural ganglia, and send a pair of thick pedal cords backward symmetrically in the foot. The pleural ganglia are attached to the ventro-lateral body wall, and both innervate mantle margin by separating into anterior and posterior pallial nerves. The right pleural ganglion gives a thick connective to the supraesophageal ganglion, and the left pleural gaglion to the subesophagear ganglion which comes out to the right side of the esophagus, thus the

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125eE 130e 1350 149" 145'

Fig. 16. Ybyoiacmea oyamai; geographic distributien. Star, type locality; circles, localities of materials examined. t' Yi,i-" ti'Sdi'i cDrk-A9;}dii

pleuro-supraesophageal commissure crosses and runs over the pleuro-subesophageal ganglion. The visceral ganglion are contiguous and fused with supraesophageal and subesophageal ganglia, creating a narrow visceral loop to the right side of the esophagus. The supra-esophageal ganglion leads to the left osphradial ganglion from which osphradial and ctenidial nerves originate. The visceral ganglion is associated with digestive duct and gland, the sub-esophageal ganglion gives a connective to the right osphradial ganglion which innervates right osphradium, and mantle margin as well. The statocysts lie on the posterior wall of each pleural ganglion. Reproductive system: The gonad is situated in the bottom of the visceral mass and partly emerges into dorsal surface between pericardium and fourth loop of the intestine (Fig. 5). into The dorsal part then leads to a thin gonoduct passing under the rectum, and opens the right kidney. The sex can be deteTmined by the color and superficial appearance when is the animal is gravid. The testis is creamy white and cotton-like, while the evary purplish of red and granular. The gonad matures at least from May to June in the Pacific coast

central Honshu. Distribution: Japan Sea north to Niigata Prefecture, and Pacific coast north to Boso Peninsula

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and south to Okinawa Islands and Ogasawara Islands (Fig. 16). No specimens from the outside of the above-mentioned area were included in the molluscan coTlections examined. 7zpe locality: Not given in the original description (Habe, 1955), but later (Inaba and Oyama, 1977) designated as Manshozaki, Shirahama, Wakayama Prefecture (Kii Peninsula). 7ype material: Holotype, NSMT-Mo 39646, 4.8x3.6x2.2 mm. Materials examined for distribution: Japan Sea coast of Honshu- Aikawa, Sado Island (K. Hasegawa) ; Kashiwazaki, Niigata (K. Hasegawa); Takeno, Hyogo (S. Hori); Mishima Island, Yamaguchi (NSMT Mo-45819 and S. Hori); Abu, Yamaguchi (S. Hori); Tsunoshima Island, Yamaguchi (S. Hori). Pacific coast of Henshu- Kominato, Boso Peninsula (T. Okutani and K. Tsuchiya); Mera, Boso Peninsula (K. Tsuchiya); Banda, Boso Peninsula (T. Sasaki); Kurosaki, Miura Peninsula (MSNT Mo-13530 and K. Tsuchiya); Enoshima (NSMT Mo- 13427); Shirahama, Izu Peninsula (NSMT Mo-13435); Shimoda, Izu Peninsula (K. Hasegawa and H. Fukuda); Nishiizu, Izu Peninsula (T. Sasaki); Goza, Shima Peninsula (NSMT Mo-39642); Kushimoto, Wakayama (H. Ishikawa); Shionomisaki (NSMT Mo-39647, H. Ishikawa, and K. Hasegawa). Shikoku- Toyo, Kochi (H. Ishikawa); Komuronohama, Okitsu, Kochi (H. Saito); Nagahama, Ehime (H. Ishikawa); Honai, Ehime (H. Ishikawa); Ikata, Ehime (H, Ishikawa); Seto, Ehime (H. Ishikawa); Misaki, Ehime (H. Ishikawa); Uwajima, Ehime (H. Ishikawa); Misyo, Ehime (H. Ishikawa). Kyushu- Shikanoshima, Fukuoka (H. Ishikawa); Okinoshima, Kamae, Oita (H. Ishikawa); Nomozaki, Nagasaki (T. Sasaki); Tomioka, Amakusa Islands (NSMT Mo-39624) ; Ushibuka, Amakusa Islands (H. Ishikawa); Tashironohama, Yakushima Island (H. Ishikawa); Kuchinoerabu Island (H. Ishikawa). Izu- Ogasawara Islands- IzuOshima Island (T. Okutani); Hachijo Island (NSMT Mo-45894 and K. Tange); Chichijima Island (H. Fukuda); Hahajima Island (H. Fukuda). Amami- Okinawa Islands- Naze, Amami-Oshima (NSMT Mo-39645); Tsuchihama, Amami-Oshima (T. Sasaki); Okinoerabu Island (H. Ishikawa); Naha, Okinawa Island (NSMT Mo-39640); Sashiki, Okinawa Island (NSMT Mo-36941); Tokashiki Island (T. Sasaki); Akashima Island (T. Habe and M. Osawa). Habitat: This species dwells and feeds on red coralline algae grown on the rock surface in Etklonia zone in Honshu (Figs. 17, 18). In subtropical islands, it is collected on calcareous substratum derived from eoral. The shell is encrusted with coralline algae for the most part, therefore, and partly because of its smallness, special attention is required to find live speci-

men. Vertical distribution ranges from the lowest intertidal zone to the subtidal zone down to the depth of 12 m (H. Ishikawa, personal communication).

DiscussiQn

Ybyoiacmea n. gen. is different from the genus Collisetla ( ==Lottia) at subfamily level in shell structure and radula morphology.

In the current systematics, three subfamilies of the Lottiidae, Rhodopetalinae, Patelloidi- nae, and Lottiinae, are clearly defined by shell structure (Lindberg, 1981b; 1988a, b; Lind- berg and Vermeij, 1985; Sasaki and Okutani, 1993). Shells of the Patelloidinae consist of

four shell layers, on the other hand the Lottiinae has five layers with one additional layer,

"ColtiseUa" M + 2 fibrous prismatic layer. ayamai has four-layered shell and, therefore,

does not belong to the subfamily Lottiinae, but to the Patelloidinae.

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"euOit)r-rrf'i Figs. 17-18. }'ayoiacmea ayamai. 17. Natural habitat on coralline algae. Scale=S mm. EJI(ff.Ac7)td'J?frMlt,fi.e IS. Grazing scars on coralline algae. Scale=O.5 mm. h'Jy(1'･nt [iobftftfi

In the subfamily Patelloidinae, three genera, Patettoidu Quoy and Gaimard, 1834, Niveotectura Habe, 1944, E7ginus Jefferys, 1877 (=Probtacmea is synonymized with by Lind- berg, 1988a) are included (Lindberg, 1988b; Lindberg and Marincovich, 1988). The radula of Ratelioida has two pairs of marginal teeth and three pairs of lateral teeth whose innermost and middle ones are aligned longitudinally (Habe, 1944; Ponder and Creese, 1980; Lindberg and Vermeij, 1985), whereas Niveotectura has no marginal teeth, and three paris of lateral teeth of this genus are of equal size and are arranged obliquely like in inverted V-shape (Habe, 1944). thginus has similar radula configuration to Niveotectura (Lindberg, 1976; Galkin and Moskalev, 1978), but the middle and outermost lateral teeth are obliquely fused. The

radula of Ylrryoiacmea has a similarity to that of Erginus in the configuration of innerrnost and middle lateral teeth, but middle and outermost lateral teeth are completely fused laterally just like a single bicuspid tooth. This type of radula teeth is unusual among this family, and it is the key character to define this new genus. The interpretation of teeth fusion in the Lottiidae has been a matter of controversy. Christiaens (1975) regarded the lateral teeth of some genera being two pairs, but Lindberg and McLean (1981) considered that they are three pairs by taking the number of lateral plates on which teeth lie. In the present study, the growth process of the radula teeth (Fig. 12) confirmed that they are essentially composed of three pairs, because they initially have individual ehitinous origins on each lateral plate. Therefore, the apparent cusps with any degree of fusion should be regarded as individual pair of lateral teeth. This interpretation should be applied for all docoglossate limpet radulae. In the very specialized cases in recently established Serradonta and Bathyacmea of the deep-sea Acmaeidae, however, the radula is considered as a single pair with three cusps that share a common shaft at the base (Okutani et

al., 1992). Anatomical studies in the family Lottiidae has been concentrated on the subfamily Lottii- nae, such as Scurria (Thiem, 1917), Lottia (Fisher, 1904; Righi, 1966), M)oponaemea (Sasaki & Okutani, 1993), and Atatacmea (Willeox, 1898), and the subfamily Rhodopetalinae (Lind- berg, 1981b). In the subfamily Patelloidinae, the genus E7ginus is clearly discriminated from

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206 VENUS: Vol. 52, No.3(1993)

the others by possession of penis-like copulating organ and brooding behavior (Golikov and Kussakin, 1972; Lindberg, 1988a). But, anatomical information for other genera is, in most cases, restricted to those of radula (Habe, 1944; Ponder and Creese, 1980; Lindberg and

Vermeij, 1985).

Several anatomical features of Yayoiacmea is unusual or hitherto unknown in the Lottii-

dae, such as, sagittally aligned osphradium, smooth licker without lamellate sculpture, elongated right excretory pore, closely located pedal ganglia, and the narrowest visceral nerve loop. In the Lottiidae, a pair of osphradia is transversely elongated in Scurria (Thiem, 1917), Lottia (Sasaki, unpublished), and Nipponacmea (Sasaki and Okutani, 1993), or absent in

7lectura vit:ginea (Haszprunar, 1985). The licker of Scurria has a lot of V-shaped sculptures (Thiem, 1917), and in the Patellidae, it has more sharply iameliate sculptures (Graham, 1964; Sttitzel, 1984), although little attention has been paid to these differentiations. The right excretory pore is normally short and papillate in the Lottiidae (Fretter and Graham, 1962; Sasaki and Okutani, 1993), and 71ectura virginea alone was known to have elongated right

excretory pore (Fretter and Graham, 1962). In the nervous system, Ybyoiacmea has more closely situated pedal ganglia and narrower visceral nerve loop than Lottia (Fisher, 1904) and IVimponacmea (Sasaki and Okutani, 1993). Furthermore, the topological relationship among the anterior aorta, right salivary gland and the visceral nerve ring is markedly different from those of 7Vimponacmea (Sasaki and Okutani, 1993) and Lottia (Sasaki, unpublished): In IVimponacmea and Lottia, the anterior

rs9

p p

Fig.19. Diagrammatic representation of topological relationship of visceTal nerve Loop. anterior aorta, and right salivary gland in three tottiid =Lk1tJ-rfflf"3KV:thsl･t4 ･R genera. a) o) i IJeluaipt+}, Iif/ri]J.:fuua, timpi}itnM fttlwues reu

a. IVipponacmea and Lottia 7th'dtsthtffiac b. }Jdeyoiacmea. t fi' i as aa, anterior aorta; sd, salivary duct; ppc, pleural-supraesophageal connective; psc, pleural-subesophageal connective; rsg, right salivary gland; yg, visceral ganglion.

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Sasaki & Okutani: New Limpet Genus ftiyoiacmea 207

aorta runs under the visceral ganglion but over the pleuro-supraesophageal connective, and the right salivary duct from buccal cavity reaches the salivary gland after tracked under the 19a), In con- visceral ganglion, accordingly both pass threugh the visceral nerve loop (Fig, trast, in Ybyoiacmea the anterior aorta extends under both visceral ganglion and pleuro-

supraesophageal connective, and the right salivary gland ends immediately anterior to the visceral nerve loop without crossing it (Fig. 19b). This difference is considered to reflect the differentiation at morphogenesis among related taxa. However, the systematic significance of such differences is still obscure. At present state, we conclude that the genus Yiryoiacmea is the closest to Erginus in radula configuration as well as reddish small shell, although they differ from each other in reproductive system and strategy. for the first Habitat preference of Ytryoiacmea ayamai to coralline algae is reported here time. When the other limpets associated with coralline algae, e.g. Niveoteetura pattida, E7gi- nus moskatevi, Patelloida signatoides, and IVijoponacmea gloriosa, are taken into account, there seem to be a certain convergent characters among such type of limpets: (1) The shell is eolored in red andlor white; (2) the radula has blunt cusps of equal size; (3) the soft frequently have part is basically pale and always lacking black pigmentation; and (4) they However, simply red ovary (Habe, 1944; Sasaki & Okutani, 1993; Sasaki, unpublished). whitish shell and animal that lacks pigmentation are also true for subtidal and deep-sea limpets, e.g. Lepetidae and Acmaeidae. The lack of black pigmentatien are not always unique to coralline algae feeder, and the relation between limpet's food and the color of ovary is to not evident. The blunt lateral teeth are certainly represent convergent character peculiar

these species. Geographic distribution of lhyoiacmea ayamai is ranged from warrn temperate to subtropical region in Japan. In the subfamily Patelloidinae, the genus PoteUolda widely dis- tributed in tropical to temperate Indo-Pacific waters (Habe, 1944; Habe and Kosuge, 1966; Ponder and Creese, 1980; Lindberg and Vermeij, 1985), and the genera Niveotectura and thginus are restricted to subarctic Pacific (Habe, 1944; Lindberg, 1988a). Thus, Ybyoiacmea appears to be associated with Ratelloidu rather than Er:ginus and IViveotectura in terms of geographic distribution. However, from the view point of radula morphology as was mentioned above, Ybyoiacmea is particularly related to the cold-water group such as Elrginus

rather than tropical to temperate PateUoida. Further discussion on the phylogenetic relation among the Patelloidin taxa must require more extensiye comparative anatomy as well as paleontological consideration.

Acknowleagments : - We wish to express our gratitude to Dr. T, Habe for valuable suggestien on nomen- clatural treatment and literature, and for permission to examine specimens collected by him and deposited in the National Science Museum Tokyo. Thanks are also due to Dr. H. Saito, National Science Museum Mr. H. Ishikawa, Uwajima, Tokyo fer materials and some important literatures. We are indebted to Ehime Prefecture, for special effort to collect specimens with soft part and shell specimens from a great S. Hori, number of localities, and to Dr, K. Tsuchiya, Mr, K. Hasegawa, Mr. M, Osawa, and Mr. and Mr. K. Tange, all Tokyo University of Fisheries, Mr. H. Fukuda, Tokyo Metropolitan University, habitat of this in- Kamakura, Kanagawa Prefecture, for materials and information on distribution and teresting limpet,

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208 VENUS ： Vol ．52， No ．3 （1993）

要約

ヤヨイハナガサガイは従来 Coliisc〃a （＝Lottia）属に所属させられてきたが，解剖学的研究の結果．，新．でこエハ属あるとが明らかになった。特に歯田は，盈 g∫η 邯ゾノナガサガイ属のものに最も近縁である

と思われるがのどにおいてい，爾舌歯配列な他に類を見な形態を示し明らかに異なっている n

Family Lottiidae Gray 1940 ユキノカガ，サイ科は 4 − − ．殻 6 殻層からなる。筋痕の内側（M 1 層）は例なでは外く放射状交差板構造殻表稜柱構造。．を M ＋ ll はの〜つ栗状構造欠き，曽大部分が放射状交差構造、，歯舌は，3 本側歯と 0 2 本の縁歯を持、，

Subfamily Patclleidinae Chapman and Gabrie］，1923 ウノアシガイ亜科．殻は，稜柱構造（M ＋ 2 層），同心円状交差（M ← 1 構造層），貝殻筋付着層（M 層），放射状交差

板構造（M ＋ 2 層）の 4 t からなるはののつ殻曽。歯舌， 3 本側歯外側に，2 本の縁歯を持か，あるいは

全く欠く。

Genus Yayoiacmea nov ．ヤヨイハナガサガイ属（新属）．歯舌は 3 本の側歯からのみなり，中央の側歯は，内側の側歯に対し斜め後方に位置し，外側の縁歯とは全にして．・のでの完癒合，単歯あるかように見える。

Yayoiacmea oyamai （Habe ，1955）ヤヨイハナガサガイ（模式種）〜殻は小さく，6 7mm 前後。殻表は白字に淡紅色の放射状模様を呈し，彫刻は同心円状の成長線のみ。・分布：房総半島新潟県以南〜小笠原・沖縄

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[Received: May 28, 1993]

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