Gaza compta, Simone & Cunha, 2006

Simone, Luiz Ricardo L. & Cunha, Carlo M., 2006, Revision of genera Gaza and Callogaza (Vetigastropoda, Trochidae), with description of a new Brazilian species, Zootaxa 1318 (1), pp. 1-40 : 4-10

Gaza compta new species

( Figs. 1–10 , 49–52 , 67–77 , 92 )

Types: Holotype MZSP 40324 ; Paratypes: MZSP 40325 , 5 specimens ; ANSP 413312 , 1 shell; MNRJ 10531, 1 shell; ZSM 20060173, 1 shell, all from type locality.

Type locality: BRAZIL: off Cabo Frio , Rio de Janeiro, 22º53’S 42º01’W, 700–800 m depth (otter trawl, i/2004. C.M. Cunha leg.) .

Diagnosis: Shell color pale­beige iridescent, first 2 whorls of teleoconch with purple color, strong axial undulations; spire low with about five whorls. Protoconch without hole in adult. Body whorl with about 55 very narrow spiral lines. Height/width 1.45 on average. Weak carina at middle level of body whorl. Umbilicus completely covered by callus. Orifices in anterior part of mesopodium: 10 on left, 8 on right side. Number of epipodial tentacles: 4 on left, 5 on right side. Rachidian tooth with square base, about 1/6 of total radular width, about 20 tall and slender marginal teeth.

Description

Shell ( Figs. 1–4 ): up to 26 mm in diameter; about five whorls, first 2 whorls purple, remainder pale­beige iridescent. Protoconch ( Figs. 2, 4 ) cream in color, low, of about one whorl, surface smooth, transition with teleoconch unclear. First two teleoconch whorls sculptured only with axial lines ( Fig. 4 ), narrow, spaced by distance equivalent to their width; on third whorl, spiral lines of equal strength of axial lines gradually appearing, producing reticulate shell surface; spiral lines gradually becoming predominant, about 30 on penultimate whorl, about 55 on body whorl; spiral lines very narrow low, close to each other. Tip of spire blunt ( Fig. 1 ), about as high as body whorl, about half of its volume; profile of whorls rounded; suture somewhat shallow, but well marked. Umbilicus only visible in young specimens, wide, deep, width about 1/4 of shell diameter. Peristome preceded by portion of body whorl weakly projecting downwards, amount of deflection equal to 3–4 spiral lines of sculpture ( Fig. 1 ). Outer lip of determinate growth, marked by short, thick projection towards exterior. Inner lip lower (siphonal) region as continuation of outer lip; upper 2/3 of inner lip as part of columella, upper half marked by a very thin, semi­transparent callus ( Fig. 3 ); lower half marked by large callus, with somewhat thin walls, covering entire ventral opening of umbilicus, attached to umbilicus at its edges.

Head­foot ( Figs. 9 , 67, 68 , 92 ): Total length slightly less than half whorl when contracted. Head bulging, located approximately in middle region of head­foot. Snout wide, cylindrical; distal end wider than base; distal surface plane, papillated, with papillae larger at edge, smaller close to mouth ( Fig. 9 ). Papillae long, cylindrical, with rounded tips, separated from each other by about half width of papillae. Mouth located in middle of snout’s ventral surface. Pair of cephalic lappets on dorsal surface of snout, uniting median region of snout with middle region of tentacles’ base ( Figs. 67, 68 : cf); both cephalic lappets separated from each other in median line by distance equivalent to half of cephalic lappets’ width. Cephalic tentacles about 1/3 longer than snout; narrowing gradually up to somewhat pointed tip; tentacles covered by small, microscopic papillae, large cilia seen at high magnifications. Ommatophores located on outer base of cephalic tentacles, about 1/5 of tentacles’ length, almost as wide as their base. Eyes relatively large, dark, occupying most of ommatophores. Foot thick, occupying about half of total head­foot length; divided into mesopodium and epipodium; epipodium ( Figs. 67, 68 : ep) surrounding lateral­dorsal region of mesopodium, equidistant from sole and snout tip. Foot’s anterior orifices located along lateral­dorsal region of foot, on both sides, forming arch from anterior region of anterior edge of foot, at some distance from median line, up to middle region of lateral surface of mesopodium, covered by epipodium ( Fig. 92 ); 10 orifices on left, 8 on right side. Anterior pedal margin wider than remainder of foot, pointed laterally, projecting slightly beyond. Furrow of pedal glands present along entire anterior edge of foot; relatively deep, wide; single aperture of pedal glands relatively broad, located in median region of this furrow. Anterior third of epipodium forming one pair of wide horizontal flaps, anterior end close to ommatophores’ base, abruptly widening near its posterior end. Remaining 2/3 of epipodium relatively low, thick; 5 right, 4 left long, slender epipodial tentacles inserted at its distal edge. Epipodial tentacles located somewhat equidistantly, well spaced from each other, symmetrical on both sides (except in number), becoming shorter from anterior to posterior; anterior epipodial tentacle about half as long as foot; tip pointed. Pair of columellar muscles thick, of about 1/4 whorl, broadly fused with each other in median line ( Fig. 68 : cm). Posterior end of mesopodium with longitudinal, shallow furrow separating it into two halves ( Fig. 67 ). Haemocoel antero­posteriorly elongated, about 2/3 of head­foot width.

Operculum ( Figs. 5, 6 ): Rounded, horny, multispiral, yellow. Nucleus central. Inner edge sigmoid, as inner mold of inner apertural lip.

Mantle organs ( Figs. 71, 73 ): Mantle border relatively thick, simple, white. Pallial cavity of about 3/4 whorl. Osphradium forming node located at base of gill suspensory stalk, weakly dislocated to left ( Fig. 71 : os). Osphradium possessing two nerves inserted at opposite sides; on left side, large nerve coming from nerve ring; on right side, nerve going to distal section of gill suspensory stalk. Gill located on left side of pallial cavity; of about 3/4 of its length; projecting anteriorly by wide, tall suspensory stalk. Anterior end of gill narrow, rounded, projecting outside cavity; gradually increasing towards posterior; posterior end abrupt. Left gill filaments about twice size of right filaments ( Fig. 73 ), possessing ventral­left, pointed projection; right filaments simple. Afferent gill vessel coming from left region of kidney, lying obliquely about 1/4 of its length free from gill filaments; running after in gill distal region of central axis, just distal to gill muscle. Ctenidial vein or efferent gill vessel about three times wider than afferent vessel, running in basal region of gill central axis; its posterior 1/4 free from gill filaments, lying parallel, at left from afferent vessel up to pericardium. Gill muscle running along distal region of gill central axis. Between gill and rectum an area on average of about 1/3 width of pallial cavity roof. No clear hypobranchial gland. Rectum about 1/4 as wide as pallial cavity, sigmoid, posterior region with loop turned to left surrounding kidney ( Fig. 71 : rt), close to median line abruptly curving anteriorly, gradually towards right up to anus. Anus wide, short free end, located on anterior right side of pallial cavity, close to mantle border.

Visceral mass: Not studied.

Circulatory and excretory systems ( Fig. 71 ): Not seen in details because of preservation problems. Pericardium located between pallial cavity and visceral mass, just posterior to kidney, close to median line, slightly to right; its left side receiving ctenidial vein; inner structures (auricles, ventricle) not seen. Single kidney examined, wide, dorsoventrally flattened, pale brown, located in posterior­right region pallial cavity posterior end. Inner renal cavity filled by solid glandular tissue. Nephrostome located at anteriorright region of kidney, preceded by tall, hollow stalk.

Digestive system ( Figs. 8–10 , 69–72, 74–77 ): Oral tube length about half of odontophore length and width, walls with circular muscles ( Fig. 69 : mc). Distal region of oral tube with circular fibers; basal region with oblique fibers ( Fig. 69 : mj), originating gradually from dorsal surface, close to median line, running divergently towards posterior and sides, inserting in ventral surface of odontophore. Remaining oral tube walls thin ( Fig. 8 ). Jaw plates ( Figs. 10 , 70 , 74 ) thick, rounded; cutting edge anterior, occupying most of buccal cavity’s dorsal surface; separated from each other by narrow space. Pair of dorsal folds starting at half of jaws length posterior to jaws, at level of separation between esophagus and odontophore, becoming gradually tall, narrow. Odontophore about 10% longer than snout. Odontophore muscles ( Figs. 69 , 75–77 ): m1, series of small muscles connecting buccal mass with adjacent inner surface of snout and haemocoel; m1a, 2–3 pairs of dilators of oral tube, narrow, thin, originating on lateral surface of haemocoel, in posterior position of snout, running anteriorly, covering ventral surface of mj, inserting in ventral region of oral tube, on side of m1v; m1b, pair of small retractors of buccal mass, originating on lateral surface of haemocoel on side of m1a, running shortly anteriorly, inserting on lateral­posterior surface of odontophore, dorsal most pair of m1a connected to m1b; m1v, pair of small ventral protractors of odontophore, originating on surface ventral surface of oral tube, running posteriorly away from each other, inserting in ventralposterior region of odontophore, in median surface of posterior cartilages; m2, pair of retractors of buccal mass, originating on lateral surface of haemocoel, just posterior to buccal mass level, running anteriorly, inserting in two bundles, ventral branch about half as long as dorsal branch, but spreading on lateral surface of odontophore; m4, broad pair of dorsal tensor muscles of radula, subradular membrane; originating part in anterior cartilages, along their ventral surfaces at some distance from median line, part in posterior cartilages, in their posterior, lateral surfaces, surrounding anterior cartilages lateral, ventral surfaces, inserting along subradular membrane, in its dorsal region exposed inside buccal cavity, with portion in radular ribbon in its region preceding buccal cavity; m5, pair of large ventral tensor muscles of radula, originating in ventral surface of posterior cartilages, running towards dorsal, median, subsequently running anterior, inserting in radular ribbon in its region preceding buccal cavity; m6, horizontal muscle, uniting both anterior cartilages almost along entire ventral edge (except short posterior region), in their external surface; m7, very small, thin pair of muscles, originating in inner ventral surface of radular sac, in its middle region, running anterior, covering m6, separating from each other at their middle level, inserting in terminal edge of subradular membrane; m7a, very small, thin pair of muscles, originating in haemocoelic ventral surface, running dorsally, separating from one another surrounding m7, inserting in radular sac, anterior to insertion of m7; m8, pair of broad approximator muscles of cartilages, originating in anterior cartilages, in a small area of their lateral surface, posterior to insertion of mj, running posterior, decreasing gradually, inserting in middle region of anterior surface of posterior cartilages; m8a, pair of accessories of m8, shorter, originating posteriorly on same side of anterior cartilages as m8, running parallel, posterior to m8 pair, covered by them, inserting in posterior cartilages just dorsal to m8 insertion; m11, two pairs of narrow, thin ventral tensor muscles of radula, originating in middle region of ventral surface of posterior cartilage, one separated from other by distance equivalent to their width, running anteriorly covering m6, anterior cartilage’s ventral surface, inserting in subradular membrane distal edge, some distance beyond it towards radular ribbon, along its inner surface. Odontophore non­muscular structures ( Figs. 76, 77 ): oc, pair of anterior odontophore cartilages, antero­posteriorly elongated, flat, anterior and posterior ends rounded (anterior end smaller and weakly turned medially), with about same length of odontophore; po, small pair of posterior odontophore cartilages, about 1/10 of anterior cartilages length, about half of their width; located in posterior, slightly lateral side of anterior cartilages; br, subradular membrane, covering most of odontophore exposed in buccal cavity, where most of intrinsic odontophore muscles inserts; sc, subradular cartilage, maintaining radular ribbon, expanding in buccal cavity beyond radula, covering about half of exposed portion of subradular membrane. Radular sac wide, projecting beyond posterior side of odontophore, with approximately same as length. Radular nucleus bifid, divided in middle by a furrow. Radula ( Figs. 49–52 ) symmetrical, arched. Rachidian ( Figs. 50, 52 ) with square base, about 1/6 of total radula width; cutting edge with projection turned posterior (almost 90º) covering posterior end of preceding tooth, this projection triangular, tip blunt, almost as wide as base, preceded by narrower, thickened region; interlock sub­terminal, at base of cutting projection. Six lateral teeth somewhat similar to rachidian, except for being asymmetrical, greatly curved towards medial; lateral teeth gradually becoming narrower and more elongated; lateral teeth forming curve with concave side towards radular sac, sixth lateral positioned at about same level as rachidian tooth of preceding row; tip sharply pointed; 2–3 small cusps separated from each other along both edges. About 20 marginal teeth ( Figs. 49, 51 ), tall, slender, curved inwards; teeth gradually becoming narrower towards periphery; tip sharp pointed, preceded by wider, flattened region, having about 15 small, narrow, sharply pointed, well­separated cusps on both sides; non­functional lateromarginal plate as reduced innermost marginal tooth ( Fig. 50 ). Salivary glands ( Figs. 8 , 69 , 74 : sg) small, close to origin of esophagus. Salivary ducts very short, opening almost immediately after penetration in dorsal wall of buccal cavity; salivary apertures small pores located in middle region of each dorsal fold, slightly posterior to their origin ( Fig. 74 : sa). Conspicuous series of transversal muscles separating esophageal and odontophoral branches of buccal mass ( Fig. 69 : mt). Anterior esophagus ( Figs. 8 , 69 , 74 : es) very wide, inner surface with four tall, narrow folds ( Fig. 74 : ef); two of them as continuation of dorsal folds, producing wide dorsal furrow; central region of this dorsal furrow smooth, remaining regions, including folds, completely covered by small papillae ( Fig. 74 : el); papillae low, separated by space equivalent to their size, with rounded tips. Another pair of folds running along left side, close to each other, producing narrow left furrow; ventral fold of this pair disappearing gradually in posterior level of haemocoel; dorsal fold uniting with left dorsal fold, forming small chamber, at posterior end of haemocoel. Right dorsal fold running beyond posterior end of haemocoel, becoming gradually lower. Posterior esophagus, stomach not seen in details. Intestine very wide ( Fig. 71 : in), originating in anterior­dorsal region of visceral mass, running anteriorly along haemocoel up to region close to buccal mass ( Figs. 69 , 71 ), bending abruptly, running posteriorly; in visceral mass anterior region possessing wide loop surrounding kidney, pericardium, exiting to pallial cavity in its right­posterior corner. Rectum, anus described above (pallial organs). Fecal material solid, hard, filling entirely intestine, having a middle, ventral, longitudinal furrow ( Fig. 72 ).

Genital system: Not studied.

Central nervous system ( Figs. 7 , 69 ): Nerve ring located surrounding anterior half of buccal mass. Cerebral ganglia broad, long, located on lateral region of buccal mass. Cerebral commissure thick, long. Pleural, pedal ganglia close to each other, located inside pedal musculature just below ventral surface of haemocoel. Pedal commissure very short, with both ganglia practically touching one another. Very large pedal nerve running forward from each pedal ganglion ( Fig. 7 : pn), surrounding median pedal blood sinus. Statocysts located very close to posterior side of pedal ganglion.

Etymology: The specific epithet refers to the ornamentation of the first teleoconch whorls, from the Latin comptus, meaning ornamented.

Measurements of shells (larger diameter and width in mm): Holotype. MZSP 40234: 26.0 x 19.0; MZSP 40235, #1: 25 x 18; #2: 24 x 17; #4: 25 x 17.

Distribution: Know only from the type locality.

Habitat: Rocky, 700 to 800 m depth.

Material examined: Types.

Figures

FIGURES 1–10. Gaza compta. Figs. 1–4, Shell of Holotype MZSP 40324 (diameter = 26 mm). Fig. 1: Apertural view. Fig. 2: Apical view. Fig. 3: Umbilical view. Fig. 4: Detail of spire. Fig. 5–6: Operculum, outer and inner views (length = 10 mm). Fig. 7: Pedal ganglia and adjacent region, dorsal view, dorsal structures into haemocoel removed, pedal medial sinus (ps) opened longitudinally. Fig. 8: Foregut, ventral view, odontophore removed, esophagus (es) opened longitudinally, some structures, such as nerve ring (cc, ce) and salivary gland (sg) seen by transparency. Fig. 9: Snout, ventral view, opened longitudinally along its ventral median line. Fig. 10: jaw plates, ventral view. Scale bars: 7–10 = 1 mm.

FIGURES 49–57. Radulae in SEM. Figs. 49–52: Gaza compta. Fig. 49–51: Holotype. Figure 49: entire shell; scale bar = 100 µm. Fig. 50: Detail of central and lateral teeth; scale bar = 50 µm. Fig. 51: Same, detail of marginal region; scale bar = 50 µm. Fig. 52: Paratype, central region; scale bar = 50 µm. Figs. 53–54: G. cubana. Fig. 53: Entire shell; scale bar = 100 µm. Fig. 54: Lateral teeth, scale bar = 100 µm. Figs. 55–57: G. fischeri. Fig. 55: Entire shell, scale bar = 100 µm. Fig. 56: Detail of central and lateral teeth; scale bar = 100 µm. Fig. 57: Detail of lateral region; scale bar = 50 µm.

FIGURES 67–70. Gaza compta anatomy. Fig. 67: Head­foot, apertural view. Fig. 68: Same, right view. Fig. 69: Foregut, left view, some adjacent structures of haemocoel also shown. Fig. 70: Jaws, ventral view. Scale bars = 1 mm.

FIGURES 71–74. Gaza compta anatomy. Fig. 71: Pallial cavity, mid and hindgut, ventral view, digestive tubes somewhat deflected. Fig. 72: Transversal piece of fecal bundle. Fig. 73: Transversal section of gill, showing filaments and adjacent region of mantle. Fig. 74: foregut, ventral view, esophagus (es) opened longitudinally, odontophore (of) deflected to left, in dorsal view. Scale bars = 1 mm.

FIGURES 75–77. Gaza compta odontophore. Fig. 75: General, ventral view, superficial membrane removed. Fig. 76: Dorsal view, both anterior cartilages (oc) deflected, most muscles also deflected, left m4 and m5 (right in Fig.) shown still inserted in subradular cartilage (sc), buccal cavity portion of radula and adjacent structures only partially shown. Fig. 77: Right half, dorsal­slightly lateral view, showing muscular insertions, m5 deflected. Scale bar = 1 mm.

FIGURES 89–92. Gaza spp. anatomy. Figs. 89–91: G. olivacea, Brazilian re­hydrated specimens. Fig. 89: Head­foot, frontal view. Fig. 90: Mid and hindgut as in situ, dorsal­slightly right view. Fig. 91: Foot (re­hydrated and partially damaged), head removed, foot anterior orifices (fo) shown. Fig. 92: G.compta, foot, head removed, foot anterior orifices (fo) shown. Scale bars = 2 mm.