Relichna pachys (Watson, 1883)

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 759-761

Relichna pachys (Watson, 1883)

Figs 88A-D, 89

Utriculus pachys Watson, 1883: 331 .

TYPE MATERIAL. — Two syntypes BMNH 1887.2.9.2239-40 .

TYPE LOCALITY . — Northeast of New Zealand , 37°34’S, 179°22’E, 1280 m [Challenger: stn 169]. MATERIAL EXAMINED . — Philippines. MUSORSTOM 3: stn DR 3: stn DW 07 , 24°55’S, 168°21’E, 505 m, 1 dd (Figs 88A, B) . — BE- 95, 13°56’N, 119°59’E, 865 m, 1 dd. RYX 11: stn DW 09 , 24°52’S, 168°22’E, 635-680 m, 1 dd .

Coral Sea. MUSORSTOM 5: stn 321, 21°20’S, 158°02’E, 1000 m, New Hebrides Arc. VOLSMAR: stn DW 30 , Hunter and Matthew 1 dd; stn 322, 21°19’S, 158°00’E, 975 m, 1 dd . — CORAIL 2: stn Islands, 22°17’S, 171°18’E, 450-550 m, 1 dd.

DW 172 , Mellish Reef, 18°26’S, 155°12’E, 1100 m, 4 dd. Vanuatu. MUSORSTOM 8: stn DW 987 , 19°23’S, 169°35’E, 1040- Loyalty Ridge. BIOCAL: stn KG 06, 20°35’S, 166°53’E, 735 m, 1050 m, 2 dd; stn CP 1110, 14°49’S, 167°15’E, 1360 m, 1 dd (Figs 3 dd; stn DW 79 , 20°40’S, 166°52’E, 1320-1380 m, 1 dd. — BIO- 88C, D) .

GEOCAL:stn DW 296, 20°38’S, 167°10’E, 1230-1270 m, 1 dd; stn Fiji. MUSORSTOM 10: stn CP 1361, SE of Viti Levu, 18°00’S, DW 311, 20°49’S, 166°54’E, 1620 m, 2 dd; stn DW 313, 20°59’S, 178°53’E, 1058-1091 m, 2 dd.

166°59’E, 1600-1640 m, 7 dd. Wallis and Futuna. MUSORSTOM 7: stn DW 578, Futuna Is- Norfolk Ridge. BIOCAL: stn DW 48, 23°00’S, 167°29’E, 775 m, land, 13°08’S, 176°16’W, 640-730 m, 9 dd.

11 dd; stn DW 49, 23°03’S, 167°32’E, 825-830 m, 1 dd; stn DW Tonga. BORDAU 2: stn DW 1531, Eua, 21°12’S, 174°56’W, 51, 23°05’S, 167°45’E, 680-700 m, 1 dd; stn DW 53, 23°09’S, 970-983 m, 2 dd; stn DW 1553, S of Nomuka Islands, 20°42’S, 167°43’E, 975-1005 m, 1 dd; stn DW 70, 23°25’S, 167°53’E, 965 174°54’W, 650-676 m, 1 dd.

m, 4 dd; stn CP 74, 22°14’S, 167°29’E, 1300-1475 m, 2 dd. — SMIB

DISTRIBUTION. — Originally described from northeast of New Zealand, in 1280 m (Watson 1883). Material herein collected from the Coral Sea, Fiji, Hunter and Matthew Islands, New Caledonia, the Philippines, Tonga, Vanuatu and Wallis Island (Fig. 89), in 505-2370 m.

DESCRIPTION. — Shell morphology. Length 10 mm, width 6 mm (largest specimen examined). Shell solid, short, oval, with convex sides (Figs 88A, C). Only 1 whorl visible, forming nearly the entire shell, except for a small visible portion of the top of the spire. Apex flat, umbilicate, with a deep, narrow umbilicus in some specimens (Fig. 88D) and a wide, shallow umbilicus in others (Fig. 88B), and all intermediates between these two types. Aperture lip rising from the left side. The aperture lip forms a rounded wing connected to the columellar margin. Anterior end of the shell rounded. Aperture as long as the shell, wider anteriorly and narrowing gradually at about 1/3 of its length. Columellar margin slightly thickened. Columella with 1 fold in some specimens (Fig. 88A), absent in other specimens (Fig. 88C). There are transitional forms with an inconspicuous columellar tooth. Umbilicus closed. Sculpture of a number of inconspicuous growth lines. Colour uniformly dirty white to pale brown.

Anatomy. Unknown. All shells collected lacked soft parts.

REMARKS. — The material here examined is very similar to the original description of Utriculus pachys by Watson (1883) and it is therefore assigned to this species. The original type material of U. pachys is lost, but the original description is detailed enough to allow a positive identification.

The shell morphology of U. pachys is very similar to other species of Relichna here reviewed, so it is here transferred to this genus. However, all the specimens collected lacked soft parts, so this generic placement is tentative.

Specimens of Relichna pachys here examined are very variable. Some specimens have a shallow, wide apical umbilicus, whereas others have a narrow, deep umbilicus. Additionally there are specimens with a conspicuous columellar tooth, whereas in others the columella is smooth. There are intermediate forms between all these morphologies and there seems to be no correlation between geographic range and a particular shell morphology, although specimens collected at greater depths consistently have a deeper umbilicus and a smoother columella. Because of the lack of anatomical information it is not possible to determine whether shallower-water specimens could constitute a different species.

Retusa aupouria Powell, 1937 , described from New Zealand, is very similar in shell morphology (Powell 1937) and could be a synonym. Both species were regarded as possible members of Relichna by Powell (1979).

FIG. 88. Shell morphology of species of Relichna Rudman,1971 . A, Relichna pachys (Watson,1883) , (8 mm), ventral view, New Caledonia, SMIB 3 stn DW 07; B, same shell, posterior view; C, (10 mm), ventral view, Vanuatu, MUSORSTOM 8 stn CP 1110; D, same shell, posterior view. E, Relichna sp. 1 , (9 mm), ventral view, New Caledonia, BIOCAL stn DW 53; F, same shell, posterior view. G, Relichna sp. 2 , (7 mm), ventral view, Vanuatu, MUSORSTOM 8 stn DW 1045; H, same shell, posterior view.