Archierato michaelmonti Fehse & Simone 2020, nov. sp.

Archierato michaelmonti nov. sp.

(Figs. 10−12, 42)

urn:lsid:zoobank.org:act: AD0398FA-4AEC-4488-AEA2-900339991024

Hespererato columbella: Cate, 1977: 362 (fig. 44h) (non Menke, 1847).

Types. (L, W, D, CT, LT respectivelly). Holotype: LACM 3645: 4.1 by 3.1 by 2.5, 10, 13. Paratypes. 1: MSF MAM tv12-1[subadult]: 4.3 by 3.1 by 2.5, –, 12; 2: ZSM Mol 201712014.1 by 2.7 by 2.3, –, 11; 3: DFB 7624-1: 4.5 by 3.4 by 2.8, 13, 15. Further paratypes, 23 MSF (MAM tv12) from type locality; 4 DFB (5931) from type locality; 3 DFB (7623; 7624) from off Cocos Island, W. Costa Rica; 1 DFB (7622).

Type locality. Encinitas, California, U.S.A. (33°02’04”N 117°17’38”W) [on beach at low tide, 3/1962].

Etymology. Named for Dr. Michael A. Mont, of the Molluscan Science Foundation.

Diagnosis. Shell mid-sized, 4 to 6 mm long, robust, sub-triangular, with slightly distant, irregular, coarse labral and irregular, less developed columellar dentition; ventral fold fine, 13 labral and 10 columellar teeth; maximum globosity at posterior third.

Description. Shell mid-sized, oblique sub-triangular, spire slightly elevated, and blunt. Protoconch and subsequent whorls covered by thin callus. Suture slightly indistinct. Body whorl almost 95% of total height, maximum diameter at posterior third, convexly tapering anteriorly. Anterior ventral margin indented. Dorsum roundly edged. Dorsal sulcus indicated by small dimple on anterior collar in fully adult specimens. Whole shell surface covered by very thin, sub-glossy callus. Aperture comprises ~90% of total height, straight and narrow. Labrum narrow, thickened, smooth, flattened ventrally, anteriorly declivous, posterior portion angled. Outer labral margin rounded, callused, edged at inner margin. Labral teeth coarse, strength decreases towards anterior portion, less developed, slightly distant, 13 in number, restricted to labral edge. Siphonal canal short, narrowed, rounded and slightly indented. Anal canal simple, slightly protruded. Columella almost straight, curved without inner carinal ridge and barely developed parietal lip. Columellar denticles 10 in number, irregular, somewhat obscured at mid-portion, spaced, anteriormost forming terminal ridge, posteriormost enlarged, projecting. Fossula obscured, not delimited from columella. Callosities pale green-white; dorsum, parts of ventrum, tips of canals, siphonal canal, protoconch and whorls olive.

Variability. Subadult specimens have a somewhat elevated spire because of the less developed callosities. The examined shells appear rather uniform. Only the dorsal coloration varies from olive to pale olive-brown and pale reddish-beige. In some more eroded specimens the posterior labral angel is smoothed down.

Distribution. California, U.S.A., to Manta, Ecuador. ‘ Tobago Island, Panama Bay, Pacific Panama’ (Cate 1977: 362).

Examined material. types. W Costa Rica: Cocos Island (DFB 7623; 7624). Ecuador: Manta (DFB 7622). U.S.A.: Encinitas, California (DFB 5931).

Remarks. Cate (1977: 362) suggested to lump all recent Archierato together because he was not comfortable separating them. He explained that ‘one species has several variations’. He based his opinion on specimens (1977: figs. 44a−h) with very different shell morphologies that he interpreted as intraspecific variations. However, the distinguishing features are constant. Archierato michaelmonti is distinguishable from A. columbella and A. panamaensis by the sub-triangular instead of pyriform shell outline (compare Figs. 42, 44, 45). The new species is also separated from A. columella by the pale coloration and from A. panamaensis by the green instead of pale brown coloration. Archierato michaelmonti is separated from both species also by the straight aperture; the less developed and more close-set labral denticles, the projecting posterior columellar denticle, the shorter siphonal canal, the blunt apex, the restricted indentation of the ventral margin; the roundly edged dorsum and the convexly curved labrum (compare the lateral views of the discussed taxa).

The new species is immediately distinguishable from A. galapagensis by the shell outline alone. The outline of A. galapagensis is oblong ovate with maximum width at mid-portion whereas the shell of A. michaelmonti is oblique sub-triangular with maximum width at posterior quarter. The columellar denticles are always obscured at mid-whorl in A. michaelmonti but developed in A. galapagensis. The labral denticles are fine, close-set and restricted to the inner labral edge in A. galapagensis but coarse, spaced and slightly elongated as short folds onto the labrum in A. michaelmonti. The new species possesses a coloured anterior terminal tip whereas it is colourless in A. galapagensis.