Atlanta peronii is the type species in the genus Atlanta. It attains the largest size of all atlantids (to 10 mm shell diameter). The walls of the shell are unusually thick and strong. The keel is moderately tall and rounded in side profile, with a slightly truncated leading edge. The keel base is clear in young animals, but changes with age to a light brown and then a dark yellowish-brown. The keel inserts between the fourth and fifth whorls in shells larger than about 3 mm. The spire consists of 3-1/2 to 3-3/4 whorls. The whorl surfaces are smooth. The sutures between the first and second whorls are shallow, while those between subsequent whorls are incised. Full grown shells can consist of up to 6 whorls. Shell transparent, but can become faintly yellow in large individuals. Eyes type b. Operculum type b. Radula type II, large with sexually-dimorphic marginal teeth. The species is cosmopolitan in tropical to subtropical waters. In Hawaiian waters, A. peronii is a strong nocturnal vertical migrator, ranging downward to a daytime maximum of 300 m and migrated into the upper 150 m at night.

Diagnosis

• Maximal shell diameter = 10 mm
• Shell with thick, strong walls, consisting of up to 6 whorls
  
• Shell transparent, but becomes a faint yellow in older animals
• Keel moderately tall and rounded, inserting between fourth and fifth whorls in shells larger than about 3 mm
  
• Keel base clear in young individuals, becoming brown to yellow-brown with age
• Spire consists of 3-1/2 to 3-3/4 whorls
• Sutures between the first and second whorls shallow; subsequent sutures incised
  
• Spire whorls smooth
• Eyes type b
• Operculum type b
• Radula type II; large, with sexually-dimorphic marinal teeth
  

1. Shell
1. Shell diameter to 10 mm
   
2. Shell with thick, strong walls; wall thickness = 22-25 µm (Richter, 1993)
   
3. Spire consists of 3-1/2 to 3-3/4 whorls; shell of full-grown individuals with up to 6 whorls
   
4. Surface of spire whorls smooth
5. Sutures between the first and second whorls are shallow; sutures between subsequent whorls are deeply incised (see fourth SEM image below)
   
   

   Figure. Scanning electron micrographs of a 3.8 mm Atlanta peronii shell viewed from the right side. Shell at low magnification (left) and spire at high magnification (right). Scale bars = 0.5 mm (left) and 0.1 mm (right). © Roger R. Seapy
   
   

   

   Figure. Scanning electron micrographs of a 3.8 mm Atlanta peronii shell viewed from the right side tilted. Shell at low magnification (left) and spire at high magnification (right). Scale bars = 0.5 mm (left) and 0.1 mm (right)© Roger R. Seapy

6. Keel rounded in side view, with a slightly truncated leading edge (see title illustration and first SEM image above)
   
7. Keel inserts between shell whorls beginning at about whorl 4-1/4; at a shell diameter of about 3 mm (see first SEM image above)
   
8. Keel base clear in young individuals (see photograph below), but changes with age from a light brown to a dark yellowish-brown (see title illustration) with age
   
9. Shell transparent in small to moderate sized individuals (see photograph below), becoming faintly yellow in large specimens (Richter, 1993)
   
   

   Figure. Photograph of a young Atlanta peronii. Shell diameter = 1.1 mm. © Roger R. Seapy

2. Eyes type b; with a transverse slit in the distal pigmented tissue (see photograph below)
   
   

   Figure. Right eye of Atlanta peronii, illustrating the clear transverse slit in the distal pigmented tissue that is diagnostic of the eye type. © Roger R. Seapy

3. Operculum type b (micro-oligogyre)
4. Radula type II
1. Radula large, with the number of tooth rows limited to about 60 (Richter, 1993)
2. Lateral teeth tall
   
3. Marginal teeth sexually dimorphic (Richter, 1993). In adult radulae marginal teeth of males shaped as sharply-bent hooks, with the result that they are much shorter than the respective lateral teeth. In females the marginal teeth are longer and less sharply curved (see photographs below)
   
   
   

   Figure. Sections of radulae from male (left) and female (right) Atlanta peronii. Shape and length of marginal teeth differs between the two sexes. Photograph modified from Richter (1993, Fig. 19). © 1993 G. Richter

Comments

An Atlanta peronii species group was recognized by van der Spoel (1976) that included three species; A. peronii, A. gaudichaudi and A. pacifica. Subsequently, A. pacifica was synonymized with A. peronii and A. gaudichaudi placed in its own species group that contained three species, A. gaudichaudi, A. plana and A. echinogyra (discussed in Richter and Seapy, 1999). The A. peronii species group now includes four species, A. peronii, A. rosea, A. fragilis, and A. frontieri. Richter (1993) resurrected as a valid species A. rosea, which had been described by Souleyet in 1852 but subsequently treated as a junior synonym of A. peroni by Tesch (1908, 1949), and the latter two species were described as new species. The current pair of species groups are distinguished by markedly different radulae (discussed by Richter and Seapy, 1999; see the genus Atlanta page).

Diel vertical distribution patterns of A. peronii off the leeward coast of Oahu, Hawaii was studied by Seapy (1990b, 2008). In the former study, the species ranged downward to a daytime depth of 200-300 m (the maximal depth interval sampled), and migrated into the upper 150 m of the water column at night. In the latter study, vertical distribution patterns were studied at three stations located at 1, 5 and 15 nmi offshore. The species was recorded to a daytime depth of 160-200 m at the 5 and 15 nmi stations, while at night a slight upward migration was suggested since the deepest depth interval containing specimens was 120-160 m at both stations. Also, the abundance of A. peronii decreased shoreward by 50% from the 15 nmi to the 1 nmi station (comparison based on the mean nighttime densities at each station).

Aruba, Atlantic Europe, Azores Exclusive Economic Zone, Bonaire, Cape Verde, Caribbean Sea, Colombia, Cuba, Curaçao, European waters (ERMS scope), Greek Exclusive Economic Zone, Gulf of Mexico, Indian Ocean, Jamaica, North West Atlantic, Pacific Ocean, Portuguese Exclusive Economic Zone, Puerto Rico, Spanish Exclusive Economic Zone, Venezuela

Distribution: USA: Georges Bank, North Carolina, Florida; Florida: East Florida, West Florida, Florida Keys; Mexico; Mexico: Campeche Bank; Colombia, Venezuela; Venezuela: Falcon; Bermuda, Cuba, Jamaica, Oceanic; Eastern Atlantic: St. Helena

Epipelagic

Mesopelagic

Known from seamounts and knolls

Depth range based on 59 specimens in 1 taxon.
Water temperature and chemistry ranges based on 30 samples.

Environmental ranges
  Depth range (m): 0.5 - 4766
  Temperature range (°C): 3.144 - 24.949
  Nitrate (umol/L): 0.152 - 32.343
  Salinity (PPS): 34.576 - 38.757
  Oxygen (ml/l): 1.392 - 5.529
  Phosphate (umol/l): 0.153 - 2.562
  Silicate (umol/l): 1.064 - 86.775

Graphical representation

Depth range (m): 0.5 - 4766

Temperature range (°C): 3.144 - 24.949

Nitrate (umol/L): 0.152 - 32.343

Salinity (PPS): 34.576 - 38.757

Oxygen (ml/l): 1.392 - 5.529

Phosphate (umol/l): 0.153 - 2.562

Silicate (umol/l): 1.064 - 86.775
 
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