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Aplysia parvula
Guilding in Morch, 1863
 
Aplysia parvula
Maximum size:  40 mm.

Identification:  This sea hare varies from light cream flecked with white to velvet black. (Note 1) The edges of the parapodia, rhinophores and cephalic tentacles are powder-blue. The shell is usually visible between the parapodia and there is a distinctive brown line crossing the protoconch.

Natural history:  Aplysia parvula  is a common species found in rocky habitats and Halimeda kanaloana beds from < 1 to 23 m (< 3 to 75 ft). It occurs at protected to highly exposed sites. Small animals seem to be primarily nocturnal. However, larger animals appear to be primarily diurnal with all or most mating occurring by day. When populations are high, mating pairs are commonly seen on top of coral rubble or algae and they sometimes form mating chains of up to half a dozen animals. This appears to be particularly true when they are on or near a red algae tentatively identified as Laurencia nidifica. (Note 2) They eject a purple dye when disturbed and lay a tangled, greenish-brown egg mass. The eggs hatch in about seven days in the laboratory.

Distribution:  Big Island, Maui, Oahu, Kauai, Niihau, French Frigate Shoals and Midway: circumtropical.

Taxonomic notes:  It's referred to as the "small sea hare" in Hoover, 1998 & 2006. It was first reported from Hawaii in Pease, 1860 (as Syphonata elongata) and is listed as Tethys elongata in Edmondson, 1946, Ostergaard, 1950 and Ostergaard, 1955.

Photo:  CP: 40 mm; mottled: Hekili Point, Maui; March 21, 2005.

Observations and comments:

Note 1:  On Oct. 25, 1997 a velvet-black and light animal were observed copulating in a dish. Also, dark and light mottled animals were seen paired in the field on April 10, 2008 (and on other occasions). This supports lumping the various color forms under one species.

Note 2:  Over the years, diurnal activity and mating have been observed many times in large animals living on patches of  Laurencia nidifica(?) near the reef crest at Hekili Point. Although not confined to that substrate, the behavior seems more common there than in other locations. Perhaps, activity patterns are altered by the amount of defensive compounds retained from their food?
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