Natosquilla investigatoris ( Lloyd, 1907 )

Natosquilla investigatoris ( Lloyd, 1907)

( Fig. 27 View FIGURE 27 )

Squilla investigatoris Lloyd, 1907: 7 , 10–11 [ type locality southeast coast of Arabia 200 m].— Kemp, 1913: 80, pl. 6, figs. 67, 68.— Kemp & Chopra, 1921: 298.— Chopra, 1939: 151, fig. 6.— Barnard, 1950: 849–859.

Natosquilla investigatoris .— Manning, 1978c: 40–41, fig. 25.

Material examined. Western Cape: SAMC-A008485 , 4 ♀ (TL 82–89 mm), 2 ♂ (TL 90–91 mm), False Bay, 28 Dec 1944, surface collection, coll. Dr. Molteno and Roux, det. K.H. Barnard.

Other material examined. Tanzania: SAMC-A079523 , 6 ♀ (TL 71–77 mm), 6 ♂ (TL 65–77 mm), east of Jibondo Island , 8°06’37.2”S 39°58’47.4”E, 30 Jul 2003, depth unknown, stat. Alg 122 M001, coll. Kerry Sink. GoogleMaps

Diagnosis. See genus above.

Colour in alcohol. Amber brown, fresher specimens are dark to tan-brown. Barnard (1950) described same specimens as overall grey, keels dark, telson dark brown. Uropodal endopod, protopod and proximal half of distal segment of exopod dark brown to black. Distal half of the distal segment of the uropodal exopod red.

Colour in life. Described by Lloyd (1907: 12) as very variable; overall “sand colour with minute black spots”. Telson and uropods show “a blue-black colouration irregular in its distribution”.

Measurements. ♂ (n = 8) TL 71–91 mm, ♀ (n = 10) TL 65–89 mm. CI 280–340.

Distribution and habitat. South coast of Arabia, Persian Gulf, Zanzibar, Seychelles, South Africa and now from off mainland Tanzania; 183– 220 m.

Remarks. Natosquilla investigatoris was first described by Lloyd (1907) from the south coast of Arabia at depths around 200 m, and Barnard (1950) reported large numbers from Table Bay on the west coast of South Africa. The South African specimens reported on by Barnard (1950) were examined herein examined. The recently collected specimens from the coast of Tanzania agree well with the South African specimens, as well as with Lloyd’s original description and Manning’s (1978c) diagnosis of the genus Natosquilla .

The variation in number of teeth on the dactylus of the raptorial claw has been well-documented for N. investigatoris ( Barnard 1950) . Among the six South African specimens examined, the number of dactylar teeth ranged from 11–18. Moreover, three of the females exhibit an asymmetrical tooth number having 15/16, 17/16 and 18/16 teeth on the left and right dactyli respectively. The present Tanzanian specimens ranged in tooth number between 12–17 with four specimens with asymmetrical number having 14/12, 17/16, 16/17, and 16/17 teeth on the dactyli, respectively. The small apical spine on the rostral plate observed in a single female of TL 88 mm ( Fig. 27D View FIGURE 27 ) is the first record of this variation for the species.

The large eye in adults of N. investigatoris is another distinguishing feature of the genus ( Fig. 27B, C View FIGURE 27 ). Ahyong (2001) uses the relative lengths of the cornea to the carapace to distinguish Erugosquilla from Natosquilla , the former having an eye with cornea less than one-third carapace length in adults, while Natosquilla is supposed to have the cornea greater than or equal to one-third carapace length. Although the present study found one specimen with cornea width 0.28 CL, all other examined specimens of N. investigatoris agreed with Ahyong’s (2001) account of the genus. The large eye has been speculated to be an adaptation for surface swarming behaviour ( Manning 1978c). The known species behaviour of forming pelagic swarms is corroborated by the account given in Barnard (1950) of “during darkness the surface was swarming with them” from northwest of Table Bay, Western Cape, South Africa.

Natosquilla investigatoris appears to mostly inhabit the north-western Indian Ocean, so that the single report from Table Bay on the west coast of South Africa represents an extraordinary distributional outlier, with no other records from the South African south and east coasts. Table Bay is a part of the transitional zone between the Indian and Atlantic Oceans and experiences anticyclic eddies called Agulhas rings which retroflects at the point of the Agulhas Current, transporting Indian Ocean water in a north-westerly direction into the Benguela Current system along the west coast of South Africa ( Sink et al. 2019). This process could facilitate the occupation of Table Bay by this typically (sub)tropical species. It would be interesting to investigate how far up the west coast of Africa N. investigatoris extends.