Identification of Phyllosoma Larvae of the Lobsters Acantharctus and Biarctus (Crustacea: Scyllaridae) from the SW Indian Ocean

Abstract

The accurate assignment of cryptic larvae to species-level is a key aspect of marine ecological research and can be achieved through integrated molecular and morphological studies. A combination of two mitochondrial markers (COI and 16S) and a detailed morphological analysis was used to identify phyllosoma larvae of slipper lobster (Scyllaridae) species collected during a survey in the SW Indian Ocean. Two morphotypes were tentatively assigned to Acantharctus ornatus and Biarctus pumilus, both genera for which the larval morphology was unknown. Morphological revision of an adult specimen used to generate the putative A. ornatus sequences in GenBank revealed that it was misidentified and corresponds to B. dubius. The final phyllosoma stage of B. pumilus and subfinal and final stages of A. ornatus were described, clarifying prior misidentifications in the literature. Scyllarid biodiversity in the SW Indian Ocean is underestimated and sampling of deeper water layers is recommended to complete current knowledge of species and larval stages present in the region.

Keywords: KwaZulu-Natal Bight; Morphological description; Phyllosomas; SW Indian Ocean; South Africa.

Fig. 1.

Location of 22 stations sampled by the RV Dr Fridtjof Nansen along the KwaZulu-Natal coast in eastern South Africa. Stations where phyllosomas were caught are indicated with a star.

Fig. 2.

Maximum likelihood phylogenetic trees obtained from COI (A, left) and 16S (B, right) gene alignments. Only significant bootstrap values (> 70) are shown.

Fig. 3.

Morphology comparison of the adult slipper lobster labelled as A. ornatus in GenBank and true Acantharctus. Carapace dorsal view (A–D) and sternum (E–H) for A. ornatus from Australia identified by Holthuis (A: WAM C8845, E: WAM C8846); GenBank specimen labelled as A. ornatus but being in fact Biarctus dubius (B, F: WAM C27134); A. ornatus syntype (C, G: 1967.10.1.1-3) and A. posteli (D, H: MNHN-IU-2013-14853). The diagnostic characters used to differentiate Acantharctus and Biarctus (strong dorsal carina and strong spine on the last somite of the thoracic sternum) are indicated with a circle. Scale bars = 5 mm.

Fig. 4.

Biarctus pumilus (Nobili, 1906), phyllosoma stage IX (Final) (Manta_L39). A, ventral (right) and dorsal (left) view; B, dactylus of first pereiopod; C, dactylus of second pereiopod; D, dactylus of third pereiopod; E, dactylus of fourth pereiopod; F, thorax. Scale bars: A and F = 2 mm; B–E = 200 μm.

Fig. 5.

Biarctus pumilus (Nobili, 1906), phyllosoma stage IX (Final) (Manta_L39). A, stalked eye, antennule and antenna; B, C, left and right mandibles (ventral view); D, maxillule; E, maxilla and first maxilliped; F, second maxilliped; G, pleon, fifth pereiopod, pleopods 2–5 and uropods, ventral (right) and dorsal (left) view. Scale bars: A = 500 μm, B–D = 100 μm; E–G = 200 μm.

Fig. 6.

Acantharctus ornatus (Holthuis, 1960), phyllosoma stage VIII (subfinal). A, ventral (right) and dorsal (left) view (Ring_L08); B, dactylus of first pereiopod (Manta_L31); C, dactylus of second pereiopod (Manta_L301); D, dactylus of third pereiopod (Manta_L31); E, dactylus of fourth pereiopod (Ring_L08). Scale bars: A = 2 mm; B–E = 200 μm.

Fig. 7.

Acantharctus ornatus (Holthuis, 1960), phyllosoma stage VIII (Subfinal). A, stalked eye, antennule and antenna (Ring_L08); B, C, left (Ring_ L08) and right (Manta_L30) mandibles (ventral view); D, maxillule; E, maxilla and first maxilliped (Ring_L08); F, second maxilliped (Ring_L08); G, fifth pereiopod, pleopods 2–5 and uropods (ventral view) (Ring_L08). Scale bars: A and G = 500 μm; B–D = 100 μm; E and F = 200 μm.

Fig. 8.

Acantharctus ornatus (Holthuis, 1960), phyllosoma stage IX (Final). A, ventral (right) and dorsal (left) view (Manta_L73); B, dactylus of first pereiopod (Manta_L70); C, dactylus of second pereiopod (Manta_L73); D, dactylus of third pereiopod (Manta_ L62); E, dactylus of fourth pereiopod (Manta_ L62); F, thorax (Manta_L73); G, detail of subexopodal seta (Manta_L73). Scale bars: A and F–G = 2 mm; B–E = 200 μm.

Fig. 9.

Acantharctus ornatus (Holthuis, 1960), phyllosoma stage IX (Final). A, stalked eye, antennule and antenna (Manta_L73); B, C, left (Manta_ L62) and right (Manta_L65) mandibles (ventral view); D, maxillule (Manta_L43); E, maxilla and first maxilliped (Manta_ L62); F, second maxilliped (Manta_L73); G, pleon, fifth pereiopod and pleopods 2–5 and uropods (ventral view) (Manta_L73). Scale bars: A and G = 500 μm; B–D = 100 μm; E–F = 200 μm.