Lightiella MAGDALENINA 2006, SP. NOV.

LIGHTIELLA MAGDALENINA SP. NOV. (FIGS 1–5)

Holotype: One adult kept in ethanol, October 1999, S. Stefano isle, La Maddalena Archipelago, deposited in the Swedish Natural History Museum, Stockholm (SNMH) (accession number: SMNH Type 6141).

Type locality: Italy, Sardinia, S. Stefano isle, La Maddalena Archipelago, water depth 14 m, very fine muddy sand with shells and organic material (mostly leaves of Posidonia oceanica).

Paratypes: Serial slides of cephalic appendages, trunk appendages and telson of 1 adult, October, 1999, from the type locality, deposited in the Swedish Natural History Museum, Stockholm (SMNH) (accession numbers: SMNH Type 6142).

Serial slides of cephalic appendages, trunk appendages and telson of 1 adult, October, 1999 (accession numbers DIZABceph1.1); 1 whole gold-coated adult, mounted on a stub for SEM observation and 1 dissected gold-coated adult mounted on two stubs, July, 2004 (accession numbers DIZABceph1.2); 9 adults (accession numbers DIZABceph1.3) and 15 larvae (accession numbers DIZABceph1.4) kept in an aqueous solution of 4% formalin, July and October, 2004. All these specimens are deposited in the zoological collection of the Department of Zoology and Biological Anthropology (DIZAB), Sassari University.

Etymology: The species is named after the locality where it was collected: La Maddalena Archipelago (from lat. ‘Magdalena’).

Diagnosis: This species is distinguished from congenerics on the basis of the following characters: (1) one small seta on the inner distal corner of the penultimate endopodal segment of second maxilla and thoracopods 1–5; (2) only one claw on the distal segment of the endopod of thoracopod 6.

Description

Adult (body length up to 2.6 mm) (Fig. 1A–D). Holotype. Trunk 20-segmented (including telson) and 5 times as long as cephalon. Trunk segments 1–7 with terga produced latero-ventrally forming well developed and overlapping pleura with rounded free edges (Fig. 1A). Trunk segment 8 reduced and without pleura and legs (Fig. 1B). Trunk segment 9 with highly modified legs (see detailed description below) and tergum with lateral spines (Fig. 1B). Trunk segments 10–19 without legs, and with pleura developed into strong spinose processes (Fig. 1A). Telson bearing two caudal rami, and characterized by a ventral comb of strong teeth and with two well developed dorsal spines with rounded edges (Figs 1A, C, D). Caudal rami equalling the width of telson and bearing one or two short, and two long, terminal setae (Fig. 1A).

First antenna: (Fig. 2A). 6-segmented. Length ratio formula of 3rd−6th segments: 3-1-2-3. Setal formula (from base to tip); 0; 2; 4; 0; 0; 7 + 1 aesthete.

Second antenna: (Fig. 2B). Protopod 2-segmented. Endopod 2-segmented with 2 setae on the distal margin of the first segment and three setae and two spines on the second segment. Exopod 19-segmented with setal formula: 2; 2;?;?; 0; 1; 1; 2; 0; 1; 1; 1; 1; 2; 1; 1; 1; 1; 4.

Labrum: (Fig. 2C–E). Large, broadly rounded anteriorly, acutely triangular posteriorly. Postero-ventral surface with thin setae randomly distributed.

Mandible: (Figs 3A, B). Without palp. Incisor processes bearing two teeth with one small seta in between. The molar processes with numerous small teeth.

First Maxilla: (Figs 2C, 3C–F). Biramous. Protopod with an elongate and unsegmented gnathobase bearing three indented spines and two plumose setae (Fig. 3E–F). Endopod 3-segmented. Each segment bears a small seta on its inner corner. In addition to this small seta, the last segment bears two other setae which are long and plumose (Fig. 3C, D) (for setal formula see Table 2). Exopod with 7/8 marginal plumose setae (Fig. 3C).

Second maxilla and thoracopods 1–5: (Fig. 4A–D). Biramous, with about the same length and morphology. Protopod 1-segmented, bearing 6 enditic processes on the latero-internal margin (Fig. 4C), and with 1-segmented epipod on its outer distal corner (Fig. 4A, B). Endites are armed with spines and setae. Epipod with four long-terminal setae (Fig. 4A, B). Endopod 5-segmented. Segments 1–3 bearing from 1 to 5 setae on the inner corner (see Table 2 for setal formula). Segment 4 with one seta on the inner corner and a group of three or four setae on the outer corner (Fig. 4A, B, D). Distal segment with four claws. Three of these are large, indented and decreasing in size medially. The last one is small, smooth and located on the medial side of the base of the outermost claw (Fig. 4D). Exopod 2-segmented; for setal formula, see Table 2. Segment 2 bears from 12 to 15 long setae and one spine. The latter divides the setae into two groups, with the distal group always consisting of four setae (Fig. 4A, B).

Thoracopods 6–7: (Fig. 5A–E). Slightly smaller than the previous legs. Thoracopod 6 is very similar to the others with the exception of the distal endopodal segment, which bears only one claw (Fig. 5A), and the protopod, with a genital pore on the posterior surface. The genital pore is oval, with the major axis parallel to the protopodal endites. Its opening is covered by a convex plug-like membrane and its lateral margin is covered by short thin setae (Fig. 5B, C). Thoracopod 7 similar to the previous one except for the reduced protopod, bearing only 3 endites (Fig. 5D, E).

Thoracopod 8: Absent.

Thoracopod 9: (Figs 1B, 5F). Highly modified. Inserted on the ventro-lateral surface of segment 9 and comprised of two parts: an apical part, consisting of a short cylindrical process, emerging from the lateral concave surface of a subspherical basal part.

Cladistic analysis

The analysis yielded 8 most parsimonious trees (tree length 59, consistency index 0.7288, retention index 0.7746). The analysis performed without characters 6 and 7, which are indeterminate in most of the outgroup species, yielded the same number of trees (tree length 51), same tree topography and similar values of consistency index (0.7451) and retention index (0.8088). Similarly, the use of all other cephalocarid species or H. macracantha alone as outgroup yielded identical results. Support values were generally low, strongly supporting only the monophyly of the genus Lightiella and the basal position of L. serendipita. The new species appears as a derived taxon within the genus Lightiella, nested within an unresolved and weakly supported clade including L. monniotae (from New Caledonia) and L. floridana (from Florida) (Fig. 6).