Botryllophilus nudisetatus Kim & Boxshall 2021, sp. nov.

Botryllophilus nudisetatus sp. nov.

(Figs. 63, 64)

Type material. Holotype ♀ (MNHN-IU-2018-1975) and 1 ♀ paratype (dissected, MNHN-IU-2014-17377) from budẚstçma carçlẚnense Van Name, 1945 (MNHN-IU-2008-4023 = MNHN A3 / EUD/14); Anse de Baille Argent, Guadeloupe Stn 7, Monniot coll., 19 December 1980.

Etymology. All setae on legs of B. nudẚsetatus sp. nov. are naked, and are alluded to in the name of the new species.

Description of female. Body (Fig. 63A) symmetrical, straight, 0.93 mm long. Anterior part of body markedly swollen, unsegmented, without any trace of articulation, 0.38 mm in dorsoventral depth. Posterior part of body (Fig. 63B) clearly defined from anterior part, consisting of genital somite and 4-segmented abdomen. Genital somite 82×165 μm; genital apertures large, positioned dorsally; 4 abdominal somites 58×102, 67×95, 65×85, and 109×76 μm, respectively. Caudal ramus (Fig. 63C) armed with 1 bluntly tipped and 3 pointed claws and 1 seta.

Rostrum absent. Antennule (Fig. 63D) small, 4-segmented; armature formula 9 (4 large and 5 small), 4 (2 large and 2 small), 3 (1 large and 2 small), and 11+aesthetasc. Right antenna (Fig. 63E) consisting of coxa, basis, and 2-segmented endopod; proximal 3 segments unarmed; second endopodal segment about 3.1 times longer than wide (47×15 μm), armed with 7 bluntly tipped setae, longest outer distal seta as long as segment, other setae shorter than segment. Second endopodal segment of left antenna (Fig. 63F) slightly shorter than that of right antenna, 43 μm long; 2 outer distal setae distinctly longer than those of right antenna.

Labrum (Fig. 63G) semicircular with large, soft posteromedian lobe. Mandible (Fig. 63H) with bifurcate distal tooth and 2 shorter teeth on coxal gnathobase; palp with 9 naked setae, grouped as 3, 2, 2, and 2. Maxillule (Fig. 63I) consisting of precoxa and unsegmented palp; precoxa with 6 setae on arthrite; palp with 8 setae (2 on medial margin, 3 on outer margin, and 3 on distal margin) plus 1 vestigial seta at outer proximal margin representing epipodite; endopod completely fused with basis. Maxilla (Fig. 63J) indistinctly 3-segmented, with 9 setae arranged as 2, 4, and 3. Maxilliped (Fig. 63K) relatively narrow, 4-segmented; syncoxa slightly longer than wide, unarmed and unornamented; basis with 2 small setae; short first endopodal segment unarmed; second segment with 1 denticle on inner margin and 1 small seta on distal margin; terminal claw as long as second endopodal segment, with 1 proximal and 1 subdistal denticle on inner margin.

Legs 1-4 (Fig. 64 A-H) biramous with 1-segmented exopods and 2-segmented endopods; coxa unarmed; basis with 1 seta on outer margin. Basis of legs 2-4 with small inner distal lobe bearing 2-4 spinules. Endopods of right legs 2-4 bearing 3, 1, and 3 spines, respectively. All setae on legs 1-4 naked and all spines with spinulose tip. Exopods of left legs 1, 2, and 4 each with small second outer seta. Numbers of spines (Roman numerals) and setae (Arabic numerals) on right and left legs 1-4 as follows:

Leg 5 (Fig. 64I) 104×58 μm, with broadened proximal region, not extending beyond posterior margin of ante- rior part of body; armed with 4 setae (1 proximal and 3 distal); largest of 3 distal setae as long as leg segment, twice as long as adjacent seta. Leg 6 (Fig. 64J) represented by 1 spinule on genital operculum.

Male. Unknown.

Remarks. The exopods of right legs 1-3 of B. nudẚsetatus sp. nov. are armed with 5, 4, and 3 spines, respectively. Each of these numbers of spines is less than that of any other known species of Bçtryllçphẚlus. The other rami of the swimming legs of this new species are armed with smallest number of armature elements known elsewhere within the genus. This reduced armature of the swimming legs serves to characterize the new species.

Genus Schizoproctus Aurivillius, 1885

Diagnosis (female). Body symmetrical, dorsoventrally depressed or laterally compressed, consisting of broader anterior and narrower posterior parts. Anterior part of body segmented or unsegmented; fifth pedigerous somite completely fused with fourth pedigerous somite. Posterior part of body comprising genital somite and abdomen consisting of 3 to 6 somites or annulations; abdomen occasionally unsegmented. Caudal ramus short, armed with 4 or 5 claws and 1 or 2 setae. Rostrum small or absent. Antennule 4- or 5-segmented. Antenna 4-segmented; proximal 3-segments unarmed; terminal segment (second endopodal segment) armed with 8 elements (mostly spines). Labrum not specialized. Mandible, maxillule, and maxilla as in Bçtryllçphẚlus. Maxilliped basically 4-segmented as in Bçtryllçphẚlus, but terminal segment may be fused with terminal claw. Legs 1-4 symmetrical, biramous with 1-segmented rami; coxa unarmed; basis armed with 1 seta on outer margin; exopods armed with 4 to 7 spines along outer and distal margins plus 1 rudimentary inner subdistal seta in some species. Endopods usually shorter than exopods, and usually armed with setae. Leg 5 elongate or lamellate, with 1 to 4 setae. Leg 6 represented by 1 or 2 spinules and 1 spinule-like process on genital operculum.

Type species. Schẚzçprçctus ẚnflatus Aurivillius, 1885 by original monotypy.

Remarks. According to Illg & Dudley (1980), the genus Schẚzçprçctus was a well-established, readily recognizable genus defined from Bçtryllçphẚlus by its broad, lamellate leg 5. This distinction between the two genera, on the basis of the form of leg 5, has become obscured by the discovery of new species in the present account which exhibit a mix of the key morphological features of the two genera.

In three new species to be described below (S. magnus sp. nov., S. bẚsetatus sp. nov., and S. fusẚfçrmẚs sp. nov.), left and right legs 5 are narrow and widely separated from each other, a feature corresponding to Bçtryllçphẚlus. However, the characteristics of left and right legs 1-4 of these three new species differ markedly from those in species of Bçtryllçphẚlus, but are shared with other species of Schẚzçprçctus. Comparison of the two genera leads us to redefine both genera. The most robust differences between the two genera seem to lie in the morphology of swimming legs, as follows: (1) both rami of legs 1-4 of Schẚzçprçctus are 1-segmented, but at least the endopods of legs 2-4 of Bçtryllçphẚlus species are 2-segmented (in many instances the exopods are also 2-segmented); (2) left and right legs 1-4 of Schẚzçprçctus are invariably symmetrical, in contrast to the asymmetry of these legs in Bçtryllçphẚlus (with the exception of B. macrçpus which has symmetrical legs 1-4), with spines on the exopods and setae on the endopods. We consider that these differences are more robust than the difference in the form of leg 5 between these two genera. In addition, the body and the antennae are also typically symmetrical in Schẚzçprçctus, unlike those of BçtryllçphẚlusK

Differences between the two genera are marked in the leg setation of the males, as well. While describing the male of eaplçstçma brevẚcauda (Canu, 1886), Ooishi (2004b) mentioned that the males of eaplçstçma are distinguished from the males of Bçtryllçphẚlus by having fewer spines on the third segment of leg 2 endopod. This segment is armed with 2 spines (occasionally 1 spine) plus 3 setae (formula generally II, 3 but occasionally I, 3) in eaplçstçma but 3 spines plus 3 setae (formula III, 3) in Bçtryllçphẚlus. The same segment of the leg of the male of Schẚzçprçctus pẚnguẚs sp. nov. described in the present work is armed with 1 spine plus 3 setae (I, 3). The reduction in the number of spines on legs of the male of Schẚzçprçctus is not limited to the endopod of leg 2; the armature formula for the third endopodal segment of legs 3 and 4 is I, 2 and I, 4, respectively in Schẚzçprçctus, compared to II, 2 and II, 3, respectively, in males of Bçtryllçphẚlus abbçttẚ, B. ruber, B. bamfẚeldensẚs, and B. banyulensẚs (as described by Ooishi & Illg, 1989; Ooishi, 1999; 2000; 2006, respectively). In contrast, the third exopodal segment of legs 2-4 of S. pẚnguẚs sp. nov., described below, is armed with more spines (IV, 5) than in any of the four known males of Bçtryllçphẚlus species (III, 5).

Schẚzçprçctus exhibits a range of different leg armature patterns, according to species (Table 3), which allows for easy differentiation between species.

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