Metaphrixus wehrtmanni sp. nov., 2024

Ribeiro, Felipe Bezerra, Horch, Amanda Porciuncula, Terossi, Mariana & Mantelatto, Fernando Luis, 2024, A new species of Metaphrixus Nierstrasz & Brender à Brandis, 1931 (Isopoda: Bopyridae: Hemiarthrinae) associated with an Hippolytidae shrimp from Costa Rica, Zootaxa 5501 (3), pp. 458-466 : 459-462

Metaphrixus wehrtmanni sp. nov.

( Figs. 1 and 2 )

Type material. Holotype: mature female (1.51 mm TL), Cahuita , Costa Rica, 9°44’41.4”N 82°51’12.9”W, 2002/2003, coll. I. Wehrtmann ( MZ-UCR 3824 ), infesting ventrally the pleon of Hippolyte obliquimanus (2.8 mm CL) ( MZ-UCR 3825 ).

Other material examined. Metaphrixus carolii : mature female, Florida Bay, Murray Key, United States, May 1964, coll. D. Tabb ( USNM 150536), parasitizing Hippolyte pleuracantha (Stimpson, 1871) ; mature female, Key Basin, Florida, United States, 2011, coll. Nova Southeastern University USGS Seagrass Lab ( USNM 1492305), parasitizing Hippolyte zostericola (Smith, 1873) ; mature female, Key Basin, Florida, United States, 2011, coll. Nova Southeastern University USGS Seagrass Lab ( USNM 1492306), parasitizing H. zostericola ; mature female, Biscayne Bay, Florida, United States, 2011, coll. Nova Southeastern University USGS Seagrass Lab ( USNM 1492307), parasitizing unknown shrimp; mature female, Barnes, Florida, United States, 2011, coll.Nova Southeastern University USGS Seagrass Lab ( USNM 1492303), parasitizing H. zostericola .

Etymology. Named in honor of Dr. Ingo S. Wehrtmann from the Universidad de Costa Rica for his outstanding contributions to the studies on crustaceans from Costa Rica and who collected the biological material described here.

Diagnosis. Head and pereon distinctly separated laterally but not posteriorly. Antennules of two articles and antennae unsegmented, pleopods lanceolate and curved downwards.

Description. Female holotype ( Fig. 1A–J ): total length 1.51 mm, maximal width 0.4 mm at pereomere 7, head length 0.51 mm, head width 0.51 mm, pleon length 0.48 mm. Body outline nearly circular, axis very distorted left (70°), body wider than long, broadest at pereomere 7. No apparent pigmentation ( Fig. 1A–B ).

Head subquadrangular, longer than wide, deeply set into pereon, fused with pereomere 1 posteriorly but not laterally. Eyes slender and elongated on lateral margins of head ( Fig. 1A ). Antennula of two articles each, basal article semicircular and larger, distal article smaller, both setose, terminal article with approximately four long setae on distal margin ( Fig. 1C ). Antennae long and unsegmented, covering part of antennules, with approximately seven small setae on distal margin ( Fig. 1C ). Barbula with two lanceolate projections on each side, medial margin smooth ( Fig. 1D ). Maxilliped ( Figs. 1E–F ) with semirectangular anterior article two times larger than posterior one; no palp; posterior article semicircular in shape with short spur ( Fig. 1E ), posterior margin with small setae.

Pereon with seven pereomeres. Pereomeres 1 and 2 distinct on both sides but indistinct medially, convex side enlarged ( Fig. 1A ). Pereomeres 3–7 only distinct on concave side ( Fig. 1A ). Dorsolateral bosses and coxal plates not visible ( Fig. 1A ). Marsupium closed ( Fig. 1B ). First pair of oostegites asymmetrical (Figs. G, H). Right oostegite 1 ( Fig. 1G ) oval in shape, without inner ridge; large rounded posterolateral projection with setae on distal margin. Left oostegite 1 ( Fig. 1H ) subtriangular in shape; anterior article oval and posterior one rectangular; inner ridge smooth; posterolateral point absent. Pereopods 1–7 with six articles on concave side reduced in size compared to pereopods 1 and 2 on convex side, and clustered together in a row ( Fig. 1A ). On the convex side, only pereopods 1–3 present ( Fig. 1A ). Pereopods 1 and 2 large, of six articles and positioned next to head ( Fig. 1A, I ). Pereopod 3 reduced and of only three articles, attached to inner side of oostegite 3, near distal end.

Pleon of five segments ( Fig. 1A ). Pleomeres 1–4 with uniramous ovate lateral plates ( Fig. 1A ). Four uniramous lanceolate pleopods, curved downwards and smaller than lateral plates ( Fig. 1J ). Pleomere 5 subtriangular in shape; uropods absent ( Fig. 1A ).

Male: Unknown.

Type locality. Cahuita , Costa Rica .

Distribution. This species has only been recorded for the Atlantic coast of Costa Rica (this study, Fig. 2 ).

Remarks. The characters of Metaphrixus wehrtmanni sp. nov. overall match those proposed by Nierstraz and Brender à Brandis (1931) in the original description of the genus, as well as the diagnosis presented by Markham (1985): e.g. female body axis distorted more than 90° with all seven pereopods on concave side, in orderly row; two pereopods on convex side; five pleomeres; prominent lateral plates and uniramous pleopods on pleomeres 1–4. The major difference is the presence of the pereopod 3 (reduced) on the convex side of the body, since both diagnoses of the genus only cite the presence of two pereopods on that side (Nierstraz & Brender à Brandis 1931; Markham 1985).

About thirty years following the description of the genus, Bruce (1966) described M. intutus Bruce, 1966 parasitizing Palaemonella rotumana (Borradaile, 1898) (as Palaemonella vestigialis Kemp, 1922 ), which, despite its unusual mode of infestation attached dorsolaterally on the host pleon, also presents two pereopods on the convex side. Bourdon (1967) described M. bifidus Bourdon, 1967 parasitizing Actinimenes inornatus (Kemp, 1922) (as Periclimenes inornatus Kemp, 1922 ); the presence of two well developed pereopods on the convex side led the author to provisionally place it in Metaphrixus , regardless of the presence of a reduced pereopod 3. Based on this third pereopod, together with a few other characteristics, Markham (1980) transferred Bourdon’s species to Dicropleon Markham, 1972 , a genus with three pereopods on the convex side of the body (see Markham 1972 for a discussion on the number of pereopods on Hemiarthrine genera). Later, however, Markham (1990) described M. rastriferis Markham, 1990 , which also has a reduced pereopod 3 on the convex side, but makes no discussion regarding the diagnosis of Metaphrixus , and otherwise M. rastriferis does fit well with the characteristics of the genus. Shimomura et al. (2006) described M. setouchiensis Shimomura, Ohtsuka & Sakakihara, 2006 parasitizing Hippolyte sp. , which has only the first two pereopods on the convex side. Therefore, considering the morphology of the now five species of the genus, the diagnosis of Metaphrixus should be extended to include the presence of only pereopods 1 and 2 ( M. carolii , M. intutu s, and M. setouchiensis ) or pereopods 1 and 2 plus a reduced pereopod 3 ( M. rastriferis and M. wehrtmanni sp. nov.) on the convex side of the body.

Metaphrixus wehrtmanni sp. nov. appears to be most morphologically similar to M. carolii and M. rastriferis . The new species can be distinguished from M. carolii based on the segmentation of the antennules (unsegmented on M. carolii ), and the presence of a reduced pereopod 3 on the convex side (absent on M. carolii ) (Nierstraz & Brender à Brandis 1931; this study). Five females of M. carolii deposited in the United States National Museum (USNM) collections were examined for comparison (see comparative examined material for the voucher numbers and collection data), but no males were present in any of the vials. Three of the females appeared to have previously dried, making examination harder (USNM 1492303; 1492306; 1492307), whereas the other two were in good condition (USNM 150536; 1492305). The segmentation of the antennae could not be discerned in any of the specimens due to their diminutive size and difficulty of observation without dissection. At present, we compare the antennae morphology of M. carolii described in the literature (see Nierstrasz & Brender à Brandis 1931; Markham 1985; 1988; Román-Contreras & Martínez-Mayén 2011) with the new species described here. None of the five M. carolii females examined had a pereopod 3 on the convex side, with only the pereopods 1 and 2 present and clustered close to the head. Further collections and analyses of M. carolii and M. wehrtmanni sp. nov. are needed to document the morphological variation in these species, with a special focus on confirming the antennae segmentation on M. carolii , perhaps through the use of SEM techniques. The differences observed between the new species and M. rastriferis are ( Markham 1990; this study): (1) head distinctly separated from the pereon laterally but not medially on the new species vs. completely distinct on M. rastriferis ; (2) antennules of two articles on the new species vs. three articles on M. rastriferis ; (3) barbula with two lanceolate projections on the new species vs. one long falcate outer projection and one short blunt medial projection on M. rastriferis .

Figures

FIGURE 1. Metaphrixus wehrtmanni sp. nov., female holotype (MZ-UCR 3824). A, habitus, dorsal view; B, habitus, ventral view; C, right antennula and antenna; D, barbula; E, right maxilliped, inner view; F, right maxilliped, outer view; G, right oostegite 1, outer view; H, left oostegite 1, outer view; I, pereopod 1, convex side; J, pleopods. Scale bars:A and J = 0.5 mm; B = 0.75 mm; C = 0.05 mm; D = 0.25 mm; E and F = 0.2 mm; G, H and I = 0.1 mm.

FIGURE 2. Distribution of the five species of Metaphrixus Nierstrasz & Brender à Brandis, 1931. References for all records can be found in Table 1.