A new species of Cryptopygus Willem, 1901 associated with hermit crabs living on seashores of Quintana Roo State, Mexico, is described and illustrated. It is blind, with 9–11 postlabial setae, unguis with a pair of lateral teeth, empodial appendix lanceolate and almost as long as unguis, tenaculum with 4 + 4 teeth and 3–4 setae on corpus, manubrium with 11–14 pairs of manubrial setae on anterior surface and 17–18 pairs on posterior surface, and mucro bidentate. An updated key for the identification of 29 American species of Cryptopygus complex is included.

Sand, seashore, taxonomy, Xcacel

This contribution is a part of the project aimed at the microarthropods associated with hermit crabs, in which the male of Coenaletes caribaeus Bellinger, 1985 (Coenaletidae) has been redescribed (Palacios-Vargas et al. 2000) and other Collembola and some Acari recorded from this crab (Maldonado-Vargas and Palacios-Vargas 1999).

The genus Cryptopygus Willem, 1901 sensu lato represents a complex of genera (Potapov 2001; Potapov et al. 2013). The species of this complex live in a wide variety of environments such as soil, litter, caves, and sandy beaches. Here, I use the name Cryptopygus in its broad sense. There are altogether 76 valid species involved in the genus (Bellinger et al.1996–2023), which has a global distribution. The purpose of this paper is to describe a new species of Cryptopygus found in hermit crabs collected in marine waters of Quintana Roo State, Mexico. As shown by Palacios-Vargas (1997), there are several Cryptopygus species known from Mexico, namely C. benhami Christiansen & Bellinger, 1980 found in caves from Guerrero and Mexico States and C. exilis from Veracruz State. Later, Palacios-Vargas and Thibaud (2001) described an additional species, Cryptopygus axacayacatl Vargas & Thibaud, 2001, which lives on sandy beaches from Guerrero State. Moreover, Pauropygus caussaneli (Thibaud, 1996), which belongs to the same complex, was cited from Guerrero state by Potapov et al. (2013).

The material of the new species comes from Xcacel beach, Quintana Roo State. It was found while examining the hermit crab Coenobita clypeatus (Fabricius, 1787) living in Cittarium pica (Linnaeus, 1758) shells. Hermit crabs were put in a bucket with fresh water and springtails floating on the surface were collected. The specimens were fixed in ethanol 96% and later cleared with KOH 10% and mounted on slides using Hoyer solution. To harden the solution, the slides were dried in a slide warmer at 45–50 °C for 1 week. Finally, each specimen was labeled with its collecting data. Specimens were examined with a Carl Zeiss Primo Star phase-contrast microscope. The drawings were made with the aid of a drawing tube.

Abbreviations:

Abd abdominal segment;

Ant antennal segment;

PAO postantennal organ;

S sensillum;

Tita tibiotarsus;

Th thoracic segment.

Entomobryomorpha

Isotomidae

Anurophorinae

 Cryptopygus coenobitus sp. nov.

https://zoobank.org/41349B8A-6C87-41D9-B1E3-169668996F9A

Figs 1–4, 5–8, 9–12, 13–16

Type material

Holotype. Female on slide. Paratype: male on slide. Type material kept at Facultad de Ciencias, UNAM. Slides numbered: FC-UNAM:LESM-AC: 22863 and FC-UNAM:LESM-AC: 22864.

Type locality

Mexico – Quintana Roo • Municipality of Solidaridad; Xcacel; ex. Coenobita clypeatus; 20°20'13"N, 87°20'45"W; 6 June 2022; J.G. Palacios-Vargas, M. Ojeda & A. Arango leg.

Diagnosis

White and eyeless Cryptopygus, with 9+9 to 11+11 postlabial setae, 1 pair of lateral teeth on unguis; retinaculum with 4 + 4 teeth and 3–4 setae on corpus, 11–14 pairs of manubrial setae on anterior surface, and 17–18 pairs on posterior surface, dens smooth, 4 setae on posterior basal part and 11–13 on anterior side, mucro bidentate.

Description

Setae smooth, acuminate, mostly short, some micro- and few slightly barbulated macrosetae (40–50 µm). Sensilla on terga in posterior row of setae, only slightly differentiated from ordinary setae, thinner and hyaline (Figs 1, 2). Microsensillum on Th. II normal. Abd. V and VI completely fused. Dorsal setation from Th I to Abd IV, 15,8/4,4,5,8 irregular lines (Fig. 1). Thorax without ventral setae. Abd VI without foil setae. Sensillar formula from Th II to Abd V: 3,3/2,2,2,3,2.

Figures 1–4. 

Cryptopygus coenobitus sp. nov. 1 habitus, image from phase-contrast microscope, lateral view 2 Abd II, lateral partial view 3 antenna I–IV, from I to III in ventral view, IV dorsal view 4 PAO.

Length of head 140–150 µm, length of body 750–1000 µm. Antennae 250 µm, longer than head (ratio = 1:1.75). Ratio Ant. I–IV as 1:1.5; 1.5; 2.5. Ant. I with 33–36 setae, 9 thin and short ventral sensilla; Ant. II with 54 setae with few microsensilla and one thick, long sensillum on ventral–distal position (Fig. 3). Ant. III with 44 setae, antennal organ III with 2 microsensilla, 2 fine guard sensilla and 1 ventro-external microsensillum. Ant IV with about 70 setae, and 8 long and fine sensilla. Apex of the segment with a microsensillum and a small organite, apical bulb absent. Eyes absent, postantennal organ oval (25 × 12 µm), surrounded by 5 setae (Fig. 4). Labrum with 4 short, thin prelabral setae; 4 long setae in anterior row, 5 spiniform setae in median row, and 4 spiniform setae in posterior row, formula 4/4,5,4. With 4 sublobal hairs on outer maxillary lobe; labium with full set of guards on papillae A–E, and 3 proximal and 4 baso-median setae. Postlabial setae 9+9-11+11 (Fig. 5). Mandibles with 3–4 apical teeth and molar surface well developed (Fig. 6). Maxilla with 6 lamellae, with some plumose (Fig. 7).

Figures 5–8. 

Cryptopygus coenobitus sp. nov. 5 postlabial setae 6 mandible 7 maxilla 8 tita III and magnification of foot complex.

Thorax without ventral setae. All femora with 1 ventral acuminate tenent hair. Tita with 2,3,3 acuminate tenent hairs and without a distal subsegment (Fig. 8). Tita I = 60 µm, Tita = 80 µm. Unguis I = 13 µm, unguiculus I = 11 µm. Unguis with 1 pair of lateral teeth in the median part. Unguiculus lanceolate, acuminate, not lamellate, almost as long as unguis. Ventral tube with 4 + 4 basal setae and 5 + 5 latero-distal setae (Fig. 9). Abd. IV on ventral surface with 4+5 setae by side; anterior subcoxa furcalis with 19–20 setae; posterior subcoxa furcalis with 10 setae, 4 of them longer than others (Fig. 10).

Figures 9–12. 

Cryptopygus coenobitus sp. nov. 9 ventral tube, lateral view 10 coxae furcalis anterior and posterior 11 tenaculum 12 manubrium, anterior view.

Tenaculum with 4+4 teeth, corpus with 3–4 setae (Fig. 11). Furcula well developed, manubrium with 11–14 pairs of anterior setae (Fig. 12), 3 small lateral setae and 18 pairs of setae on posterior side. (Fig. 13). Dens smooth, only 4 setae of different size on posterior basal part and 10–14 subequal setae on anterior surface (Fig. 14). Manubrium 80 µm, dens 100 µm, mucro 25 µm. Ratio 1:1.25; 0.3. Mucro bidentate. Genital plate of female with 2 eugenital setae and 5 pairs of pregenital setae (Fig. 15). Male with 4 pairs of eugenital setae and a few circumgenital setae (Fig. 16).

Figures 13–16. 

Cryptopygus coenobitus sp. nov. 13 manubrium latero-posterior view, line shows midline 14 dens and mucro 15 female genital plate 16 male genital plate.

Etymology

This species is a noun in apposition after the genus of the hermit crab in which it was found.

Distribution

Cryptopygus coenobitus sp. nov. is only known from Xcacel, Quintana Roo State, Mexico.

Cryptopygus coenobitus sp. nov. is similar to Proisotomodes axayacatl, Mucrosomia caeca, Cryptopygus benhami, C. elegans, C. exilis, C. yosiii, and Pauropygus caussaneli in lacking eyes and pigment, but these species have four basal setae and 4+4 setae on ventral tube (vs 8 basal and 5+5 in the new species) and four teeth on the ramus of the tenaculum and one seta on the corpus (vs 3–4 on corpus in the new species). Most species have one or two pairs of setae on the anterior side of the manubrium, in contrast to 18 pairs in the new species. Moreover, the new species has many postlabial setae (9–11 pairs), an unguis with a pair of lateral teeth but without an internal tooth, a lanceolate empodium that is almost as long as the unguis, a manubrium with 8+8 anterior setae, and a tridentate mucro with two basal spines.

When C. coenobitus sp. nov. is compared with Isotominella laterochaeta from South Africa, there are some characters common, such as the lack of eyes and pigment and the presence of numerous setae on ventral side of head, mainly along the ventral line. The furcula is also very similar in shape, there are four setae on posterior basal part and 11–13 on anterior surface, and the mucro is bidentate. The main differences are that C. coenobitus lacks ventral setae on thorax III, and the ventral tube has 5 + 5 laterodistal and 4 + 4 posterior setae (vs 5–8+5–8 laterodistal and 6–9 posterior in I. laterochaeta). The tenaculum has 4+4 teeth, and the corpus bears three or four setae (vs 4+4 teeth and 2 setae on corpus).

There are some important characters that have been omitted in the descriptions of many species of the Cryptopygus complex, such as (1) postlabial chaetotaxy, which usually represents four or five pairs of setae, (2) the shape of maxillary lamellae, which can be modified depending on food preferences, and (3) the setation of coxae furcalis, but this last charactive might have important diagnostic value.

Cryptopygus coenobitus sp. nov. seems to be psammobiotic, and its morphology does not appear modified for living in association with hermit crabs. The maxillae are plumose, as an adaptation for filtration of food particles from the water, and the mandibles are normal, not modified, as in Coenaletes spp. (Coenaletidae) which live between the Cittarium pica shell and the hermit crab occupant. The new Cryptopygus species has been found in the sand but is able to enter to the shells occupied by hermit crabs, as in other Collembola genera such as Cyphoderus and additional microarthropods as found by Maldonado-Vargas and Palacios-Vargas (1999).

This research is part of the author’s sabbatical leave, approved by Dr Víctor Velázquez Aguilar, principal of the Faculty of Sciences, UNAM. Angela Arango, Eduardo Pacheco, and Margarita Ojeda assisted at field and laboratory work, and the latter also photographed the habitus of the new species. Figures were prepared by Jair Páez. The author expresses his gratitude to Dr Ľubomír Kováč and Dr Mikhail Potapov for their constructive criticism that improved the manuscript.