Phyllocnistis cretacea nov. spec.

Fischer, Thilo C., 2021, In search for the unlikely: Leaf-mining caterpillars (Gracillariidae, Lepidoptera) from Upper Cretaceous and Eocene ambers, Zitteliana 95, pp. 135-145 : 135

Species Phyllocnistis cretacea nov. spec.

Etymology.

The species name ‘’ Phyllocnistis cretacea " refers to the Cretaceous age of the species.

Holotypus.

Specimen ex coll. Fischer no. 7513, Fig. 3 .

Locus typicus. Sediments of Hukawng Valley (Myanmar).

Stratum typicum.

Earliest Cenomanian, determined 99 m.y. ( Cruickshank and Ko 2003; Shi et al. 2012).

Repository.

Bavarian State Collection of Zoology, Munich, Germany; accession number SNSB-ZSM-LEP amb004.

Description of holotype.

The caterpillar is 7 mm long and flat, maximum width 1.18 mm (in T2). The thorax (T1 to T3) is 1.06 mm long. Dorsal prothoracic plates of roughly triangular form are present (figuring alike in Hering (1951: fig. 85a). The broadest segment of the abdomen is A6 with 0.88 mm, the abdomen is 5.78 mm long. The head is 0.53 mm long and 0.75 mm broad, depressed, triangular, and prognathous. Mandibles are developed, antennae are minuscule. The spinneret is well-developed and 0.05 mm long. Legs and prolegs are not developed. The longest abdominal segment is 0.68 mm (A3), the shortest abdominal segment is 0.38 mm (A9).

There are each two lateral bulges (dorsal and ventral ones) on either side of all abdominal segments, each bulge carries a prominent seta; these setae are maximal 0.2 mm in length and bent backwards. The terminal segment is 0.28 mm long and 0.5 mm broad.

There are several syninclusions preserved in the same amber: Coleoptera (5 taxa), Hymenoptera (a wasp), Psocoptera, trichomes, a 4 mm wood fragment, arthropod feces, undefinable plant, and chitin detritus.

Description of paratype I.

The caterpillar (coll. Fischer no. 7790) is 6.5 mm long and subcylindrical, maximum width 1.02 mm (in T3) (Fig. 4 ). The thorax (T1 to T3) is 1.25 mm long. The broadest segment of the abdomen is A4 with 0.88 mm, the abdomen is 4.41 mm long. The head is 0.39 mm long and 0.65 mm broad, depressed, triangular, and prognathous. Mandibles and antennae are developed. A visible leg is 0.26 mm long. The longest abdominal segment is 0.77 mm (A4), the shortest abdominal segment is 0.26 mm (A9). There are no prolegs. There are each two lateral bulges (dorsal and ventral) on either side of all abdominal segments. There are at least two setae in lateral positions on either side of each segment, these are maximal 0.16 mm in length. The terminal segment is 0.3 mm long and 0.32 mm broad.

Remark: The paratype is non-compressed, but part of the head is not well preserved. Dorsal prothoracic plates may be present, impressions with similar form are visible. A spinneret is not visible, but the head is partly hidden by some chitinous membrane.

Description of paratype II.

The caterpillar (coll. Fischer no. 7512) is 4 mm long and subcylindrical, maximum width 0.83 mm (in T1) (Fig. 5 ). The thorax (T1 to T3) is 1.2 mm long. The broadest segment of the abdomen is A3 with 0.7 mm, the abdomen is 2.93 mm long. The head is partly retracted in the thoracic segment T1, 0.69 mm long (visible through T1) and 0.56 mm broad, depressed, triangular, and prognathous. Head and thorax are significantly thicker than abdomen in general outline. Mandibles and antennae are developed but tiny. There are no legs and prolegs. The abdomen is 2.93 mm in length, the longest abdominal segment is 0.39 mm (A5), the shortest abdominal segment is 0.17 mm (A10). There are each two lateral bulges (dorsal and ventral) on either side of all abdominal segments. The terminal segment is 0.17 mm long and 0.3 mm broad. There are no setae visible.

Remark.

There are feces preserved which were produced by the caterpillar. Some trichomes are also preserved in the amber.

Diagnosis of Phyllocnistis cretacea .

Subcylindrical caterpillars, up to 7 mm long (in known specimens and instars), head depressed, triangular and prognathous, head partly retracted or retractable in thorax, mandibles developed, minuscule antennae present, spinneret at least in late instars present, thorax with T1 having the largest diameter of all segments, tiny legs may be developed, each segments with two lateral bulges (dorsal and ventral) on either side of all abdominal segments, setae can be present, spinneret and dorsal prothoracic plates of roughly triangular form may be developed, there are no prolegs.

Remarks.

Among Lepidoptera, an affiliation to Phyllocnistis is affirmed by typical traits of the genus, such as having a triangular prognathous head, and lateral bulges of segments. However, the lack of prolegs casts some doubt on the identification. Most likely, at least the holotype and paratype I, but possibly also paratype II, represent late or last instars and prolegs would be expected on A3, A4 and A5 ( Potts and Peterson 1960; Fracker 2015). However, the prolegs may be too tiny to be detectable with respect to the preservation state. It is assumed here that reduction of proleg development for some larval stages could occur at species level as reduction of legs and prolegs is common in mining Lepidoptera (Hering, 1951). Future finds of such caterpillars hopefully will allow to differentiate larval stages or related species.

Figures

Figure 3. Holotype of Phyllocnistis cretacea, A: larva, dorsal view, B: ventral view (inclusion deeper within the amber), C: head in detail, dorsal view, D: terminal segments in detail, dorsal view. Scale bar: 1 mm.

Figure 4. Paratype I of Phyllocnistis cretacea, A: larva, dorsal view, B: ventral view, length of caterpillar 6.5 mm. Scale bar: 1 mm.

Figure 5. Paratype II of Phyllocnistis cretacea, A: larva, dorsal view, B: ventral view, length of caterpillar 4 mm. Scale bar: 1 mm.